Hallo Almal

Ons hoop die planter verloop seep glad in julle area. Ons het besluit om ‘n gesamentlike nuusbrief vir April en Mei uit te bring en dus hoekom die nuusbrief so lywig is. Ingesluit is baie interessante leesstof en ook inligting rakende die Bewaringsweek en groentoere van die vereniging. Ons wil net graag ook van die geleentheid gebruik maak om dit duidelik te maak dat die nuusbrief daar is om inligting deur te gee rakende verskeie aspekte van bewaringslandbou. Ons besef dat dit nie altyd onderwerpe is waarmee almal saam stem nie, maar ons voel dit is belangrik dat ons produsente so veel as moontlik inligting tot hulle beskiking moet hê om besluitneming te vergemaklik. As daar spesi�eke onderwerpe is waarop julle voel ons moet konsentreer is julle welkom om dit deur te gee.

GroeteDie Redakteur

Hi Everybody

We hope that your planting season has been progressing smoothly. We have decided to combine the April and May issues of the newsletter. Included is a number of very interesting articles as well as information of the Conservation week and green tours of the association.We would also like to make it clear that the role of the newsletter is to supply information about di�erent aspects of conservation agriculture. The idea is to supply as much information as we can so that producers can make more informed decisions. If there is speci�c topics that you would like more information on please let us know.

RegardsThe Editor

A word of welcome

BLWK/CAWC: Your monthly guide

April/May 2016 Issue/Uitgawe 44

Newsletter

» Swellendam groentoer: 8 Junie » Langgewens Walk-and-Talk 21 Julie » 2 Augustus – BLWK praktiese dag » 3 Augustus – BLWK konferensie dag

Contents• Welcoming .................................. 1• Planterdag - 20 April ................ 2• Practical Day / Praktiese dag . 4• Weervoorspelling ..................... 6• Will we allow soil carbon to feed

our needs? ................................... 7• BEWARINGSWEEK ...................22• Photos .........................................24

Upcoming farmers’ days and events:

Groentoer in Junie op Swellendam

1BLWK - CAWC

2 BLWK - CAWC

Planterdag - 20April

Hierdie dag was die gevolg van besluite wat op die bestuursvergadering geneem is, om die praktiese gedeelte van die Bewaringslandbouweek, op een plaas te doen om die ryery van die verlede uit te skakel. Verder sal die dag ook wissel tussen die Suidkaap en die Swartland.Vir die 2016 praktiese dag is besluit om met verskeie skyfplanters oor n groot area te plant en gesamentlik ook te kyk na vooropkoms onkruiddoders se e�ek op ontkieming en ontwikkeling van koring. Daar is ook twee bemestingspraktyke gevolg. Die uitnodiging is wyd uitgestuur en op die ou end het 4 maatskappye hulle skyfplanters beskikbaar gestel. Caledon se Claas agentskap het die perdekrag voorsien vir die dag.Die maatskappye wat deelgeneem het in alfabetiese volgorde: Agrico met John Deere (enkelskyf ), DBXtreme (dubbelskyf ), Equilizer (enkelskyf ) en Rovic Leers met ‘n Kuhn planter (dubbelskyf ). Verder het die Rovic dubbellepel panter as kontrole gedien. Daar is twee bane deur elke skyfplanter geplant. Een met skoon saad en een met kunsmis by. Verder is daar breedwerpig kunsmis toegedien voorplant.

Die vooropkoms onkruiddoders is ook in bane gespuit voor daar dwarsoor geplant is met die verskillende

planters. Daar is sewe enkel middel behandelings en 5 kombinasies. Planttellings en onkruid tellings sal onder andere gedoen word gedurende die seisoen.

Die plant dag self was oop vir belangstellendes, maar was nie ‘n formele BLWK byeenkoms nie. Met die feit dat die nuwe seisoen se aanplantings al begin het was daar nie baie produsente teenwoordig nie, maar die wat wel daar was was beide positief en sekties. Ons sien uit na die praktiese dag in Augustus waar daar na al die masjienerie gekyk sal word en ek glo

daar sal baie besprekings wees rondom die resultate.Tydens die praktiese dag sal al die vervaardigers met hul masjienerie teenwoordig wees, ons gaan pro�el gate grou om na wortelontwikkeling te kyk (elke pro�el gat sal n grondkundige hê), die vooropkomsmiddels sal bespreek word, daar gaan dekgewasse wees om te besigtig asook ‘n gedeelte koring wat oor die vorige jaar se dekgewasproewe geplant is.Hoop om julle almal die 2de Augustus op Klipfontein te sien.Johann Strauss

Planterdag – 20 AprilPlek: Klipfontein op die Caledon/Villiersdorp pad

3BLWK - CAWC

Planterdag - 20April

4 BLWK - CAWC

Practical Day / Praktiese dag

Planter praatjies

Kom besigtig die verskillende planters wat die proewe

geplant hetVerska�ers sal gesels oor hulle produkte

Koring Geplant met verskillende skyfplanters en tandplanter as kontroleWortelontwikkeling onder twee verskillende bemestingsprogrammeVooropkomsmiddels saam met skyfplanters

Dekgewasse

Koring na vorige dekgewaskombinasiesDemonstrasie proef

Sprekers

Prof Ruttan Lal - Ohio State Universiteit - Die boustene van bewaringslandbou en hoe dit inmekaar skakel Groepsbespreking: “Back to basics” – Is ons boustene in plek?Lourens van Eeden – Hoe sien ek bewaringslandbou in my omgewingProf John Howieson – Sentrum vir Rhizobium Studies, Murdoch University Wes-Australië - Rizobium en die belang van peulplante - Prof Brad Nutt – Sentrum vir Rhizobium Studies, Murdoch University Wes-Australië - Serredella en verbetering van grondfertiliteit in sanderige grondeDanie Slabber – 2015 Vrystaat Jong Boer van die jaar – My no-till verhaal

Kostes:Konferensie + Praktiese Dag = R500 per persoon (R150 vir studente)Slegs praktiese dag = R50 per persoon

BLWK “Jack Human” Bewaringslandbou Week 2016

Seeder talks

Come see the di�erent seeders that took part in the trial dayCompanies will give info on their equipment

WheatPlanted with di�erent disc seeders and tine seeder as control Large scale)Root development under two di�erent fertiliser regimesPre-emergent herbicides and disc seeders

Cover crops

Wheat following di�erent cover crops Demonstration trial

Speakers

Prof Ruttan Lal - Ohio State University - The building blocks of conservation Agriculture and how they interlink Group discussion: “Back to basics” – Is our building blocks in place?Lourens van Eeden – How do I see conservation agriculture in my areaProf John Howieson – Centre for Rhizobium Studies, Murdoch University Western Australia - Rizobium and the importance of legumes Prof Brad Nutt – Centre for Rhizobium Studies, Murdoch University Western Australia - Serredella and the improvement of soil fertility of sandy soilsDanie Slabber – 2015 Freestate Young farmer of the year – My no-till story

Costs:Conference + Practical Day = R500 per person (R150 for students)Only Practical Dag = R50 per person

CAWC “Jack Human” Conservation Agriculture Week 2016

Praktiese dag – 2 Augustus 2016

Practical day – 2 August

Konferensie dag – 4 Augustus 2016

Conference day – 4 August

5BLWK - CAWC

Practical Day / Praktiese dag

WERKSWINKEL: Kleingraansiektes van die Wes-Kaap onder die vergrootglas

Hierdie werkswinkel is ideaal vir almal wat betrokke is in klein graanverbouing in die Wes-Kaap.

Die program sluit in ’n algemene oorsig oor plantsiektes, hoe hul lewenssikluse werk, en wanneer infeksies plaasvind. Virus en bakteriese siektes sal kortliks bespreek word. Daarna word swamsiektes van saad, wortels, stamme, blare en are in diepte bespreek.

Wenke vir in-seisoen beheer, met fokus vanuit ’n gewasver-bouings oogpunt, sal ook bespreek word. Die werkswinkel is informeel, gee geleentheid vir interaktiewe gesprek en beloof om baie leersaam te wees.

JUNIE 2016 S T E L L E N B O S C H

09H00 - 15H00 R 1 2 5 0 P E R P E R S O O N

* Koste sluit verversings en ’n ligte middagete in

Indien u belangstel: Kontak Dr Ida Wilson vir ’n inskrywingsvorm ida@experico.co.zaof registreer telefonies by 021 8871134

Hierdie werkswinkel sal op versoek op lokaliteite in die Swartland en Overberg ook aangebied kan word. Kontak ons gerus indien u so behoefte het.

Die aanbieder is Dr Ida Wilson. Sy is ’n plantsiektekundige het meer as 10 jaar ervaring op kleingraanesiektes.

EXPERICO (AGRI-RESEARCH SOLUTIONS) a Division of Agri R&D (Pty) Ltd * Reg no 2013/165062/07Kantore : Leliestraat, Stellenbosch, 7600 * Posbus 4022, Ida’s Vallei, Stellenbosch, 7609, Suid-Afrika

WERKSWINKEL: Kleingraansiektes van die Wes-Kaap onder die vergrootglas

Hierdie werkswinkel is ideaal vir almal wat betrokke is in klein graanverbouing in die Wes-Kaap.

Die program sluit in ’n algemene oorsig oor plantsiektes, hoe hul lewenssikluse werk, en wanneer infeksies plaasvind. Virus en bakteriese siektes sal kortliks bespreek word. Daarna word swamsiektes van saad, wortels, stamme, blare en are in diepte bespreek.

Wenke vir in-seisoen beheer, met fokus vanuit ’n gewasver-bouings oogpunt, sal ook bespreek word. Die werkswinkel is informeel, gee geleentheid vir interaktiewe gesprek en beloof om baie leersaam te wees.

JUNIE 2016 S T E L L E N B O S C H

09H00 - 15H00 R 1 2 5 0 P E R P E R S O O N

* Koste sluit verversings en ’n ligte middagete in

Indien u belangstel: Kontak Dr Ida Wilson vir ’n inskrywingsvorm ida@experico.co.zaof registreer telefonies by 021 8871134

Hierdie werkswinkel sal op versoek op lokaliteite in die Swartland en Overberg ook aangebied kan word. Kontak ons gerus indien u so behoefte het.

Die aanbieder is Dr Ida Wilson. Sy is ’n plantsiektekundige het meer as 10 jaar ervaring op kleingraanesiektes.

EXPERICO (AGRI-RESEARCH SOLUTIONS) a Division of Agri R&D (Pty) Ltd * Reg no 2013/165062/07Kantore : Leliestraat, Stellenbosch, 7600 * Posbus 4022, Ida’s Vallei, Stellenbosch, 7609, Suid-Afrika

WERKSWINKEL: Kleingraansiektes van die Wes-Kaap onder die vergrootglas

Hierdie werkswinkel is ideaal vir almal wat betrokke is in klein graanverbouing in die Wes-Kaap.

Die program sluit in ’n algemene oorsig oor plantsiektes, hoe hul lewenssikluse werk, en wanneer infeksies plaasvind. Virus en bakteriese siektes sal kortliks bespreek word. Daarna word swamsiektes van saad, wortels, stamme, blare en are in diepte bespreek.

Wenke vir in-seisoen beheer, met fokus vanuit ’n gewasver-bouings oogpunt, sal ook bespreek word. Die werkswinkel is informeel, gee geleentheid vir interaktiewe gesprek en beloof om baie leersaam te wees.

JUNIE 2016 S T E L L E N B O S C H

09H00 - 15H00 R 1 2 5 0 P E R P E R S O O N

* Koste sluit verversings en ’n ligte middagete in

Indien u belangstel: Kontak Dr Ida Wilson vir ’n inskrywingsvorm ida@experico.co.zaof registreer telefonies by 021 8871134

Hierdie werkswinkel sal op versoek op lokaliteite in die Swartland en Overberg ook aangebied kan word. Kontak ons gerus indien u so behoefte het.

Die aanbieder is Dr Ida Wilson. Sy is ’n plantsiektekundige het meer as 10 jaar ervaring op kleingraanesiektes.

EXPERICO (AGRI-RESEARCH SOLUTIONS) a Division of Agri R&D (Pty) Ltd * Reg no 2013/165062/07Kantore : Leliestraat, Stellenbosch, 7600 * Posbus 4022, Ida’s Vallei, Stellenbosch, 7609, Suid-Afrika

Konferensie dag – 4 Augustus 2016

Conference day – 4 August

Die droogte van die afgelope seisoen laat nog hier en daar sy merke in die Wes-Kaap soos byvoorbeeld in die Sentrale Karoo en in die stand van damme, veral aan die westekant van die provinsie. Die winterreëns van April het welkome verligting gebring in die graangebiede van die Swartland.

Vervolgens die seisoenale voorspellings vir die periode Mei tot Julie in die Swartland en die Rûens. Kortliks word geen ekstreme gevalle voorspel vir hierdie periode nie wat dus oor die algemeen normale reënval en temperature vir beide die Swartland en Rûens impliseer. Die Suid-Afrikaanse Weerdiens dui wel ondergemiddelde reënval aan vir die Overberg area maar binne die konteks van hoë onsekerheid en beveel derhalwe aan dat nuutste medium en kort termyn voorspellings gereeld nagegaan word.

Weervoorspelling

6

Weervoorspelling

BLWK - CAWC

Links of the month

http://ensia.com/features/weve-changed-a-life-giving-nutrient-into-a-deadly-pollutant-how-can-we-change-it-back/

http://thehill.com/blogs/pundits-blog/energy-environment/275050-carbon-farming-is-a-zero-risk-strate-gy-for-curbing#.VwUn8opsNW0.twitter

http://harvestingthepotential.org/brownrevolution/assets/doc_09.pdf

http://extension.psu.edu/publications/ee0174/view

http://www.farminguk.com/News/Global-agri-companies-may-be-forced-to-re-engineer-business-models-as-farmers-adopt-technology_39625.html

http://ensia.com/features/weve-changed-a-life-giving-nutrient-into-a-deadly-pollutant-how-can-we-change-it-back/

http://www.blogs.nrcs.usda.gov/wps/portal/nrcs/blogdetail/nrcsblog/home/?cid=NRCSEPPD257875

Click on the link to visit the website.Please note you will need an internet connection

1

234567

7BLWK - CAWC

future science group 237ISSN 1758-300410.4155/CMT.10.25

If Earth is the mother of all living things, then soil must be its womb, bearing richness beyond comprehen-sion. Then too, carbon in soil should be considered the blood energizing the entire body, enabling the Earth to provide a multitude of ecosystem services.

