Naomi Asagi and Hideto Ueno. Ehime Univ, Ko 498, Hattanji, Matsuyama, Ehime, Japan
We have conducted a study to build a sustainable agricultural system with legume-cover crops in rice paddy field. It has been found that white clover can produce a high level of biomass and can fixed an enough amount of nitrogen for rice plant but only a small amount of the fixed nitrogen was taken up by rice plant in the past, because of the discrepancies in N patterns between N supply from the legume and N uptake by the crop. Irrigation is one of the practical methods that can control the timing of deadening and decomposing the legume and following N mineralization. The objectives of the present study are to evaluate the effects of irrigation timing on N concentration in the soil, plant growth and yield. The treatments consisted of conventional control (CC), legume incorporation (LI), and cover crop with irrigation 10 days before transplanting (10DBT, the past irrigation) and that 10 and 30 days after transplanting (10DAT and 30DAT, respectively). Concentration of inorganic N in the soils of all treatment increased by 30 days after transplanting and then gradually decreased. Ammonium N in the flooded water in paddy field of CC, 10DBT, 10DAT, and 30DAT demonstrated a peak at 22, 5, 22 and 42 DAT, respectively. The peaks were detected at delaying 12 or 15 days after the beginning of irrigation suggesting that the delay of irrigation timing could retard legume decomposition and N mineralization. At harvest, plant height and number of tiller in 30DAT was significantly higher than 10DBT. The yield in 30DAT increased by 13.7% comparing with 10DBT due to the increase in percentage of ripened grain and 1000 grain weight. It is assumed that the delay of N mineralization would supply available N to the crop effectively.
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