SOIL DEPTH ASSESSMENT OF SAGEBRUSH GRAZING TREATMENTS USING ELECTROMAGNETIC INDUCTION

Depth to a root restricting layer affects both soil moisture and nutri ent availability, resources strongly correlated to plant cover and pro duction. We evaluated the potential of 2 electromagnetic induction met ers (EM38 and EM31) for non-destructively assessing soil depth to bedr ock in 2 long-term seasonal sagebrush steppe sheep grazing treatments with different vegetational compositions. Apparent conductivity readin gs, measured with the EM38 and EM31 in both the horizontal (H) and ver tical (V) dipole orientations, were positively related to soil depth. Apparent conductivity measured with the EM31H (r(2) = 0.78) and EM38V (r(2) = 0.75) were the best predictors of depth. Soil depth distributi ons were similar between grazing treatments based on Kolmogorov-Smirno v (K-S) tests of the EM38H apparent conductivity (P = 0.47) and EM38V apparent conductivity (P = 0.56), In constrast, K-S tests for the EM31 H apparent conductivity (P = 0.09) and EM31V apparent conductivity (P < 0.01) indicated the fall-grazed treatment had a larger area in which soil depth exceeded 150 cm, Because less than 2% of each grazing trea tment was predicted to have soils deeper than 150 cm, however, overall site differences between the 2 treatments appeared to be minor. There fore, the vegetational differences between the treatments have probabl y resulted more from differences in the seasonality of grazing rather than ecological site characteristics as reflected in soil depth. Maps of soil depth indicated both treatments consisted of intermittent shal low and deep soils, created by several parallel basalt pressure ridges . Results suggest electromagnetic induction can effectively assess the spatial variability of soil depth and could aid in selecting sites fo r rangeland monitoring or manipulation.