We, as human civilization, ‘need’ many things – not necessarily cell phones to be continuously in contact with our co-workers and friends, not necessarily televi-sion to see who will be scoring points, not necessarily watches to know when to drink tea; these are more like desserts after the main course. The main course to feed our ‘needs’ comes from the ecosystem services supplied by Nature. Figure 1 outlines the packages of ecosystem services that are essential for the inhabitants of the Earth [1]. Lest we ignore our essential diet derived from the main course, the desserts we pleasure will simply not be satisfying in the future.

Importance of soilWhere would we be if we did not have air, water, soil and the sun? Even without one of these essential eco-system elements, our survival on Earth would be dis-mal. Since carbon forms the ‘backbone’ biochemical

structure of all living things, it is intimately associated with the various processes involving air, water, soil, and the sun. One vitally essential process that starts the carbon cycle is photosynthesis, which embodies all four of these elements in a magical moment that occurs every day all over the Earth – photonic energy from the sun is captured within chloroplasts of green plants that encase water imbibed from the soil in a conglomeration of cells structurally arranged to allow oxygen and CO

2

to permeate its boundaries to create a chemical cocktail of carbohydrates that eventually forms the web of life for animals and decaying organisms. Carbohydrates fuel plant growth and their utilization releases CO

2

and water vapor back to the atmosphere. A key carbon pathway in the global carbon cycle is the transfer of carbon resources from living plants to soil organisms through decomposition, which eventually enriches soil organic carbon pools.

Soil properties and processes have underlying impor-tance in addressing many global issues facing society during the coming decades [2]. How can we grow food for billions more people without harming the environ-ment even further? How can we manage soils in order to

Carbon Management (2010) 1(2), 237–251

Will we allow soil carbon to feed our needs?

Alan J Franzluebbers†

Humans need many things, but unacknowledged by many of us are the intricately critical in�uences that soil with high organic carbon has on our life support system. Soil is as vital to human survival as air, water and the sun; its protection and enrichment with organic carbon are needed for the future sustainability of our planet. Curiously, the growing possibility of trading carbon in a global marketplace may actually help us to better appreciate the enormous value of soil carbon on how our world functions and how we have the in�uence to preserve and enhance critical ecosystem functions or continue to degrade them with reckless abandonment. With the expected rise in human population and the need for even more food to be produced on already stressed landscapes, widespread adoption of conservation agricultural systems is necessary to build a more resilient global food production system that can also help to mitigate climate change and improve our relationship with nature.

PERSPECTIVE

†USDA–Agricultural Research Service, 1420 Experiment Station Road, Watkinsville GA 30677, USATel.: +1 706 769 5631; Fax: +1 706 769 8962; E-mail: alan.franzluebbers@ars.usda.gov

For reprint orders, please contact reprints@future-science.com

Cultural servicesNon-material benefits

obtained throughcognitive development,aesthetic experience,spiritual enrichment,

recreation and reflection.

Provisioning servicesProducts obtained

from ecosystems, includinggenetic resources, food, feed,

fiber, fuel and fresh water.

Regulatory servicesBenefits obtained fromregulation of ecosystem

processes, includingclimate, water and human diseases.

Supporting servicesEssential to other services, including biomass production,

production of atmospheric oxygen, soil formation and retention,nutrient cycling and provisioning of habitat.

Carbon Management (2010) 1(2) future science group238

Perspective Franzluebbers

obtain a better balance for the dwin-dling pools of fresh water between agricultural irrigation and munici-pal needs? With increasing cost and scarcity of nutrients, how do we pre-serve and enhance the fertility of our soils while expecting larger harvests? How can we manage land to accom-modate for the increasing demand for bio-based energy? How will impending climate change affect the productivity and resilience of our soils and broader environment?

How can we better understand and enhance the diver-sity of organisms within and upon the soil to create more resilient and fructuous ecosystems? How can we better use soils as biogeochemical reactors to recycle wastes, thereby avoiding environ mental contamination and maintaining soil productivity? How can we develop a seamless global perspective of lands, but still optimize management practices for local places and cultures? These are all important questions evolving from the relatively unknown world beneath our feet, the quality of which is dependent upon carbon.

What is soil carbon?Carbon is found in soil as organic matter and carbon-ate minerals (e.g., CaCO

3). Soil organic matter is an

assorted mixture of organic compounds, having been processed over varying lengths of time by soil organ-isms. It may be living (e.g., plant roots, insects, fungi, protozoa or bacteria) or it may be dead, dying or par-tially decayed. The most abundant constituent of soil organic matter is carbon (50–58%), hence the con-gruence between soil organic carbon and soil organic matter. Living components of soil organic matter are rather small in percentage (<10%), but play enormously important roles in decomposition, nutrient cycling, plant root zone modification, soil structural manipula-tion, aggregate stabilization and ecological resilience through underground biodiversity development. The living components of soil have been investigated only scantily compared with other components [3]. Nonliving components of soil organic matter are categorized in different manners according to the complexity of the compounds. A traditional approach has been through a fractionation scheme that first removes relatively large particles of organic matter (>50 µm) and water-soluble organic matter to yield humus. Humus can then be

further subdivided into nonhumic biopolymers (e.g., polysaccharides, sugars, proteins, amino acids, fats, waxes, other lipids and lignin), humic acid (soluble in alkaline solu-tion, but precipitate when acidified), fulvic acid (soluble in alkaline solu-tion and remains soluble when acidi-fied), and humin (insoluble in alka-line solution). Another approach for the fractionation of soil organic matter has been based on decom-position rate, where at least three pools of organic matter are charac-terized on a continuum from read-ily decomposable to recalcitrant forms through laboratory or field incubations (i.e., active, slow and passive) [4].

Soil carbon in a global contextGlobal plant biomass captures approximately 110 Pg (1015 g) C year-1 from the atmosphere through photosynthesis. Maintenance and decay of plants and animals occurs simultaneously and returns approx-imately 110 Pg C year-1 as CO

2 to

the atmosphere through autotro-phic respiration (50 Pg C year-1)

Figure 1. Categories of ecosystem services provided by Nature. Supporting services underlie all other functions and services. Cultural services form the pinnacle in response to e�ective functioning of supporting, regulating and provisioning services. Adapted from [1].

Key terms

Ecosystem services: Properties and processes of the natural world that contribute to the well-being of plants, animals, and humans in a holistic and global context.

Soil organic carbon: Living and nonliving carbon in soil that contributes as a food source for soil biological activity, as a chemical structure to store a wide diversity of nutrients, and as a physical component of soil that controls water and gas �ow into and out of soil.

Soil organic carbon (g kg-1)0 1 2 3 4 5

So

il w

ater

co

nte

nt

(m3

m-3)

0.0

0.1

0.2

0.3

0.4

0.5Sand

0 1 2 3 4 5

Silt loam

Fieldcapacity

Wiltingpoint

Plant-available

water

0.08

0.19 0.16

0.35

Plant-available

water

Soil organic carbon (g kg-1)

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 239

and heterotrophic respiration (60 Pg C year-1). Soil to a depth of 1 m stores approximately 1600 Pg C in organic matter; an additional 700 Pg C is stored in soil as carbonate minerals [4]. The atmosphere contains approximately 800 Pg C as CO

2 and has been increas-

ing in CO2 concentration since the beginning of the

20th Century. Estimates from the first decade of the 21st Century indicate emissions of 7.7 Pg C year-1 from the burning of fossil fuels and 1.4 Pg C year-1 from deforestation [5]. Sinks for this additional CO

2 in the

atmosphere have been 2.3 Pg C year-1 in the oceans and 2.7 Pg C year-1 to land biomass, leaving behind 4.1 Pg C year-1 accumulating in the atmosphere [5].

Assuming a global loss of 20% organic carbon from soils (i.e., 400 Pg from an original level of 2000 Pg) via historical land clearing that caused erosion and oxidation of organic matter [6,7], there is an enormous potential to recapture at least 400 Pg of organic car-bon in soil with technological innovations and resto-ration activities. Assuming that an aggressive global restoration could occur within the next century, nearly all of the current rate of CO

2 increase in the

atmosphere (i.e., 4.1 Pg C year-1) could be mitigated through soil restoration (400 Pg C/5 billon ha of agri-cultural land/100 years = mean soil organic carbon sequestration rate of 0.8 Mg C ha-1 year-1; certainly a tremendous goal, but also plau-sible). Clearly, the potential for soil restoration with organic car-bon could have a major impact on the atmosphere; it is our collective willingness to achieve this goal that may be questioned. Obviously, the time required to fully restore soil organic carbon may be longer than a century and the rate of release of fossil fuel-derived CO

2 cannot

be considered static. In addition, Lal more conservatively suggested that only 42–78 Pg C might have been lost from soils worldwide [8,9], although estimates have varied from 44 to 537 Pg C.

How does soil carbon a�ect ecosystem properties & services?Soil organic carbon is a vital compo-nent of ecosystem properties, pro-cesses and functions. It has highly relevant physical, chemical and bio-logical features. This wide diversity of features has given soil organic carbon deserved attention as a key

indicator of soil quality (i.e., how soil management affects the functioning of soil) [10].

Attributes of soil organic carbon that affect soil and ecosystem properties include:

Physical

Color: the dark color of organic matter alters t hermal properties (i.e., absorbing heat);

Low solubility: ensures that organic matter inputs are retained and are not rapidly leached from the soil profile;

Water retention: directly helps to absorb several times its mass of water and indirectly retains water through its effect on pore geometry and soil s tructure (Figure 2) [11];

Stabilization of soil structure: binding of mineral particles to form water-stable aggregates and improve water infiltration into the surface soil.

Chemical

Cation exchange capacity: high charge enhances retention of nutrient cations, such as Al, Fe, Ca, Mg and NH

4 (Figure 3);

Figure 2. E�ect of soil organic carbon concentration on plant-available water in sand soils from Florida and silt loam soils from Iowa, Kansas, Minnesota and Wisconsin, USA. Plant-available water is the dierence between �eld capacity (upper line; calculated as water content following free drainage of saturated soil) and wilting point (lower line; calculated as water content that causes plants to wilt permanently). With four-times greater soil organic carbon concentration, these two dierent soil types would hold 2.2–2.5-times more water in the same volume. Adapted with permission from data presented in [11].

Cultural servicesNon-material benefits

obtained throughcognitive development,aesthetic experience,spiritual enrichment,

recreation and reflection.

Provisioning servicesProducts obtained

from ecosystems, includinggenetic resources, food, feed,

fiber, fuel and fresh water.

Regulatory servicesBenefits obtained fromregulation of ecosystem

processes, includingclimate, water and human diseases.

Supporting servicesEssential to other services, including biomass production,

production of atmospheric oxygen, soil formation and retention,nutrient cycling and provisioning of habitat.

Carbon Management (2010) 1(2) future science group238

Perspective Franzluebbers

obtain a better balance for the dwin-dling pools of fresh water between agricultural irrigation and munici-pal needs? With increasing cost and scarcity of nutrients, how do we pre-serve and enhance the fertility of our soils while expecting larger harvests? How can we manage land to accom-modate for the increasing demand for bio-based energy? How will impending climate change affect the productivity and resilience of our soils and broader environment?

How can we better understand and enhance the diver-sity of organisms within and upon the soil to create more resilient and fructuous ecosystems? How can we better use soils as biogeochemical reactors to recycle wastes, thereby avoiding environ mental contamination and maintaining soil productivity? How can we develop a seamless global perspective of lands, but still optimize management practices for local places and cultures? These are all important questions evolving from the relatively unknown world beneath our feet, the quality of which is dependent upon carbon.

What is soil carbon?Carbon is found in soil as organic matter and carbon-ate minerals (e.g., CaCO

3). Soil organic matter is an

assorted mixture of organic compounds, having been processed over varying lengths of time by soil organ-isms. It may be living (e.g., plant roots, insects, fungi, protozoa or bacteria) or it may be dead, dying or par-tially decayed. The most abundant constituent of soil organic matter is carbon (50–58%), hence the con-gruence between soil organic carbon and soil organic matter. Living components of soil organic matter are rather small in percentage (<10%), but play enormously important roles in decomposition, nutrient cycling, plant root zone modification, soil structural manipula-tion, aggregate stabilization and ecological resilience through underground biodiversity development. The living components of soil have been investigated only scantily compared with other components [3]. Nonliving components of soil organic matter are categorized in different manners according to the complexity of the compounds. A traditional approach has been through a fractionation scheme that first removes relatively large particles of organic matter (>50 µm) and water-soluble organic matter to yield humus. Humus can then be

further subdivided into nonhumic biopolymers (e.g., polysaccharides, sugars, proteins, amino acids, fats, waxes, other lipids and lignin), humic acid (soluble in alkaline solu-tion, but precipitate when acidified), fulvic acid (soluble in alkaline solu-tion and remains soluble when acidi-fied), and humin (insoluble in alka-line solution). Another approach for the fractionation of soil organic matter has been based on decom-position rate, where at least three pools of organic matter are charac-terized on a continuum from read-ily decomposable to recalcitrant forms through laboratory or field incubations (i.e., active, slow and passive) [4].

Soil carbon in a global contextGlobal plant biomass captures approximately 110 Pg (1015 g) C year-1 from the atmosphere through photosynthesis. Maintenance and decay of plants and animals occurs simultaneously and returns approx-imately 110 Pg C year-1 as CO

2 to

the atmosphere through autotro-phic respiration (50 Pg C year-1)

Figure 1. Categories of ecosystem services provided by Nature. Supporting services underlie all other functions and services. Cultural services form the pinnacle in response to e�ective functioning of supporting, regulating and provisioning services. Adapted from [1].

Key terms

Ecosystem services: Properties and processes of the natural world that contribute to the well-being of plants, animals, and humans in a holistic and global context.

Soil organic carbon: Living and nonliving carbon in soil that contributes as a food source for soil biological activity, as a chemical structure to store a wide diversity of nutrients, and as a physical component of soil that controls water and gas �ow into and out of soil.

