The Stability of Individual Macroaggregate Size Fractions of Ultisol and Oxisol Soils

Aggregate stability is an important soil property because it dictates how strongly a soil can resist water erosion. The objectives in this study were: (1) to compare the stability of six soil aggregate size fractions, primarily to determine if aggregate stability varies with aggregate size, and (2) to determine with which aggregate size fraction the stability of most soils would be different from one another. Eight soils classified as Ultisols and Oxisols and from varying land uses, of different textures and overall acceptable aggregate stability were sampled and each separated into six aggregate size fractions of: 5-8, 3-5, 2-3, 1-2, 0.5-1, and 0.25-0.5 mm. Aggregate stability of whole soils and of individual aggregate size fractions were determined through wet-sieving, using nested sieves. It was shown that: (1) the kind of relationship between soil aggregate stability and aggregate size depended on both factors of soil type and individual aggregate size; (2) the stability of any two soil aggregate size fractions would become progressively less linearly related as the differences in aggregate size became more pronounced; (3) for the same soil, the stability of the large aggregate size fractions of > 0.5 mm were significantly different from that of the small aggregate size fractions of 0.25-0.5 mm; and (4) the differences in aggregate stability among whole soils were due more to the differences in the stability of the soil aggregate sizes larger than 3 mm. The study revealed that for Ultisol and Oxisol soils, it was not necessary to measure the stability of individual aggregate size fractions. Instead, the stability of a single aggregate size fraction could be used to represent the macroaggregate stability of whole soils.