A new approach to determining water stable aggregation

Abstract

A new method is introduced to measure water stability of soil aggregates. The wrist‐action shaker is a simple, inexpensive tool that provides highly accurate data for the assessment of soil erodibility. Three soils from Hawaii (two Oxisols and one Vertisol) with different mineralogies, management histories, and potassium (K)‐factors were examined in this study. Six indices of water stable aggregation were determined after rapid immersion of air‐dry aggregates, followed by gentle wet‐sieving. Single‐sieve indices of percent water stable aggregates (WSA) < 0.063 mm, > 0.25 mm, and > 1.00 mm, were highly correlated. Additionally, these indices were highly correlated with three multiple sieve indices, namely geometric mean aggregate diameter (GMAD), arithmetic mean aggregate mass diameter (MAMD), and the coarse‐to‐fine index (CFI = % WSA > 1.00 mm / % WSA < 0.063 mm). Analysis of WSA data indicated that the relative soil erodibility ranking, from high to low, would be: Lualualei Vertisol > Molokai Oxisol > Kaneloa Oxisol. Discriminant analysis using GMAD and % WSA > 1.00 mm correctly classified 55 of 56 soil samples into their respective soil series.