Soil organic carbon (g kg-1)0 1 2 3 4 5

So

il w

ater

co

nte

nt

(m3

m-3)

0.0

0.1

0.2

0.3

0.4

0.5Sand

0 1 2 3 4 5

Silt loam

Fieldcapacity

Wiltingpoint

Plant-available

water

0.08

0.19 0.16

0.35

Plant-available

water

Soil organic carbon (g kg-1)

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 239

and heterotrophic respiration (60 Pg C year-1). Soil to a depth of 1 m stores approximately 1600 Pg C in organic matter; an additional 700 Pg C is stored in soil as carbonate minerals [4]. The atmosphere contains approximately 800 Pg C as CO

2 and has been increas-

ing in CO2 concentration since the beginning of the

20th Century. Estimates from the first decade of the 21st Century indicate emissions of 7.7 Pg C year-1 from the burning of fossil fuels and 1.4 Pg C year-1 from deforestation [5]. Sinks for this additional CO

2 in the

atmosphere have been 2.3 Pg C year-1 in the oceans and 2.7 Pg C year-1 to land biomass, leaving behind 4.1 Pg C year-1 accumulating in the atmosphere [5].

Assuming a global loss of 20% organic carbon from soils (i.e., 400 Pg from an original level of 2000 Pg) via historical land clearing that caused erosion and oxidation of organic matter [6,7], there is an enormous potential to recapture at least 400 Pg of organic car-bon in soil with technological innovations and resto-ration activities. Assuming that an aggressive global restoration could occur within the next century, nearly all of the current rate of CO

2 increase in the

atmosphere (i.e., 4.1 Pg C year-1) could be mitigated through soil restoration (400 Pg C/5 billon ha of agri-cultural land/100 years = mean soil organic carbon sequestration rate of 0.8 Mg C ha-1 year-1; certainly a tremendous goal, but also plau-sible). Clearly, the potential for soil restoration with organic car-bon could have a major impact on the atmosphere; it is our collective willingness to achieve this goal that may be questioned. Obviously, the time required to fully restore soil organic carbon may be longer than a century and the rate of release of fossil fuel-derived CO

2 cannot

be considered static. In addition, Lal more conservatively suggested that only 42–78 Pg C might have been lost from soils worldwide [8,9], although estimates have varied from 44 to 537 Pg C.

How does soil carbon a�ect ecosystem properties & services?Soil organic carbon is a vital compo-nent of ecosystem properties, pro-cesses and functions. It has highly relevant physical, chemical and bio-logical features. This wide diversity of features has given soil organic carbon deserved attention as a key

indicator of soil quality (i.e., how soil management affects the functioning of soil) [10].

Attributes of soil organic carbon that affect soil and ecosystem properties include:

Physical

Color: the dark color of organic matter alters t hermal properties (i.e., absorbing heat);

Low solubility: ensures that organic matter inputs are retained and are not rapidly leached from the soil profile;

Water retention: directly helps to absorb several times its mass of water and indirectly retains water through its effect on pore geometry and soil s tructure (Figure 2) [11];

Stabilization of soil structure: binding of mineral particles to form water-stable aggregates and improve water infiltration into the surface soil.

Chemical

Cation exchange capacity: high charge enhances retention of nutrient cations, such as Al, Fe, Ca, Mg and NH

4 (Figure 3);

Figure 2. E�ect of soil organic carbon concentration on plant-available water in sand soils from Florida and silt loam soils from Iowa, Kansas, Minnesota and Wisconsin, USA. Plant-available water is the dierence between �eld capacity (upper line; calculated as water content following free drainage of saturated soil) and wilting point (lower line; calculated as water content that causes plants to wilt permanently). With four-times greater soil organic carbon concentration, these two dierent soil types would hold 2.2–2.5-times more water in the same volume. Adapted with permission from data presented in [11].

Carbon Management (2010) 1(2) future science group240

Perspective Franzluebbers

Buffering capacity and pH effects: avoids large swings in pH to keep acidity/alkalinity in a more acceptable range for plants;

Chelation of metals: complexation with metals to enhance dissolution of minerals, enhance avail- ability of phosphorus, reduce losses of micronutrients and reduce toxicity;

Interactions with xenobiotics: alter biodegrade- ability, activity, and pers istence of pesticides and other organic contaminants, such as antibiotics and endocrine-disrupting chemicals.

Biological

Reservoir of metabolic energy: energy embedded in organic molecules to drive biological processes;

Source of macronutrients: mineralization of organic matter releases nitrogen, phosphorus, sulfur and other elements (Figure 4) [12];

Enzymatic activities: both enhancement and inhibition of enzymes are possible by various humic materials;

Ecosystem resilience: accu-mulat ion of soi l organic mat ter can enhance the ability of an eco system to recover from various disturbances (e.g., drought, flooding, tillage and fire).

Soil formation is a geologically time consuming process driven by the influences of CLORPT [13]:

Climate: whereby temperature and moisture alter chemical reactions;

Organisms: whereby plant roots penetrate and deposit residues, ani-mals burrow and create cavities, and bacteria feed upon organic remains;

Relief: whereby the shape and direction of land surface affect sun-light and moisture exposure;

Parent material: whereby the underlying bedrock provides differ-ent minerals that contribute the chemical and physical conditions of soil;

Time: whereby different numbers of millennia allow the other factors to take place.

These same factors have a large influence on soil organic matter formation and its capacity to sustain ecosystem functions. It may have taken nature 200 years to form 1 cm of soil, but it took humans about that same amount of time to enable nature to erode the entire Southern Piedmont landscape (a region of hilly land southeast of the Appalachian Mountains from Alabama to Virginia in the USA) when previously for-ested land was denuded and covered only intermittently with a sparse cotton crop; the process of which eventu-ally removed 18 cm of soil from the entire 17 Mha of land [14]. It is small wonder that soils of the southeastern USA are considered poor and infertile when more than 30 Mg C ha-1 would have been lost from the upper soil horizon (calculation of author based on presumed mean soil organic carbon concentration of 12 g C kg-1 soil and bulk density of 1.4 Mg m-3 in surface 18 cm of soil).

Soil organic carbon accumulates predominately in the upper horizons of soils. Without disturbing soil with tillage, soil organic carbon accumulates as plant residues cover the soil and slowly decompose following intermit-tent precipitation events (Figure 5) [15]. Protection of the soil surface with plant residues and high soil organic carbon concentration is important for getting rainfall

Soil organic carbon (g kg-1)

0 10 20 30 40 50 600

100

200

300

400

500

Ca = 40 + 4.7 (SOC)

r 2 = 0.29

Meh

lich

-1 e

xtra

ctab

le c

alci

um

(m

g k

g-1)

Figure 3. Relationship between concentration of soil organic carbon and extractable calcium in pastures in the Piedmont of Georgia, USA. In general, soil with 10 g kg-1 of organic carbon contained only a third as much calcium as soil with 50 g kg-1 of organic carbon (87 vs 275 mg Ca kg-1 soil). Soil organic matter retains nutrients within various organic structures and these nutrients can be released through mineralization of organic matter. Data from [AJ Franzluebbers, RL Haney, Unpublished data].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 241

to infiltrate soil (i.e., lower runoff) and keep the soil surface from wash-ing away (i.e., lower soil loss). By helping to control soil erosion and alter the water cycle, soil organic carbon supports and regulates ecosystem services.

With the adoption of inorganic fertilizer application in the 20th Century, the nutrient supply-ing capacity of soil organic matter became widely underappreciated. Application of inorganic fertilizer can overcome nutrient deficiencies, even in poorly structured soils with low organic matter. However, within a particular soil, the level of organic carbon can have a profound influ-ence on the capacity of the soil to produce food, feed, fiber and fuel (Figure 6) [16]. When soils are main-tained with high surface-soil organic carbon rather than depleted with accelerated oxidation from repeated tillage operations, productivity can also be enhanced due to non-nutri-ent attributes of soil organic matter (Figure 7) [17].

Accumulation of plant residues and organic carbon in the soil sur-face is also extremely important for protecting the off-site quality of surface waters in nearby streams and lakes. With increasing surface residue and soil organic C, the percentage of rainfall as runoff declines, soil loss declines, and nutrients lost in runoff declines (Figure 8) [18].

In ancient times, soil was thought to be at its best when cultivated with implements to release the nutri-ents stored within organic matter. Lessons from the American frontiers have informed us that preservation of soil organic matter without soil disturbance is a far better goal for preserving the quality of soil for future gen-erations [19]. The key to sustaining fertility is to match nutrient requirements of crops with various amend-ments, whether these come from inorganic or organic sources, such as commercial fertilizers, animal manures, nitrogen-fixing green manures, or various industrial or rurally derived composts. The European-influenced cul-ture of clean, bare soil as a vision of agrarian charm has rightfully been replaced in America with the modern vision of crop residue-blanketed fields protected from the fierce elements of wind and water that can be both bane and blessing for the American landscape.

Can management increase the stock of soil organic carbon?As seen from how agricultural land use affects depth dis-tribution of soil organic carbon in Figure 5, management is an important factor in altering soil organic carbon concentration. In the business world of carbon account-ing and trading, stock change in soil organic carbon needs to be calculated from the change in soil organic carbon concentration, the change in bulk density of soil, the soil depth of inference, and the time period of evaluation. Stock changes in soil organic carbon at the field level are typically reported in Mg C ha-1 year-1 (1 Mg = 106 g), while stock changes at the farm, county, regional, national or global level can be simply upscaled to various units of Tg C year-1 (1 Tg = 1012 g), Pg C year-1 (1 Pg = 1015 g), or Gt C year-1 (1 Gt = 1015 g). If conver-sion to CO

2 equivalence (CO

2e) is desired, then a factor

of 3.67 should be multiplied by the value of carbon in order to account for molecular weight differences (i.e., 1 Mg C ha-1 year-1 = 3.67 Mg CO

2-e ha-1 year-1).

Flush of CO2-C following rewetting of dried soil (µg g-1 3 d-1)

0 200 400 600 800 1000

Net

nit

rog

en m

iner

aliz

atio

n (

µg

g-1 2

4 d

-1)

0

50

100

150

200

r 2 = 0.72

Figure 4. Relationship between the most active fraction of soil organic carbon (i.e., the  ush of CO2 evolved from soil immediately after rewetting) and the amount of nitrogen released into soil solution. The initially linear phase of the relationship indicates that a steady supply of inorganic nitrogen is made available from the decomposition of easily decomposed organic matter. The peak phase of the relationship and the subsequent decline indicates that immobilization of nitrogen into the rapidly growing microbial biomass can occur with excessively reactive carbon substrates. Symbols represent di�erent levels of silage harvest intensity (  = low,  = medium and  = high).Adapted from [12].

Carbon Management (2010) 1(2) future science group240

Perspective Franzluebbers

Buffering capacity and pH effects: avoids large swings in pH to keep acidity/alkalinity in a more acceptable range for plants;

Chelation of metals: complexation with metals to enhance dissolution of minerals, enhance avail- ability of phosphorus, reduce losses of micronutrients and reduce toxicity;

Interactions with xenobiotics: alter biodegrade- ability, activity, and pers istence of pesticides and other organic contaminants, such as antibiotics and endocrine-disrupting chemicals.

Biological

Reservoir of metabolic energy: energy embedded in organic molecules to drive biological processes;

Source of macronutrients: mineralization of organic matter releases nitrogen, phosphorus, sulfur and other elements (Figure 4) [12];

Enzymatic activities: both enhancement and inhibition of enzymes are possible by various humic materials;

Ecosystem resilience: accu-mulat ion of soi l organic mat ter can enhance the ability of an eco system to recover from various disturbances (e.g., drought, flooding, tillage and fire).

Soil formation is a geologically time consuming process driven by the influences of CLORPT [13]:

Climate: whereby temperature and moisture alter chemical reactions;

Organisms: whereby plant roots penetrate and deposit residues, ani-mals burrow and create cavities, and bacteria feed upon organic remains;

Relief: whereby the shape and direction of land surface affect sun-light and moisture exposure;

Parent material: whereby the underlying bedrock provides differ-ent minerals that contribute the chemical and physical conditions of soil;

Time: whereby different numbers of millennia allow the other factors to take place.

These same factors have a large influence on soil organic matter formation and its capacity to sustain ecosystem functions. It may have taken nature 200 years to form 1 cm of soil, but it took humans about that same amount of time to enable nature to erode the entire Southern Piedmont landscape (a region of hilly land southeast of the Appalachian Mountains from Alabama to Virginia in the USA) when previously for-ested land was denuded and covered only intermittently with a sparse cotton crop; the process of which eventu-ally removed 18 cm of soil from the entire 17 Mha of land [14]. It is small wonder that soils of the southeastern USA are considered poor and infertile when more than 30 Mg C ha-1 would have been lost from the upper soil horizon (calculation of author based on presumed mean soil organic carbon concentration of 12 g C kg-1 soil and bulk density of 1.4 Mg m-3 in surface 18 cm of soil).

Soil organic carbon accumulates predominately in the upper horizons of soils. Without disturbing soil with tillage, soil organic carbon accumulates as plant residues cover the soil and slowly decompose following intermit-tent precipitation events (Figure 5) [15]. Protection of the soil surface with plant residues and high soil organic carbon concentration is important for getting rainfall

Soil organic carbon (g kg-1)

0 10 20 30 40 50 600

100

200

300

400

500

Ca = 40 + 4.7 (SOC)

r 2 = 0.29

Meh

lich

-1 e

xtra

ctab

le c

alci

um

(m

g k

g-1)

Figure 3. Relationship between concentration of soil organic carbon and extractable calcium in pastures in the Piedmont of Georgia, USA. In general, soil with 10 g kg-1 of organic carbon contained only a third as much calcium as soil with 50 g kg-1 of organic carbon (87 vs 275 mg Ca kg-1 soil). Soil organic matter retains nutrients within various organic structures and these nutrients can be released through mineralization of organic matter. Data from [AJ Franzluebbers, RL Haney, Unpublished data].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 241

to infiltrate soil (i.e., lower runoff) and keep the soil surface from wash-ing away (i.e., lower soil loss). By helping to control soil erosion and alter the water cycle, soil organic carbon supports and regulates ecosystem services.

With the adoption of inorganic fertilizer application in the 20th Century, the nutrient supply-ing capacity of soil organic matter became widely underappreciated. Application of inorganic fertilizer can overcome nutrient deficiencies, even in poorly structured soils with low organic matter. However, within a particular soil, the level of organic carbon can have a profound influ-ence on the capacity of the soil to produce food, feed, fiber and fuel (Figure 6) [16]. When soils are main-tained with high surface-soil organic carbon rather than depleted with accelerated oxidation from repeated tillage operations, productivity can also be enhanced due to non-nutri-ent attributes of soil organic matter (Figure 7) [17].

