Nitrogen accumulation in paddy rice irrigated with water containing ammonium and nitrate during the reproductive growth period

Abstract

In the process of reutilization of secondary sewage effluent as irrigation water for rice cultivation, inorganic nitrogen at high concentrations in the water is the most crucial substance for rice growth and production. A pot experiment using 15N-labeled nitrogen sources was conducted to evaluate the accumulation of nitrogen from ammonium and nitrate nitrogen (7 and 14 mg L−1) contained in water irrigated during the reproductive growth period to rice plants, which received a medium rate of fertilizer nitrogen to adjust the number of grains. The supply of both the forms of nitrogen from water in addition to topdressed nitrogen did not always lead to a sizeable yield increase although ammonium nitrogen increased straw and total dry matter production. The supply of nitrogen, especially ammonium nitrogen, from water during the early half (22 d) of the reproductive growth period significantly increased the nitrogen concentration in grains, due to the higher recovery rate and accumulation of nitrogen supplied from water during this period. © 2002 Taylor & Francis Group, LLC.