Tree-crop interactions and nutrient dynamics in agroforestry systems

In agroforestry systems, on acid infertile soils, crop yield reduction and soil nutrients decline are caused by negative effects of the tree-crop interactions. To prevent crop yield reduction and soil nutrients decline, the effects of the components of the tree-crop interaction and soil nutrients dynamics were studied. Components of the tree crop interactions are the effects of mulch, and trees on crop production and soil nutrients dynamics. Tree effects can be separated in above and below ground effects caused by shoots or roots respectively. In the Bolivian tropics, in a soil classified as coarse-loamy mixed isohyperthermic Fluventic Dystropept, two leguminous trees Inga edulis (Mart.) and Senna reticulata Willd were planted as hedges and intercropped with rice (Oriza sativa L.) and cowpea (Vigna unguiculata L., Walp). Two pruning regimes were applied to the trees. Mulch applications did not affect rice or cowpea grain yields or straw production, suggesting that short term improvements of soil chemical parameters did not occur or were not large enough to affect crop production. The inclusion of trees in the system reduced grain yields in 20% and 25% for rice and cowpea compared to plots without trees. Root competition varied with age of trees and climatic conditions, generating between 8% to 30% grain yield reduction in rice. The pruning regimes did not affect crop production. Yields in agroforestry systems compared to tree less systems, were 95% and 80% for rice and cowpea, and the yields were 94% and 83% for Inga and Senna respectively. Mulch applications to plots without trees caused Ca, Mg, and K availability in the soil to decrease with time of cultivation. Higher P levels were observed in plots with trees compared to plots without trees. Results suggest, for the Chapare area of Bolivia, that sequential agroforestry systems would be more advantageous than simultaneous ones, because the sensitivity of the crops to above and below ground competition. Farmers will be more likely to benefit from the utilization of managed fallows or of cover crops because trees will not be present in the field at the same time as the crops.