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Corn Response to S-Coated and Non-Coated Superphosphates and Residual Effects¹

Maintaining sufficient available P to crops, including com (Zea mays L.), has long been recognized as a limiting feature to maximum production in most soils. Providing the P in a pellet should permit soluble P to saturate the soil with P at the pellet while preserving a portion as reserve in the pellet. To test this hypothesis, pelletized ordinary superphosphate (OSP), concentrated superphosphate uncoated (CSP), or coated with S and sealant (SCSP) were compared in a Rhodic Paleudult (a Red Bay, fine, sandy loam), previously uncultivated. This soil was gibbsitic and gave a maximum P sorption of 2,670 kg/P ha and had, at preplant, 11 kg P/ha extractable by 0.03 N NH₄F in 0.1 N HC1. The major experiment was a randomized block design with each main plot split for banded and broadcast P placement with the CSP and SCSP compared at 28, 56, 112, and 140 kg P/ha. A secondary experiment compared OSP and SCSP combinations, all broadcast at 84 kg P/ha. The first year, corn cultivar ‘Pioneer 3009B’ was grown. The second year, plots previously receiving broadcast P were refertilized at one-half the prior P level of CSP and SCSP while plots with banded P received no further P. The third year, no further P was added. The latter 2 years, corn cultivar ‘Pioneer 3369A’ was planted.

Greatest increase in corn grain yield was obtained for the first 28 kg P/ha and further response was linear at 200 kg/ha yield for each additional 28 kg/P applied. Yield response was not significantly different either for P sources or for placement. The second year, residual P from that applied the first year gave linear corn grain yield response which was similar to that found when an additional P fertilization was made. The third year, grain yields gave better response to two, rather than one, annual P fertilization. There was no grain yield advantage to blending OSP and SCSP pellets either in the first or third year. Soil test values and ear leaf P values showed linear responses to rates of applied P.

Key Words: Residual soil P.

² Nat. Def. Educ. Title IV fellow, now assistant professor, Soil Sci. Dep., North Carolina State Univ., Raleigh, 26707, professor of soil sci., and associate professor statistics, Univ. of Florida, Gainesville. FL 32611, respectively.

Received for publication April 5, 1979.