Abstract
A simple disk meter was calibrated for predicting the herbage mass (HM) of rotationally grazed pastures dominated by Phleum pratense L. in 1991-1992. A total of 696 paired observations were made on disk height (DH) and HM > 4 cm. The samples were classified for three different statuses: spring growth, post grazing and aftermath. In 1991 three different disk weights (c. 3.5, 5.0 and 6.5 kg/m2) were compared and the lightest disk was chosen for further studies in 1992. The variation in HM was adequately explained by linear models. There were only small differences between the predictive ability of different disk weights, the lightest disk having the highest r2 values. Post grazing and aftermath samples could be pooled, whilst spring growth samples needed a separate model. Year had no significant effect on the parameters of any model. The models chosen were: spring growth HM = -406.7 + 113.4(DH); r2 = 0.95, post grazing and aftermath HM = -629.1 + 122.1(DH); r2 = 0.88. The disk meter is a potential tool for predicting the HM of rotationally grazed timothy pastures.
Highlights
Even including the time for calibration, the disk meter is still preferred to the clipping method when estimating the herbage mass (HM) of large areas
The disk meter was calibrated by developing regression equations between the meter readings and herbage mass at the Karelia Research Station in 1991 and 1992
The variation in HM was adequately explained by linear models
Summary
Due to the considerable variability within a grazed sward, a large number of direct samples are often needed to get reliable HM estimates. To overcome the need for large sample numbers and to find nondestructive methods for HM estimation several procedures have been developed, e.g. visual estimation, determination of sward height with a ruler or a disk meter, measurements with a capacitance meter and spectral analysis (Frame 1981, Burns et al 1990). Powell 1974, Castle 1976, Bransby et al 1977, Griggs and Stringer 1988, Mould 1990). Even including the time for calibration, the disk meter is still preferred to the clipping method when estimating the HM of large areas Several reports of HM estimation of tall fescue swards (Festuca arundinaceae Schreb.) have been published (Bransby et al 1977, Vartha and Matches 1977, Bryan et al.1989)
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