Agroforestry System Rapid Field Assessment Proposed outline for report

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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

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Cycling and storage of water, nutrients, and
carbon

• October 6, 2009

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Effects of trees on water uptake/cycling in
agroforestry 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 gt PE) little effect
• Semi-arid climates (ppt lt 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!

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Temperate Alley CroppingBlack 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)

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Grain yield of maize under different treatments
and tree species


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• (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
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Daily Precipitation, May-Sept. 1996
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Soil water content under different treatments
black walnut
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Soil water content under different treatments
red oak
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G

• Tree Fine Root Biomass with
• Distance from
• the Tree

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Maize fine root biomass
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Tree MaizeWater Uptake(during one
growing season)
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• Leaf Area
• Expansion
• In Maize
• Under
• Different
• Treatments

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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
• Butwhat about nutrients?

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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

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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
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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 (CN)
• Black Walnut 26
• Red Oak 58
• Substrate quality for leaves (CN)
• 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

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Tasks

• Group 1 Explain Table 1
• Group 2 Explain Table 2
• Group 3 Explain Figures 3 4

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Biomass, N content, NDF, UFNin Maize
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Biomass, N content, NDF, UFSin Trees
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Leaf root decomposition change in residual
mass and carbon
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Leaf and root decompositionPatterns of N P
release
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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)

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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

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Nutrient cycling the ideal
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Litter quality and decomposition key to
nutrient availability

• CN 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 CN, 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

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Leaf characteristics decomposition patterns for
tropical agroforestry species
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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

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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

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Cumulutative root length fraction by depth for 3
agroforestry species, growing in acid soils in W.
Kenya
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Nitrate-N undby depth under 3 agroforestry
species, growing in acid soils in Kenya
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Nutrient cycling in the tropics the reality
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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 lt15 yield increase, considered unattractive

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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.
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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

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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

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Recycling Index Shade coffee systems