Effects of Nitrogen Application Rates on Rice Grain Yield,Nitrogen-Use Efficiency,and Water Quality in Paddy Field

Excessive nitrogen (N) fertilizer application is common in the central Zhejiang Province area, China. A three-year (2009–11) experiment was conducted to determine the optimum N application rate for this area by studying the effects of various N rates on rice (Oryza sativa L.) yield, N-use efficiency (NUE), and quality of paddy field water. Results showed that no significant yield differences were observed under N rates from 180 to 315 kg ha^?1. The NUE could be improved by reducing N application rates without significantly decreasing yield. Due to high ammonia (NH₄⁺-N) and nitrate (NO₃^—N) concentrations, 5–7 days after N application was a critical stage for reducing N pollution. The N rate for the greatest yield was 176 kg ha^?1, accounting for 65 percent of the conventional N rate (270 kg ha^?1). The N-rate reduction in this area may be necessary for maintaining high yield, improving NUE, and reducing environmental pollution.