Effects of climate and soil properties on regional differences in nitrogen use efficiency and reactive nitrogen losses in rice

Nitrogen (N) use efficiency worldwide varies greatly due to climate, agronomic, and soil factors. However, the information on individual effects of these factors on N use efficiency is crucial but has remained scanty. Given that climate cannot be regulated, understanding the relative importance of fertilizer and soil variations on regional differences in N use efficiency is critical. Here, we constructed a database of 302 studies from 1986 to 2020 in East and Northeast China to determine the effects of climate, soil properties, and fertilizer N (FN) rate on variations in N use efficiency (agronomic efficiency (AE), apparent recovery efficiency (RE), physiological efficiency (PE), N harvest index, partial factor productivity), N surplus, grain N content, and reactive N (Nr) losses (N2O emissions, NH3 volatilization, Nr leaching, and runoff). Rice yield was comparable between two regions under farmers' N practices, yet the N input was considerably higher in East China. All indices of N use efficiency, except RE, are higher in Northeast China. Differences in AE were dominated by the ability of the plant to mobilize N (PE) rather than N uptake (RE), FN, or Nr loss. Soil properties and FN related to optimizable N management accounted for 29% (RE), 39% (PE), and 43% (Nr losses) of the variations, of which key factors as pH showed a negative effect while available N (AN) correlated positively to the N use efficiency. To realize high N use efficiency, pivotal effects of pH, AN, and FN on N use efficiency under certain climate zone should be considered.