Nuus/News

Hallo Almal

Na die eerste kort nuusbrief verlede week, is uitgawe 31 propvol inligting.

Ons hoop en vertrou dat julle dit interessant sal vind.

‘n Handtjie vol (5) van ons gaan ’n besoek af lê by die Ottosdal No-till

boeredae in Maart, en beloof om iets in die nuusbrief te skryf as ons terug

kom. Onthou asb die Algemene Jaarvergadering die komende don-

derdag by die Koringaar op Caledon. Ondersteun asb ook die eerste

bruintoer vir die jaar die 18de Februarie op Tygerhoek Navorsingsplaas

by Riviersonderend. Albei byeenkomste begin om 10vm.

RSVP aan johannst@elsenburg.com

Groete van huis tot huis

Johann Strauss

2014

NUUSBRIEF / NEWSLETTER 08/02/2015

ISSUE 31

UITGAWE 31

Comparison 2

Phosphorous 4

Soil security 9

CA and sustainable

agriculture

16

BLWk inligitng 28

Inside this issue: Inhoud:

Upcoming farmers’ days and events:

AGM—12 Februarie—

Koringaar op Caledon

10vm

Bruintoer—18 Feb

Tygerhoek Navorsing-

splaas—10vm

Overberg Agri Voor-

saaidag 12 Maart—

Rietpoel

SKOG voorsaaidag—18

Maart Moorreesburg

Groentoer Tygerhoek—

Junie

Riversdal Boeredag—

26 Augustus

BLWK bewar-

ingsweek—7,8 en 10

Septemeber

SKOG—9 September

Moorreesburgskou—9

tot 12 September

A compilation of data by Lal 2014 that constructs a comparison of environmental indicators in 1992

and 2014 based on information by Brown 2010; Le Quere et al. 2013; Houghton 2003; WMO 2013;

IPCC 1990, 2013; UN 2014; FAO 2011, 2014; IFDC 2010; World Bank 2014 and UNICEF/WHO 2014.

Lal loc c i t . s tates the point that these data make as fol lows:

"The term “sustainable development” as perceived in Agenda 21 refers to a broader goal on strat-

egy toward sustainable development with due consideration to the environment (concerns about

climate change) and availability of natural resources (land, water, etc.). The data in the table be-

low show that neither the anthropogenic emissions have been reduced nor the concentrations of

GHGs stabilized. The goals of eliminating hunger, poverty and malnutrition remain as elusive as ever

a n d m e r e l y a m i r a g e . ”

The percentage change calculations in column 4 were added by the contributing author who

constructed this interactive table in EcoPort. These percentages underscore Lal's conclusion as fol-

lows:

the parameters shaded light grey, which are all deleterious to sustainable development, have all

increased by the percentages shown in the last column,

the only two positive improvements are revealed in (i) in Emissions from tropical deforestation which

have decreased by 63.3%,

and (ii) in the massive, 606% increase in Ethanol production an ostensible exception and

'improvement', which is an improvement only to the extent that one believes that ethanol and oth-

er bio-fuels do not have anywhere near the same negative carbon footprint (or other socio-

ecologocal vices) as fossil fuels,

while the other important social parameters of human prosperity in dignity, such as poverty have all

deteriorated. For example, available, per capita arable land, has decreased by 26.9%.

Thus, and overwhelmingly, the aspects that shouldn't have increased did, while the parameters

t h a t s h o u l d h a v e d e c r e a s e d , s u c h a s p o v e r t y , d i d n ' t .

But, anybody who denies that we humans (Homo stupidiensis?), right now in the Anthropocene,

are liquidating the earth's natural capital and consuming the proceeds as income to finance com-

pulsive over-population and run-away avarice, surely, and at the very least, needs psychiatric

treatment.

Page 2

A comparison of environmental indicators

Insert by Toney Putter

http://ecoport.org/ep?SearchType=reference&ReferenceID=560333http://ecoport.org/ep?SearchType=reference&ReferenceID=560334http://ecoport.org/ep?SearchType=reference&ReferenceID=560335http://ecoport.org/ep?SearchType=reference&ReferenceID=560336http://ecoport.org/ep?SearchType=reference&ReferenceID=560337http://ecoport.org/ep?SearchType=reference&ReferenceID=560338http://ecoport.org/ep?SearchType=reference&ReferenceID=560339http://ecoport.org/ep?SearchType=reference&ReferenceID=560340http://ecoport.org/ep?SearchType=reference&ReferenceID=560341http://ecoport.org/ep?SearchType=reference&ReferenceID=560342http://ecoport.org/ep?SearchType=reference&ReferenceID=560343http://ecoport.org/ep?SearchType=reference&ReferenceID=560344http://ecoport.org/ep?SearchType=reference&ReferenceID=560345

Page 3

Parameters 1992 2014 % Change

Total population (109) 5.49 7.24 31.8

Urban population (109) 2.57 3.88 51.0

Energy use (EJ) 365 600 64.4

Fossil fuel emission (Pg C) 6.2 10.1 62.9

Emission from tropical de-

forestation (Pg C) 2.18 0.8 -63.3

Water use (km3) 0.56 0.70 25.0

Fertilizer use (106 Mg) 125 190 52.0

Per capita arable land (ha) 0.26 0.19 -26.9

Atmospheric carbon diox-

ide concentration (ppm) 354 400 13.0

Atmospheric methane

concentration (ppm) 1,720 1,831 6.5

Atmospheric nitrous oxide

concentration (ppm) 310 327 5.5

Per capita grain production

(kg) 359 344 -87

Poverty (109; US$1.25 d–1) 1.9 1.5 -21.1

Ethanol production (109 L) 17 120 605.9

Hunger prone population

(106) 1,000 842 -15.8

Lack of clean drinking wa-

ter (people 109) 1.32 0.81 -51.0

Lack of access to sanita-

tion (people 109) 2.90 2.60 -10.3

Introduction

Phosphorus (P) is an essential macronutrient required in almost every aspect of plant functions. It is a vital

component of compounds required to build proteins, plant structure, seed yield and genetic transfer. Symp-

toms of P deficiency in maize include stunted growth, delayed maturity, purplish hues, poor root development

and reduced yield potential. Phosphorus is the second most important fertiliser applied to soils for improving

soil fertility after nitrogen (N) in maize production. Cultivated soils in South Africa are deficient in P and fertiliser

compounds have to be supplied to soils in large quantity to meet maize P requirements. Meanwhile, it is re-

ported that the world’s P stocks are dwindling and P production will not be able to meet half the world’s

needs by the year 2050.1 Global P fertiliser prices are on the increase1,2 and eating into the profits of farmers.

It is becoming increasingly imperative for maize farmers to adopt low-cost farming strategies that increase P

availability in the soil, conserve soil P and optimise its use.

