Tree and crop productivity and soil organic matter changes as influenced by Leucaena hedge-row management in sub-humid India

Graduation date: 1997The overall objective of this study was to evaluate biomass production and soil ameliorative potential of alley farming in sub-humid India. Effect of the cutting height (40, 80, 120, 160 cm) of Leucaena hedges and root barriers on biomass yield of Leucaena and maize and wheat crops were examined. Trees were pruned at sowing of crops and pruned biomass recycled as surface mulch at the rate of 0, 1.5, 3, 4.5 and 6 Mg ha⁻¹ twice every year. Biomass production from the trees increased with increasing cutting height up to 120 cm without any substantial reduction in the crop yields. Root barriers had little effect on trees, no effect on maize, but significantly increased\ud wheat grain and straw yield near the trees indicating competitive below ground\ud interaction between Leucaena and wheat. Some alteration in pruning timing may help to minimize tree-crop competition. Crop yields sharply increased with increasing mulch levels when compared on a net-cropped-area basis. However, growing of higher levels of\ud mulch material rapidly reduced area under crops. When adjusted for loss in crop area, a reduction in the grain production was estimated with increasing mulch levels. Estimates based on tree-crop interactions observed in this study show that an alley cropping system with 20% area under Leucaena hedge-rows would provide about 12% lower grain yield and 15% higher fodder yield from crops compared to sole cropping system. In addition, trees would provide about 3.2 Mg\ud ha⁻¹ fuel wood. In such an arrangement, about 3 Mg ha⁻¹yr⁻¹ mulch can be recycled which will have little soil ameliorative value as it showed only marginal increase in soil organic matter (SOM). The system should, however, maintain current yield levels. I used a simulation model SCUAF (Soil Changes Under Agro-Forestry) for predicting expected changes in SOM under different mulch levels. The predicted changes in SOM after a period of 25 years were of the same magnitude as observed changes in soil microbial biomass (Bc) during the 3 year study. Results of this study support the hypotheses that the Bc:Oc ratio tends to return to a climate induced equilibria and early changes in Bc may be used for providing quantitative projections of changes in SOM under different land\ud management options. However, this relationship needs to be validated with long-term field data