| Summary: | Excessive use of inorganic nitrogen (N) fertilizers is the primary anthropogenic cause of low N use efficiency and environmental damage in wetland rice agriculture. However, little is known about the performance of traditional inorganic N sources used in paddy rice production. Biochar (BC) is considered to be a climate change mitigation tool that can enhance N uptake and utilization in N-fertilized crops. To test this hypothesis, we performed a pot experiment to study the fate of 15N-labeled urea, ammonium nitrate, and ammonium sulfate with and without BC at tillering, heading, and maturity stages of rice in the early and late seasons of 2019. Fertilizer N leaching was significantly reduced by 75.69% and 110.32% in BC vs. non-BC treatments across growth stages in the early and late seasons. The rate of leaching was lower for urea than for ammonium nitrate and ammonium sulfate. Furthermore, the addition of BC resulted in 55.58% and 41.33% higher soil 15N concentrations in the early and late season, respectively, indicating that BC increased N adsorption. 15N uptake by roots, stems, leaves, panicles, and grains averaged 52.39%, 37.14%, 40.86%, 36.37%, and 29.94% higher in BC-amended pots than in BC-free pots in both seasons. There were significant differences (p < 0.05) among N sources in terms of fertilizer N loss, residual N, and N uptake, and performance was ranked in the order urea > ammonium sulfate > ammonium nitrate. Overall, our results indicate that urea with BC is a preferable N source for double rice cropping systems compared with ammonium nitrate and ammonium sulfate. © 2020 The Authors. GCB Bioenergy Published by John Wiley & Sons Ltd
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