Graduate Thesis Or Dissertation
 

Performance of Leucaena, sorghum or cowpea and resource sharing in an agrisilviculture system in semi-arid India

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  • In an agrisilviculture system, trees and crops compete for above and below ground resources. This study aimed at quantifying the effect of shoot pruning and root barriers around pollarded trees on the production of crop and tree components with and without application of fertilizer to the crop. Sorghum (1991 & 1992) and cowpea (1993 & 1994) were grown as intercrops with Lezicaena trees on a shallow red soil (alfisol) under rain fed conditions at Hyderabad, India. Crops grown with pruned trees had higher leaf area index and dry matter than did those with unpruned trees. The grain yield of sorghum was 76% and 39% of the pure crop yield (1553 kg ha⁻¹) with pruned and unpruned trees with no root barriers. The corresponding values for cowpea were 49% and 26% of the pure crop yield (1075 kg ha⁻¹). Intercropped sorghum and cowpea responded to fertilizer application more strongly than their respective pure crops, suggesting a need for fertilizer application in an agrisilvi-system. impact of root bamers was not significant on either crop. The study suggested that competition for light was stronger than for soil water. Straw and grain yield of sorghum, and dry matter yield of cowpea were found to be roughly proportional to the amount of light intercepted by the crop at harvest. Pruning of trees twice during the cropping season reduced tree diameter growth and branch and foliage yield compared to no pruning. Unpruned trees yielded 5643 kg ha⁻¹ yr⁻¹ of branches and foliage compared to 2028 kg ha⁻¹ yr⁻¹ by pruned trees. Pruning eliminated litter fall and nutrient input to the soil nutrient pool because pruned material was utilized as fodder. Unpruned trees contributed 103 kg of nitrogen and 6.4 kg of phosphorus per hectare annually to the soil nutrient pool through litter fall. During the cropping season, soil water content was higher near the surface in tree plots compared to pure crop plots. Tree transpiration declined only after more than half of the leaf area was removed. Pruning of roots to a depth of 60 cm caused no decline in transpiration suggesting trees can draw water equally well from deeper or shallow soil layers. The study highlighted the competitive interaction between trees and crops. The agrisilvi-system produced about 50% more biomass with unpruned trees than with pure crop or pure tree. Based on cash value (fodder yield equivalent) it would require 1.55 times as much land if trees and crops were grown separately compared to agrisilvi-system with unpruned trees. Soil nitrogen economy and stability of fodder and fuelwood production can be achieved with pollarded-unpruned leucaena trees in an agrisilvi-system but grain crop yields are severely depressed. Thus, there was little advantage of the agrisilvi-system over pure cropping for meeting the present and increasing demand of food production. For this agrisilvi-system to be adopted by subsistence farmers in India further refinements must be developed so that crop yields are maintained.
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