Accumulation of plant residues and organic carbon in the soil sur-face is also extremely important for protecting the off-site quality of surface waters in nearby streams and lakes. With increasing surface residue and soil organic C, the percentage of rainfall as runoff declines, soil loss declines, and nutrients lost in runoff declines (Figure 8) [18].

In ancient times, soil was thought to be at its best when cultivated with implements to release the nutri-ents stored within organic matter. Lessons from the American frontiers have informed us that preservation of soil organic matter without soil disturbance is a far better goal for preserving the quality of soil for future gen-erations [19]. The key to sustaining fertility is to match nutrient requirements of crops with various amend-ments, whether these come from inorganic or organic sources, such as commercial fertilizers, animal manures, nitrogen-fixing green manures, or various industrial or rurally derived composts. The European-influenced cul-ture of clean, bare soil as a vision of agrarian charm has rightfully been replaced in America with the modern vision of crop residue-blanketed fields protected from the fierce elements of wind and water that can be both bane and blessing for the American landscape.

Can management increase the stock of soil organic carbon?As seen from how agricultural land use affects depth dis-tribution of soil organic carbon in Figure 5, management is an important factor in altering soil organic carbon concentration. In the business world of carbon account-ing and trading, stock change in soil organic carbon needs to be calculated from the change in soil organic carbon concentration, the change in bulk density of soil, the soil depth of inference, and the time period of evaluation. Stock changes in soil organic carbon at the field level are typically reported in Mg C ha-1 year-1 (1 Mg = 106 g), while stock changes at the farm, county, regional, national or global level can be simply upscaled to various units of Tg C year-1 (1 Tg = 1012 g), Pg C year-1 (1 Pg = 1015 g), or Gt C year-1 (1 Gt = 1015 g). If conver-sion to CO

2 equivalence (CO

2e) is desired, then a factor

of 3.67 should be multiplied by the value of carbon in order to account for molecular weight differences (i.e., 1 Mg C ha-1 year-1 = 3.67 Mg CO

2-e ha-1 year-1).

Flush of CO2-C following rewetting of dried soil (µg g-1 3 d-1)

0 200 400 600 800 1000

Net

nit

rog

en m

iner

aliz

atio

n (

µg

g-1 2

4 d

-1)

0

50

100

150

200

r 2 = 0.72

Figure 4. Relationship between the most active fraction of soil organic carbon (i.e., the  ush of CO2 evolved from soil immediately after rewetting) and the amount of nitrogen released into soil solution. The initially linear phase of the relationship indicates that a steady supply of inorganic nitrogen is made available from the decomposition of easily decomposed organic matter. The peak phase of the relationship and the subsequent decline indicates that immobilization of nitrogen into the rapidly growing microbial biomass can occur with excessively reactive carbon substrates. Symbols represent di�erent levels of silage harvest intensity (  = low,  = medium and  = high).Adapted from [12].

Carbon Management (2010) 1(2) future science group242

Perspective Franzluebbers

Conservation agricultural systems have great poten-tial to sequester soil organic carbon, which would help mitigate greenhouse gas emissions contributing to cli-mate change and increase soil productivity and avoid further environmental damage from unsustainable use of inversion tillage systems – issues that threaten water quality, reduce soil biodiversity and erode soil

around the world. Conservation agricultural systems have three guiding principles that can be globally applied:

Minimize soil disturbance, consistent with susta inable production;

Maximize soil surface cover by managing crops, pastures and crop residues;

Stimulate biological activity through crop rotations, cover crops and integrated nutrient and pest management.

Impacts from conservation tillage cropping on soil organic carbon sequestration have received a great deal of research attention during the past couple of decades owing to the expansion of this technology through-out the world. Derpsch and Friedrich have estimated that conservation agriculture is practiced on 105 Mha throughout the world, with 26.6 Mha in the USA, 25.5 Mha in Brazil, 19.7 Mha in Argentina, 13.5 in Canada and 12.0 in Australia [20]. Globally, conser-vation agriculture is practiced on only approximately 7% of cropland, suggesting that major expansion of conservation agricultural production is still possible.

Significant soil organic carbon sequestration has occurred with adoption of conservation tillage by farmers in the southeastern USA (Figure 9) [21]. Most notable changes in the stock of soil organic carbon with adoption of conservation tillage occur in the surface 5 cm. This dramatic change in surface-soil organic carbon is a result of crop residues that lie at the surface (blanketing the soil surface with protec-tion from wind and water erosion), undergoing slow decomposition to form stable soil organic matter in immediately underlying soil. The combination of crop residue cover and high surface-soil organic carbon is an ideal habitat for a diverse range of organisms, includ-ing earthworms, beetles, ants, springtails, nematodes, fungi and bacteria [22].

The type of cropping system can also affect the quan-tity of carbon fixed and subsequently available for soil organic carbon accumulation. In a review of 147 studies across the southeastern USA, the rate of soil organic carbon sequestration was greater in cropping systems with winter cover crops (0.55 ± 0.06 Mg C ha-1 year-1, n = 87) than in cropping systems without winter cover crops (0.30 ± 0.05 Mg C ha-1 year-1, n = 60) [23]. Winter cover crops can provide 2–4 Mg C ha-1 year-1 additional above-ground carbon input, plus the same magnitude of below-ground carbon input, whch can contribute to formation of soil organic matter. Obviously, the highly conducive environment for decomposition in the southeastern USA requires a large input of plant biomass for significant changes in soil organic carbon to occur. From cropping systems in South-Central Texas, USA (20°C and 978 mm mean annual temperature and precipitation respectively), the fraction of carbon input from above- and below-ground sources that was seques-tered as organic carbon in the surface 20 cm of soil was estimated to be 0.09 ± 0.04 g g-1 under conventional tillage and 0.22 ± 0.02 g g-1 under no tillage [24]. Higher retention rates could be expected in colder and drier climates and lower retention rates could be expected in warmer and wetter climates. In addition to the quan-tity of organic matter input controlling soil organic car-bon content, tillage, crop rotation and cover cropping

Figure 5. Depth distribution of soil organic carbon concentration by agricultural land management system in the Piedmont of Georgia, USA. Soil organic carbon is often uniformly distributed within the tillage zone (15-cm depth in conventional tillage system). With many years of undisturbed soil using conservation tillage to grow crops, soil organic carbon increases at the surface and declines with depth. Even greater increases in surface soil organic carbon can occur with perennial pastures that are not disturbed by tillage, that have a diversity of plants growing in the spring, summer, and autumn, and that have a large portion of the plant biomass grazed by animals and a portion of that harvested biomass subsequently returned to the soil in undigested form via animal manure. Reproduced with permission from [15].

Key terms

Conservation tillage: Method of plant production that leaves more than 30% residue cover after planting to control erosion and build soil organic carbon; includes minimum tillage, reduced tillage, ridge tillage, direct seeding and no tillage.

Conservation agriculture: Environmental approach to agricultural production that recognizes the appropriateness of multiple soil and water conservation practices to build a sustainable system within a particular region. Three key principles of conservation agriculture are: minimizing soil disturbance, maximizing soil surface cover and stimulating biological activity.

4000

3000

2000

1000

0

0 20 40 60 80

Yie

ld (

kg h

a-1)

Soil organic C (Mg ha-1)

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 243

can alter the quality of soil organic matter, thereby affecting nutrient cycling, aggregation and hydraulic processes [25,26].

Cropping systems with greater amounts of time when soil is cov-ered and plants are growing have greater opportunities to fix car-bon and subsequently store car-bon in soil organic matter. With increasing cropping intensity, soil microbial biomass carbon (and soil organic carbon) increased, irrespec-tive of whether soil was tilled or not (Figure 10) [24]. With an effect on soil organic carbon sequestration simi-lar to that of cover cropping, crop rotations with multiple-season sequences, high biomass produc-tion, and plant diversity offer pro-ducers additional opportunities to reduce the risk of crop failure due to extreme weather events and build resilience with farm production diversification.

Perennial pastures have great potential to sequester soil organic carbon, because land is left rela-tively undisturbed for several years to several decades. The magnitude and rate of change in soil organic carbon will depend on climatic conditions, soil type and condi-tion of land prior to establishment. Perennial pastures often contain a diversity of forages that grow dur-ing different parts of the year, and, therefore, offer extended root-growing opportunities for depositing carbon in soil. In addition, although perennial pastures are often grazed by ruminant animals, a significant amount of carbon contained in ingested plant mate-rial is actually returned to the soil as manure [14]. Soil organic carbon sequestration with the establishment of perennial pastures in the southeastern USA is highly significant (Figure 11) [21]. Compared with sequestration of soil organic carbon under conservation-tillage crop-land, perennial pastures offer greater quantities and increased depth accumulation of soil organic carbon. Management-intensive pasture approaches may be able to sequester even greater quantity and depth distribu-tions of soil organic carbon, assuming a robust forage mixture with deep-rooting capabilities and abundant and diverse supply of nutrients via various organic amendments [27].

Some researchers have recently become concerned with the apparent lack of significance in soil organic car-bon content between conservation agricultural systems and conventional systems [28–30]. Although conservation and conventional systems promote soil organic carbon accumulation in different layers of the rooting zone, which could lead to differences in soil organic carbon sequestration depending upon the depth of sampling (Figure 5), it is the random variation in soil organic car-bon concentration with depth that is of critical concern. Soil organic carbon concentration is often highest near the soil surface and declines with depth, while its relative variation often increases with increasing soil depth (Figure 12) [31]. Experimenters’ ability to detect a statistically sig-nificant difference in soil organic carbon content between two land

Figure 6. Wheat grain yield as a function of soil organic carbon content from 134 farmer trials in the Pampas region of Argentina. With degraded soils having soil organic carbon content of 10 Mg C ha-1, 3-year average wheat grain yield was only 20% of that achieved in high-quality soils with 40 Mg C ha-1 (600 vs. 2800 kg ha-1). Soil with 40 Mg C ha-1 could be expected to contain 4000 kg ha-1 of nitrogen, while a soil with only 10 Mg C ha-1 could be expected to contain only 1000 kg ha-1 of nitrogen. Assuming 2.5% release of nitrogen each year through mineralization of organic matter, then high-quality soil would be expected to release 100 kg ha-1 of nitrogen, while low-quality soil would be expected to release only 25 kg ha-1

of nitrogen. Reproduced with permission from [16].

Key term

Microbial biomass carbon: Small fraction of the soil organic carbon pool composed of bacteria, fungi and actinomycetes that control nutrient cycling though decomposition and mineralization of organic matter.

Carbon Management (2010) 1(2) future science group242

Perspective Franzluebbers

Conservation agricultural systems have great poten-tial to sequester soil organic carbon, which would help mitigate greenhouse gas emissions contributing to cli-mate change and increase soil productivity and avoid further environmental damage from unsustainable use of inversion tillage systems – issues that threaten water quality, reduce soil biodiversity and erode soil

around the world. Conservation agricultural systems have three guiding principles that can be globally applied:

Minimize soil disturbance, consistent with susta inable production;

Maximize soil surface cover by managing crops, pastures and crop residues;

Stimulate biological activity through crop rotations, cover crops and integrated nutrient and pest management.

Impacts from conservation tillage cropping on soil organic carbon sequestration have received a great deal of research attention during the past couple of decades owing to the expansion of this technology through-out the world. Derpsch and Friedrich have estimated that conservation agriculture is practiced on 105 Mha throughout the world, with 26.6 Mha in the USA, 25.5 Mha in Brazil, 19.7 Mha in Argentina, 13.5 in Canada and 12.0 in Australia [20]. Globally, conser-vation agriculture is practiced on only approximately 7% of cropland, suggesting that major expansion of conservation agricultural production is still possible.

Significant soil organic carbon sequestration has occurred with adoption of conservation tillage by farmers in the southeastern USA (Figure 9) [21]. Most notable changes in the stock of soil organic carbon with adoption of conservation tillage occur in the surface 5 cm. This dramatic change in surface-soil organic carbon is a result of crop residues that lie at the surface (blanketing the soil surface with protec-tion from wind and water erosion), undergoing slow decomposition to form stable soil organic matter in immediately underlying soil. The combination of crop residue cover and high surface-soil organic carbon is an ideal habitat for a diverse range of organisms, includ-ing earthworms, beetles, ants, springtails, nematodes, fungi and bacteria [22].

The type of cropping system can also affect the quan-tity of carbon fixed and subsequently available for soil organic carbon accumulation. In a review of 147 studies across the southeastern USA, the rate of soil organic carbon sequestration was greater in cropping systems with winter cover crops (0.55 ± 0.06 Mg C ha-1 year-1, n = 87) than in cropping systems without winter cover crops (0.30 ± 0.05 Mg C ha-1 year-1, n = 60) [23]. Winter cover crops can provide 2–4 Mg C ha-1 year-1 additional above-ground carbon input, plus the same magnitude of below-ground carbon input, whch can contribute to formation of soil organic matter. Obviously, the highly conducive environment for decomposition in the southeastern USA requires a large input of plant biomass for significant changes in soil organic carbon to occur. From cropping systems in South-Central Texas, USA (20°C and 978 mm mean annual temperature and precipitation respectively), the fraction of carbon input from above- and below-ground sources that was seques-tered as organic carbon in the surface 20 cm of soil was estimated to be 0.09 ± 0.04 g g-1 under conventional tillage and 0.22 ± 0.02 g g-1 under no tillage [24]. Higher retention rates could be expected in colder and drier climates and lower retention rates could be expected in warmer and wetter climates. In addition to the quan-tity of organic matter input controlling soil organic car-bon content, tillage, crop rotation and cover cropping

Figure 5. Depth distribution of soil organic carbon concentration by agricultural land management system in the Piedmont of Georgia, USA. Soil organic carbon is often uniformly distributed within the tillage zone (15-cm depth in conventional tillage system). With many years of undisturbed soil using conservation tillage to grow crops, soil organic carbon increases at the surface and declines with depth. Even greater increases in surface soil organic carbon can occur with perennial pastures that are not disturbed by tillage, that have a diversity of plants growing in the spring, summer, and autumn, and that have a large portion of the plant biomass grazed by animals and a portion of that harvested biomass subsequently returned to the soil in undigested form via animal manure. Reproduced with permission from [15].

