Acid-modified biochar increases grain yield and reduces reactive gaseous N losses and N-related global warming potential in alternate wetting and drying paddy production system

Abstract

Biochar amended soils reduce fertilizer N losses and suppress greenhouse gas emissions. However, biochar can increase NH3 volatilization. H2SO4- modified biochar has been studied as a means to achieve the advantages of biochar while reducing volatilization, especially under alternate wetting and drying irrigation (IAWD). In contrast to continuously flooded irrigation (ICF), IAWD is a water-saving technology that repeatedly dries and re-floods fields. A 3-year field experiment was conducted with two irrigation regimes (ICF and IAWD) as main plots and 0 (control), 20 t ha−1 biochar, and 20 t ha−1 H2SO4-modified biochar as subplots. IAWD produced 7.6–14.8% more reactive gaseous N losses (NH3 and N2O) and emitted 2.02 times N-related global warming potential (GWPN) of ICF. Biochar increased NH3 volatilization by 35.6% in the first year and decreased it by 22.4% and 24.8% in the second and third years, respectively, while H2SO4-modified biochar decreased NH3 volatilization each year. The increased NH3 volatilization was caused by the higher NH4+ concentration and pH in the floodwater and surface soil due to increasing N inputs and alkalinity from biochar. The decrease in the following two years was attributed to pH returning to the pre-treatment level and continued biochar absorption of NH4+ from the floodwater. Both biochar and H2SO4-modified biochar significantly reduced seasonal N2O emissions. H2SO4-modified biochar coupled with IAWD mitigated the initial increases in NH3 volatilization and reactive gaseous N losses in the first year, and increased grain yield, decreased reactive gaseous N losses, and GWPN compared with the IAWD without biochar throughout the three years. The use of acid-modified biochar could produce higher grain yield with lower reactive gaseous N losses and GWPN for application in the IAWD paddy systems, which benefits sustainable agricultural production.