Spatiotemporal variations of soil nitrate accumulation in the cropland of North China Plain

Excessive application of nitrogen (N) fertilizer has led to significant nitrate accumulation in agricultural soils, resulting in water pollution and ecosystem degradation. Many studies have examined the effects of environmental and/or management drivers on the soil nitrate accumulation, but the interacting effects of these drivers remain poorly understood. Here we investigated the spatiotemporal variations of soil nitrate accumulation and the underlying drivers in the North China Plain (NCP) using meta-analysis. The soil nitrate accumulation showed a nonlinear temporal trend from 1995-2024, increasing from 129 kg N ha -1 between 1995-2000 to 322 kg N ha -1 between 2011-2015 and declining to 72 kg N ha -1 between 2021-2024, and reflected the strong impacts of governance such as fertilizer “Zero Growth” policy initiated in 2015. Spatially, the soil nitrate accumulation in the southwestern regions of the NCP peaked at 505 kg N ha -1 between 2006-2015. The cropping system also affected the soil nitrate accumulation, with wheat fields accumulating more nitrate (245 kg N ha -1 ) than maize fields (214 kg N ha -1 ). Random forest analysis revealed that N fertilizer application was the primary driver of soil nitrate accumulation in both wheat and maize fields, followed by irrigation in the wheat fields and precipitation in the maize fields. These results emphasize the necessity of crop-specific N fertilize use and water management strategies to optimize the nitrate accumulation in agricultural soils.