Evaluation of gridded cropland phosphorus budget and use efficiency in China.

Changes in soil phosphorus (P) distribution and budget critically impact the sustainability of agricultural systems. Yet, few studies have examined the long-term evolution of cropland (and crop-specific) P budget and use efficiency (PUE) at a grid level. Here, we conducted a comprehensive evaluation of the cropland P budget and PUE and their human-environmental drivers in China during 1992-2018 at a spatial resolution of 0.1°. The results reveal a significant shift in China's cropland P budget from a deficit of -3.70 Tg P yr in 1992 to a surplus of 0.31 Tg P yr in 2018, mainly driven by increased fertilizer application and decreased soil erosion by water. The concurrent national average cropland PUE initially decreased from 0.51 in 1992 to 0.34 in 2003, but afterwards increased to 0.39 in 2015. An environmental-Kuznets-curve-like (EKC) relationship was identified between the national average P budget (inverted U-shaped) or PUE (U-shaped) and per capita GDP in China, with the turning point occurring in 2013 for the previous and at per capita GDP of US$8.85 k (constant 2017 US$) for the latter. But PUE had been well below a threshold of 0.40 at the national level after crossing the turning point and showed a considerable trend divergence among crops, particularly for cash ones. Spatially, northern and northwestern China exhibited high positive P budget but achieved relatively low PUE in the 2010s. Crop leaf area, irrigation, fertilizer input, and precipitation were identified as the most important factors determining the multi-year spatial pattern of P budget, while fertilizer input, temperature, and residue return played a dominant role in regulating PUE. Our findings highlight the need for a long-term commitment to regionalized and crop-specific synthetic management practices for controlling P inputs and minimizing P loss in the context of global change in China.