Conservation agriculture (CA) is an important farming practice for conserving soil resources, including P,

through retention of crop residues and minimising soil erosion.3 In CA, the practices of crop rotation, no till and

permanent cover through crop residues and cover crops contribute immensely to soil quality and nutrient dy-

namics. A number of winter cover crops, which are legumes or small grains, can be grown between regular

grain crop production periods for the purpose of protecting and improving the soil through their high biomass

production.4 Through their extensive root systems, leguminous winter cover crops can explore subsoil nutrient

pools, whereas grass species can increase P uptake by both the cover crop and the succeeding crop

through enhancement of viable mycelia of mycorrhizal fungi in soils.5,6 Almost no P is added to the soil by

winter cover crops; they only take up P from the soil solution and return it to the same soil. However, high bio-

mass yielding winter cover crops can increase surface organic matter significantly.7

In warm temperate regions such as the Eastern Cape Province of South Africa, planting a winter cover crop

before the summer maize crop is possible as an entry point into CA, provided irrigation water is available.7,8

Grazing vetch (Vicia dasycarpa) and oats (Avena sativa) are examples of fast-growing, winter hardy cover

crops which can provide high biomass (> 6 t/ha) in this system.8 The maize is planted immediately after cover

crop termination onto winter cover crop residue mulches. Decomposition of the winter cover crop residues

and subsequent mineralisation of organic P (Po) plays an essential role in P-cycling and maintenance of

plant-available P in this system.9 The major source of P in unfertilised low P soils is Po.9,10 When no winter cover

crops are used, biomass production tends to be lower, reducing the size of the Po pool. However, where high

amounts of organic matter are generated in situ from winter cover crops, P may be temporarily immobilised in

Page 4

High biomass yielding winter cover crops can improve phosphorus

availability in soil

Ernest Dube ,Cornelius Chiduza, Pardon Muchaonyerwa

Abstract from article published in the South African Journal of Sience

Volume 110 | Number 3/4

March/April 2014

the organic matter accumulated on the soil surface, especially if the C:P ratio is greater than 300:1.11 There

is therefore a need to investigate the effects of winter cover crops on maize P nutrition, especially during the

early crop growth stages. Adequate P nutrition at the seedling stage in maize is critical because deficiency

at this stage cannot be remedied by side-dressing as a result of a lack of P mobility in soils.

The size of the Po pool that undergoes rapid mineralisation contributing to plant available P over

at least one growing season, known as labile P, may be dependent on crop residue quality, soil

and environmental characteristics, and the duration and type of the cropping system.12,13 Bicar-

bonate extractable P (NaHCO3-P) and microbial biomass-P fractions constitute labile P in the

soil.10,14 The soil microbial biomass may be considered as a reservoir of potentially plant-available

nutrients, including P.14 It is important to understand the effects of winter cover crops on these P

pools in low fertiliser input CA systems for the development of effective fertiliser management strat-

egies that maximise maize yield and profit. In this paper, we report the effects of winter cover

crops on soil P pools and maize P nutrition during early growth in a low fertiliser input CA system.

Materials and methods

A long-term field experiment was established in 2007 on a research farm to study the effects of

winter cover crops and fertiliser on biomass input, soil organic matter and maize yield under no-till

and irrigation conditions.8 The farm is located at 32°46′ S 26°50′ E and at 535 m above sea level in

the Eastern Cape Province of South Africa.

The six treatment combinations and the amount of P fertiliser applied are presented in Table 1.

Page 5

Soil P was separated into labile, moderately labile and non-labile organic and inorganic pools fol-

lowing the sequential fractionation scheme.12,15 In this method, the labile P pool was extracted us-

ing 0.5 M NaHCO3 at pH 8.5, while the microbial biomass-P was determined through a chloroform

(CHCl3) fumigation–extraction technique.8 The moderately labile pool was extracted with 1.0 M

HCl, followed by 0.5 M NaOH.

Results and discussion

Winter cover crop type × fertiliser interaction effect on total soil P was not significant (p>0.05). Cover

crop type effects were significant (p0.05).

The soil on maize–oats rotation had higher microbial-P than the soil on either the maize–grazing

vetch or maize–fallow rotation (Figure 1). Oats residues tend to have a slower decomposition rate

than vetch residues.7 In this case, most mineral soil P in the soil under oats residues may be convert-

ed into microbial biomass.

Soil on the maize–oats and maize–grazing vetch rotations had higher HCl-Pi than that on the maize–

fallow rotation (Figure 1). This high level of the inorganic pool of HCl-P fraction in the cover crop

treatments suggests that when the large biomass decomposes a greater proportion of the mineral P

produced forms calcium phosphates,20 and a portion is taken up by soil microbial biomass. Dissolu-

tion of these calcium phosphates makes moderately labile P (HCl-P) available to crops

Fertiliser had no significant (p>0.05) effect on all the soil P pools except for NaHCO3-Po (Table 2) for

which the fertilised maize rotations had a higher amount (6.78 mg/kg) than the non-fertilised ones

(4.33 mg/kg). Winter cover crop × fertiliser interaction had a significant (p

acid-P while the fertilised maize–fallow had the lowest amount (Figure 2). Whereas humic-P in

the maize–vetch rotation was not increased by fertiliser application, humic-P in the maize–oats

and maize–fallow rotations was higher when unfertilised. Although humic-P and H2SO4-P are con-

sidered non-labile, their effects as a slow supply of plant available P over the long term could be

significant.

Page 7

Soluble plant litter P can also be released to the soil from cover crop residues as an initial

flush of Pi with rainfall or irrigation for utilisation by the maize crop during early stages of

rowth.23 Decomposition of the cover crop residues can further increase P availability by re-

leasing CO2, which forms H2CO3 in the soil solution, resulting in the dissolution of primary P-

containing minerals.24

Conclusions

The maize–winter cover rotations increased total P and some labile P pools in the surface

soil when compared with the maize–fallow rotation, and this effect was positively correlat-

ed to cover crop biomass. The HCl- Pi pool was strongly correlated to maize seedling tissue

P concentration and thus P supply for early maize growth. Non-application of fertiliser to

maize, however, increased the accumulation of the recalcitrant humic-P fraction on the

maize–oats rotation. Overall, the contribution from the winter cover crops to P availability in

the surface soil suggests that, in the long term, fertiliser P could be reduced in low fertiliser

input CA systems. Further work is recommended to evaluate the effects of winter cover

crops on other soil nutrient pools such as Zn and Cu.

Page 8

Soil security: responding to the global soil crisis Soil security is a new concept that has aris-

en during a time of emerging international response to the increasingly urgent problems

that face the global soil stock. Soil security refers to the maintenance and improvement of

the world’s soil resources so that they can continue to provide food, fiber and fresh water,

make major contributions to energy and climate sustainability, and help maintain biodi-

versity and the overall protection of ecosystem goods and services (Koch et al., 2012). His-

tory stands as a warning to our modern societies. Whole civilizations have fallen and col-

lapsed when their stock of fertile soils washed or blew away. Many clarion calls to pre-

serve our soil stocks have been made; they must not be ignored (Jacks and Whyte, 1939;

Hammond, 1939; Hyams, 1952; Kellogg, 1956; Hillel, 1992; Montgomery, 2007). Can clear

hindsight be used to avoid repeating the past?

The global soil crisis

The world now faces a modern soil crisis that eclipses those of the past. Soil degradation –

the decline in soil function or its capacity to provide economic goods and ecosystem ser-

vices (Lal, 2010) – is a global phenomenon with many faces. The pressures on soil are

widespread and varied and the challenges created by these demands drive deep into

our continued ability to provide sufficient resources for the world’s growing population.

