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A Comparison of Sampling Procedures in Making Pasture Yield Determinations

Illinois Agricultural Experiment Station, Urbana

ABSTRACT

The sampling method of determining pasture yields is a simple and valuable tool in pasture research. Satisfactory yield determinations of blue-grass, bromegrass, and presumably other grass pastures which respond well with renewed growth after close cutting, can be made by this method.

The direct harvest plan of sampling is characterized by smaller standard errors and lower coefficients of variability than the difference plans. Tests of the variance of the data obtained in this investigation by four plans of sampling procedure show significant F values, for the direct harvest plan in a number of instances where such a finding would be expected, but no such values for the other plans. The direct harvest plan is advantageous in showing period yields and in computing yields where grazing is delayed because of a rotation plan of pasturing, or for other reasons. These advantages, together with its simplicity, make it highly suitable as the one plan of sampling where only yield determinations of grass pastures are desired.

The difference plans provide a valuable check on the direct harvest plan. They are much more satisfactory than the direct harvest plan in determining yields of crops such as soybeans and sweet clover, which may either be killed or greatly retarded in growth by frequent close cutting, and are also valuable in computing period-by-period amounts of herbage consumed in grazing. Statistical interpretations of the data show the difference plans to be somewhat less reliable than the direct harvest plan in determining yields of grass pastures.

Difference plan No. 2, in which open pasture yields of the previous sampling date are substracted from the protected area samples, is proposed as an improved plan of calculating yields over difference plan No. 1, in which open pasture yields are subtracted from the protected area yields of the same date.

Grazing trials with yearling dairy heifers furnished data for a comparison of bluegrass pasture yields, as determined by animals; with those obtained in the various sampling plans. The amount of liveweight maintained per acre, one of the valuable measurements of pasture yield, and the amount of animal weight gained per acre, served as a basis for the calculation of pasture yields in terms of total digestible nutrients. The total digestible nutrient values were more closely related to the yields of dry matter found by the direct harvest plan of sampling than to yields determined by the difference plans. The direct harvest plan of sampling, therefore, appears to be the most satisfactory one of the four plans of sampling for determining the yields of bluegrass pastures.