Anaerobic digester liquor replacing chemical fertilizer in reducing greenhouse gas emissions under drip irrigation: Factors, pathways, and strategies

Abstract

Anaerobic digester liquor (ADL) is a widely used alternative to mineral fertilizers, especially in the context of drip irrigation. However, differences in the manner in which drip irrigation systems are configured could alter the dynamics of the greenhouse gas emissions inherent in the use of ADL by the agricultural sector. Column experiments and structural equation modeling were used to explore the factors and pathways of drip irrigation methods (surface and subsurface drip irrigation) and substitution ratios of ADL (full, partial, and no substitution) on greenhouse gas emissions. The results showed that compared with surface drip irrigation, subsurface drip irrigation reduced daily and cumulative CO2 and N2O emissions but led to an increase in CH4 emissions. Similarly, substituting ADL for chemical fertilizers can also reduce greenhouse gas emissions, and when combined with subsurface drip irrigation, it can reduce the global warming potential (GWP) by up to approximately 50%. Over time, the contribution rates of the three greenhouse gases to the GWP remained essentially unchanged, mainly dominated by CO2 and N2O emissions. Drip irrigation methods and substitution ratios can drive differences in soil physiochemical properties. These differences directly or indirectly affect gas emission quantities and pathways. Soil water, carbon, and pores are important factors and mediators of gas-emission pathways. Overall, adopting the strategy of fully substituting subsurface drip irrigation of ADL for chemical fertilizer can significantly reduce greenhouse gas emissions and enhance the carbon sequestration effect.