Detrimental consequences include threats to agricultural productivity and food security,

fresh water retention and biodiversity – all of these rely on the functions of soil. The threat

of increasing carbon dioxide and methane emissions through soil degradation, including

accelerated erosion (Lal, 2004) and permafrost thaw, is substantial (Shuur and Abbott,

2011) Some forms of soil degradation – erosion, fertility loss, salinity, acidification, compac-

tion and the loss of soil carbon – are natural processes that can be accelerated 1000- fold

by excessive land clearing and inappropriate farming practices that are not fit for pur-

pose (van Lynden et al.,1998). Amelioration and changes to land management practice

can sometimes reverse the degradation, but this is often not affordable. Other problems

stem from not recognizing soil as a vital resource. Practices such as the use of topsoil to

produce bricks and other building materials, and the paving over of high-quality agricul-

tural soils for urban development, sometimes referred to as ‘soil sealing’ (Burghardt, 2006),

contribute significantly to the loss of global soil productivity. An estimated 55 per cent of

the world’s desertified land is attributable to soil degradation (Lal, 2010). Land degrada-

tion is estimated to affect 23.5 per cent of global land area (Bai et al., 2008) and has re-

sulted in 1–2.3 million hectares of agricultural land becoming unsuitable for cultivation

Page 9

Soil Security: Solving the Global Soil Crisis

Koch et al

(Lambin and Meyfroidt, 2011). Much of this degraded area faces increasing pressure from

development as a result of increasing population (Barbier, 2010). Around 1.3 billion people

in developing economies live in marginal areas and on ecologically fragile lands that are

prone to severe land degradation (World Bank, 2003). Permanent topsoil loss is already limit-

ing sustainable development in many local economies (Pimental, 2006). Lack of attention

to soil degradation leaves the extent of these losses largely unmeasured and undocument-

ed. The loss of soil, loss of access to soil or its extreme degradation does pose an existential

threat to humanity because our global food production systems are almost completely reli-

ant on soil. In short, the natural capital of soil has been greatly undervalued (Dominati et al.,

2010; Robinson et al., 2009) and the importance of halting and reversing the degradation

and loss remains unacknowledged.

Soil and sustainable development

These problems are not new. Soil scientists have been articulating the threats to global soil

stocks for some time (Banwart, 2011; ISRIC, 2012; Kaiser, 2004). Since the first UN Conference

on Environment and Development (UNCED) in 1992, links between science and policy on

issues of sustainable development have become increasingly sophisticated. Independent

assessments, scientific expert panels and subsidiary bodies have been established to pro-

vide expert information on global issues related to sustainable development, including cli-

mate change,biodiversity and water availability (Kohler et al., 2012).

The role of soil in providing ecosystem services is scientifically established (Baker et al., 2001;

Janzen et al.,2011) but these insights and other advances in soil science over the past two

decades have not yet flowed through into international policy instruments. As a result, key

initiatives and interventions focused on sustainable development risk failure, as they have

not taken the underpinning role of soil into consideration.

The Millennium Ecosystem Assessment (MEA) report defined provisioning and regulating

ecosystem services, but under-recognized soil as the key delivery platform underpinning

many of these services (MEA, 2005). A degrading soil stock will directly impact food, fiber

and fresh water provision. More broadly, soil forms the basis of the landscapes and ecosys-

tems that provide biophysical, economic, cultural and spiritual services to humanity.

Despite its critical importance in the carbon cycle, soil is frequently left out of climate

change debates (Schmidt et al., 2011). Soil contains at least twice as much carbon as the

atmosphere, and cycles it over much longer timescales (Lal, 2004) making it an equal part-

ner to the atmosphere and oceans in the global carbon cycle (Lal, 2004); we directly influ-

ence and manage soils in ways that we cannot manipulate these other pools.

Discussions around biodiversity loss seldom refer to soil even though soil contains the most

diverse and complex ecosystems on the planet. Soils contain over 98 per cent of the genet-

ic diversity in terrestrial ecosystems (Fierer et al., 2007) however soil biodiversity is not ad-

dressed in the Global Biodiversity Outlook (GBO-3) from the UN Convention on Biological

Diversity (Secretariat of the CBD, 2010), and is not referred to in the popular International

Union for Conservation of Nature (IUCN) Red List of Threatened Species (UCN, 2012).

Page 10

Recent attempts to develop a global framework for assessing planetary resources also fail

to recognize the vital role of soil in the biosphere. The Stockholm Resilience Centre led an

effort to define the key planetary boundaries that face anthropogenic pressure Rock-

strom et al., 2009). This important work is influential in current reviews of sustainable devel-

opment, but does not address soil as a critical contributor to buffering the thresholds of

those boundaries. The closest mechanism that the international community has to address

concerns about soil degradation is the UN Convention to Combat Desertification

(UNCCD).

Historically, the UNCCD has focused largely on land degradation and drought in Africa

and in arid and semi-arid landscapes. Although regenerating soils in underdeveloped re-

gions can make significant gains in reversing desertification, a worldwide approach to soil

degradation is critical to address the wider problems from local to national to continental

scales. There are many contributors to the identified disconnect existing between science

and international policy, but in this article we address two. The first relates to the use of ter-

minology; the second is the lack of a sufficient framework to bridge the divide.

Page 11

Terminology: distinguishing between ‘soil’ and ‘land’

For many people the word ‘soil’ is interchangeable with the word ‘land’. This lack of dis-

tinction in terminology results in an oversight of the underpinning role of soil within land-

scapes. Soil is a distinct living entity that is one of the core building blocks of land. Land

consists of soils, rocks, rivers and vegetation (Lal, 2010). Soil contributes five principal func-

tions within a landscape:

1. nutrient cycling;

2. water retention;

3. biodiversity and habitat;

4. storing, filtering, buffering and transforming compounds;

and

5. provision of physical stability and support (Blum,

1993).

By failing to identify soil as a discrete component in discussions about land, we lose visibil-

ity of these functions. This is reinforced by the often poor representations of soil in compre-

hensive hydrological and climatic simulation models that form the basis of many policy

measures (Bouma et al., 2011). Making the distinction between land and soil in our lan-

guage and policies, together with a better understanding of soil as one of the discrete

components of land is important.

A soil-centric framework is needed

The international community lacks a policy framework for addressing specific issues of soil

degradation in relation to sustainable development. Attempts to address problems

through the lenses of existing instruments have forced too narrow a focus on particular

subsets of issues and regions (Sanchez and Swaminathan, 2005).

A fully functioning soil lies at the heart of solving the big issues of food security, biodiversity,

climate change and fresh-water regulation, but to date there has been no easy way to

communicate these linkages. The narrative on soils must be improved and its voice must

be raised if the required response is to be achieved. A soil-centric framework is needed to

generate policies that raise awareness of, and reverse, soil degradation and simultane-

ously recognize its essential co-benefits for sustainable development.

The concept of soil security can be used to address this shortage – it provides a useful

mental model that links soil with good outcomes in sustainable development (see Figure

1).

When the five functions of soil are aligned against critical issues for society and sustainable

development, the linkages become clear – as outlined in

Table 1.

