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The Correlation of Soil Phosphorus with the Yields of Ladino Clover¹

ABSTRACT

Ladino clover (Trifolium repens) was grown in 11- by 6-foot concrete-walled field bins that contained three soil types representing large acreages in Alabama, namely Norfolk sandy loam, Eutaw clay, and Cecil clay. Soil samples were taken from the bins prior to seeding the clover and were extracted for soluble phosphorus by three extracting solutions. The solutions used were 0.05N HCl + 0.025N H₂SO₄, 0.5M NaHCO₃, and 0.03N NH₄F + 0.1N HCl. The procedure used with each solution can readily be adapted for rapid, relatively inexpensive tests as is required of a method to be used in a soil testing laboratory. The study consisted of 40 bins of each soil type, and because of past phosphorus treatments within a soil type, the bins differed greatly with respect to the amounts of soluble phosphorus present.

Six harvests were taken from the bins, three each in 1954 and 1955. The following correlations were made: relative yields for 1954 with soil test P₂O₅ values as determined by each solution on each soil type, relative yields for 1955 with soil test P₂O₅ values, and P₂O₅ values for one solution with values for another solution on a given soil type. All correlation coefficients were highly significant. Regressions equations were calculated for the regression of soil test P₂O₅ values on 1954 relative yield, 1955 relative yield, and total relative yield. Classes of soil test P₂O₅ values were calculated from the regression equations on the basis of the amount of P₂O₅, as indicated by soil tests, required to give a specified relative yield.

Data presented show that either of the three soil testing methods can be used satisfactorily as a basis for making phosphorus recommendations for the soils and crop studied. No one solution proved to be statistically better than the other two. All solutions tended to give higher correlation coefficients for the Eutaw and Cecil soils rather than for the Norfolk.

Contribution from the Department of Agronomy and Soils, Agr. Exp. Sta. of the Alabama Polytechnic Institute, Auburn, Alabama. Published with the approval of the Director. This material was taken from a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree. The investigation was supported in part by a grant from the Spencer Chemical Company which is gratefully acknowledged.

Received for publication September 11, 1957. Accepted for publication June 19, 1957.