Abstract

The data available measuring the relative efficiencies of acidulated rock phosphate at various levels of applied P are limited, and further investigation of this subject is warranted. Florida rock phosphate was acidulated with H₃PO₄ at 20 and 100% of that required to convert rock phosphate to concentrated superphosphate. These two materials plus a check (0 P) were applied as treatments for corn (Zea mays L.) during three consecutive years on an acid soil in field experiments. Rates of total P from each source were 0, 10, 20, 30, and 100 kg/ha, which was broadcast and disked in each year just prior to planting.

There was an excellent response to P fertilization. Corn yields were similar from both sources of P at some rates of applied P, while at other rates, P from concentrated superphosphate appeared to be the superior source. Phosphorus content of the ear leaves was not affected by P source in 1968, but differences were evident in 1969 and 1970. Leaf K content in 1970 was significantly increased by the highest rate of applied P from both P sources. There was an increase in available soil P only at the highest rates of applied P.

At low rates of applied P, CSP was the most economical source of P. At the highest rate of P application, the 20% acidulated rock phosphate appeared to be more economical

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