Page 12

The key aim in securing soil is to maintain and optimize its functionality: its structure and

form, its diverse and complex ecosystems of soil biota, its nutrient cycling capacity, its

roles as a substrate for growing plants, as a regulator, filter and holder of fresh water, and

as a potential mediator of climate change through the sequestration of atmospheric car-

bon dioxide.

Page 13

Maintaining the myriad of interactions between these processes is what gives soil its resili-

ence, productivity and efficiency. Permanent loss of soil natural capital through erosion, loss

of structure, soil sealing and other types of degradation will severely impact the delivery of

these ecosystem services.

Emerging soil policy initiatives

Over the past few years a number of new initiatives to give soils a policy focus have

emerged. The UN Food and Agriculture Organization (FAO) launched the Global Soil Part-

nership (GSP) in conjunction with the EC in 2011, ‘to provide support and facilitate joint ef-

forts towards sustainable management of soil resources for food security and climate

change adaptation and mitigation’ (GSP, 2012).

Luc Gnacadja, Executive Secretary of the UNCCD has stated that healthy soil is critical for

securing food, water and energy, and that ‘soil’s caring capacity is often forgotten in glob-

al policies for sustainable development’ (UNCCD, 2012).

The UN FAO, the EC, the UNCCD and the United Nations Environment Programme (UNEP)

partnered with the Global Soil Forum based at the Institute for Advanced Sustainability

Studies (IASS) in Germany to hold the inaugural Global Soil Week in Berlin during November

2012. This event deepened the discourse on soils as a fundamental pillar for sustainable de-

velopment and developed an agenda to improve the sustainable management of soils

(IASS, 2012).

As these policy initiatives develop and mature, a new policy framework for assessing and

discussing soils as a resource for sustainable development becomes critical. Building on the

definition of soil security proposed by Koch et al. (2012), Figure 1 and Table 1 provide an ex-

panded conceptual framework that could be used as the basis of a policy framework. Fur-

ther work must be done to fully develop the required soil policy framework, the dimensions

of soil security that must be addressed, a means of assessment and establishment of global

targets and indicators.

This requires a multidisciplinary approach that extends beyond soil science sensu stricto. En-

gaging the fields of ecology and economics to determine the value of the natural capital

of soil, as well as the social sciences to determine how we can better connect society with

the fundamental functions of soil in landscapes will be key. Determining policy instruments

that can work at the international level, and yet be implemented at local scales will be criti-

cal, and may need instruction from other resource policy areas such as water and air.

Soil carbon: an exemplar indicator of soil security

Soil scientists from the International Union of Soil Sciences (IUSS) established the Global Soil

Map project in 2009 to develop a global digital map of the world’s soils and key soil attrib-

utes that can be used to define potential soil use and monitor temporal trends in soil quality

(Sanchez et al., 2009). This project is akin to ‘going from a 1980s printed road atlas to

Page 14

Google Earth in one giant leap’, and progress to date is impressive (Fisher, 2012).

Given the right resources, the Global Soil Map project could be enhanced to provide a

global early warning system for soils that are reaching critical thresholds of sustainability. The

question then becomes, what aspects of soil would such a system track in order to monitor

soil condition globally?

Soil organic carbon (soil carbon) is one of the significant universal indicators. There are oth-

er indicators, including soil pH but carbon is a workable exemplar and is easily understood

by policy makers and the wider community. The Soil Carbon Initiative (SCI), an international

coalition of eminent soil scientists who came together in Sydney in February 2011 to consid-

er the potential of soil to sequester atmospheric carbon (Stockmann et al., 2013), agreed

that tracking changes in soil carbon helps to identify dangerous thresholds in degrading

soils (SCI, 2011).

Soil carbon is routinely measured and plays a vital role in soil function. Generally, soils lower

in carbon are less functional; soils higher in carbon have enhanced resilience. The net flux in

soil carbon over time becomes an overall indicator for the natural capital of the soil. In-

creasing and managing soil carbon and the biota that transform soil carbon is a key mech-

anism for improving and maintaining the functionality of soil and its ability to support eco-

system service delivery (Soil Carbon Initiative, 2011). This can be achieved through agricul-

tural and land management practices that are known to increase soil carbon (Hutchinson

et al., 2007; Sanderman et al., 2010; Minasny et al., 2011; Minasny et al., 2012). Supporting

this view, UNEP identified better management of soil carbon to restore degraded soils as

one of two critical emerging issues for the global environment in its 2012 Yearbook (UNEP,

2012).

Conclusions

Soil security provides the community with a conceptual framework that puts soil at the cen-

ter of addressing some of the big problems that face humanity. Getting the word ‘soil’

back into discussions and debates about land will help. Developing the concept into a pol-

icy framework will provide a platform for emerging soil policy initiatives to address soil deg-

radation. The fact that science now links soil carbon with soil function, not only as a poten-

tial mechanism for climate change mitigation, but also with fundamental provision of food,

fiber, water and biodiversity provides insight into a far broader set of environmental, eco-

nomic and social outcomes for the planet. As the broader community realizes the critical

value of the world’s soil resource, this should encourage the ambition of policy makers to

aim for soil security. The question remains: can we use clear hindsight to avoid repeating

the past? Following the American dustbowl of the 1930s, Franklin D. Roosevelt famously

said, ‘the Nation that destroys its soil destroys itself’ (Roosevelt, 1937). Eight decades later

we might paraphrase his famous statement in a global context and say, ‘the world that se-

cures its soil will sustain itself’.

Page 15

1. INTRODUCTION

Conservation agricul ture (CA) defined (see FAO CA web si te:

http://www.fao.org/ag/ca/1a.html ) as minimal soil disturbance (no-till, NT) and permanent

soil cover (mulch) combined with rotations, is a recent agricultural management system

that is gaining popularity in many parts of the world. Cultivation is defined by the Oxford

English dictionary as ‘the tilling of land’, ‘the raising of a crop by tillage’ or ‘to loosen or

break up soil’. Other terms used in this dictionary include ‘improvement or increase in (soil)

fertility’. All these definitions indicate that cultivation is synonymous with tillage or ploughing.

The other important definition that has been debated and defined in many papers is the

word ‘sustainable’. The Oxford English dictionary defines this term as ‘capable of being

borne or endured, upheld, defended, maintainable’. Something that is sustained is ‘kept up

without intermission or flagging, maintained over a long period’. This is an important con-

cept in today’s agriculture, since the human race will not want to compromise the ability of

its future offspring to produce their food needs by damaging the natural resources used to

feed the population today.

This paper will introduce and promote CA as a modern agricultural practice that can ena-

ble farmers in many parts of the world to achieve the goal of sustainable agricultural pro-

duction. But first, the paper discusses some issues related to tillage.

2. CULTIVATION TECHNIQUES OR TILLAGE

The history of tillage dates back many millennia when humans changed from hunting and

gathering to more sedentary and settled agriculture mostly in the Tigris, Euphrates, Nile,

Yangste and Indus river valleys (Hillel 1991). Reference to ploughing or tillage is found from

3000 BC in Mesopotamia (Hillel 1998). Lal (2001) explained the historical development of

agriculture with tillage being a major component of management practices. With the ad-

vent of the industrial revolution in the nineteenth century, mechanical power and tractors

became available to undertake tillage operations; today, an array of equipment is availa-

ble for tillage and agricultural production. The following summarizes the reasons for using

tillage.

