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.

1. 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

2. Sylvopasture Riparian buffer
Alleycropping
Windbreaks
Mixed planting
Agroforestry

3. - 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

4. - 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

5. - 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

7. - 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

8. 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

9. 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
Riparian buffer Mixed planting
- Intercropping was shown
to increase P availability
in rhizospheres
- P availability was
enhanced especially in a
low P soil

10. 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

11. Benefits of agroforestry on phosphorus mining restoration

12. 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

13. Risk areas for P runoff

14. 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.

15. - Reducing over-fertilization
- Creating buffer zones
Suggested management strategy
- Agroforestry as sustainable
approach to use soil P
Riparian buffer Mixed planting

16. P situation in
agricultural
land
P source Solution Suggested tree
species
High soil P
concentration
Natural deposits Stabilize P in the system: e.g., by permanent crop
cover, trees, dense root networks, buffer zones to
reduce run-off in water bodies
Fabaceae
(Leguminous) species:
e.g. Albezia,
Dalbergia , Millettia,
Crotalaria
Over-fertilization
with mineral
fertilizer
Short term solution possible by reducing the input to
an optimum
Over-fertilization
with organic
fertilizer
Structures of high livestock densities and resulting
over-fertilization often develop based on local
demands and market structures, difficult to solve in
the short term à Stabilize P in the system: e.g., by
permanent crop cover, trees, dense root networks,
buffer zones to reduce run-off in water bodies, while
working on long-term solutions to reduce manure
input.
P deficiency Depleted soils/
naturally low
concentrations +
economic situation
doesn’t allow for
fertilizer use
Trees that can utilize less available P sources and thus
increase P availability to adjacent crops
Broussonetia, Grewia,
Erythrina, Leucaena,
Michelia, Robinia,
Shorea, Zizyphus
species.
Acacia species
Immobilized P
resources
Enhance soil microbial activity (P mobilization)

17. - Provides context-specific solutions
- Dynamic: does not imply only a certain scenario, but is applicale on a
huge variety of problems
Agroforestry - Conclusion

18. Thank you for your attention!
Stefanie D. Goldberg Anne OstermannKai YanPeter E. MortimerJianchu Xu
Email: j.c.xu@cgiar.org