Suitability of phosphogypsum as an ameliorant for soil acidity in laterite soil

Phosphogypsum (PG), a by-product of phosphatic fertilizer industry, is used as an ameliorant in acid soils that are rich in Fe and Al. It is also a source rich in Ca and S. A field experiment was carried out in a Typic Kandiudult to study the acid neutralizing ability of phosphogypsum and its influence on crop growth and yield of cowpea. The treatments include absolute control, package of practices recommendation of Kerala Agricultural University –200 kg ha⁻¹ (POP), lime/PG @ full lime requirement (1 LR) and half LR, respectively and two combination treatments of both lime and PG each at ½ and ¼ LR, respectively. Application of PG had significant influence on the acidity components except exchangeable hydrogen. The lowest values for both exchangeable acidity and Al were recorded under PG at full LR and were significantly superior to rest of the treatments. But lime was more efficient in reducing the exchangeable hydrogen content of soil and improving soil pH, compared to PG. Phosphogypsum had significant influence on the grain yield of cowpea with PG @ 1 LR recording the highest grain yield followed by the combination treatment of lime and PG each @ ¼ LR which was on par with the former. Application of PG significantly increased the uptake of N, P, K, Ca and S and the highest values were recorded under 1 LR of PG. The residual crop also followed the same trend. But Mg uptake was highest in the treatment which had received lime @ half LR and application of PG at 1 LR recorded a very low value.