Quantifying the contribution of phyllosilicate mineralogy to aggregate stability in the East Asian monsoon region

Aggregate stability strongly influences soil function and has been a key indicator of soil quality and susceptibility to erosion. Although clay mineralogy has been recognized to have substantial effects on aggregate stability, little quantitative information is available on the specific contribution of various phyllosilicates in clay fraction. This study aimed to quantify the individual and combined effects of phyllosilicate minerals and their interaction with other soil properties on aggregate stability and breakdown mechanisms. A wide range of soil types in heavy textures from quaternary sediments were sampled under three land uses (forest, grass and arable) and at different genetic horizons along the mid-temperate to tropical climate gradient in the East Asian monsoon region. Soil aggregate stability against slaking (MWDFW), mechanical breakdown (MWDWS) and differential swelling (MWDSW) was determined, as well as phyllosilicate mineralogy by X-ray diffraction and a series of soil properties related to porosity, texture, organic matter, sesquioxides, and exchangeable cations. Aggregate stability generally exhibited a unimodal geographic trend (MWDSW in 1.85 similar to 3.49 mm, MWDWS in 0.76 similar to 3.22 mm and MWDFW in 0.14 similar to 2.74 mm), which became more remarkable with increased disruptive forces (coefficient of variation in 9 similar to 59%). Correspondingly, the dominant mechanisms of aggregate breakdown shifted from both slaking and mechanical breakdown to only slaking with increased soil weathering. The profile variation of aggregate stability and the land use effect differed with soil type and disruptive force. For phyllosilicate mineralogy, vermiculite had the largest explanatory power in aggregate stability (R-2 = 54%, p < 0.001), followed by kaolilite and 1.4 nm intergrade mineral (R-2 = 28 similar to 32%, p < 0.01), while illite explained little variance (R-2 = 6%, p > 0.05), demonstrating the more prominent role of phyllosilicate mineralogy than other soil properties (R-2 < 43%) in aggregate stabilization. Besides the dominant effect of vermiculite, soil organic carbon, exchangeable sodium and calcium exerted a complimentary effect (R-2 = 12%). Collectively, aggregate stability is predominantly influenced by phyllosilicate mineralogy (especially swelling minerals) at the regional scale and by soil organic matter and exchangeable cations at the soil pedon scale.

Automated summary

Aggregate stability strongly depends on the phyllosilicate mineralogy, particularly vermiculite, showing a dominant role. Geographic location shows a unimodal trend in influencing aggregate stability, with greater disruptive forces leading to more prominent effects. In combination, soil organic carbon, exchangeable sodium, and calcium play a complementary role in affecting aggregate stability.