Characteristics and drivers of daily nitrogen and phosphorus losses from rice-rapeseed rotation systems in the middle reaches of the Yangtze River.

Crop production systems involving the use of high rates of fertilizer application caused significant losses of nitrogen (N) and phosphorus (P) to the environment, resulting in air pollution and water body eutrophication. Quantitating N and P losses and its drivers in crop production systems was critical for optimizing water and fertilizer management measures to mitigate the nutrient losses. However, N and P losses estimation remains highly uncertain in the field at event scale. We here quantify daily N and P losses and its drivers (daily N and P water input, N and P uptake, N and P water surplus, water loss, etc.) in rice-rapeseed growing systems by high-frequency field experiments at event scale in Central China. Results revealed that there were significant trade-off relationships between daily uptake and surplus for N and P during the whole growing stages both for rice and rapeseed. Although it was not significantly related in heading to mature stage for rapeseed, synergies between daily input or surplus and loss were found for N. Redundancy analysis revealed that water input and leaching loss contributed most for N and P loss in rice and rapeseed. The nutrient losses in easier stages should be reduced by postponing the base fertilizer and making it in line with the crop uptake. The study enhanced our knowledge of N and P losses mechanism for crop production systems and provided a scientific basis for optimization of water and fertilizer managements and N and P loss estimation models.