Agroforestry
Agroforestry
This domain tests deliberate integration of trees with crops, livestock or horticultural crops. Questions cover systems, tree-crop interactions, species choice, windbreaks and boundary plantations.
Core rules
- Agrisilviculture combines trees with crops; silvopasture combines trees with pasture and livestock; agri-horticulture combines crops with fruit trees; alley cropping uses hedgerows with crops between alleys.
- Trees can improve soil organic matter, reduce erosion, provide shade, fodder, fuel and timber, and fix nitrogen if leguminous. They can also compete for water, light and nutrients.
- Pruning and root pruning can reduce competition, but excessive pruning reduces growth and litter. Selection should match rainfall, soil depth, salinity and farmer needs.
- Windbreaks reduce wind speed and erosion. Protection generally extends about 10-20 times the tree height downwind, with some effect upwind.
Worked example
A windbreak is 10 m tall. Expected protected zone downwind = 10 x tree height to 20 x tree height = 100-200 m. A 100 m x 100 m field with the windbreak on the windward edge is therefore mostly within the protected distance. The reasoning uses height, not age or trunk diameter, because the shelter effect scales with height and porosity.
Traps
Agroforestry is not merely leaving trees in a field; it is deliberate integration. Nitrogen fixation by legumes does not immediately supply all crop N. Dense shade can reduce crop yield. Do not plant deep-rooted trees over shallow soils without checking water competition. Windbreak protection is not infinite downwind.