Journal of Taiwan Agricultural Research

Author:Chi-Ling Chen* and Shen Lian

Abstract:

    This paper reviews changes of organic matter content in the soils of some long-term experiments conducted in Taiwan and Japan, where different rates of crops residues or organic manure had been applied continuously. The decomposition and accumulation of organic matter in the soils were simulated as the first order reaction and the model was used to estimate the input of organic manure required to maintain different levels of organic matter in the soils. The experiments of Taiwan consist of a 48-year field trial with the cropping system of two crops paddy rice per year in Taipei, a 14-year field trial with the cropping system of rice-rice-soybean per year in Pingtung and a 9-year field trial with the cropping system of 2-3 crops soybean per year. The experiments of Japan consist of a 60-year field trial with the cropping system of one crop paddy rice per year in Saitama, Japan and a 9-year field trial with the cropping system of onion-cabbage per year in Kanagawa. The results indicate that soil organic matter can maintain a higher level generally in the Temperate than in the Tropics, and in paddy than in upland. The long-term application of chemical fertilizer did not deplete the content of soil organic matter but even increase slightly compared to the soil without application of fertilizers. A stabilized content (3.0%) of organic matter was, in fact, maintained in the soil without application of fertilizer in this paddy soil; the rice stubble and roots remained in the soil after the harvests were enough to maintain this level of organic matter without any tendency of depletion. On the other hand, the long-term application of green manure did not increase the content of soil organic matter as significantly as that of compost did, although it did increase slightly higher than the soil with the application of chemical fertilizer. Apparently, the increase of soil organic matter through the application of organic manure is more difficult in Taiwan than in Japan due to its higher rate of decomposition. This characteristics, however, is advantageous for agricultural land to act as disposal places for the harmless organic waste produced by animal husbandry. The reasonable rate of application, however, should be evaluated so that environmental impact will be minimized. According to the results of the experiments and simulation analysis, the continuous application of 17 Mg/ha/year (fresh weight basis) of farm yard manure for 70 years is required to raise soil organic matter from the level of 3.5% to 4.5%, both at nearly steady state, in the paddy field of Taipei . The rate of N release at steady status maintaining 4.5% organic matter is 180 kg N/ha/year. On the other hand, the continuous application of 110 Mg/ha/year (fresh weight basis) of bagasse filter cake compost for 30 years is required to raise soil organic matter from the level of 1% to 2%, both at nearly steady state, in the upland field of Tainan. The rate of N release at steady state maintaining 2% organic matter is 740 kg N/ha/year. The long-term continuous application of 110 Mg/ha/year (fresh weight basis) of bagasse filter cake compost apparently will cause pollution to the environment.

Key words:Soil organic matter, Turnover, Modeling

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