Trade-off between soil carbon emission and sequestration for winter wheat under reduced irrigation: The role of soil amendments

Abstract

Underground water source in North China Plain (NCP) is limited and extensively explored for wheat irrigation, which has caused high carbon emission. Reduced irrigation strategies and soil amendments have been advocated for sustainable agricultural production. However, the interactive effects of irrigation schedule and soil amendment on direct and indirect greenhouse gas (GHG) emissions, soil organic carbon (SOC) sequestration and carbon footprint (CF) have rarely been systematically quantified. A two-year field study was conducted in wheat season under three irrigation schedules (W0: pre-sowing irrigation only, W1: pre-sowing + jointing irrigation, and W2: pre-sowing + jointing + anthesis irrigation) and three fertilization types (Fc: chemical fertilizer only, Fm: chemical fertilizer + manure, and Fb: chemical fertilizer + biochar). In the Fc treatments, direct emissions from soil N2O and CH4 significantly decreased from W2 or W1 to W0, but SOC also decreased from W2 to W1 or W0. Net GHG emissions (GHGnet) was 14.6% higher in W1 +Fc but 6.0% lower in W0 +Fc compared with W2 +Fc because of the difference in electricity use for irrigation. Notably, the CF in W1 +Fc and W0 +Fc was 40.9% and 63.8% higher than in W2 +Fc mainly due to yield loss. Compared with Fc, direct emissions averaged 63.1% higher under Fm coupled with increased soil nitrate content, microbial biomass carbon (MBC) and nitrogen (MBN). The SOC significantly decreased from W0, W1 to W2 under Fm. Under the identical irrigation level, SOC stocks were 40.0% and 53.9% higher in Fm than in Fc under W1 and W0, while no significant difference under W2. Relative to Fc treatments, under Fm, CF was 28.5% lower in W0 but 6.2% and 45.7% higher in W1 and W2. Compared with Fc, direct emissions averaged 7.7% lower under Fb due to smaller MBN and higher soil porosity under Fb. The CF was lower in Fb than in Fc resulting from SOC increase. Thus, manure and biochar amendment could decrease CF following reduced irrigation, although manure application increased the risk of C loss.