Rice Genomics and Genetics 2024, Vol.15, No.4, 203-211 http://cropscipublisher.com/index.php/rgg 207 4.2 Comprehensive effects of long-term cultivation on soil health Long-term rice cultivation has comprehensive effects on soil health, influencing various soil properties and processes. The incorporation of organic materials, such as rice straw and manure, has been shown to improve soil structure, increase soil organic carbon (SOC) content, and enhance soil microbial activity (Ku et al., 2019; Yu et al., 2020a). These changes contribute to better soil fertility and higher crop yields. For example, long-term organic material applications in paddy fields significantly increased SOC, microbial biomass carbon (MBC), and active organic carbon (AOC), which are essential for maintaining soil structure and fertility (Yu et al., 2020a) PLS-SEM analysis showed that soil microbial biomass carbon (MBC) had a significant effect on the physical components of organic carbon, but had no significant effect on the chemical structure of carbon in microaggregates and macroaggregates. These results indicate that soil microorganisms are the driving force for the accumulation of physical components of organic carbon (POC and MOC). By continuously adding exogenous organic matter (OM treatment), microorganisms were stimulated, accelerating the decomposition and renewal of organic matter. Soil organic fragments digested by microorganisms were captured by soil clay minerals or aggregates, gradually forming MOC or POC and becoming primary soil particle units (possibly microaggregates). These primary soil particle units continue to aggregate to form larger aggregates (Figure 2) (Zhao et al., 2023). Figure 2 Schematic overview of soil aggregation process and organic C accumulation mechanisms in aggregates (Adopted from Zhao et al., 2023) This aggregate formation mechanism is consistent with the aggregate hierarchy theory. According to the characteristics of electron microscope images, the silt+clay components and microaggregates are independent monomers, but small and large macroaggregates are soil complexes composed of multiple soil particle units
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