Key terms

Conservation tillage: Method of plant production that leaves more than 30% residue cover after planting to control erosion and build soil organic carbon; includes minimum tillage, reduced tillage, ridge tillage, direct seeding and no tillage.

Conservation agriculture: Environmental approach to agricultural production that recognizes the appropriateness of multiple soil and water conservation practices to build a sustainable system within a particular region. Three key principles of conservation agriculture are: minimizing soil disturbance, maximizing soil surface cover and stimulating biological activity.

4000

3000

2000

1000

0

0 20 40 60 80

Yie

ld (

kg h

a-1)

Soil organic C (Mg ha-1)

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 243

can alter the quality of soil organic matter, thereby affecting nutrient cycling, aggregation and hydraulic processes [25,26].

Cropping systems with greater amounts of time when soil is cov-ered and plants are growing have greater opportunities to fix car-bon and subsequently store car-bon in soil organic matter. With increasing cropping intensity, soil microbial biomass carbon (and soil organic carbon) increased, irrespec-tive of whether soil was tilled or not (Figure 10) [24]. With an effect on soil organic carbon sequestration simi-lar to that of cover cropping, crop rotations with multiple-season sequences, high biomass produc-tion, and plant diversity offer pro-ducers additional opportunities to reduce the risk of crop failure due to extreme weather events and build resilience with farm production diversification.

Perennial pastures have great potential to sequester soil organic carbon, because land is left rela-tively undisturbed for several years to several decades. The magnitude and rate of change in soil organic carbon will depend on climatic conditions, soil type and condi-tion of land prior to establishment. Perennial pastures often contain a diversity of forages that grow dur-ing different parts of the year, and, therefore, offer extended root-growing opportunities for depositing carbon in soil. In addition, although perennial pastures are often grazed by ruminant animals, a significant amount of carbon contained in ingested plant mate-rial is actually returned to the soil as manure [14]. Soil organic carbon sequestration with the establishment of perennial pastures in the southeastern USA is highly significant (Figure 11) [21]. Compared with sequestration of soil organic carbon under conservation-tillage crop-land, perennial pastures offer greater quantities and increased depth accumulation of soil organic carbon. Management-intensive pasture approaches may be able to sequester even greater quantity and depth distribu-tions of soil organic carbon, assuming a robust forage mixture with deep-rooting capabilities and abundant and diverse supply of nutrients via various organic amendments [27].

Some researchers have recently become concerned with the apparent lack of significance in soil organic car-bon content between conservation agricultural systems and conventional systems [28–30]. Although conservation and conventional systems promote soil organic carbon accumulation in different layers of the rooting zone, which could lead to differences in soil organic carbon sequestration depending upon the depth of sampling (Figure 5), it is the random variation in soil organic car-bon concentration with depth that is of critical concern. Soil organic carbon concentration is often highest near the soil surface and declines with depth, while its relative variation often increases with increasing soil depth (Figure 12) [31]. Experimenters’ ability to detect a statistically sig-nificant difference in soil organic carbon content between two land

Figure 6. Wheat grain yield as a function of soil organic carbon content from 134 farmer trials in the Pampas region of Argentina. With degraded soils having soil organic carbon content of 10 Mg C ha-1, 3-year average wheat grain yield was only 20% of that achieved in high-quality soils with 40 Mg C ha-1 (600 vs. 2800 kg ha-1). Soil with 40 Mg C ha-1 could be expected to contain 4000 kg ha-1 of nitrogen, while a soil with only 10 Mg C ha-1 could be expected to contain only 1000 kg ha-1 of nitrogen. Assuming 2.5% release of nitrogen each year through mineralization of organic matter, then high-quality soil would be expected to release 100 kg ha-1 of nitrogen, while low-quality soil would be expected to release only 25 kg ha-1

of nitrogen. Reproduced with permission from [16].

Key term

Microbial biomass carbon: Small fraction of the soil organic carbon pool composed of bacteria, fungi and actinomycetes that control nutrient cycling though decomposition and mineralization of organic matter.

Cov

er c

rop

bio

mas

s (M

g h

a-1 y

ear-1

)

0

2

4

6

8

10

12

CT CTNT NT

Rye/sorghum Wheat/pearl millet

NT > CT16%

NT > CT34%

Carbon Management (2010) 1(2) future science group244

Perspective Franzluebbers

management systems is several-fold greater in the surface 10 cm of soil than in a deeper zone (e.g., 70–100 cm). Assuming a goal of achieving a 25% increase in soil organic carbon during 10 years of management, a total of seven samples would have to be collected and ana-lyzed to meet the goal of +5.0 Mg C ha-1 in the surface 10 cm of soil, with a starting value of 20 Mg C ha-1 and co efficient of variation of 25%. By contrast, a total of 37 samples would have to be collected and analyzed in order to meet a goal of +2.5 Mg C ha-1 in the 70–100 cm zone of soil with a starting value of 10 Mg C ha-1 and coefficient of variation of 75%. The goal of achieving a 25% increase in soil organic carbon in the surface 10 cm within 10 years of management is reasonable (i.e., 0.5 Mg C ha-1 year-1), but it is likely that it would take 25 years to achieve a 25% increase in soil organic car-bon in the 70–100 cm zone (i.e., 0.1 Mg C ha-1 year-1). Therefore, if sampling is too deep, statistical significance

of soil organic carbon sequestration between two management systems will almost never be achieved within typical field experiments evaluated for below 10 years and outreach programs to promote best manage-ment practices for sequestration of soil organic carbon will be misin-formed and misled. Furthermore, soil organic carbon is much easier to manage at the surface than deeper in the soil profile.

Determining the actual change in soil organic carbon with the adop-tion of an improved management practice, set of management practices or a complete management system is no trivial matter. Although measure-ment of soil organic carbon and its change with time in response to a particular management approach is common practice in a research agenda, it would be impractical within a measurement, monitoring and validation (MMV) protocol owing to the enormous resources needed in skilled labor hours to determine the sampling approach, collecting the large number of soil samples to achieve representativeness and sheer cost of numerous analyses. An alternative approach for MMV would be to use a model (or even a set of different models) to estimate the change in soil organic carbon. Modeling has the advantages of

being a powerful and relatively inexpensive tool for esti-mating soil organic carbon in a large number of scenar-ios. Skilled technical labor is still needed to run models and continually check for potential discrepancies with actual data. Robust, process-based models would be best to describe a broad range of unique conditions, but simpler index-type models could also be used if a mini-mum number of management choices were evaluated. There are many different process-based and index mod-els that could currently be used to estimate soil organic carbon, including CENTURY [32], Rothamsted carbon model (ROTHC) [33], denitrification and decomposi-tion model (DNDC) [34], introductory carbon balance model (ICBM) [35], CQESTR [36], and soil conditioning index (SCI) [37]. However, a key determinant to their success, is sufficient testing and modification to suit the expected diversity of experimental conditions. If, for example, a widely tested model were used in a unique

Figure 7. Above-ground biomass production of rye (in rye/sorghum cropping system) and pearl millet (in wheat/pearl millet cropping system) under CT and NT on a Piedmont soil in Georgia, USA. Winter cover crop production of rye was the average over 3 years and summer cover crop production of pearl millet was the average of over 4 years. Each cropping system followed a 20-year period of perennial pasture, which resulted in a high accumulation of soil organic matter. Although nutrients were released from stimulation of soil organic matter decomposition with CT during the initial 3–4 years, greater cover crop biomass production occurred with NT than with CT due to non-nutrient-related physical and/or biological factors. Therefore, preservation of soil organic matter with NT was more important for subsequent production than stimulation of nutrient release with CT. CT: Conventional tillage; NT: No tillage. Data from [17].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 245

0

10

20

30

40

50

n = 15 n = 15 n = 2

a

b b

0

2

4

6

8

n = 14n = 14

n = 3

a

bb

0

1

2

n = 7 n = 6n = 4

a

b

b

Total

Dissolved

Conventionaltillage

cropping

Notillage

cropping

Perennialpasture

Wat

er r

un

off

(% o

f p

reci

pit

atio

n)

So

il lo

ss v

ia r

un

off

(M

g h

a-1)

Lo

ss o

f p

ho

spo

rus

in r

un

off

(kg

ha-1

)

A

B

C

Figure 8. Summary of how agricultural land use a�ects (A) water runo� volume, (B) soil loss and (C) runo� loss of phosphorus in a variety of studies conducted throughout the eastern USA. Although soil organic carbon was not reported in all studies, presumed soil organic carbon concentration at the soil surface ranged from lowest in conventional-tillage cropping, intermediate in no-tillage cropping and highest in perennial pasture. With increasing soil organic carbon following adoption of conservation agricultural management (i.e., no-tillage cropping and perennial pasture), water runo� is reduced, soil erosion is reduced and nutrient movement into surface water bodies is reduced. With conservation agricultural management, on-site soil quality is enhanced and o�-site sedimentation and water quality impairment are greatly reduced. Data from multiple sources reported in [18].

ecological condition, simulations may not be accurate on a specific project basis, but would probably be precise enough over a bundling of projects across a region. Critical in the use of models to estimate soil organic carbon (and certainly this is the only practical approach, rather than direct measurements) is that a large research support structure justifies the validity of the model under all of the ecological condi-tions in which the model might be used. Therefore, a great deal of up-front and robust research is needed when selecting a particular model for wide-scale implementation.

Who will bene�t from increased soil organic carbon?Farmers and landowners are the primary beneficiaries of soil with higher organic matter content, because they are rewarded with bet-ter tilth, higher nutrient-supplying capacity, improved capacity of soil to withstand drought and store water in the rooting zone, more resilient soil to perturbations from the environment, and abundant biological diversity to support vig-orous plants and sustained ecosys-tem services. However, despite all the benefits that greater soil organic carbon provides to farmers and landowners, there are still a multi-tude of additional beneficiaries to all of society – the local engineer-ing department that does not have to clear the ditches of sediment; rec-reational and professional fishermen who have unpolluted water so that they can catch an abundant supply of fish; highway drivers who can see the road rather than fight the dust blowing around from barren fields; taxpayers who do not have to pay for dredging waterways; emergency management officials who do not have to clean up and make disaster payments to overcome f looding, silting and drought; and consum-ers who can enjoy high quality food without pesticide contamination

Cov

er c

rop

bio

mas

s (M

g h

a-1 y

ear-1

)

0

2

4

6

8

10

12

CT CTNT NT

Rye/sorghum Wheat/pearl millet

NT > CT16%

NT > CT34%

Carbon Management (2010) 1(2) future science group244

Perspective Franzluebbers

management systems is several-fold greater in the surface 10 cm of soil than in a deeper zone (e.g., 70–100 cm). Assuming a goal of achieving a 25% increase in soil organic carbon during 10 years of management, a total of seven samples would have to be collected and ana-lyzed to meet the goal of +5.0 Mg C ha-1 in the surface 10 cm of soil, with a starting value of 20 Mg C ha-1 and co efficient of variation of 25%. By contrast, a total of 37 samples would have to be collected and analyzed in order to meet a goal of +2.5 Mg C ha-1 in the 70–100 cm zone of soil with a starting value of 10 Mg C ha-1 and coefficient of variation of 75%. The goal of achieving a 25% increase in soil organic carbon in the surface 10 cm within 10 years of management is reasonable (i.e., 0.5 Mg C ha-1 year-1), but it is likely that it would take 25 years to achieve a 25% increase in soil organic car-bon in the 70–100 cm zone (i.e., 0.1 Mg C ha-1 year-1). Therefore, if sampling is too deep, statistical significance

of soil organic carbon sequestration between two management systems will almost never be achieved within typical field experiments evaluated for below 10 years and outreach programs to promote best manage-ment practices for sequestration of soil organic carbon will be misin-formed and misled. Furthermore, soil organic carbon is much easier to manage at the surface than deeper in the soil profile.

Determining the actual change in soil organic carbon with the adop-tion of an improved management practice, set of management practices or a complete management system is no trivial matter. Although measure-ment of soil organic carbon and its change with time in response to a particular management approach is common practice in a research agenda, it would be impractical within a measurement, monitoring and validation (MMV) protocol owing to the enormous resources needed in skilled labor hours to determine the sampling approach, collecting the large number of soil samples to achieve representativeness and sheer cost of numerous analyses. An alternative approach for MMV would be to use a model (or even a set of different models) to estimate the change in soil organic carbon. Modeling has the advantages of

being a powerful and relatively inexpensive tool for esti-mating soil organic carbon in a large number of scenar-ios. Skilled technical labor is still needed to run models and continually check for potential discrepancies with actual data. Robust, process-based models would be best to describe a broad range of unique conditions, but simpler index-type models could also be used if a mini-mum number of management choices were evaluated. There are many different process-based and index mod-els that could currently be used to estimate soil organic carbon, including CENTURY [32], Rothamsted carbon model (ROTHC) [33], denitrification and decomposi-tion model (DNDC) [34], introductory carbon balance model (ICBM) [35], CQESTR [36], and soil conditioning index (SCI) [37]. However, a key determinant to their success, is sufficient testing and modification to suit the expected diversity of experimental conditions. If, for example, a widely tested model were used in a unique

Figure 7. Above-ground biomass production of rye (in rye/sorghum cropping system) and pearl millet (in wheat/pearl millet cropping system) under CT and NT on a Piedmont soil in Georgia, USA. Winter cover crop production of rye was the average over 3 years and summer cover crop production of pearl millet was the average of over 4 years. Each cropping system followed a 20-year period of perennial pasture, which resulted in a high accumulation of soil organic matter. Although nutrients were released from stimulation of soil organic matter decomposition with CT during the initial 3–4 years, greater cover crop biomass production occurred with NT than with CT due to non-nutrient-related physical and/or biological factors. Therefore, preservation of soil organic matter with NT was more important for subsequent production than stimulation of nutrient release with CT. CT: Conventional tillage; NT: No tillage. Data from [17].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 245

0

10

20

30

40

50

n = 15 n = 15 n = 2

a

b b

0

2

4

6

8

n = 14n = 14

n = 3

a

bb

0

1

2

n = 7 n = 6n = 4

a

b

b

Total

Dissolved

Conventionaltillage

cropping

Notillage

cropping

Perennialpasture

Wat

er r

un

off

(% o

f p

reci

pit

atio

n)

So

il lo

ss v

ia r

un

off

(M

g h

a-1)

Lo

ss o

f p

ho

spo

rus

in r

un

off

(kg

ha-1

)

A

B

C

Figure 8. Summary of how agricultural land use a�ects (A) water runo� volume, (B) soil loss and (C) runo� loss of phosphorus in a variety of studies conducted throughout the eastern USA. Although soil organic carbon was not reported in all studies, presumed soil organic carbon concentration at the soil surface ranged from lowest in conventional-tillage cropping, intermediate in no-tillage cropping and highest in perennial pasture. With increasing soil organic carbon following adoption of conservation agricultural management (i.e., no-tillage cropping and perennial pasture), water runo� is reduced, soil erosion is reduced and nutrient movement into surface water bodies is reduced. With conservation agricultural management, on-site soil quality is enhanced and o�-site sedimentation and water quality impairment are greatly reduced. Data from multiple sources reported in [18].

ecological condition, simulations may not be accurate on a specific project basis, but would probably be precise enough over a bundling of projects across a region. Critical in the use of models to estimate soil organic carbon (and certainly this is the only practical approach, rather than direct measurements) is that a large research support structure justifies the validity of the model under all of the ecological condi-tions in which the model might be used. Therefore, a great deal of up-front and robust research is needed when selecting a particular model for wide-scale implementation.