Page 16

The role of conservation agriculture in

sustainable agriculture

Peter R. Hobbs1,*, Ken Sayre2 and Raj Gupta3

1Department of Crops and Soil Science, Cornell University, Ithaca, NY 14853, USA

2CIMMYT Apdo, Postal 6-641, 06600 Mexico DF, Mexico

3ICARDA-CAC office, P.O. Box 4564, Tashkent 700000, Uzbekistan

(i) Tillage was used to soften the soil and prepare a seedbed that allowed seed to be

placed easily at a suitable depth into moist soil using seed drills or manual equipment. This

results in good uniform seed germination.

(ii) Wherever crops grow, weeds also grow and compete for light, water and nutrients.

Every gram of resource used by the weed is one less gram for the crop. By tilling their

fields, farmers were able to shift the advantage from the weed to the crop and allow the

crop to grow without competition early in its growth cycle with resulting higher yield.

(iii) Tillage helped release soil nutrients needed for crop growth through mineralization and

oxidation after exposure of soil organic matter to air.

(iv) Previous crop residues were incorporated along with any soil amendments (fertilizers,

organic or inorganic) into the soil. Crop residues, especially loose residues, create prob-

lems for seeding equipment by raking and clogging.

(v) Many soil amendments and their nutrients are more available to roots if they are incor-

porated into the soil; some nitrogenous fertilizers are also lost to the atmosphere if not in-

corporated.

(vi) Tillage gave temporary relief from compaction using implements that could shatter

belowground compaction layers formed in the soil.

(vii) Tillage was determined to be a critical management practice for controlling soil-

borne diseases and some insects.

There is no doubt that this list of tillage benefits was beneficial to the farmer, but at a cost

to him and the environment, and the natural resource base on which farming depended.

The utility of ploughing was first questioned by a forward-looking agronomist in the 1930s,

Edward H. Faulkner, in a manuscript called ‘Ploughman’s Folly’ (Faulkner 1943). In a fore-

word to a book entitled ‘Ploughman’s folly and a second look’ by EH Faulkner, Paul Sears

notes that:

Faulkner’s genius was to question the very basis of agriculture itself—the plough. He be-

gan to see that the curved moldboard of the modern plough, rather than allowing organ-

ic matter to be worked into the soil by worms and other burrowing animals, instead buries

this valuable material under the subsoil where it remains like a wad of undigested food

from a heavy meal in the human stomach.

(Faulkner 1987, p. x)

The tragic dust storm in the mid-western United States in the 1930s was a wake-up call to

how human interventions in soil management and ploughing led to unsustainable agricul-

tural systems. In the 1930s, it was estimated that 91 Mha of land was degraded by severe

soil erosion (Utz et al. 1938); this area has been dramatically reduced today.

Page 17

3. CONSERVATION TILLAGE AND CONSERVATION AGRICULTURE

Since the 1930s, during the following 75 years, members of the farming community have

been advocating a move to reduced tillage systems that use less fossil fuel, reduce run-off

and erosion of soils and reverse the loss of soil organic matter. The first 50 years was the start

of the conservation tillage (CT) movement and, today, a large percentage of agricultural

land is cropped using these principles. However, in the book ‘No-tillage seeding’, Baker et

al. (2002; a second edition of this excellent book was published in 2006) explained ‘As soon

as the modern concept of reduced tillage was recognized, everyone, it seems, invented a

new name to describe the process’. The book goes on to list 14 different names for re-

duced tillage along with rationales for using these names. The book is also an excellent re-

view of the mechanization and equipment needs of no-tillage technologies. Baker et al.

(2002) defined CT as:

the collective umbrella term commonly given to no-tillage, direct-drilling, minimum-tillage

and/or ridge-tillage, to denote that the specific practice has a conservation goal of some

nature. Usually, the retention of 30% surface cover by residues characterizes the lower limit

of classification for conservationtillage, but other conservation objectives for the practice

include conservation of time, fuel, earthworms, soil water, soil structure and nutrients. Thus

residue levels alone do not adequately describe all conservation tillage practices.

(Baker et al. 2002, p. 3)

This has led to confusion among the agricultural scientists and, more importantly, the farm-

ing community. To add to the confusion, the term ‘conservation agriculture’ has recently

been introduced by the Food and Agriculture Organization (see FAO web site), and others,

and its goals defined by FAO as follows:

Conservation agriculture (CA) aims to conserve, improve and make more efficient use of

natural resources through integrated management of available soil, water and biological

resources combined with external inputs. It contributes to environmental conservation as

well as to enhanced and sustained agricultural production. It can also be referred to as re-

source efficient or resource effective agriculture. (FAO)

This obviously encompasses the ‘sustainable agricultural production’ need that all mankind

obviously wishes to achieve. But this term is often not distinguished from CT. The FAO men-

tions in its CA website that:

Conservation tillage is a set of practices that leave crop residues on the surface which in-

creases water infiltration and reduces erosion. It is a practice used in conventional agricul-

ture to reduce the effects of tillage on soil erosion. However, it still depends on tillage as the

structure forming element in the soil. Never the less, conservation tillage practices such as

zero tillage practices can be transition steps towards Conservation Agriculture.

In other words, CT uses some of the principles of CA but has more soil disturbance.

4. CONSERVATION AGRICULTURE DEFINED

The FAO has characterized CA as follows:

Page 18

Conservation Agriculture maintains a permanent or semi-permanent organic soil cover.

This can be a growing crop or dead mulch. Its function is to protect the soil physically from

sun, rain and wind and to feed soil biota. The soil micro-organisms and soil fauna take

over the tillage function and soil nutrient balancing. Mechanical tillage disturbs this pro-

cess. Therefore, zero or minimum tillage and direct seeding are important elements of CA.

A varied crop rotation is also important to avoid disease and pest problems.

(see FAOweb site)

Data reported by Derpsch (2005) indicate that the extent of no-tillage adoption world-

wide is just over 95 Mha. This figure is used as a proxy for CA although not all of this land is

permanently no-tilled or has permanent ground cover. Table 1 details the extent of no-

tillage by country worldwide. Six countries have more than 1 Mha. South America has the

highest adoption rates and has more permanent NT and permanent soil cover. Both Ar-

gentina and Brazil had significant lag periods to reach 1 Mha in the early 1990s and then

expanded rapidly to the present-day figures of 18.3 and 23.6 Mha, respectively, for these

countries. By adopting the no-tillage system, Derpsch (2005) estimated that Brazil in-

creased its grain production by 67.2 million tons in 15 years with additional revenue of 10

billion dollars. Derpsch also estimated that at an average rate of 0.51 t haK1 yrK1 Brazil se-

questered 12 million tons of carbon on 23.6 Mha of no-tillage land. Tractor use is also signif-

icantly reduced saving millions of litres of diesel. The three key principles of CA are perma-

nent residue soil cover, minimal soil disturbance and crop rotations. The FAO recently add-

ed controlled traffic to this list. Each of these will be briefly dealt with before providing

some case studies. Table 2 shows a comparison of CA with CTand traditional tillage (TT).

