Amendment-driven regulation of soil organic matter accumulation and soil health enhancement

Abstract

Soil health in rice paddies is a key determinant of sustainable agriculture, as it directly affects both crop productivity and long-term soil quality. This study investigated the effects of different organic amendments on soil health in subtropical rice fields in Zhejiang Province, China, using the Soil Health Index (SHI) as an integrative assessment. Results showed that organic amendments significantly enhanced soil health, particularly in the treatment combining conventional fertilization with biochar-based organic fertilizer (BF), which achieved the highest SHI. Improvements were mainly associated with increases in soil pH, nutrient availability, and microbial biomass. Carbon- and phosphorus-related indicators, along with microbial biomass, contributed most to SHI improvement, suggesting that microbial-mediated C and P cycling play pivotal roles in soil health enhancement. Metagenomic analyses revealed enhanced microbial functions related to carbon fixation and phosphorus mobilization under organic treatments. Organic amendments enhanced microbial carbon and phosphorus cycling by increasing the relative abundance of key genes related to CO₂ fixation such as K14465, methane oxidation such as frmB, and phosphorus mobilization such as aepW, thereby reinforcing carbon and phosphorus transformation processes essential for soil health. Key microbial families, including Nitrosopumilaceae and Xanthobacteraceae, were enriched, indicating greater functional specialization and nutrient transformation capacity. Overall, the synergistic application of biochar- and bio-organic fertilizers improved soil structure, nutrient cycling, and microbial functionality. These findings provide valuable insights for optimizing organic fertilization strategies to sustain soil productivity and ecological stability in paddy ecosystems.

Graphical abstract

Keywords

organic amendment / soil health index / microbial functional genes / carbon cycling / phosphorus cycling

Highlight

	● Soil Health Index (SHI) effectively quantified soil quality improvement under organic amendments in subtropical paddy soils.
	● Organic amendments supply readily available carbon and energy sources that trigger the activation and functional specialization of the soil microbiome.
	● The synergistic application of bio-organic and biochar-based fertilizers improved soil physicochemical properties, microbial activity, and nutrient cycling, providing a mechanistic basis for sustainable paddy soil management.

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