Corn and soybean yields on Allerton Trust Farms, Piatt County, Illinois for the period 1950-1976 are studied. Statistical analyses indicate that the description of yield increases by linear trend equations could not be significantly improved by use of various non-linear trend formulations. The adequacy of the linear trend description also applied when the effects of weather were taken into account. Thus, on these well-managed farms, the yield patterns do not suggest that a plateau is being reached. Adjusting for weather effect significantly increased the average yield increases, from 0.182 metric tons per hectare per year to 0.207 metric tons per hectare per year for corn and from 0.028 metric tons per hectare per year to 0.034 metric tons per hectare per year for soybeans. Thus, weather factors have depressed yield increases during this period. Assuming that the yield trends represent the effects of technology, a linear trend indicates that the supply of economical technology has become available at a constant (absolute) rate over this period. A comparison of Allerton Trust Farm yields with Piatt County yields shows that Allerton corn yields are 13% higher than Piatt County yields and that soybean yields are 9% higher. Because this ratio has not changed over the period there apparently has been a rather constant stock of economical, but unused, yield-increasing technology. © 1979.
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