Author : Duque, Conrado M. Sr.

Summary : The potential of competitive anion adsorption for phosphate using silicate and sulfate as a possible management strategy to increase phosphate availability to corn was tested on two extremely acidic, phosphorus (P) dificient soils: Luisiana clay and Adtuyon clay. This study was conducted to: 1) evaluate the effects of calcium, magnesium, potassium, and sodium silicates on P sorption, available P, and dry matter yield of corn: b) to evaluate the effects of calcium, magnesium, potassium and sodium sulfates of P sorption, available P, and dry matter yield of corn; and c) to evaluate the effects of calcium silicate and calcium sulfate on available P, soil pH, exchangeable aluminum, and grain yield corn. Application of 250 ppm and 500 ppm silicate in the form of calcium silicate on Luisiana clay decreased the P sorption maximum of the soil from 2.4522 to 2.4237 and 2.2969 mg P g (superscript -1), respectively. Other silicate sources had lesser effect than calcium silicate in decreasing the P aorption maximum of the soil. Sulfate application resulted to a very slight decrease in the maximum P sorption of the soil. On Luisiana clay not fertilized with phosphorus, application of different silicate and sulfate compounds did not increase dry matter yield of corn but phosphorus application resulted in significantly higher dry matter yield. Combined application of 160 ppm P and 250 ppm silicate (calcium silicate and potassium silicate) significantly increased dry matter yield of corn. On Adtuyon clay, the application of either 60 kg P (subscript 2) O (subscript 5)/ha,120 kg P (subscript 2) O (subscript 5/ha, or 250 kg silicate/ha as calcium silicate significantly increased with the application of either 250 kg silicate/ha as calcium silicate or 120 kg P (subscript 2) O (subscript 5)/ha. The application of silicate and sulfate alone or in combination with phosphorus did not increase soil P test value at silking stage over the P treatments.