An evaluation on using soil aggregate stability as the indicator of interrill erodibility

Aggregate stability is a very important predictor of soil structure and strength, which influences soil erodibility. Several aggregate stability indices were selected for estimating interrill erodibility of four soil types with contrasting properties from temperate and subtropical regions of China. This study was conducted to investigate how closely the soil interrill erodibility factor in the Water Erosion Prediction Project (WEPP) model relates to soil aggregate stability. The mass fractal dimension (FD), geometric mean diameter (GMD), mean weight diameter (MWD), and aggregate stability index (ASI) of soil aggregates were calculated. A rainfall simulator with a drainable flume (3.0 m long x 1.0 m wide x 0.5 m deep) was used at four slope gradients (5A degrees, 10A degrees,15A degrees and 20A degrees), and four rainfall intensities (0.6, 1.1, 1.7 and 2.5 mm/min). Results indicated that the interrill erodibility (Ki) values were significantly correlated to the indices of ASI, MWD, GMD, and FD computed from the aggregate wet-sieve data. The K (i) had a strong positive correlation with FD, as well as a strong negative correlation with ASI, GMD, and MWD. Soils with a higher aggregate stability and lower fractal dimension have smaller K (i) values. Stable soils were characterized by a high percentage of large aggregates and the erodible soils by a high percentage of smaller aggregates. The correlation coefficients of K (i) with ASI and GMD were greater than those with FD and MWD, implying that both the ASI and GMD may be better alternative parameters for empirically predicting the soil K (i) factor. ASI and GMD are more reasonable in interrill soil erodibility estimation, compared with K (i) calculation in original WEPP model equation. Results demonstrate the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to erosion in contrasting soil types in China.