Soil aggregate stability as affected by long-term tillage and clay mineralogy

Soil aggregate breakdown and dispersibility under rain depends on clay mineralogy. Little is known about effects of mineralogy on aggregate stability for long-term cultivated soil which was the objective of our study. Soil samples representing a range of agricultural soils (no-till and tilled) of humid and semi-and zones with predominantly kaolinitic, smectitic, and/or illitic clays were studied. Aggregate stability was determined using high-energy moisture characteristic methods (HEMC), where the destructive force used to break down aggregates was accurately controlled by wetting rate. Stability ratio was calculated based on the differences in pore size distribution after fast and slow wetting. Aggregates from minimum tilled or virgin soils, and soils with predominantly kaolinitic type of mineralogy, were more stable. Long-term tillage significantly decreased organic matter, drainable porosity and aggregate stability of illitic and smectitic soils. No-till significantly increased aggregate stability of the clayey soils with a predominance of 2:1 minerals. In these soils stability ratio correlated well with clay content and erosion data. For humid zone with predominantly kaolinitic soils, clay dispersibility and associated minerals related better to soil loss. The mechanisms describing the effects of soil mineralogy, texture and tillage on aggregate stability, runoff and erosion are discussed.