The environmental trade-offs of applying soil amendments: Microbial biomass and greenhouse gas emission dynamics in organic rice paddy soils

Abstract

A major challenge of organic rice production is obtaining optimal nutrient levels while maintaining environmental sustainability. Here, we investigated the effects of organic management practices via the application of organic soil amendments on soil microbial biomass and changes in greenhouse gas (GHG) emissions in rice paddy, affecting global warming potential (GWP) and greenhouse gas intensity (GHGI). Different N sources: chicken liter pellet (CLP), NatureSafe® (NS), and their mixture (CLP + NS) were amended to rice paddy field at varying N rates: 0, 50, and 150 kg N ha⁻¹. Organic management in rice paddy resulted in a range of outcomes, including variations in soil microbial biomass carbon (C) and nitrogen (N), CO₂ and CH₄ emissions, GWP, and GHGI. A notable increase in microbial biomass was observed in the rice paddy when CLP was applied at 150 kg N ha⁻¹. No significant difference in the cumulative CO₂ emissions was observed across most treatments, except for the treatment with NS applied at 50 kg N ha⁻¹, which emitted significantly less CO₂. Significant positive correlations were identified between different N application rates of organic soil amendments and the soil microbial biomass, the emissions of CO₂ and CH₄, and the GWP rate but negatively correlated with the GHGI. Amending paddy soils with NS at 150 kg N ha⁻¹ significantly enhanced rice yield, thereby offsetting the GHG emissions per unit of production. This study highlights that applying NS at this rate serves as a potential mitigation strategy, achieving both high-yielding rice production and minimizing greenhouse effect.