A NEW APPROACH TO DETERMINING WATER-STABLE AGGREGATION

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