Who will bene�t from increased soil organic carbon?Farmers and landowners are the primary beneficiaries of soil with higher organic matter content, because they are rewarded with bet-ter tilth, higher nutrient-supplying capacity, improved capacity of soil to withstand drought and store water in the rooting zone, more resilient soil to perturbations from the environment, and abundant biological diversity to support vig-orous plants and sustained ecosys-tem services. However, despite all the benefits that greater soil organic carbon provides to farmers and landowners, there are still a multi-tude of additional beneficiaries to all of society – the local engineer-ing department that does not have to clear the ditches of sediment; rec-reational and professional fishermen who have unpolluted water so that they can catch an abundant supply of fish; highway drivers who can see the road rather than fight the dust blowing around from barren fields; taxpayers who do not have to pay for dredging waterways; emergency management officials who do not have to clean up and make disaster payments to overcome f looding, silting and drought; and consum-ers who can enjoy high quality food without pesticide contamination

Carbon Management (2010) 1(2) future science group246

Perspective Franzluebbers

because pests are under better control in fields rich in fertility and resistant to pestilence.

If beneficiaries are expanded outside of the human domain, then the Earth and its ecosystems and eco-system services are hugely improved with soils having greater soil organic carbon. Agriculture is fundamen-tally an extractive process serving humankind, but if soils can be managed with conservation agricultural principles (i.e., avoiding disturbance of soil, leaving resi-dues on the surface and diversifying to obtain biologi-cal synergies), humankind can become closer aligned with nature. Environmental benefits associated with conservation agriculture include [101]:

Favorable hydrologic balance and flows in rivers to withstand extreme weather events;

Reduced incidence and intensity of desertification, which allows ecosystems to rejuvenate following extreme weather events;

Increased soil biodiversity, which builds resilience to perturbations;

Less soil erosion resulting in less sediment in rivers and dams and flourishing aquatic ecosystems;

Potential for reduced emissions of other greenhouse gases, including methane and nitrous oxide, if com-paction is avoided, such as with the adoption of controlled traff ic-strategies;

Reduced deforestation owing to land intensification and more relia-ble and higher crop yield, which cre-ates a more favorable balance between agricultural lands and con-servation reserves that are left undisturbed;

Less water pollution from pesti-cides, applied fertilizer nutrients, and antibiotics and other pharma-ceuticals from irrigation and waste water applications, which keeps aquatic systems healthy and avoids further landscape manipulations to prevent water pollution;

Less hypoxia of coastal ecosys-tems, thereby allowing these diverse aquatic systems to properly function in cycling nutrients at the interface of fresh and salt-water ecosystems.

Barriers to adoption of conservation agricultural practicesWith so many beneficiaries from increased soil organic carbon, why is this natural resource so greatly underap-preciated? Why also are conservation agricultural sys-tems, which help promote soil organic carbon accumula-tion, largely not widely adopted by farmers? Some reasons are technological, some are programmatic, and some are simply sociological.

Technologically, developing agricultural systems with minimal soil disturbance, maximum soil cover, and heightened diverse biological activity (i.e., the three essential elements of conservation agriculture in a system that can promote soil organic carbon accu-mulation) is relatively easy. There are under developed regions of the world that do not have access to equip-ment or financial resources to adopt direct seeding to minimize soil disturbance, apply herbicides rather than use tillage to control weeds, or apply inorganic or organic fertilizers instead of land clearing to create fertile conditions. Adequate machinery and appropriate herbicides were previously a limitation in developed

Soil organic carbon sequestration (Mg ha-1 year-1)

-1.0 -0.5 0.0 0.5 1.0

So

il d

epth

(cm

)

-20

-15

-10

-5

0

*0.41

0.08

-0.03

----------------------------------0–20 cm

Difference in SOC betweenconservation tillage andconventional tillage(SOCconserv-SOCconvent)/years

0.45 ± 0.13

Figure 9. Soil organic carbon sequestration with the adoption of conservation tillage compared with conventional tillage on 29 farms throughout the southeastern USA. Sequestration of carbon occurred primarily in the surface 5 cm of soil. The value of 0.45 ± 0.13 Mg C ha-1 year-1 represents the mean ± standard error among 29 comparisons throughout the 20-cm sampling depth. Conservation tillage systems were sampled at the end of 12 ± 6 years of continuous implementation in Alabama, Georgia, South Carolina, North Carolina and Virginia (USA). Similar positive response to conservation tillage was observed in soil microbial biomass carbon, potential soil microbial activity and water-stable aggregation. SOC: Soil Organic Carbon. Data from [21].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 247

countries, but technological inno-vations and active networking among farmers and industry repre-sentatives overcame many of these technological limitations. Even in nonmechanized agricultural sys-tems, no-till farming can be suc-cessfully developed through inno-vations by farmers and conservation professionals [38].

Programmatically, government policies can have a large influence on adoption of conservation agri-cultural systems by providing pack-aged incentives to promote envi-ronmental stewardship, maintain productive capacity, and support rural development. Currently, there are only a few examples of govern-ment programs specifically designed to support farmers for adopting conservation agricultural systems; currently in the USA there is the Environmental Quality Incentives Program (EQIP) [102] and the Conservation Stewardship Program (CSP) [103] administered by the US Department of Agriculture – Natural Resources Conservation Service (NRCS). Reauthorized in the 2002 Farm Bill, EQIP provides financial and technical assistance to farmers and ranch-ers who adopt environmentally sound practices on eli-gible agricultural land. Program practices and activities are carried out in an EQIP program plan that identifies appropriate conservation practices addressing a specific resource concern. Practices are subject to NRCS tech-nical standards adapted for local conditions. National priorities addressed by EQIP are:

Reduction of nonpoint source pollution, such as nutrients, sediment or pesticides;

Reduction of groundwater contamination;

Conservation of ground and surface water resources;

Reduction of greenhouse gas emissions;

Reduction in soil erosion and sedimentation from unacceptable levels on agricultural land;

Promotion of habitat conservation for at-risk species.

A voluntary conservation program, the CSP encour-ages producers to address resource concerns in a comprehensive manner by:

Undertaking additional conservation activities;

Improving, maintaining, and managing existing conservation activities.

The CSP altered how NRCS provides conservation program payments. Instead of using the traditional compensation model that pays a per-acre rental rate or a percentage of the estimated cost of installing a practice, CSP pays for conservation performance – the higher the performance, the higher the payment. Previously the CSP was limited to targeted watersheds, but currently is open to all program-eligible producers throughout the country. Ranking period 2 in 2010 allows for either:

‘Enhancement payment’; targeting conservation activities that exceed the sustainable level for a given resource concern used to treat natural resources and greatly improve conservation performance; enhance-ment practices may be single or bundles, in which a group of specific enhancements when installed as a group address resource concerns synergistically; or

0.3 0.4 0.5 0.6 0.7 0.8 0.9

So

il m

icro

bia

l bio

mas

s ca

rbo

n (

kg h

a-1)

0

500

1000

1500

2000

2500

Conventional tillageSMBC = 50 + 306 (intensity)–186 (intensity)2

r2 = 0.99 **

No tillageSMBC = 148 + 81 (intensity)r2 = 0.99 **

Cropping intensity (fraction of year that a crop is in the field)

Soybean

Sorghum

WheatSorghum–wheat/soybean

Wheat/soybean

Adjacent long-term pasture = 3360

Figure 10. E�ect of increasing cropping intensity on soil microbial biomass carbon under conventional and no tillage. Soil microbial biomass carbon is the active portion of soil organic carbon and is highly related to the total amount of carbon in soil. Increasing opportunities exist to feed soil microorganisms and build soil organic carbon with greater cropping intensity. Seasonal variations in soil microbial biomass are denoted in error bars for each cropping system. SMBC: Soil microbial biomass carbon. Adapted from [24].

Carbon Management (2010) 1(2) future science group246

Perspective Franzluebbers

because pests are under better control in fields rich in fertility and resistant to pestilence.

If beneficiaries are expanded outside of the human domain, then the Earth and its ecosystems and eco-system services are hugely improved with soils having greater soil organic carbon. Agriculture is fundamen-tally an extractive process serving humankind, but if soils can be managed with conservation agricultural principles (i.e., avoiding disturbance of soil, leaving resi-dues on the surface and diversifying to obtain biologi-cal synergies), humankind can become closer aligned with nature. Environmental benefits associated with conservation agriculture include [101]:

Favorable hydrologic balance and flows in rivers to withstand extreme weather events;

Reduced incidence and intensity of desertification, which allows ecosystems to rejuvenate following extreme weather events;

Increased soil biodiversity, which builds resilience to perturbations;

Less soil erosion resulting in less sediment in rivers and dams and flourishing aquatic ecosystems;

Potential for reduced emissions of other greenhouse gases, including methane and nitrous oxide, if com-paction is avoided, such as with the adoption of controlled traff ic-strategies;

Reduced deforestation owing to land intensification and more relia-ble and higher crop yield, which cre-ates a more favorable balance between agricultural lands and con-servation reserves that are left undisturbed;

Less water pollution from pesti-cides, applied fertilizer nutrients, and antibiotics and other pharma-ceuticals from irrigation and waste water applications, which keeps aquatic systems healthy and avoids further landscape manipulations to prevent water pollution;

Less hypoxia of coastal ecosys-tems, thereby allowing these diverse aquatic systems to properly function in cycling nutrients at the interface of fresh and salt-water ecosystems.

Barriers to adoption of conservation agricultural practicesWith so many beneficiaries from increased soil organic carbon, why is this natural resource so greatly underap-preciated? Why also are conservation agricultural sys-tems, which help promote soil organic carbon accumula-tion, largely not widely adopted by farmers? Some reasons are technological, some are programmatic, and some are simply sociological.

Technologically, developing agricultural systems with minimal soil disturbance, maximum soil cover, and heightened diverse biological activity (i.e., the three essential elements of conservation agriculture in a system that can promote soil organic carbon accu-mulation) is relatively easy. There are under developed regions of the world that do not have access to equip-ment or financial resources to adopt direct seeding to minimize soil disturbance, apply herbicides rather than use tillage to control weeds, or apply inorganic or organic fertilizers instead of land clearing to create fertile conditions. Adequate machinery and appropriate herbicides were previously a limitation in developed

Soil organic carbon sequestration (Mg ha-1 year-1)

-1.0 -0.5 0.0 0.5 1.0

So

il d

epth

(cm

)

-20

-15

-10

-5

0

*0.41

0.08

-0.03

----------------------------------0–20 cm

Difference in SOC betweenconservation tillage andconventional tillage(SOCconserv-SOCconvent)/years

0.45 ± 0.13

Figure 9. Soil organic carbon sequestration with the adoption of conservation tillage compared with conventional tillage on 29 farms throughout the southeastern USA. Sequestration of carbon occurred primarily in the surface 5 cm of soil. The value of 0.45 ± 0.13 Mg C ha-1 year-1 represents the mean ± standard error among 29 comparisons throughout the 20-cm sampling depth. Conservation tillage systems were sampled at the end of 12 ± 6 years of continuous implementation in Alabama, Georgia, South Carolina, North Carolina and Virginia (USA). Similar positive response to conservation tillage was observed in soil microbial biomass carbon, potential soil microbial activity and water-stable aggregation. SOC: Soil Organic Carbon. Data from [21].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 247

countries, but technological inno-vations and active networking among farmers and industry repre-sentatives overcame many of these technological limitations. Even in nonmechanized agricultural sys-tems, no-till farming can be suc-cessfully developed through inno-vations by farmers and conservation professionals [38].

Programmatically, government policies can have a large influence on adoption of conservation agri-cultural systems by providing pack-aged incentives to promote envi-ronmental stewardship, maintain productive capacity, and support rural development. Currently, there are only a few examples of govern-ment programs specifically designed to support farmers for adopting conservation agricultural systems; currently in the USA there is the Environmental Quality Incentives Program (EQIP) [102] and the Conservation Stewardship Program (CSP) [103] administered by the US Department of Agriculture – Natural Resources Conservation Service (NRCS). Reauthorized in the 2002 Farm Bill, EQIP provides financial and technical assistance to farmers and ranch-ers who adopt environmentally sound practices on eli-gible agricultural land. Program practices and activities are carried out in an EQIP program plan that identifies appropriate conservation practices addressing a specific resource concern. Practices are subject to NRCS tech-nical standards adapted for local conditions. National priorities addressed by EQIP are:

Reduction of nonpoint source pollution, such as nutrients, sediment or pesticides;

Reduction of groundwater contamination;

Conservation of ground and surface water resources;

Reduction of greenhouse gas emissions;

Reduction in soil erosion and sedimentation from unacceptable levels on agricultural land;

Promotion of habitat conservation for at-risk species.

A voluntary conservation program, the CSP encour-ages producers to address resource concerns in a comprehensive manner by:

Undertaking additional conservation activities;

Improving, maintaining, and managing existing conservation activities.

