Potential of Irrigation and Biochar on Reduction Methane Emission and Leaching Nitrate into Groundwater

Agricultural by-products such as rice husks are very popular in Vietnam, which are often burned in the fields, causing an increase in dust smoke and greenhouse gas (GHG) emissions. To study the effects of different irriga - tion methods, quality of irrigation water and additive biochar from rice husk (BFRH) on leaching nitrate from paddy fields into shallow groundwater and methane (CH 4 ) emissions, we investigated a two-season experiment (2021–2023) under two irrigation methods: water-saving irrigation and flood irrigation with 120 kg N/ha. The results illustrated that seasonal CH 4 emissions and leaching nitrate were affected by irrigation practices and significantly correlated with the quality of irrigation and the amount of BFRH added. To compare of control, the flood irrigation water increased the leaching of GHG and NO 3-into shallow groundwater from 27.3–32.4% and 16.4–31.25%, respectively. Meanwhile, the saving water irrigation reduced CH 4 and leaching of NO 3-into shallow groundwater from 13.3–17.8% and 15.63–18.9%, respectively. Applying biochar with controlling fertilizer reduces CH 4 and NO 3-content in surface field water, contributing to the decreased leaching of NO 3-into groundwater. Reducing 20% fertilizer rate of N (96 kg N/ha) with application biochar of 5% without a change in yield reduces NO 3-content into shallow groundwater from 13.7–14.3%. We conclude that water-saving irrigation combined with biochar from rice husk incorporation simultaneously mitigates CH 4 emissions, improves yield, and reduces leaching nitrate into groundwater, making it a suitable environment-friendly nitrogen management practice for sustainable farming in northern Vietnam.