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An Evaluation of Phosphorus Fertilizers Applied Broadcast on Calcareous Soils for Corn¹

ABSTRACT

Five field experiments were conducted in which several slightly water-soluble P sources were compared with concentrated superphosphate (CSP) for use in broadcast applications for corn. The tests involved rates of 30 and 60 pounds of available P₂O₅ per acre and were located on calcareous Webster soils which tested low in available P.

The sources could be ranked into three groups as measured by their effect upon the concentration of P in corn leaves and upon corn yields. CSP and dicalcium phosphate dihydrate were the most effective sources, with the former being slightly superior. Anhydrous dicalcium phosphate, calcium metaphosphate, and a chemical blend of mono-and dicalcium phosphate were of intermediate effectiveness, producing yield increases of about 70 to 80% of that given by CSP. Granular calcium metaphosphate was the least effective source, being about 60% as effective as CSP in promoting yield increases.

It was concluded that on calcareous soils a highly water soluble source of P, such as CSP, is likely to be more effective in broadcast applications for corn than are most slightly soluble sources. However, other characteristics of the fertilizer may be of equal importance in determining their value. Some evidence was also obtained which indicated that increasing the granule size of the less soluble fertilizers tended to reduce their effectiveness.

¹ Journal Paper No. J-3895 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project 1189. This work was supported in part by the Tennessee Valley Authority and W. R. Grace and Company.

² Associate Professor, Research Associate, and Professor of Soils, respectively.

Received for publication June 20, 1960. Accepted for publication January 5, 1961.