The CSP altered how NRCS provides conservation program payments. Instead of using the traditional compensation model that pays a per-acre rental rate or a percentage of the estimated cost of installing a practice, CSP pays for conservation performance – the higher the performance, the higher the payment. Previously the CSP was limited to targeted watersheds, but currently is open to all program-eligible producers throughout the country. Ranking period 2 in 2010 allows for either:

‘Enhancement payment’; targeting conservation activities that exceed the sustainable level for a given resource concern used to treat natural resources and greatly improve conservation performance; enhance-ment practices may be single or bundles, in which a group of specific enhancements when installed as a group address resource concerns synergistically; or

0.3 0.4 0.5 0.6 0.7 0.8 0.9

So

il m

icro

bia

l bio

mas

s ca

rbo

n (

kg h

a-1)

0

500

1000

1500

2000

2500

Conventional tillageSMBC = 50 + 306 (intensity)–186 (intensity)2

r2 = 0.99 **

No tillageSMBC = 148 + 81 (intensity)r2 = 0.99 **

Cropping intensity (fraction of year that a crop is in the field)

Soybean

Sorghum

WheatSorghum–wheat/soybean

Wheat/soybean

Adjacent long-term pasture = 3360

Figure 10. E�ect of increasing cropping intensity on soil microbial biomass carbon under conventional and no tillage. Soil microbial biomass carbon is the active portion of soil organic carbon and is highly related to the total amount of carbon in soil. Increasing opportunities exist to feed soil microorganisms and build soil organic carbon with greater cropping intensity. Seasonal variations in soil microbial biomass are denoted in error bars for each cropping system. SMBC: Soil microbial biomass carbon. Adapted from [24].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 249

through newly incentivized con-servation agricultural systems on 120 Mha of privately owned agri-cultural land in the USA, this could lead to sequestration of 220 Tg of CO

2 per year, equivalent to 4%

of the approximately 5.8 Pg CO2

emitted in the USA each year.

AcknowledgementsAppreciation is extended to Steve Knapp for technical assistance and to ARS scien-tists involved with and supporting the cros s- locat ion re search pro jec t of GRACEnet (Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network).

Financial disclosureThis review was prepared as part of official duties with the US Department of Agriculture – Agricultural Research Service. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. No writing assistance was utilized in the production of this manuscript.

Soil organic carbon (g kg-1)

0 5 10 15 20 25

So

il d

epth

(m

)

-1.5

-1.2

-0.9

-0.6

-0.3

0.0

Coefficient of variation (%)

27

32

51

61

113

97

61

Figure 12. Typical soil organic carbon concentration (mean ± standard deviation among 122 cores within a 15-ha �eld) and coe cient of variation throughout a 1.5-m soil pro�le in the Piedmont of Georgia, USA. Soil organic carbon concentration and absolute variation are highest near the soil surface and decline with depth. Relative variation (i.e., the percentage of variation per unit of the mean value; coe�cient of variation) increases with sampling depth and makes it very di�cult to detect actual changes in soil organic carbon with increasing soil depth. To overcome the large coe�cient of variation with increasing depth, researchers must sample a �eld intensively with either numerous cores or frequent samplings over time; both of which are costly and laborious. Adapted with permission from [31].

BibliographyPapers of special note have been highlighted as:

of interestof considerable interest

1 Millennium Ecosystem Assessment. Ecosystems and Human Well-being: Synthesis. Island Press, DC, USA (2005).

2 Janzen HH, Fixen P, Franzluebbers AJ et al. Global prospects rooted in soil science. Soil Sci. Soc. Am. J. DOI: 10.2136/sssaj2009.0216 (2010).

Discussion of several key soil-science influenced issues of great importance to society.

3 Sugden A, Stone R, Ash C. Ecology in the underworld. Science 304, 1613 (2004).

Highlighting the broad recognition of the value of soil to ecosystem functioning from a global perspective.

4 Brady NC, Weil RR. The Nature and Properties of Soils. (12th Edition). Prentice Hall, NJ, USA 881 (1999).

Textbook reference of soil properties and processes and their relation to ecosystem services.

5 Le Quéré C, Raupach MR, Canadell JG et al. Trends in the sources and sinks of carbon dioxide. Nature Geosciences 2, 831–836 (2009).

6 Mann LK. Changes in soil carbon storage after cultivation. Soil Sci. 142, 279–288 (1986).

7 Davidson EA, Ackerman IL. Changes in soil carbon inventories following cultivation of previously untilled soils. Biogeochemistry 20, 161–193 (1993).

8 Lal R. Soil carbon sequestration impacts on global climate change and food security. Science 304, 1623–1627 (2004).

9 Lal R. Farming carbon. Soil Tillage Res. 96, 1–5 (2007).

10 Doran JW, Coleman DC, Bezdicek DF, Stewart BA. Defining Soil Quality for a Sustainable Environment. Soil Science Society of America Special Publ. 35. WI, USA 244 (1994).

Early and thorough compilation of how soil management affects numerous soil properties within the context of soil sustainability.

11 Hudson BD. Soil organic matter and available water capacity. J. Soil Water Conserv. 49(2), 189–194 (1994).

12 Franzluebbers AJ, Brock BG. Surface soil responses to silage cropping intensity on a Typic Kanhapludult in the piedmont of North Carolina. Soil Tillage Res. 93, 126–137 (2007).

13 Jenny H. Factors of Soil Formation: A System of Quantitative Pedology. Dover Press, NY, USA (1994).

Carbon Management (2010) 1(2) future science group248

Perspective Franzluebbers

‘Supplemental payment’ when adopting resource-conserving crop rotations that include at least one resource conserving crop (determined by specific State Conservationist), reduces erosion, improves soil fertility and tilth, interrupts pest cycles, and reduces depletion of soil moisture or otherwise reduces the need for irrigation (typically a grass; legume for use as forage, seed for planting, or green manure; legume–grass mixture; or small grain grown in combination with a grass or legume green manure crop).

Since producers are already incentivized to adopt conservation practices, it would seem a relatively small step for them to enter a regulatory carbon market, in which they could provide offsets to industrial emitters that might not meet their cap. Voluntary carbon offsets have been marketed through a cur-rently depressed system implemented by the Chicago Climate Exchange [104]. In addition, the Voluntary

Carbon Standard is reviewing protocols for soil carbon seques-tration [105]. General lack of con-fidence in current voluntary mar-kets has depressed prices and there is bated anticipation regarding energy and federal cap and trade legislation, which has no clear programmatic structure as of yet. A piece of pending legislation is the ‘American Clean Energy and Security Act of 2009.’ Its broad goal is “to create clean energy jobs, achieve energy independence, reduce global warming pollution and transition to a clean energy economy.” This legislation has not yet been enacted owing to political differences of opinion in Congress and lack of precedence.

Sociologically, the majority of farmers tend to be quite conserva-tive in their approach. Therefore, unwillingness to change man-agement practices and enroll in untried programs has caused some trepidation and lack of participa-tion. Leadership from key farming organizations will be needed for the process of carbon market trading in the agricultural sector to move forward more quickly than in the past with other programs. Some other sociological issues concerning

why farmers do not adopt conservation agricultural systems include tradition or prejudice and having sufficient knowledge and institutional support for adopting practices [20].

Future perspectiveSoil organic carbon is an invaluable resource on pro-ductive and sustainable farms. Commoditization of carbon in a developing market place, should a regu-latory approach be instituted in the USA, will yield a noncompeting value for carbon that farmers can use to further improve the environmental, social and economic well-being of their communities and region. Monetizing the value of carbon may be a necessary future step towards increasing the public’s perception of how important soil is for numerous ecosystem serv-ices that are currently taken for granted. Marketing carbon stored on agricultural lands will bring renewed vigor and appreciation for land stewardship. Assuming that an average of 0.5 Mg C ha-1 year-1 can be stored

Soil organic carbon sequestration (Mg ha-1 year -1)

-1.0 -0.5 0.0 0.5 1.0

So

il d

epth

(cm

)

-20

-15

-10

-5

0

*0.53

0.17

0.05

----------------------------------

0–20 cm 0.74 ± 0.12

Difference in SOC betweenperennial pasture andconventional tillage(SOCpasture–SOCconvent)/years

*

Figure 11. Soil organic carbon sequestration with the adoption of perennial pastures compared with conventional tillage on 29 farms throughout the southeastern USA. Sequestration of carbon occurred primarily in the surface 12 cm of soil. The value of 0.74 ± 0.12 Mg C ha-1 year-1 represents the mean ± standard error among 29 comparisons throughout the 20-cm sampling depth. Pastures were sampled at the end of 24 ± 11 years of continuous implementation in Alabama, Georgia, South Carolina, North Carolina and Virginia (USA). When comparing these results with those in Figure 9, SOC sequestration with perennial pastures was 64% greater than with conservation-tillage cropping, along with signi�cantly greater accumulation at lower depths. SOC: Soil organic carbon. Data from [21].

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 249

through newly incentivized con-servation agricultural systems on 120 Mha of privately owned agri-cultural land in the USA, this could lead to sequestration of 220 Tg of CO

2 per year, equivalent to 4%

of the approximately 5.8 Pg CO2

emitted in the USA each year.

AcknowledgementsAppreciation is extended to Steve Knapp for technical assistance and to ARS scien-tists involved with and supporting the cros s- locat ion re search pro jec t of GRACEnet (Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network).

Financial disclosureThis review was prepared as part of official duties with the US Department of Agriculture – Agricultural Research Service. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. No writing assistance was utilized in the production of this manuscript.

Soil organic carbon (g kg-1)

0 5 10 15 20 25

So

il d

epth

(m

)

-1.5

-1.2

-0.9

-0.6

-0.3

0.0

Coefficient of variation (%)

27

32

51

61

113

97

61

Figure 12. Typical soil organic carbon concentration (mean ± standard deviation among 122 cores within a 15-ha �eld) and coe cient of variation throughout a 1.5-m soil pro�le in the Piedmont of Georgia, USA. Soil organic carbon concentration and absolute variation are highest near the soil surface and decline with depth. Relative variation (i.e., the percentage of variation per unit of the mean value; coe�cient of variation) increases with sampling depth and makes it very di�cult to detect actual changes in soil organic carbon with increasing soil depth. To overcome the large coe�cient of variation with increasing depth, researchers must sample a �eld intensively with either numerous cores or frequent samplings over time; both of which are costly and laborious. Adapted with permission from [31].

BibliographyPapers of special note have been highlighted as:

of interestof considerable interest

1 Millennium Ecosystem Assessment. Ecosystems and Human Well-being: Synthesis. Island Press, DC, USA (2005).

2 Janzen HH, Fixen P, Franzluebbers AJ et al. Global prospects rooted in soil science. Soil Sci. Soc. Am. J. DOI: 10.2136/sssaj2009.0216 (2010).

Discussion of several key soil-science influenced issues of great importance to society.

3 Sugden A, Stone R, Ash C. Ecology in the underworld. Science 304, 1613 (2004).

Highlighting the broad recognition of the value of soil to ecosystem functioning from a global perspective.

4 Brady NC, Weil RR. The Nature and Properties of Soils. (12th Edition). Prentice Hall, NJ, USA 881 (1999).

Textbook reference of soil properties and processes and their relation to ecosystem services.

5 Le Quéré C, Raupach MR, Canadell JG et al. Trends in the sources and sinks of carbon dioxide. Nature Geosciences 2, 831–836 (2009).

6 Mann LK. Changes in soil carbon storage after cultivation. Soil Sci. 142, 279–288 (1986).

7 Davidson EA, Ackerman IL. Changes in soil carbon inventories following cultivation of previously untilled soils. Biogeochemistry 20, 161–193 (1993).

8 Lal R. Soil carbon sequestration impacts on global climate change and food security. Science 304, 1623–1627 (2004).

9 Lal R. Farming carbon. Soil Tillage Res. 96, 1–5 (2007).

10 Doran JW, Coleman DC, Bezdicek DF, Stewart BA. Defining Soil Quality for a Sustainable Environment. Soil Science Society of America Special Publ. 35. WI, USA 244 (1994).

Early and thorough compilation of how soil management affects numerous soil properties within the context of soil sustainability.

11 Hudson BD. Soil organic matter and available water capacity. J. Soil Water Conserv. 49(2), 189–194 (1994).

12 Franzluebbers AJ, Brock BG. Surface soil responses to silage cropping intensity on a Typic Kanhapludult in the piedmont of North Carolina. Soil Tillage Res. 93, 126–137 (2007).

13 Jenny H. Factors of Soil Formation: A System of Quantitative Pedology. Dover Press, NY, USA (1994).

Carbon Management (2010) 1(2) future science group248

Perspective Franzluebbers

‘Supplemental payment’ when adopting resource-conserving crop rotations that include at least one resource conserving crop (determined by specific State Conservationist), reduces erosion, improves soil fertility and tilth, interrupts pest cycles, and reduces depletion of soil moisture or otherwise reduces the need for irrigation (typically a grass; legume for use as forage, seed for planting, or green manure; legume–grass mixture; or small grain grown in combination with a grass or legume green manure crop).

Since producers are already incentivized to adopt conservation practices, it would seem a relatively small step for them to enter a regulatory carbon market, in which they could provide offsets to industrial emitters that might not meet their cap. Voluntary carbon offsets have been marketed through a cur-rently depressed system implemented by the Chicago Climate Exchange [104]. In addition, the Voluntary

Carbon Standard is reviewing protocols for soil carbon seques-tration [105]. General lack of con-fidence in current voluntary mar-kets has depressed prices and there is bated anticipation regarding energy and federal cap and trade legislation, which has no clear programmatic structure as of yet. A piece of pending legislation is the ‘American Clean Energy and Security Act of 2009.’ Its broad goal is “to create clean energy jobs, achieve energy independence, reduce global warming pollution and transition to a clean energy economy.” This legislation has not yet been enacted owing to political differences of opinion in Congress and lack of precedence.

Sociologically, the majority of farmers tend to be quite conserva-tive in their approach. Therefore, unwillingness to change man-agement practices and enroll in untried programs has caused some trepidation and lack of participa-tion. Leadership from key farming organizations will be needed for the process of carbon market trading in the agricultural sector to move forward more quickly than in the past with other programs. Some other sociological issues concerning

why farmers do not adopt conservation agricultural systems include tradition or prejudice and having sufficient knowledge and institutional support for adopting practices [20].

