Nitrogen and phosphorus dynamics of systems integrating trees and annual crops in the tropics
Alley-cropping is a system of agroforestry which mixes legume trees with annual crops with the aim of combining the soil improving effects of a tree fallow with continuous cropping. At CATIE, Costa Rica I carried out research on an established alley-cropping experiment to study how the trees improve soil fertility and why, despite competition from the trees, the crops yield more in their presence. The decomposition of the higher inputs of mulch in the presence of the trees released large quantities of nitrogen, leading to higher rates of nitrogen mineralization in the soil. The increased supply of nitrogen caused faster establishment and growth of the crop. The increased rates of nitrogen mineralization with the trees was due to a build up in the readily mineralizable soil organic matter over a number of years. 15N tracer studies have shown that only 10 percent of the nitrogen released from the mulch in one season is taken up by the crop growing in that season, and this mulch nitrogen contributes only 10 percent of the total crop nitrogen uptake. There is no effect of the presence of the trees on the soil microbial nitrogen while the maize is growing, but when the maize has matured the trees maintain the microbial nitrogen pool while it declines in their absence. Phosphorus availability in the soil as measured by bioassay is lower in the presence of the trees, problably due to the trees removing phosphorus. However the greater cycling of phosphorus with the trees appears to maintain the supply of phosphorus to the crop. Competition between the tree and crop is reduced by pollarding the trees prior to sowing the crop. The crop is then able to take advantage of the high nutrient availability while the trees recover.
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| Format: | biblioteca |
| Published: |
Cambridge (RU)
1990
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| Subjects: | CULTIVO EN CALLEJONES, ZEA MAYS, ARBOLES, CULTIVOS ANUALES, COBERTURA VERDE, FERTILIDAD DEL SUELO, NITROGENO, FOSFORO, SUELO, CICLO BIOGEOQUIMICO, BIOMASA, COSTA RICA, |
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