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How Accurate is a Summary of Soil Test Information?¹

ABSTRACT

Chemical analyses of soils from 1184 systematically sampled fields in Duplin County, N. C., were compared with results from 538 voluntary farmer samples sent into the Soil Testing Division. Cropping history for fields included in both samples was obtained by personal contact and by correspondence, respectively. Results were compared on the basis of the previous crop as well as on the basis of the general mean of the two samples.

The pH and content of organic matter and potassium were significantly higher in the farmer samples but the differences were small in magnitude. The calcium and magnesium were distinctly higher in the farmer samples. On the other hand, the phosphorus was significantly lower in the farmer sample but again the difference was small. The tendency for higher levels of pH, potassium, calcium and magnesium may serve to substantiate the idea that the better farmers are sending in the majority of the samples. However, the difference in results for pH, organic matter, phosphorus and potassium is not considered sufficiently great to invalidate a summary of results from farmer samples. Seasonal effects on values obtained for pH, phosphorus and potassium present a problem. However, assuming the same type of seasonal distribution from year to year and the same type of farmers sending in samples, relative differences among areas, among crops, or in trends can be established.

¹ Published with the approval of the Director of Research, North Carolina Agr. Exp. Sta. as Journal Paper No. 521. Taken from a thesis submitted by the senior author in partial fulfillment of the requirements for the degree of Master of Science, North Carolina State College, Raleigh, N. C. This investigation was supported in part by a grant from the American Plant Food Council, Inc. Presented in Division IV, Soil Science Society of America at Dallas, Texas, Nov. 19, 1953.

² Formerly Graduate Assistant, now Graduate Assistant, University of Illinois and Professor, Department of Agronomy, N. C. State College. The authors are indebted to A. L. Finkner, Associate Professor of Statistics, for statistical assistance. The assistance of Lewis Williams in taking the 1950 samples is acknowledged.

Received for publication November 12, 1953.