(a) Permanent or semi-permanent organic soil cover

Unger et al. (1988) reviewed the role of surface residues on water conservation and indi-

cates that this association between surface residues, enhanced water infiltration and

evaporation led to the adoption of CT after the 1930s dust bowl problem. Research since

that time has documented beyond doubt the importance of surface residues on soil wa-

ter conservation and reduction in wind and water erosion (Van Doran & Allmaras 1978;

Unger et al. 1988). Bissett & O’Leary (1996) showed that infiltration of water under long-

term (8–10 years) conservation tillage (zero and subsurface tillage with residue retention)

was higher compared to conventional tillage (frequent plowing plus no residue retention)

on a grey cracking clay and a sandy loam soil in south-eastern Australia. Allmaras et al.

(1991) reviewed much of the literature on CTup to that time and goes on to describe a

whole array of CT-planting systems operating in the US, their adoption and benefits. This

paper will not go into detail about other soilconserving practices that are used throughout

the world and over time, like terracing or contour bunds that are essentially designed to

prevent soil erosion on sloping lands. Lal (2001) described some of these systems and

notes that the effectiveness of these systems depends on proper construction and regular

maintenance; if not done properly degradation can be catastrophic.

Page 19

Kumar & Goh (2000) reviewed the effect of crop residues and management practices on

soil quality, soil nitrogen dynamics and recovery and crop yield. The review concluded that

crop residues of cultivated crops are a significant factor for crop production through their

effects on soil physical, chemical and biological functions as well as water and soil quality.

They can have both positive and negative effects, and the role of agricultural scientists is to

enhance the positive effects. This paper will restrict the discussion of crop residues to their

benefits when used as mulch. Crop residues result when a previous crop is left anchored or

loose after harvest or when a cover crop (legume or non-legume) is grown and killed or cut

to provide mulch. Externally applied mulch in the formof composts andmanures can also

be applied, although the economics of transport of this bulky material to the field may re-

strict its use to higher-value crops like vegetables.

The energy of raindrops falling on a bare soil result in destruction of soil aggregates, clog-

ging of soil pores and rapid reduction in water infiltration with resulting runoff and soil ero-

sion. Mulch intercepts this energy and protects the surface soil from soil aggregate destruc-

tion, enhances the infiltration of water and reduces the loss of soil by erosion

(Freebairn&Boughton 1985;McGregor et al. 1990; Dormaar&Carefoot 1996).Topsoil losses of

46.5 t haK1 have been recorded withTTon sloping land after heavy rain in Paraguay com-

pared with 0.1 t haK1 under NT cultivation (Derpsch & Moriya 1999). NT plus mulch reduces

surface soil crusting, increases water infiltration, reduces run-off and gives higher yield than

tilled soils (Cassel et al. 1995; Thierfelder et al. 2005). Similarly, the surface residue, anchored

or loose, protects the soil from wind erosion (Michels et al. 1995). The dust bowl is a useful

reminder of the impacts of wind and water erosion when soils are left bare.

Surface mulch helps reduce water losses from the soil by evaporation and also helps mod-

erate soil temperature. This promotes biological activity and enhances nitrogen mineraliza-

tion, especially in the surface layers (Dao 1993; Hatfield & Pruegar 1996). This is a very im-

portant factor in tropical and subtropical environments but has been shown to be a hin-

drance in temperate climates due to delays in soil warming in the spring and delayed ger-

mination (Schneider & Gupta 1985; Kaspar et al. 1990; Burgess et al. 1996; Swanson & Wil-

helm 1996). Fabrizzi et al. (2005) showed that NT had lower soil temperatures in the spring in

Argentina, but TT had higher maximum temperatures in the summer, and that average

temperatures during the season were similar.

Karlen et al. (1994) showed that normal rates of residue combined with zero-tillage resulted

in better soil surface aggregation, and that this could be increased by adding more resi-

dues. Recent papers confirm this observation; Madari et al. (2005) showed that NT with resi-

due cover had higher aggregate stability, higher aggregate size values and total organic

carbon in soil aggregates than TT in Brazil; Roldan et al. (2003) showed that after 5 years of

NT maize in Mexico, soil wet aggregate stability had increased over conventional tillage (TT)

as had soil enzymes, soil organic carban (SOC) and microbial biomass (MBM). They con-

clude that NT is a sustainable technology.

Page 20

A cover crop and the resulting mulch or previous crop residue help reduce weed infesta-

tion through competition and not allowing weed seeds the light often needed for germi-

nation. There is also evidence of allelopathic properties of cereal residues in respect to in-

hibiting surface weed seed germination (Steinsiek et al. 1982; Lodhi & Malik 1987; Jung et

al. 2004).

Weeds will be controlled when the cover crop is cut, rolled flat or killed. Farming practice

that maintains soil micro-organisms and microbial activity can also lead to weed suppres-

sion by the biological agents (Kennedy 1999).

Cover crops contribute to the accumulation of organic matter in the surface soil horizon

(Roldan et al. 2003; Alvear et al. 2005; Diekow et al. 2005; Madari et al. 2005; Riley et al.

2005), and this effect is increased when combined with NT. Mulch also helps with recycling

of nutrients, especially when legume cover crops are used, through the association with

below-ground biological agents and by providing food for microbial populations. Greater

carbon and nitrogen were reported under no-tillage and CT compared with ploughing (

TT; Campbell et al. 1995, 1996a,b). Others have shown that this is restricted to the surface

horizons, and that the reverse occurs at greater depths in humid soils of eastern Canada

(Angers et al. 1997). Schultz (1988) showed that C and N declined by 6% with burning but

increased by 1% with stubble retention. Vagen et al. (2005) concluded that the largest

potential for increasing SOC is through the establishment of natural or improved fallow

Page 21

systems (agroforestry) with attainable C accumulation rates from 0.1 to 5.3 Mg C haK1 yrK1.

They continue to say that in cropland, addition of crop residues or manure in combination

with NT can yield attainable C accumulation rates up to 0.36 Mg C haK1 yrK1. SOC is a key

indicator of soil quality and Lal (2005) calculated that increasing SOC by 1Mg haK1 yrK1

can increase food grain production by 32 million Mg yrK1 in developing countries.

Heenan et al. (2004) in Australia showed that changes in SOC at the surface ranged from a

loss of 8.2 t haK1 for continuous tilled cereals and residues burnt to a gain of 3.8 t haK1

where stubble was retained and soil no-tilled. Nitrogen content followed similar trends. If the

rotation included a legume, SOC accumulation was the highest. Soil microbial biomass

(SMB) has commonly been used to assess below-ground microbial activity and is a sink and

source for plant nutrients. Amendments such as residues and manures promote while burn-

ing and removal of residues decrease SMB (Doran 1980; Collins et al. 1992; Angers et al.

1993a,b; Heenan et al. 2004; Alvear et al. 2005). Balota et al. (2004) in Brazil in a 20-year ex-

periment showed that residue retention and NT increased total C by 45% and SMB by 83%

at 0–50 cm depth compared with TT. Soon & Arshad (2005) showed that SMB was greater

with NT than TT by 7–36%; frequent tillage resulted in a decrease in both total and active

MBC. Increased SMB occurs rapidly in a few years following conversion to reduced tillage

(Ananyeva et al. 1999; Alvarez & Alvarez 2000). Increased MBM increased soil aggregate

formation, increased nutrient cycling through slow release of organically stored nutrients

and also assisted in pathogen control (Carpenter-Boggs et al. 2003).

