Soil nitrogen dynamics regulate differential nitrogen uptake between rice and upland crops

Nitrogen use efficiency in rice is lower than in upland crops, likely due to differences in soil nitrogen dynamics and crop nitrogen preferences. However, the specific nitrogen dynamics in paddy and upland systems and their impact on crop nitrogen uptake remain poorly understood. The N dynamics and impact on crop N uptake determine the downstream environmental pollution from nitrogen fertilizer. To address this poor understanding, we analyzed 2,044 observations of gross nitrogen transformation rates in soils from 136 studies to examine nitrogen dynamics in both systems and their effects on nitrogen uptake in rice and upland crops. Our findings revealed that nitrogen mineralization and autotrophic nitrification rates are lower in paddies than in upland soil, while dissimilatory nitrate reduction to ammonium is higher in paddies, these differences being driven by flooding and lower total nitrogen content in paddies. Rice exhibited higher ammonium uptake, while upland crops had over twice the nitrate uptake. Autotrophic nitrification stimulated by pH reduced rice nitrogen uptake, while heterotrophic nitrification enhanced nitrogen uptake of upland crops. Autotrophic nitrification played a key role in regulating the ammonium-to-nitrate ratio in soils, which further affected the balance of plant nitrogen uptake. These results highlight the need to align soil nitrogen dynamics with crop nitrogen preferences to maximize plant maximize productivity and reduce reactive nitrogen pollution.