Temporal variations of N and P losses via surface runoff from Chinese farmland after fertilisation

The loss of nitrogen (N) and phosphorus (P) via surface runoff induced by fertilisation leads to water pollution and aggravates water scarcity. Studies estimating N and P losses from farmland have focused on the efficacy of agricultural management actions at reducing the amount of N and P lost. However, a gap remains in understanding the dynamics of N and P losses from farmland, especially differences among types of farmland, crop and fertiliser. Thus, the temporal variations of N and P losses via surface runoff from farmland induced by fertilisation were estimated using 5530 groups of paired observations collected in China. The results showed that N and P losses via surface runoff from paddy fields associated with fertilisation were greater than losses from upland fields. However, after > 90 days post-fertilisation, the effects of fertilisation on N and P loss from paddy fields were non-significant, while the effects of fertilisation on N and P losses from upland fields remained significant. Organic fertilisation decreased N losses from upland and paddy fields, but at more than 60 days post-fertilisation, N and P losses from upland fields were greater with organic than chemical or combined fertilisation. Increasing the fertilisation rate led to higher N and P losses from upland and paddy fields and extended the occurrence time of N and P loss from paddy fields. Overall, this study demonstrates the dynamic processes associated with fertilisation underlying N and P losses from farmland via surface runoff.