Water-washed hydrochar in rice paddy soil reduces N2O and CH4 emissions: A whole growth period investigation

Hydrochar (HC), an environment-friendly material, enhances soil carbon sequestration and mitigate greenhouse gases (GHGs) emissions in croplands. In this study, the water-washed HC (WW-HC) was applied to paddy soil to investigate effects on nitrous oxide (N2O) and methane (CH4) emissions during rice growth period. Four treatments, namely control (without N fertilizer andWW-HC), N fertilizer (WW-HC00), N fertilizer with 0.5 wt% WW-HC (WW-HC05) and N fertilizer with 1.5 wt% WW-HC (WW-HC15), were established. Results showed theWW-HC addition reduced N2O and CH4 emissions, global warming potential (GWP) and greenhouse gas intensity (GHGI) during the growing season. Moreover, theWW-HC application reduced N2O cumulative emission (P < 0.05) (by 28.6% and 23.8% for WW-HC05 and WWHC15, respectively). It was mainly due to the reduced ratio of (nirK thorn nirS) to nosZ under WW-HC15 (P < 0.05). Compared with WW-HC00, the WW-HC05 reduced CH4 cumulative emissions by 14.8%, while the WW-HC15 increased by 9.7%. This might be ascribed to the significantly reduced expression of the methanogenic mcrA gene and ratio of mcrA to pmoA by WW-HC (P < 0.05). The WW-HC05 amendment decreased GWP and GHGI by 18.6% and 32.5%, respectively. Furthermore, the WW-HC application greatly improved nitrogen use efficiency by 116e145% compared with the control. Our study indicates the WW-HC application is a promising GHGs mitigation practice in paddy fields. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The addition of water-washed hydrochar (WW-HC) to paddy soil can reduce N2O and CH4 emissions, decrease global warming potential (GWP) and greenhouse gas intensity (GHGI), and improve nitrogen use efficiency.