Evaluation of a Rising Plate Meter for Use in Multispecies Swards

Abstract

Core Ideas The accuracy of rising plate meter in multispecies swards has not been tested thoroughly. Forcing X intercept to zero increases the precision of the calibration equations. Higher‐order polynomial regressions do not result in more accurate forage estimates. The rising plate meter (RPM) provides rapid estimates of herbage mass (HM). Accurate calibration of the RPM is difficult due to variability in forage management, growth, and species composition. The RPM is typically calibrated by linear regression of HM and RPM height; however, the r2 is usually low. Curvilinear regression, with the X intercept set to zero, could provide a more robust calibration equation and decrease variability in RPM estimates. Three Pennsylvania organic dairy farms grazing lactating dairy cattle on multispecies pastures were used to determine measured HM and estimated HM using a RPM. Removal of the X intercept increased the adjusted r2 of all equations between 42.8 and 89.0%. Use of quadratic and cubic regression only resulted in 0.01 to 0.02 increase in adjusted r2. Linear regression remains the simplest and preferred method of calibration; however, error can be reduced by setting calibration equations so that zero RPM height is associated with zero HM.