Estimating Forage Yield with a Disk Meter1

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Abstract
The disk meter technique of estimating forage dry matter yields has been used by many researchers in recent years. However, few comparisons have been made on which size, weight, and technique of use gives the most precise results, or if species of grass has any effect on the results. A simple‐disk and a weighted‐disk were evaluated as techniques for estimating forage dry matter yield on several grasses. Predictions of dry matter yield were based on settling heights measured with the meters. Yield estimates were made on annual ryegrass (Lolium multiflorum Lam.) pastures, and swards of bahiagrass (Paspalum notatum Flügge), digitgrass (Digitaria decumbent Stent.), and limpograss [Hemarthria altissima (Poir.) Stapf et C. E. Hubb]. Separate linear regression relationships between dry matter yield and settling height were calculated (Y = bX). Correlation coefficients (r) of 0.79 to 0.99 with most r values exceeding 0.92 were found between height and dry matter yield. Standard deviations from regression ranged from 73.2 to 282.4 kg/ha for different sampling techniques, disk sizes, and grass types. Increasing the disk size (0.25 to 0.75 m2) increased the correlation and regression coefficients, and reduced standard error from regression. The largest disk provided contact with a greater area of biomass and resulted in yield estimates of greater precision, but the additional precision obtained by using the 0.75‐m2 disk over the 0.50‐m2 disk does not offset the reduced ease of use of the larger disk. In addition, the 0.25‐ and 0.50‐m2 disks gave more uniform b values across grasses than the other disks. Thus, one combined b value was found to adequately describe the relationship between settling height and dry matter yield for all four grasses with these two disks. These results substantiate that the disk meter is a useful, practical, and versatile instrument for estimating forage dry matter yield in small plots and grazed pastures. The simple‐disk meter proved to be equal to the weighted meter for predicting dry matter yield, however, the simple‐disk has the advantage over the weighted meter because it is much easier to use in the field.