Improving water management practices to reduce nutrient export from rice paddy fields

Abstract

Nitrogen (N) and phosphorus (P) loss from rice paddy fields represents a significant threat to water quality in China. In this project, three irrigation–drainage regimes were compared, including one conventional irrigation–drainage regime, i.e. continuous submergence regime (CSR), and two improved regimes, i.e. the alternating submergence–nonsubmergence regime (ASNR) and the zero‐drainage irrigation technology (ZDIT), to seek cost‐effective practices for reducing nutrient loss. The data from these comparisons showed that, excluding the nutrient input from irrigation, the net exports of total N and total P via surface field drainage ranged from −3.93 to 2.39 kg ha−1 and 0.17 to 0.95 g ha−1 under the CSR operation, respectively, while N loss was −2.46 to −2.23 kg ha−1 and P export was −0.65 to 0.31 kg ha−1 under the improved regimes. The intensity of P export was positively correlated to the rate of P application. Reducing the draining frequency or postponing the draining operation would shift the ecological role of the paddy field from a nutrient export source to an interception sink when ASNR or the zero‐drainage water management was used. In addition, since the rice yields are being guaranteed at no additional cost, the improved irrigation–drainage operations would have economic as well as environmental benefits.