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Effect of Partial Acidulation and Elemental Sulfur on Availability of Phosphorus in Rock Phosphate1
Contribution from the Department of Soils, University of Wisconsin, Madison. Published with the approval of the Director, Wisconsin Agr. Exp. Sta. Part of dissertations submitted by the senior author and first co-author in partial fulfillment of the requirements for the Ph.D. degree, University of Wisconsin. Presented before Divs. S-4 and S-8, Soil Science Society of America, Columbus, Ohio, November 3, 1965. Study supported in part by funds provided by the International Minerals and Chemical Corp. and the Sulphur Institute.
A study was made of the effect of partial acidulation of rock phosphate, coating with elemental S, granule size, placement, and soil pH on yield and uptake of P and S by ryegrass grown on Miami (pH 6.7) and Dubuque (pH 6.0 and 7.0) silt loams in the greenhouse. In most cases, both yield and P uptake increased with each increase in level of acidulation; however, the results for the 50 and 100% levels were quite similar. Total P recovery by the ryegrass was highly correlated with the percentage of total P that was available (water soluble plus citrate soluble) in the fertilizer. Mixing of the granules with the soil gave higher yields and P recovery than banding, and the 10- to 20-mesh granules were generally more effective than the 5- to 10-mesh size on the soil at pH 6.0. Coating of the granules with elemental S gave no significant increases in yield but increased P recovery significantly from the 5- to 10-mesh granules in several cases. Both yield and P uptake for rock phosphate were higher at pH 6.0 than 7.0.