POTENTIAL OF EPPAWALA APATITE AS A DIRECTLY APPLIED LOW-COST FERTILIZER FOR RICE PRODUCTION IN SRI LANKA

摘要

Apatite in Sri Lanka is mined from Eppawala (Eppawala Rock Phosphate or ERP). The finely ground product is used as a direct application fertilizer for tea, rubber and coconut. ERP is an indiscriminate mixture of more soluble primary crystals and a less soluble secondary phosphate matrix rich in ferruginous and aluminous compounds with an average P2O5 content of 30%. The primary crystals can easily be separated from the groundmass by mechanical separation to produce selectively mined primary crystals (SERF) which has higher P2O5 (35 to 42%) and lower R(2)O(3) contents (around 1%) than the matrix. The ground SERF shows promise, as measured using yield and bicarbonate-extractable soil P, as fertilizer for rice grown in lowland and midland acid soils. In the second crop residues of SERF produced larger yields and bicarbonate-extractable P than Triple super phosphate (TSP) for the first crop. TSP is imported and its price is four times that of SERF. Therefore SERF is a potentially more profitable alternative fertilizer for TSP for rice on Sri Lankan acid soils.