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Abstract
Soil nutrient dynamics during the cropping phase of shifting cultivation was studied. Following the initial enrichment of soil with major nutrient elements by the slash and burn practice, various loss processes set in, such as erosion, leaching and crop uptake. The most remarkable loss in nutrients was due to erosion that was caused by premonsoon showers even before seeding of the first crop of maize. Thus the initial enrichment was directly followed by a severe initial loss, and this loss appeared to some extent inevitable under the conditions of monsoon tropics with distinct wet and dry seasons.
The nutrient loss process is, however, by no means simple and uniform. A factor that complicates the process is the release of nutrients from decomposing organic matter. In order to evaluate a steady-state rate of decomposition of soil organic matter under the natural forest, Kira’s model was applied to the data of soil respiration and forest ecology. In comparison with the steady-state rate, the swidden field had twice as rapid a rate of decomposition in the first year and nearly 30% of the total stock of soil organic matter was decomposed during the two years of the cropping phase.
The nutrient balance was computed for the cropping period, in compiling all the data collected. The results suggested that the decline of soil fertility would not be the cause of the shift in this particular experiment of shifting cultivation.