Future perspectiveSoil organic carbon is an invaluable resource on pro-ductive and sustainable farms. Commoditization of carbon in a developing market place, should a regu-latory approach be instituted in the USA, will yield a noncompeting value for carbon that farmers can use to further improve the environmental, social and economic well-being of their communities and region. Monetizing the value of carbon may be a necessary future step towards increasing the public’s perception of how important soil is for numerous ecosystem serv-ices that are currently taken for granted. Marketing carbon stored on agricultural lands will bring renewed vigor and appreciation for land stewardship. Assuming that an average of 0.5 Mg C ha-1 year-1 can be stored

Soil organic carbon sequestration (Mg ha-1 year -1)

-1.0 -0.5 0.0 0.5 1.0

So

il d

epth

(cm

)

-20

-15

-10

-5

0

*0.53

0.17

0.05

----------------------------------

0–20 cm 0.74 ± 0.12

Difference in SOC betweenperennial pasture andconventional tillage(SOCpasture–SOCconvent)/years

*

Figure 11. Soil organic carbon sequestration with the adoption of perennial pastures compared with conventional tillage on 29 farms throughout the southeastern USA. Sequestration of carbon occurred primarily in the surface 12 cm of soil. The value of 0.74 ± 0.12 Mg C ha-1 year-1 represents the mean ± standard error among 29 comparisons throughout the 20-cm sampling depth. Pastures were sampled at the end of 24 ± 11 years of continuous implementation in Alabama, Georgia, South Carolina, North Carolina and Virginia (USA). When comparing these results with those in Figure 9, SOC sequestration with perennial pastures was 64% greater than with conservation-tillage cropping, along with signi�cantly greater accumulation at lower depths. SOC: Soil organic carbon. Data from [21].

Carbon Management (2010) 1(2) future science group250

Perspective Franzluebbers

Executive summary

Importance of soil Soil is as vital to human survival as air, water and the sun are; its protection and enrichment with organic carbon are needed for the future

sustainability of our planet. Many global issues are intricately linked to soil properties and processes, including food availability, fresh water availability, need for

external nutrients, production of bio-based energy, climate change, biodiversity and ecosystem resilience, waste recycling, and addressing local issues within a global context.

What is soil carbon? Soil carbon is composed of inorganic carbonates and organic matter – living roots, insects and microorganisms as well as dead, dying and

partially decayed organic matter. Soil organic matter is composed of 50–58% carbon. Soil organic carbon is a critical driver for improving physical, chemical and biological processes and properties of soil quality; also, it

controls landscape and global level processes of hydrologic function, nutrient cycling, and greenhouse gas emission and mitigation.Soil carbon in a global context

Soil carbon is the largest pool of global terrestrial carbon – 1600 Pg (1015 g) of carbon stored in soil to a depth of 1 m as organic matter and 700 Pg of carbon stored in soil as carbonate minerals.

With approximately 4 Pg of additional carbon accumulating in the atmospheric pool (~800 Pg) each year, complete restoration of the estimated 20% loss of soil organic carbon that occurred during the past 200 years of cultivation could fully counteract the current rate of CO2 accumulation in the atmosphere during the next century.

How does soil carbon a�ect ecosystem properties & services? Soil organic carbon is a key indicator of soil quality, because of its bene�cial e�ects on physical characteristics (e.g., color, solubility,

water retention and soil structure), chemical qualities (e.g., cation exchange capacity, bu�ering, pH, chelation of metals and interactions with xenobiotics), and biological attributes (e.g., reservoir of metabolic energy, source of macronutrients, enzymatic activities and ecosystem resilience).

Soil organic carbon accumulates predominately in the upper horizon of soil, which is important for water in�ltration, nutrient cycling and protection of o�-site water quality.

Can management increase the stock of soil organic carbon? Loss of soil organic carbon has occurred in the past due to deforestation and cultivation of native ecosystems; great potential exists to

replenish soil organic carbon, because of this historic loss. Adoption of conservation agricultural systems will sequester soil organic carbon at a generally observed rate of 0.25–1.0 Mg C ha-1 year-1. Conservation agricultural management may include conservation tillage, diverse crop rotations, cover cropping, manure application, and

integration of perennial forages and animal grazing with cropping.

Who will bene�t from increasing soil organic carbon? Increasing soil organic carbon rewards farmers and landowners with better tilth, higher nutrient-supplying capacity, improved resilience to

perturbations and weather extremes, and abundant biological diversity to support vigorous plants and sustained ecosystem services. Society bene�ts from cleaner water, cleaner air, and low-cost and healthy supply of food products.

Barriers to adoption of conservation agricultural practices Adoption of various conservation agricultural management approaches is a human choice to build a positive relationship with Nature;

allowing us to sustain our food production systems and improve the environment into the future. Carbon trading may eventually become a marketing tool that helps broaden society’s appreciation for the inherent value of soil carbon as

a fundamental basis for sustainability.

14 Trimble SW. Man-Induced Soil Erosion on the Southern Piedmont: 1700–1970. Soil and Water Conservation Society, IA, USA 180 (1974).

15 Schnabel RR, Franzluebbers AJ, Stout WL, Sanderson MA, Stuedemann JA. The effects of pasture management practices. In: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect. Follett RF, Kimble JM, Lal R (Eds). Lewis Publishers, FL, USA 291–322 (2001).

16 Diaz-Zorita M, Duarte GA, Grove JH. A review of no-till systems and soil management for sustainable crop production in the subhumid and semiarid Pampas of Argentina. Soil Tillage Res. 65, 1–18 (2002).

17 Franzluebbers AJ, Stuedemann JA. Crop and cattle responses to tillage systems for integrated crop-livestock production in the Southern Piedmont, USA. Renew. Agric. Food Syst. 22(3), 168–180 (2007).

18 Franzluebbers AJ. Linking soil and water quality in conservation agricultural systems. J. Integr. Biosci. 6(1), 15–29 (2008).

19 Lal R, Reicosky DC, Hanson JD. Evolution of the plow over 10,000 years and the rationale for no-till farming. Soil Till. Res. 93, 1–12 (2007).

20 Derpsch R, Friedrich T. Global overview of conservation agriculture adoption. In: Proceedings of the 4th World Congress on

Conservation Agriculture. New Delhi, India 14 (2009).

21 Causarano HJ, Franzluebbers AJ, Shaw JN, Reeves DW, Raper RL, Wood CW. Soil organic carbon fractions and aggregation in the Southern Piedmont and Coastal Plain. Soil Sci. Soc. Am. J. 72(1), 221–230 (2008).

22 Coleman DC, Crossley DA Jr. Fundamentals of Soil Ecology (2nd Edition). Academic Press, San Diego, CA 386 (2004).

23 Franzluebbers AJ. Achieving soil organic carbon sequestration with conservation agricultural systems in the southeastern United States. Soil Sci. Soc. Am. J. 74(2), 347–357 (2010).

Will we allow soil carbon to feed our needs? Perspective

future science group www.future-science.com 251

Regional review of soil organic carbon and discussion of sampling issues to overcome natural variability.

24 Franzluebbers AJ, Hons FM, Zuberer DA. In situ and potential CO

2 evolution from a

Fluventic Ustochrept in southcentral Texas as affected by tillage and cropping intensity. Soil Till. Res. 47, 303–308 (1998).

25 Arshad MA, Schnitzer M, Angers DA, Ripmeester JA. Effects of till vs no-till on the quality of soil organic matter. Soil Biol. Biochem. 22, 595–599 (1990).

26 Ding G, Liu X, Herbert S, Novak J, Amarasiriwardenae D, Xing B. Effect of cover crop management on soil organic matter. Geoderma 130, 229–239.

27 Conant RT, Six J, Paustian K. Land use effects on soil carbon fractions in the southeastern United States. I. Management-intensive versus extensive grazing. Biol. Fertil. Soils 38(6), 386–392.

28 Baker JM, Ochsner TE, Venterea RT, Griffis TJ. Tillage and soil carbon sequestration: what do we really know? Agric. Ecosyst. Environ. 118, 1–5 (2007).

29 Angers DA, Eriksen-Hamel NS. Full-inversion tillage and organic carbon distribution in soil profiles: a meta-ana lysis. Soil Sci. Soc. Am. J. 72(5), 1370–1374 (2008).

30 Blanco-Canqui H, Lal R. No-tillage and soil-profile carbon sequestration: an on-farm assessment. Soil Sci. Soc. Am. J. 72, 693–701 (2008).

31 Franzluebbers AJ, Stuedemann JA. Bermudagrass management in the Southern Piedmont USA: VII. Soil-profile organic carbon and total nitrogen. Soil Sci. Soc. Am. J. 69(5), 1455–1462 (2005).

32 Parton WJ, Stewart JWB, Cole CV. Dynamics of C, N, S, and P in grassland soils: a model. Biogeochemistry 5, 109–131 (1987).

33 Jenkinson DS, Hart PBS, Rayner JH, Parry LC. Modelling the turnover of organic matter in long-term experiments. INTECOL Bull. 15, 1–8 (1987).

34 Li C, Frolking S, Harriss R. Modelling carbon biogeochemistry in agricultural soils. Global Biogeochem. Cycles 8, 237–254 (1994).

35 Kätterer T, Andrén O. Long-term agricultural field experiments in Northern Europe: analysis of the influence of management on soil carbon stocks using the ICBM model. Agric. Ecosyst. Environ. 72, 165–179 (1999).

36 Rickman RW, Douglas CL Jr, Albrecht SL, Bundy LG, Berc JL. CQESTR: a model to estimate carbon sequestration in agricultural soils. J. Soil Water Conserv. 56, 237–242 (2001).

37 Hubbs MD, Norfleet ML, Lightle DT. Interpreting the soil conditioning index. In: Proc. 25th Southern Conserv. Tillage Conf. Sustainable Agric. Auburn AL, USA 192–196 (2002).

38 World Association of Soil and Water Conservation. No-Till Farming Systems. Goddard T, Zoebisch MA, Gan Y, Ellis W, Watson A, Sombatpanit S (Eds). Funny Publishing, Bangkok, Thailand, 544 (2008).

Websites101 United Nations Food and Agriculture

Organization – Conservation Technology Information Center. Soil Carbon Sequestration in Conservation Agriculture: a Framework For Valuing Soil Carbon as a Critical Ecosystem Service. 2 (2008).www.fao.org/ag/ca/doc/ CA_SSC_Overview.pdf (Accessed 30 July 2010).

102 United States Department of Agriculture – Natural Resources Conservation Service. Environmental Quality Incentives Program. www.nrcs.usda.gov/programs/eqip/

103 United States Department of Agriculture – Natural Resources Conservation Service. Conservation Stewardship Program. www.nrcs.usda.gov/programs/ new_csp/csp.html

104 Chicago Climate Exchange. CCX Offsets Program. http://theccx.com/content.jsf?id=23

105 Voluntary Carbon Standard. Agriculture, Forestry and Other Land-use. http://v-c-s.org/afl.html

22

BEWARINGSWEEK

Die inskrywings is nou oop vir die BLWK “Jack Human” Bewaringslandbou Week in Augustus. Aangeheg by die nuusbrief is die inskrywingsvorm. Let asb daarop dat die inskrywingsvorm eers voltooi moet word en na Gerty Mostert (inligting aan die einde van die vorm) ge-epos of gefaks moet word. Sy sal dan ‘n faktuur uitmaak met die nodige verwysing op wanneer u daarna kan betaal. Ons doen dit vanjaar soom seker te maak dat ons name aan betalings kan koppel.

Kostes:

Slegs Praktiese dag R50 per personKonferensie dag en Praktiese dag R500 per person R150 per student (heg afskrif van geldige studentekaart aan)

Inskrywings vir die konferensie sluit die 22ste Julie. Laat registrasie vir konferensie R600 per persoon)

Entries are now open for the CAWC “Jack Human” Conservation Agriculture week during August. Attached to the newsletter is an entry form. Please note that the entry form must be submitted before you make any payments. Complete the form and email or fax it to Gerty Mostert (details on the bottom of the application form. She will then send you an invoice with the necessary reference number for payment. We have decided to do it this way to clear any confusion in missing references.

Costs:

Only Practical day R50 per personConference day and practical day R500 per person R150 per student (attach copy of current student card) Entries for the week close on the 22nd of July. Late registration cost R600 per person)

CONSERVATION AGRICULTURE WEEKENTRY OPEN FOR THE CONSERVATION AGRICULTURE WEEK

BLWK - CAWC

BEWARINGSWEEKINSKRYWINGS OOP VIR DIE BEWARINGSWEEK IN AUGUSTUS

23BLWK - CAWC

BEWARINGSWEEK

Titel / TitleVoorletters

Initials Van / Surname

Prof/Dr/Mr/Ms

epos / email

Only practical day (R50)

Lecture and Practical Day (R500)

Student 2 en 4 Augustus (R150) Student 2 and 4 August (R150)

Moet asb nie geld inbetaal alvorens U die faktuur ontvang het niePlease do not deposit any money before you have received the invoice

BLWK Jack Human Bewaringslandbou WeekCAWC Jack Human Conservation Agriculture Week

Inskrywingsvorm / Application form

Lesings en Praktiese dag (R500)

Dui asb aan watter geleenthede u wil bywoonPlease Indicate which of the following you will attend

Slegs praktiese dag (R50)

Plaas / Besigheid / Organisasie aan wie rekening moet gaanFarm / Company / Organisation to whom account must go

Adress / Address

BTW nommer indien nodig / Vat number if needed

Kontact nommer Contact Number

MG Lötter – devlei@whalemail.co.zaSakkie Rust – sakkie@rautenbachtransport.co.za Hoppies Uys – hoppies@swdconnect.co.za / hoppies@easycoms.co.za Pieter-Jan Delport – jpdelport@telkomsa.netJakobus Mouton – andre@patat.za.netAmelia Genis – agenis@landbou.com Johann Strauss – johannst@elsenburg.comPieter Blom (SSK) – pblom@ssk.co.za Francois Human (Overberg Agri) - Francoish@overbergagri.co.za Wynand Heunis (Overberg Agri) - WynandH@overbergagri.co.za Louis Coetzee (Kaap Agri) - louis.coetzee@kaapagri.co.za

BLWK Bestuurspan / CAWC Management Team Lede

CAPTION: sumquunt adi aut aut atis quiscia pro ini-mos que di dus conecuptas as maximo que n quiscia pro inimos que di dus que

Photos

24 BLWK - CAWC

Click on the email address to send a person an email

Plant van proewe op plaas in Riversdal