Bio‐Organic Substitutions Reinforce Soil Quality Driven by Fungal Necromass and Soil Structure in a Light Saline Soil

ABSTRACT Intensive agriculture may cause substantial soil quality deterioration, leading to decreased crop production, especially under over‐use of chemical fertilizers. Despite this, the effects of bio‐organic substitutions on soil quality development via soil organic carbon (SOC) chemistry and soil structure remain largely unexplored. Herein, we characterized the changes in soil aggregation and cementing agents involved, image‐based pore structure, hydraulic functions, and their connections to soil quality index from a 4‐year field trial in North China. Four treatments included: chemical fertilizer alone (CF), 20% bio‐organic fertilizer substitution (Bio 20 ), 50% bio‐organic fertilizer substitution (Bio 50 ), and 100% bio‐organic fertilizer substitution (Bio 100 ). The results showed that Bio 20 and Bio 100 enhanced soil macroaggregates by 57.0%–61.1% and mean weight diameter by 71.5%–75.4% in comparison to CF. This improvement may likely be attributed to the increased cementing agents (e.g., SOC, extracellular polymeric substances, glomalin‐related soil proteins). Bio 50 and Bio 100 also enhanced fungal necromass C and its contribution to SOC compared to CF. Bio‐organic substitutions enhanced the 3D pore structure, showing higher image‐identified porosity by 1.0–2.9 times, and pore anisotropy by 48.8%–63.2%. The enhanced soil structure in the bio‐organic substituted soils potentially improved water holding capacity by 32.3%–51.6% and saturated hydraulic conductivity by 0.7–1.8 times versus control. Overall, bio‐organic substitutions improved S value by 71.3%–144.2%, indicator of soil physical quality, and soil quality index by 25.9%–34.7% relative to control. Collectively, substituting partial chemical fertilizers with bio‐organic fertilizers could boost soil quality via augmenting fungal necromass and soil structure, offering effective and economic solutions for revitalizing light saline soil under an intensive cropping system.