Rotokawa sulphur in phosphate rock/sulphur granules — a greenhouse study

Abstract

Phosphate rock/sulphur granules (pR/S) prepared from Rotokawa S ore upgraded to 950/0 purity and North Carolina PR (NC) were evaluated as phosphate fertilisers in a pot experiment using a highly P-retentive volcanic ash soil limed to pH 5.8. Granules of 2 size ranges, 0.2-1.0 mm and 1-2 mm and 4 PR:S ratios ranging from 3:1 to 6:1 were used. Dry matter yield and P uptake response curves showed that the PR/S prepared using Rotokawa S were as effective as those using flowers of S. Both these products gave almost the same DM yields and P uptakes as superphosphate at equal P input. There was no significant difference in yield between the 2 granule sizes studied. Increasing the PR:S ratio from 3:1 to up to 6: 1 decreased the DM yields to a small but significant extent (P<0.01).