Cover crops help promote biological soil tillage through their rooting; the surface mulch

provides food, nutrients and energy for earthworms, arthropods and micro-organisms below

ground that also biologically till soils. Use of deep-rooted cover crops and biological agents

(earthworms, etc.) can also help to relieve compaction under zero-tillage systems. There is

a lot of literature that looks at the effects of burning, incorporation and removal of crop res-

idues on soil properties, and much less where mulch is left on the surface. An early paper by

McCalla (1958) showed that bacteria, actinomycetes, fungi, earthworms and nematodes

were higher in residue-mulched fields than those where the residues were incorporated.

More recent studies also show more soil fauna in no-tillage, residue-retained management

treatments compared with tillage plots (Kemper & Derpsch 1981; Nuutinen 1992; Hartley et

al. 1994; Karlen et al. 1994; Buckerfield & Webster 1996; Clapperton 2003; Birkas et al. 2004;

Riley et al. 2005). Tillage disrupts and impairs soil pore networks including those of mycorrhi-

zal hyphae, an important component for phosphorus availability in some soils (Evans & Mil-

ler 1990; McGonigle & Miller 1996).

Zero-tillage thus results in a better balance of microbes and other organisms and a healthier

soil. Ground cover promotes an increase in biological diversity not only below ground but

also above ground; the number of beneficial insects was higher where there was ground

cover and mulch (Kendall et al. 1995; Jaipal et al. 2002), and these help keep insect pests

in check. Interactions between root systems and rhizobacteria affect crop health, yield and

soil quality. Release of exudates by plants activate and sustain specific rhizobacterial

Page 22

communities that enhance nutrient cycling, nitrogen fixing, biocontrol of plant pathogens,

plant disease resistance and plant growth stimulation. Sturz & Christie (2003) gave a re-

view of this topic. Ground cover would be expected to increase biological diversity and

increase these beneficial effects.

(b) Minimal soil disturbance

Many of the benefits of minimal soil disturbance were mentioned in the above section on

permanent soil cover, and, in fact, combining these two practices is important for obtain-

ing the best results.The following comparisons between tillage and zero-tillage systems are

made to highlight some other benefits not mentioned above. Tractors consume large

quantities of fossil fuels that add to costswhile also emitting greenhouse gases (mostly

CO2) and contributing to global warming when used for ploughing (Grace et al. 2003).

Animal-based tillage systems are also expensive since farmers have tomaintain and feed

a pair of animals for a year for this purpose. Animals also emit methane, a greenhouse gas

21 times more potent for global warming than carbon dioxide (Grace et al. 2003). Zero-

tillage reduces these costs and emissions. Farmer surveys in Pakistan and India show that

zero-till of wheat after rice reduces costs of production by US$60 per hectare mostly due

to less fuel (60–80 l haK1) and labour (Hobbs & Gupta 2004).

Tillage takes valuable time that could be used for other useful farming activities or em-

ployment. Zerotillage minimizes time for establishing a crop. The time required for tillage

can also delay timely planting of crops, with subsequent reductions in yield potential

(Hobbs & Gupta 2003). By reducing turnaround time to a minimum, zero-tillage can get

crops planted on time, and thus increase yields without greater input cost. Turnaround

time in this rice–wheat system from rice to wheat varies from 2 to 45 days, since 2–12 pass-

es of a plough are used by farmers to get a good seedbed (Hobbs & Gupta 2003). With

zero-till wheat this time is reduced to just 1 day.

Tillage and current agricultural practices result in the decline of soil organic matter due to

increased oxidation over time, leading to soil degradation, loss of soil biological fertility

and resilience (Lal 1994). Although this SOM mineralization liberates nitrogen and can lead

to improved yields over the short term, there is always some mineralization of nutrients and

loss by leaching into deeper soil layers. This is particularly significant in the tropics where

organic matter reduction is processed more quickly, with low soil carbon levels resulting

only after one or two decades of intensive soil tillage. Zero-tillage, on the other hand,

combined with permanent soil cover, has been shown to result in a build-up of organic

carbon in the surface layers (Campbell et al. 1996a; Lal 2005). No-tillage minimizes SOM

losses and is a promising strategy to maintain or even increase soil C and N stocks (Bayer

et al. 2000).

Although tillage does afford some relief from compaction, it is itself a major cause of com-

paction, especially when repeated passes of a tractor are made to prepare the seedbed

or to maintain a clean fallow. Zerotillage reduces dramatically the number of passes over

the land and thus compaction. However, natural compaction mechanisms and the one

Page 23

pass of a tractor-mounted zero-till drill will also result in compaction. The FAO CA web site

now includes ‘controlling in-field traffic’ as a component of CA; this is accomplished by

having field traffic follow permanent tracks. This can also be accomplished using a ridge-till

or permanent bed planting system rather than planting on the flat (Sayre & Hobbs 2004).

Some farmers feel that sub-soiling or chiselling may be needed to resolve below-ground

compaction layers before embarking on a NT strategy, especially in drier areas. Higher bulk

densities and penetration resistance have been reported under zero-tillage compared with

tillage (Gantzer & Blake 1978) and are described as natural for zero-tillage. This problem is

greater in soils with low-stability soil aggregates (Ehlers et al. 1983).

Bautista et al. (1996) working in a semi-arid ecosystem found that zero-tillage plus mulch re-

duced bulk density (BD). The use of zero-till using a permanent residue cover, even when

BD was higher, resulted in higher infiltration of water in NT systems (Shaver et al. 2002; Sayre

& Hobbs 2004). Scientists hypothesized that continued use of reduced, shallow and zero-

tillage would require a shift to short-term TT to correct soil problems. However, Logsdon &

Karlen (2004) showed that BD is not a useful indicator and confirm that farmers need not

worry about increased compaction when changing from TT to NT on deep loess soils in USA.

Fabrizzi et al. (2005) also showed higher BD and penetration resistance in NTexperiments in

Argentina, but the values were below thresholds that could affect crop growth; wheat

yields were the same as in the tilled treatments. This experiment left residues on the surface

in NT. The authors concluded that the experiment had a short time frame and more time

was needed to assess the effect on BD.

The role of tillageon soil diseases is discussed byLeake (2003) with examples of the various

diseases affected by tillage. He concluded that the role of tillage on diseases is unclear

and acknowledges that a healthy soil with high microbial diversity does play a role by be-

ing antagonisticto soil pathogens. He also suggested that NT farmers need to adjust man-

agement to control diseases through sowing date, rotation and resistant cultivars to help

shift the advantage from the disease to the crop. A list of the impacts of minimum tillage on

specific crops and their associated pathogens can be found in Sturz et al. (1997).

An added economic consideration is that tillage results in more wear and tear on machin-

ery and higher maintenance costs for tractors than under zero-tillage systems.

(c) Rotations

Crop rotation is an agricultural management tool with ancient origins. Howard (1996) re-

viewed the cultural control of plant diseases from an historical view and included examples

of disease control through rotation.

