A comparison of a rising-plate meter and an electronic capacitance meter for estimating the yield of pastures grazed by dairy cows

The performances of a rising-plate meter and a single-probe electronic capacitance meter were compared for estimating the herbage mass of irrigated pastures both before and after grazing by dairy cows. Mean CV for the rising plate meter and the single-probe meter were 12.7% and 13.3% respectively when herbage mass was measured before grazing, and 21.8% and 15.4% respectively immediately after grazing. These coefficients of variation indicate that while the performance of the two meters was similar when herbage mass was measured before grazing, the single-probe meter was a more precise instrument for estimating herbage mass after grazing.
Trampling of herbage prior to measurement had a major effect on the regressions of both meters; the regression intercept was increased by 2800 kg dry matter (DM) ha⁻¹ for the rising-plate meter and by 2580 kg DM ha⁻¹ for the single-probe meter. The slopes of the graphs, however, remained unchanged.
It was concluded that while the single-probe meter performed better than the rising-plate meter for estimating the mass of post-grazing herbage when trampling was negligible, the large effect that trampling had on the post-grazing calibration regressions precluded both instruments from general use in dairy cattle research. This indicates that another technique is required in circumstances in which pastures are heavily trampled.