CHANGES IN SOIL FERTILITY AND TILTH UNDER SHIFTING CULTIVATION : III. Soil Respiration and Soil Tilth

概要

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Soil respiration was measured at 2 week intervals during the two years of the cropping phase of experimental shifting cultivation at Nam Phrom in northeast Thailand. The results clearly indicated an enhancement of soil organic matter decomposition by the clearing of the forest. Soil temperature rise as high as 5℃ at the depth of 10 cm from the surface was a factor that significantly accelerated the decomposition process. Altogether about 16.5-17 tons of carbon per hectare evolved as soil respiration in the first year after burning, which exceeded by 4-5 tons the value recorded under the natural forest. In the second year the difference became much less pronounced than in the first year. Effect of burning and protracted drought on the acceleration of soil organic matter decomposition was evident. Soil tilth as determined by the total pore volume, bulk density and moisture retention characteristics showed a change towards degradation. The fact that the plot that underwent tillage operations showed a greater change suggested that the major cause of dererioration of soil tilth was the mechanical disturbance. A rapid loss of soil organic matter could be an additional cause. Based on the experimental results, the significance of the zero-tillage practice adopted by shifting cultivators was discussed in relation to the establishment of sustained upland farming in the monsoon tropics.
社団法人日本土壌肥料学会の論文