Effect of Particle Size on Availability and Mobility of Fused Tricalcium Phosphate and Rock Phosphate Compared with other Phosphates in Contrasting Soil Types1

Abstract

The availability of the phosphorus of fused tricalcium phosphates of 10and 40-mesh sizes was compared with that of the phosphorus of dicalcium phosphate, basic slag, and of rock phosphates ground so that 85% for one lot and 50% of the other passed the 200-mesh sieve. The experiments were conducted in lysimeters and in the greenhouse. Growth of millet on Leon fine sand, limed to pH 5.8, was decidedly better for the fused tricalcium and the dicalcium phosphates than for the rock phosphate. Onethird of the phosphorus of the dicalcium and 40-mesh tricalcium phosphates, 1/8 of the phosphorus of the 10mesh tricalcium phosphate, and less than 1/100 of the phosphorus of rock phosphate was found in the leachates. Growth of corn on limed Leon fine sand was significantly better for the 40-mesh than for the 10-mesh tricalcium phosphates. Growth of corn in limed Tifton fine sandy loam was about the same for both phosphates and for basic slag. Corn growth on non-phosphated portions of these soils exhibited a marked phosphorus deficiency. Phosphorus deficiency symptoms were also present on the phosphated Tifton fine sandy loam and the phosphorus content of the corn leaves was less than 0.1%. Radioactive superphosphate was used to compare the availability of the phosphorus of 10and 40-mesh fused tricalcium phosphates and triple superphosphate. Uptake of the labelled phosphorus by oats on Leon fine sand was less where superphosphate had been used. The reverse was true for Red Bay fine sandy loam. This indicates that the phosphorus of the superphosphate went into solution quicker than that of the tricalcium phosphates and was more quickly immobilized by the fixation activities of the soil. The phosphorus of the 40-mesh tricalcium phosphate was somewhat more available than that of the 10-mesh but not significantly (LSD 0.05). View complete article To view this complete article, insert Disc 2 then click button8