A GLASSHOUSE EVALUATION OF SULFUR FERTILIZER SOURCES FOR CROPS AND PASTURES .2. A COMPARISON OF SULFUR COATED TRIPLE SUPERPHOSPHATES AND GYPSUM

In many parts of the world it has become more economical to use triple superphosphate (TSP) rather than single superphosphate (SSP) as a pas ture fertilizer where only P deficiency exists. Coating TSP with eleme ntal S is an attractive alternative to SSP for situations where P and S deficiency exists. A pot experiment was conducted on an S deficient Aquic Haplustalf soil to compare the ability of gypsum (G) and S coate d TSP to supply S to a ryegrass/white clover pasture over 14 repeated harvests over a 96 week period. The adhesives used to coat S to TSP we re UNE1, UNE3, UNE2 and a commercial product (HF). The reverse dilutio n S-35 technique was used to calculate fertilizer S uptake. Total yiel ds were highest with G and UNE1. Total fertilizer S recovery by the pa sture was 64.4% for G and 52.3% and 52.9% for UNE1 and UNE3 respective ly. These amounts were significantly higher than from UNE2 or HF. The time course of fertilizer S release varied between products and shows that bonding method can affect S availability from S coated TSP produc ts.