Jianchu Xu, Stefanie D. Goldberg, Peter E. Mortimer, Anne Ostermann, Kai Yan

AGROFORESTRY – a new opportunity for P pollution management

and ecological restoration

Sep 9th 2016

SylvopastureRiparianbuffer

Alleycropping

Windbreaks

Mixedplanting

Agroforestry

-  Agroforestry systems: adaptable to the needs of farmers, crops, the landscape and local environment

-  Systems include: Mixed planting, alleycropping, windbreaks, riparian buffers and sylvopasture

-  Systems selected according to local needs and requirements, eg: shade tolerant crops -mixed planting, high light crops -wind breaks or alleycropping.

-  Tree and crop management: canopy pruning; pollarding; understory and litter management; cropping density; soil management

Types of agroforestry systems

-  Use of agroforestry system as a means of rehabilitating degraded landscapes – above and below ground restoration, social upliftment, ecosystem productivity

-  “Return to function” for damaged ecosystems

Agroforestry concept

-  Agriculture is the largest anthropogenic land use (38% of the land surface of the earth)

-  Long-term sustainability of agricultural systems requires that soils stay productive and that necessary inputs remain available in the future

-  Soil loss occurs more rapidly than soil creation in many agricultural landscapes, and the soil that remains declines in quality

-  One-way fertilizer nutrient flows simultaneously cause pollution and scarcity

-  E.g., Phosphorus: essential plant nutrient; expected to become increasingly expensive to mine and process; at the same time, P runoff causes eutrophication of water bodies

Agriculture – challenges of growing demand

-  Growing consumption of inorganic phosphorus (P) fertilizers derived from mining has contributed to major increases in crop yields since the 1950s

-  Concurrent growth in fertilizer use and livestock production has more than tripled global P flows to the biosphere over preindustrial levels, resulting in P accumulation in some agricultural soils that acts as a driver of eutrophication in freshwater and coastal systems

-  At the same time, limited availability of P fertilizers in other regions has contributed to prolonged P deficits that can deplete soil P and limit crop yields. Although agricultural P surpluses and deficits have been documented for several regions, there is still limited understanding of the spatial patterns of P imbalances at the global scale.

Imbalances of agronomic P

MacDonald et al. 2011. Agronomic phosphorus imbalances across the world's croplands. Proceedings of the National Academy of Sciences, 108(7), 3086-3091.

P balances calculated by spatial estimates of P inputs (P fertilizer and manure applications) and outputs (P in harvested crops) for cropland soils

Spatial patterns of agronomic P imbalances

Different soil P management strategies

Soil P deficit -  Liming acid soils, -  Increasing organic matter, -  Proper placement of P

fertilizer affecting how efficiently P is used by crops

Soil P surplus -  Reducing over-fertilization

and thereby reducing P losses due to erosion and runoff

Agroforestry is a suitable tool to address both issues

-  Permanent vegetation on agricultural watersheds as upland buffers and streamside riparian buffers has been shown to improve water quality parameters: reduce runoff, sediment, TN, and TP losses

RiparianbufferMixedplanting

-  Intercropping was shown to increase P availability in rhizospheres

-  P availability was enhanced especially in a low P soil

Different strategies of trees to mobilize P

-  Dual symbiotic trees: symbiosis with two different types of mycorrhiza, that both have different strategies to access P (e.g., Alnus nepalensis)

-  Non-mycorrhizal trees; forming cluster roots (e.g., Macademia)

-  Creation of diverse agroforestry systems to increase P mobilization due to different strategies and/or rooting depths

naturalmedicinefacts.info resilience.org infonet-biovision.org

Benefits of agroforestry on phosphorus mining restoration

Benefits of agroforestry on over-fertilized sites

-  Trees stabilize the soil reducing run-off, while the intercrops are typically of high P demand and successive harvests remove the excess P

Risk areas for P runoff

Example of P pollution

-  Lake Dianchi is the sixth largest lake in China (ca. 298 km2).

-  Large P deposits are located in the southern and south-eastern areas of the Dianchi basin.

-  Following the government’s "reform and openness" policy, industry and agriculture developed rapidly and Lake Dianchi became seriously polluted.

The continued pollution has been under control, but P content still high, and ecosystem needs further recovery.

-  Reducing over-fertilization -  Creating buffer zones

Suggested management strategy

-  Agroforestry as sustainable approach to use soil P

Riparianbuffer Mixedplanting

Psituationinagriculturalland

Psource Solution Suggestedtreespecies

HighsoilPconcentration

Naturaldeposits StabilizePinthesystem:e.g.,bypermanentcropcover,trees,denserootnetworks,bufferzonestoreducerun-offinwaterbodies

Fabaceae(Leguminous)species:e.g.Albezia,Dalbergia,Millettia,Crotalaria

Over-fertilizationwithmineralfertilizer

Shorttermsolutionpossiblebyreducingtheinputtoanoptimum

Over-fertilizationwithorganicfertilizer

Structuresofhighlivestockdensitiesandresultingover-fertilizationoftendevelopbasedonlocaldemandsandmarketstructures,difficulttosolveintheshorttermàStabilizePinthesystem:e.g.,bypermanentcropcover,trees,denserootnetworks,bufferzonestoreducerun-offinwaterbodies,whileworkingonlong-termsolutionstoreducemanureinput.

Pdeficiency Depletedsoils/naturallylowconcentrations+economicsituationdoesn’tallowforfertilizeruse

TreesthatcanutilizelessavailablePsourcesandthusincreasePavailabilitytoadjacentcrops

Broussonetia,Grewia,Erythrina,Leucaena,Michelia,Robinia,Shorea,Zizyphusspecies.Acaciaspecies

ImmobilizedPresources

Enhancesoilmicrobialactivity(Pmobilization)

-  Provides context-specific solutions -  Dynamic: does not imply only a certain scenario, but is applicale on a

huge variety of problems

Agroforestry - Conclusion

Thank you for your attention!

Stefanie D. Goldberg Anne Ostermann Kai Yan Peter E. Mortimer Jianchu Xu

Email:j.c.xu@cgiar.org