[Differences in uptake, utilization and loss of nitrogen and phosphorus in a Chinese double rice cropping system...

In order to optimize water and fertilizer use in the double-cropping rice in eastern Fujian Province, a field runoff plot experiment was conducted to investigate rice yield, nutrient uptake, and runoff losses of N (nitrogen) and P (phosphorus) in the T₀(no chemical fertilization with traditional flooding irrigation), T₁(common chemical fertilizer of 273 kg N·hm^-2, 59 kg P·hm^-2, and 112 kg K·hm^-2 combined with traditional flooding irrigation), T₂(chemical fertilizer of 240 kg N·hm^-2, 52 kg P·hm^-2, and 198 kg K·hm^-2 combined with traditional flooding irrigation) and T₃(chemical fertilizer combined with shallow intermittent irrigation) treatments. Results showed that early rice grain yield in the T₁, T₂ and T₃ treatments significantly increased by 0.7, 1.0, 1.1 times, late rice grain yield significantly increased by 0.9, 1.1, 1.0 times compared to that in the T₀ treatment, respectively. The T₁, T₂ and T₃ treatments significantly increased the uptake of N and P in aboveground parts of the plants, especially in grains. The T₁, T₂ and T₃ treatments significantly increased N uptake by 1.1, 1.2, 1.2 times, increased P uptake by 0.9, 1.4, 1.6 times in early-season grains, and significantly increased N uptake by 0.8, 1.0, 1.0 times, increased P uptake by 0.7, 0.9, 0.9 times in late-season grains, compared to T₀, respectively. Furthermore, T₃ increased agronomic N use efficiency (AEN) and agronomic P use efficiency (AEP) by 71.1% and 69.2% in early rice plants, increased AEN and AEP by 26.4% and 25.0% in late rice plants, whereas T₃ decreased total dissolved N (DN) by 16.0% in comparison with T₁. Dissolved inorganic N loss in surface runoff occurred mainly in the form of NO₃^--N (nitrate N) under different water and fertilizer regimes. However, there were no significant differences in AEN and AEP between T₂ and T₃ treatments. These findings suggested that optimal applications of water and fertilizers (T₃) might increase N and P uptake in rice plants, maintain yield, and reduce N loss, especially in the form of NO₃^--N in surface water from early rice field. In general, this study could provide theoretical support for the optimization of irrigation and fertilization and for the control of N and P non-point source pollution from the double cropping rice paddy fields in eastern Fujian Province.