Relative erodability of soils

Abstract

To provide design data for conservation farm plans, evaluation of a soil's inherent erodibility is essential. Available literature and the possible methods of evaluating a soil's erodibility are critically reviewed. Development of a method to evaluate the erodibility of soils in a relatively short time and with a fairly high degree of confidence was considered desirable. A laboratory method of soil-loss measurement, from a soil prepared and placed in a standard fashion into a soil- bed of 9ft x 3ft x 1ft under simulated rainfall, was used as a standard to compare with easily measurable properties of soil which have been reported to be indices of erodibility by previous workers. Such properties as particle size distribution, suspension percentage, dispersion ratio, aggregate size distribution and the water stability of aggregates, aggregation index, mean weight diameter of aggregates, Atterburg limits, percent organic matter content, were included. An erodibility equation recently developed in the U.S.A. was also used to test the relative erodibility of soils. From all three methods a Waipara soil sample was shown to be higher in erodibility than Takahe and Timaru soil samples, while no definite difference between the Takahe and Timaru samples was established. The results of this study are encouraging and the method of assessing erodibility by relating the soil properties to soil loss measured in a standard way seems promising .