Evaluation of a single probe capacitance meter for estimating herbage yield

Abstract

A single probe electronic capacitance meter for estimating herbage yields was field tested on 2 western wheatgrass (Pascopyrum smithii (Rydb.) Löve), a blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths), crested wheatgrass (Agropyron cristatum (L.) Gaertn.), and Russian wildrye (Psathrostachys juncea (Fisch.) Nevski) stands in the Northern Great Plains. This single probe meter is lightweight, portable, and allows the user to estimate yields of single plants to determine productivity of individual species. Linear regression equations were fitted between probe readings and the green and dry weight of forage clipped from individual plants within a $78.5-cm2 circular plot. An overall coefficient of determination (r2) of 0.50 was obtained with linear relationships being statistically significant between the probe readings and green and dry weight of forage for all regressions (P=0.10). Considering the regression estimates for r2, standard error of the estimate and F values, the best model fit occurred in the western wheatgrass and crested wheatgrass stands. Presence of a litter mat in 1 western wheatgrass stand had little influence on the precision of the instrument, but phenology of the plants strongly influenced meter readings. Therefore, regression lines within a species could not be pooled across all sampling dates. Comparing yields of individual species from the small plots of the single probe meter to yields from a larger, $1,858-cm2 rectangular plot estimated with a multi-probe capacitance meter showed comparisons were not statistically different 50% of the time. A sample size of approximately 150 plots per species was required for each sample period for the single probe meter.