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Crop Response to NPK Fertilizers Varying in Granule Size and Water Solubility of the Phosphorus¹

ABSTRACT

Crop response to 7-14-14, 6-12-12, 10-20-20, and 11-22-22 fertilizers was determined on 5 soils in 2 greenhouse experiments in Tennessee and Virginia and in 21 field experiments in Georgia, Kentucky, Mississippi, North Carolina, Tennessee, and Washington. All soils were acid to neutral in reaction. The fertilizers, separately formulated from dicalcium phosphate, ammoniated ordinary superphosphate, ammoniated concentrated superphosphate, and diammonium phosphate, had 7, 27, 60, and 100%, respectively, of the phosphorus in a water-soluble form. Each fertilizer was granulated and screened into 6–14, 14–35, and –35 mesh sizes. Early growth response, as determined in the greenhouse with oats and Sudangrass, and in the field with wheat forage and other crops, increased with smaller granule sizes of the low water-soluble fertilizers but decreased with smaller granule sizes of the high water-soluble fertilizers. This pronounced interaction of water solubility and granule size found at early growth stages did not persist in final yields of corn or wheat grain and vegetables in most experiments. Where an early growth response is desired, results indicate that fertilizers having a low water-soluble phosphorus content should be granulated more finely than those having a high content of water-soluble phosphorus.

¹ This paper summarizes a cooperative project between the Tennessee Valley Authority and seven state experiment stations. Data in addition to that obtained by the authors were supplied in reports to TVA by: J. W. Dobson, Jr., Georgia; E. C. Doll, Kentucky; W. H. Rankin, North Carolina; O. H. Long and S. H. Winterberg, Tennessee, and H. M. Reisenauer, Washington.

² Agronomist, TVA, Wilson Dam, Alabama; and Assistant Agronomist, Assistant Soil Scientist, and Assistant Agronomist, respectively, of the Mississippi, Washington, and Virginia Agr. Exp. Sta.

Received for publication May 8, 1956.