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Yield Response in Experiments With Phosphorus Fertilizers in Relation to: I. Meaningful Differences Among Sources on Acid Soils of the Southeastern States¹

ABSTRACT

Yield results from 174 phosphorus rate and source experiments conducted in the Southeast, each including a response curve with CSP (concentrated superphosphate), were examined in relation to the nature of the response and experimental error.

In only a few of the tests with various crops showing yield response to P was it possible at the 5% probability level to measure differences among citrate- and watersoluble sources which were from one-half to twice as effective as CSP. Under the conditions where grown, cotton was the poorest crop for this purpose, corn and small grain grown for grain were intermediate, and annual forage was best. The possibility of measuring differences among sources decreased with increase in soil P level and with increase in the rate of application of P at which the comparison was made.

Estimated limiting yields of cotton on low-yielding sites without applied P were lower than most of the check yields at sites of higher productivity. A similar, but less pronounced situation prevailed with corn, but not with small grain. Deficiency of water is thought to be the chief factor limiting yields of summer-grown cotton and corn at all yield levels, but not of winter-grown small grain.

¹ Contribution from the Soils and Fertilizer Research Branch, Division of Agricultural Relations, TVA, Wilson Dam, Ala. Results of the experiments summarized in this paper were reported to TVA by agricultural experiment stations of the states listed in table 1. Presented before Div. IV, Soil Science Society of America, Nov. 20, 1959, at Cincinnati, Ohio.

² Agronomist, TVA. The author wishes to express his appreciation to D. R. Bouldin, who suggested the statistical method used and offered much constructive criticism during the study.

Received for publication January 8, 1960. Accepted for publication February 24, 1960.