The rotation of different crops with different rooting patterns combined with minimal soil dis-

turbance in zero-till systems promotes a more extensive network of root channels and

macropores in the soil. This helps in water infiltration to deeper depths. Because rotations

increase microbial diversity, the risk of pests and disease outbreaks from pathogenic organ-

isms is reduced, since the biological diversity helps keep pathogenic organisms in check

Page 24

(Leake 2003). The discussion of the benefits of rotations will be handled in other chapters

of this publication. Integrated pest management (IPM) should also be added to the CA

set of recommendations, since if one of the requirements is to promote soil biological ac-

tivity, minimal use of toxic pesticides and use of alternative pest control methods that do

not affect these critical soil organisms are needed. A review of IPM in CA can be found in

Leake (2003).

5.EQUIPMENT FOR CONSERVATION AGRICULTURE

Before going on to describe a couple of case studies from Asia and Mexico, there is a

need to discuss the critical importance of equipment for success with CA; zero-till and CA

are bound to fail if suitable equipment is not available to drill seed into residues at the

proper depth for good germination. It is urgent that CA equipment is perfected, available

and adopted for this new farming system. Iqbal et al. (2005) studied NT under dryland

conditions in Pakistan and showed that NT gave lower yields than TT, but the experiment

was planted with improper equipment and with no mention of residue management; the

results are therefore suspect.

There are some excellent reviews of the equipment needs for zero-tillage systems. Baker et

al. (2002, 2006) devoted an entire book to this topic. A book on CA (‘Environment, farmer

experiences, innovations and socio-economic policy’) edited by Garcia-Torres et al.

(2003) has several papers on equipment for small- and large-scale farmers. The main re-

quirements of equipment in a CA system are a way to handle loose straw (cutting or mov-

ing aside), seed and fertilizer placement, furrow closing and seed/soil compaction. There

is also a need for small-scale farmers to adapt directdrill seeding equipment to manual,

animal or small tractor power sources (reduced weight and draft requirements) and re-

duce costs, so equipment is affordable by farmers, although use of rental and service pro-

viders allows small-scale farmers to use this system even if they do not own a tractor or a

seeder.

A simple three-row small grain seeder has been developed for small-scale animal-

powered farmers in Bolivia (Wall et al. 2003). This equipment uses a shovel rather than a

disc opener to save weight. It has straw wheels attached to the coulter to help move resi-

dues aside and reduce clogging. It also has the benefit that it can be used in ploughed or

unploughed soil. The main benefit farmers mentioned about this drill was savings in time; it

takes 10 h to plant a hectare with thismachinery and 12 days for the TT and seeding meth-

od. The conventional system also required the farmer to walk 100 km haK1 to undertake

all the tillage and seeding with his animals. The stand with the new drill was 246G 37 plants

mK2 compared with 166G39 for the conventional system. The cost of the drill was only

$330–390 in Bolivia. Similar information was provided by Ribeiro (2003) for planters in Brazil.

These can be manually applied jabber planters to animal-drawn planters. In both coun-

tries, the participation of farmers, local manufacturers and extensionists was vital for suc-

cess. Saxton & Morrison (2003) looked at equipment needs for large-scale farmers where

tractor horsepower, weight and draft are less important. Earlier machines were developed

Page 25

for clean tilled farmfields, whereas new NTmachines provide precision seed placement

through consistent soil penetration and depth and also supply fertilizer in bands which is

crucial for minimizing nutrient losses in zero-till systems. This paper discusses the use of disc

openers versus hoe and chisel openers and the use of additional straw and chaff spreading

devices.

6. CLIMATE CHANGE AND CONSERVATION AGRICULTURE

Lal (2005) suggested that by adopting improved management practices on agricultural

land (use of NTand crop residues), food security would not only be enhanced but also off-

set fossil fuel emissions at the rate 1997, 2001). The authors conclude that SMB plays a signifi-

cant role as a passive nutrient pool and suggests that its reduction, found in puddled soils in

the second half of the cropping season, could be a mechanism that contributes to declin-

ing productivity in continuous rice cropping systems. Little has been published on soil mi-

crobes in rice–wheat systems. of 0.5 Pg C yrK1. Climate change is likely to strongly affect

rice–wheat, rice–rice and maize-based cropping systems that, today, account for more

than 80% of the total cereals grown on more than 100 Mha of agricultural lands in South

Asia. Global warming may be beneficial in some regions, but harmful in those regions

where optimal temperatures already exist; an example would be the rice–wheat mega-

environments in the IGP that account for 15% of global wheat production. Agronomic and

crop management practices have to aim at reducing CO2 and other greenhouse gas

emissions by reducing tillage and residue burning and improving nitrogen use efficiency. In

the IGP, resource-conserving technologies continue to expand in the rice–wheat cropping

systems and save 50–60 l of diesel haK1 plus labour, and significantly reduce release of CO2

to the environment. Methane emissions that have a warming potential 21 times that of CO2

are common and significant in puddled anaerobic paddy fields and also when residues

are burnt. This GHG emission can be mitigated by shifting to an aerobic, direct seeded or

NTrice system. A review of the other benefits of direct seeding and NT in RW areas of South

Asia can be found in Grace et al. (2003). Nitrous oxide has 310 times the warming potential

of carbon dioxide, and its emissions are affected by poor nitrogen management. Sensor-

based technologies for measuring normalized differential vegetative index and moisture

index have been used in Mexico and South Asia to help improve the efficiency of applied

nitrogen and reduce nitrous oxide emissions.

7. CONCLUSIONS

Crop production in the next decade will have to produce more food from less land by

making more efficient use of natural resources and with minimal impact on the environ-

ment. Only by doing this will food production keep pace with demand and the productivity

of land be preserved for future generations. This will be a tall order for agricultural scientists,

extension personnel and farmers. Use of productive but more sustainable management

practices described in this paper can help resolve this problem. Crop and soil manage-

ment systems that help improve soil health parameters (physical, biological and chemical)

and reduce farmer costs are essential. Development of appropriate equipment to allow

Page 26

These systems to be successfully adopted by farmers is a prerequisite for success. Over-

coming traditional mindsets about tillage by promoting farmer experimentation with this

technology in a participatory way will help accelerate adoption. Encouraging donors to

support this long-term applied research with sustainable funding is also an urgent require-

ment.

Page 27

Page 28

Ledegeld beloop R200 per plaas, met ‘n maksimum van 2 lede wat

toegelaat word, vir elke 2 bykomende lidmaatskappe sal ‘n ver-

dere R200 betaalbaar wees.

Hierdie reëling geld ook ten opsigte van ander instansies soos che-

miese agente ens.

Aangeheg is die kontak besonderhede van ons finansiële mense.

Indien iemand wil aansluit kan hulle net ‘n e-pos stuur aan Gerty

Mostert en dan sal sy vir julle ‘n faktuur stuur.

Die ledegeld gaan vir die instandhouding van die webtuiste. Asook

vir verversings gedurende bruin– en groentoere gedurende die sei-

soen.

Kontakbesonderhede:

BLWK/CAWC

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Verskaf asb in die e-pos die naam van die plaas of instansie en die

person aan wie faktuur uitgemaak moet word.

INLIGTING TEN OPSIGTE VAN DIE

BEWARINGSLANDBOUVERENIGING SE

LEDEGELD