Material Balance and Ecological Functions of Paddy Farming in Japan

JIRCAS international symposium series
ISSN 13406108
書誌レコードID(総合目録DB) AA1100908X
In Japan, the rapid decrease in the area of paddy fields is a major cause for concern in relation to the conservation of the land and the environment. Therefore, the beneficial ecological effects of the paddy fields on the environment have been studied and are summarized below.
"Physical effects" arise from the structure of the paddy fields such as the presence of ridges, plow sole and terraces. The water-storing capacity of the rice fields which is estimated by multiplying the area of paddy fields in Japan and the effective height of water storage (height of ridge-ordinary ponding depth) is estimated at 5.4 billion m3 , a value larger than that of flood regulation reservoirs. On the other hand, the plow sole regulates the water percolation for ponding and replenishing the groundwater resources and also preventing slope collapse through the avoidance of rapid water percolation. The terracing of the paddy fields reduces considerably soil erosion on sloping fields.
"Chemical effects" arise from water ponding. Since the soil in paddy fields under water-saturated conditions becomes reductive, the assimilation and nitrification of ammonium nitrogen by bacteria are limited and the ability of nitrogen fixation by algae in ponded water amounts to 25-40 kgN /ha/yr. As a result, a rice yield of 5 tons/ha can be obtained by limited nitrogen fertilization of less than 100 kgN /ha. Furthermore, under the reductive soil conditions, the denitrification process becomes active and plays a role in the purification of nitrate-rich water. The latter capacity is estimated at around 300 kgN/ha/yr.
作成者 Hidenori Iwama
公開者 Japan International Research Center for Agricultural Sciences
開始ページ 113
終了ページ 122
言語 eng