Disk Meter for Rapid Estimation of Herbage Yield in Grazing Trials1

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Abstract
A rapid, indirect, in situ technique for making accurate estimates of pasture dry matter (DM) yield would be of great benefit in grazing trials to insure sound grazing management and meaningful interpretation of results. A disk meter, designed to estimate pasture DM, was constructed and evaluated on tall fescue (Festuca arundinacea Schreb.) pastures which were grazed by yearling steers. Fifty paired observations of bulk‐height readings with the disk meter and DM yields were used to establish the regression relationship between meter reading and yield. Separate calibrations were made for four different size disks. Area and diameter of disks, respectively, were 0.2 m2, 0.50 m; 0.4 m2, 0.71 m; 0.6 m2, 0.87 m; and 0.8 m2, 1.0 m. Relative to a constant weight per unit area of 5 kg/m2, actual disk weights were 1, 2, 3, and 4 kg, respectively, for the 0.2, 0.4, 0.6, and 0.8 m2 disks. Also, additional calibrations were made for the 0.2 m2 disk with weights of 2 and 3 kg. Correlation coefficients (r) for bulk‐height and DM yield ranged from 0.79 to 0.94, and all were significant at the 1% level of probability. Neither size nor weight of disks had any significant effect on residual standard deviation or r, although the heavier weights did alter the regression coefficient (b). Tall fescue pastures changed from reproductive growth in June to a vegetative phase in September, and this also affected b values. This study indicates that the disk meter can be useful for monitoring herbage‐on‐offer in grazing experiments which have a pure stand of tall fescue.

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