Limitations of the electronic capacitance meter in measuring yields of grazed tropical pastures

Abstract

Relationships between readings of the electronic (capacitance) pasture meter and descriptions of pasture yield were examined over the yearly growth cycle in grazed pastures of Setaria anceps cv. Nandi, with or without Macroptilium atropurpurem cv. Siratro and Desmodium intortum cv. Greenleaf. There was a poor relationship between meter reading and pasture dry matter yield (r = +0-574 pooled over pastures and seasons) but this relationship was improved to r = +0-750 by inclusion of other regressors describing pasture height and proportion of inert material. Meter reading was more closely related to fresh pasture yield (r = +0-830), water yield (r = +0-885) or dried green yield (r = +0-830), although inclusion of a pasture height term still improved the relationship slightly. Suggestions are made about using the meter to estimate dried green yield rather than total dry matter yield, and taking more consideration of the proportion of inert material when relating the meter reading to total dry matter yield.Visual estimation was also compared with actual pasture yield measured by cutting. Even though prior training for yield estimation was inadequate, the relationships between visually estimated and actual yield were as good as those from the pasture meter. It is concluded that the pasture meter will not find a regular use as a sampling tool in most grazed tropical pastures.

Evaluation of Double-Sampling Estimators of Subalpine Herbage Production

“…The need for analysis of the factors influencing the precision of various double-sampling estimators has been recognized by several authors (Morley et al 1964;Bryant et al 197 1;and Michalk and Herbert 1977). Jones et al (1977) recently investigated the effects of tropical grassland composition on electronic capacitance metering. However, similar regression studies on other double-sampling estimators are lacking.…”

“…The major objective in this study was to investigate the relationships between electronic capacitance metering (Neal et al 1976;Jones et al 1977) dry (Tadmor et al 1975) and relative (Haydock and Shaw 1975) weight estimations, and canopy cover estimation (Payne 1974) in predicting subalpine herbage yields. Of specific interest was the statistical determination, through stepwise regression analysis, of which vegetal and environmental factors were responsible for reducing their sampling precision.…”