Agroforestry System Rapid Field Assessment Proposed outline for report

1. Agroforestry System Rapid Field Assessment Proposed outline for report • Introduction • Include definition of sustainability (stability/resilience) • Objectives • Methods • Indicator development • Brief description of farms visited • Data collection process • Results • Present data collected for the indicators for each farm, using tables, graphs, diagrams, as appropriate • Land owner objectives for each farm • Synthesis & Discussion • Comparative farm analysis: sustainability strengths and weaknesses • Agronomic, environmental, social and economic • Cost-benefit trade-offs to achieving sustainability • Scale of analysis – implications for sustainability assessment • Recommendations for enhancing sustainability • Major knowledge gaps • Conclusions

2. Cycling and storage of water, nutrients, and carbon October 6, 2009

3. Effects of trees on water uptake/cycling inagroforestry systems • Hydrologic regulation - reduce water losses • Increased evapotranspiration (canopy interception + transpiration) • Increased infiltration and soil water storage capacity (soil structure) • Reduced surface runoff • Reduced soil erosion and nutrient/sediment losses • Deep percolation = ‘safety net’ (increase water use efficiency of the system) – how is this effect vary by climate? • Humid climates (ppt > PE) – little effect • Semi-arid climates (ppt < PE) – if crops using water at recharge depth, little effect • Sub-humid/savanna climates – enough ppt to recharge soil at depth – greatest opportunity for increasing total water use! (“Niche differentiation”) • Possible competitive interactions with crops!

4. Temperate Alley Cropping:Black Walnut-Red Oak-Maize • Initial tree spacing (1985) = 1.2 m within a row, 8.5 m between rows • Trees thinned to 2.4 m spacing (1995) • Annual pruning • Crop alleys machine-harvested; yield quantified • Experimental trials in 1995: 12 plots established (100 m x 11 m) • 3 Treatments with 4 Replicates • Root barrier (1.2 m) • Trench w/ root pruning (1.2 m) • No barrier (control)

5. Grain yield of maize under different treatments and tree species

6. (a) P(net) as a function of PAR in maize (b) Typical diurnal pattern of maize P(net) by row position Conclusion: Competition for light not a major constraint in these alley cropping systems – need to look at belowground competition for nutrients & water…

7. Daily Precipitation, May-Sept. 1996

8. Soil water content under different treatments: black walnut

9. Soil water content under different treatments: red oak

10. G Tree Fine Root Biomass with Distance from the Tree

11. Maize fine root biomass

12. Tree & MaizeWater Uptake(during one growing season)

13. Leaf Area Expansion In Maize Under Different Treatments

14. Evidence thus far… • Tree roots present in the ‘maize alley’ in the ‘no barrier’ treatment • Higher tree water uptake in the ‘no barrier’ treatment • Lower soil moisture in the ‘maize alley’ in the ‘no barrier’ treatment • Maize plants in the ‘barrier’ treatment had 21% higher leaf area • Grain yield in the ‘barrier’ treatment was 33-40% greater. • Reductions in leaf area and grain yield were greatest for the maize row closest to the trees for ‘no barrier’ • But…what about nutrients?

15. Nutrient cycling in AF systems • Competition for nutrients between trees & crops may reduce yields • Depends on balance between availability of different resources • Trees can enhance soil fertility in AF systems via: • Addition of OM through leaf & root decay • Biological N fixation by leguminous trees • Many temperate AF species not leguminous • Many temperate crops fertilized – competition? • Information needed on • Rates of decomposition and N/P release from leaves & fine roots • Nutrient uptake by crops and trees

16. Nutrients • Experimental design (Jose et al. 2000) • Maize fertilized each • growing season at rate of • 168 kg N/ha. • Microplots with 15N application • (in place of regular fertilizer) • Leaves and roots sampled • and analyzed for 15N • Decomposition study – litter bags • of root and leaf material Walnut tree

17. Important Background Informationto explain nutrient dynamics… • Both trees and crops have roots concentrated in the top 30 cm soil layer. • Trees begin their growth in April • Maize begins growth in mid-May • Substrate quality for roots (C:N) • Black Walnut = 26 • Red Oak = 58 • Substrate quality for leaves (C:N) • Black Walnut = 37 • Red Oak = 50 • Leaf fall • Black Walnut: September • Red Oak: November • %NDF: Percentage of plant N derived from fertilizer • %UFN: Percent utilization of fertilizer N

18. Tasks • Group 1: Explain Table 1 • Group 2: Explain Table 2 • Group 3: Explain Figures 3 & 4

19. Biomass, N content, %NDF, %UFNin Maize

20. Biomass, N content, %NDF, %UFSin Trees

21. Leaf & root decomposition: change in residual mass and carbon

22. Leaf and root decomposition:Patterns of N & P release

23. Conclusions • Low nutrient uptake by maize in ‘no barrier’ plots likely due to nutrient-water interactions: • Increased competition for nutrients with trees • Moisture stress reduces plant vitality, soil N mineralization, and N uptake rates (e.g., lower soil moisture and lower plant N uptake capacity) • Competition for water from tree roots is the primary factor causing a lower efficiency of fertilizer use. • What results would have provided conclusive evidence for competition for nutrients as the major limiting factor? • No differences in soil moisture or water uptake rates • Potential for leaf/root decomposition and nutrient release to replenish nutrients? • Low in first year • Only 5% of leaf N and 39% of root N in black walnut mineralized • Long term impacts important: OM effects on moisture retention, nutrient release, and soil structure enhance soil fertility)

24. Management options for designing alley cropping systems for maximum production… • Wider spacing • Irrigation • Root pruning • Thinning of trees • Timing of planting • Rate and placement of fertilizer

25. Nutrient cycling: “the ideal”

26. Litter quality and decomposition: key to nutrient availability • C:N ratios • 10-25 for N2-fixing species • 14-32 for non-N2-fixing species • Lignin • 5-20% green foliage; 10-40% leaf litter • Above ~15% decomposition impaired • Polyphenols (tannins • inhibit decomposers and slow decomposition • Litter with high C:N, high lignin and tannins that decompose slowly may cause immobilization of soil N • Chemical quality of litter of AF species important for making agroforestry management decisions

27. Leaf characteristics & decomposition patterns for tropical agroforestry species

28. Agroforestry and Phosphorus • Potential for AF species to increase P = limited • Many tropical soils have very low native P levels • P fixation by soils with high Fe and Al • P depletion from long-term cropping • Enhanced crop available P possible: • Decomposition of biomass (usually low) • Production of organic acids that chelate Fe and Al

30. “Safety net” potential • Highest potential when: • Trees have deep root systems • Trees have a high demand for nutrients • Sites with water and/or nutrient stress in surface soil, but high availability in subsoil • Example: western Kenya • Acid soils with large nitrate quantities at 0.5-2.0-m depth • Due to mineralization of SOM and sorption and retention of nitrates by clay minerals • Max rooting depth maize = 1.2 m • Tree roots extended to 3-4 m within 11 mo (varied by species)  reduced soil N but increased aboveground biomass N

31. Cumulutative root length fraction by depth for 3 agroforestry species, growing in acid soils in W. Kenya

32. Nitrate-N undby depth under 3 agroforestry species, growing in acid soils in Kenya

33. Nutrient cycling in the tropics: “the reality”

34. Alley Cropping • Review of 29 trials (4+ years data), over wide range of soils and climates in tropics • Compared avg yields of annual crops from intercropping vs. sole-crop systems • Some cases, sequential crops – separate data • Tree species varied by region • High variability in results: • Positive effects: 15 for cereals; 8 for noncereal crops • Negative effects: 13 for cereals; 1 for sweet potato, taro • If <15% yield increase, considered unattractive

35. Water-Nutrient Interactions Low rainfall High rainfall Competition for water outweighs positive effects of nutrient additions Abundant water, so nutrient additions have positive effect on growth.

36. Interpretation of meta-analysis • Water-limited areas: • competition with trees for water • despite improved soil fertility from trees • Poor soils: • low yield of prunings and competition with trees for nutrients • Subhumid climates • Positive yield response when soils had low fertility, and sufficient additions of nutrients from prunings • Humid climates • Also depended on whether trees enhanced soil fertility

37. Shaded perennial-crop systems • Yield of shaded perennial plants affected by interaction between light availability and soil fertility • Nutrient recycling indices provide an indication of effects of trees on nutrient availability • Comparison of shade coffee systems: • Erythrina – N2 fixing • Cordia – non-N2 fixing

38. Recycling Index: Shade coffee systems