Long term effect of three phosphate sources on rice
1996
Xaviar Arulandoo | Aziz Bidin
The unavailability of information on many phosphate sources initiated an investigation on those sources and the effect of their continuous long usage on rice yields. Three phosphate sources - a high-reactive rock phosphate HR-RP, triple superphosphate (TSP) and a `regular" rock phosphate (RP) - were used in the investigation, at Mulong Lating, Kelantan. The rates used were 0, 20, 50, 90 150 kg P2O5/ha. and an RCBD with three replications were employed. The sources were applied cumulatively for 6 seasons, after which every treatment plot was divided into smaller plots. To one of the smaller plots the phosphate sources were cumulatively added as before for another 5 seasons (cumulative), and to the other, addition of phosphate sources were stopped (residuals). Result shows that rice yield showed wide seasonal variations. No noticeable trend was observed for the early seasons but by the 6th season, HR_RP gave a more consistent enhancement of 0.5 t/ha while RP and TSP provided yield enhancement ranging 0.2-0.5 t/ha. After the plots were split, yield enhancements from the cumulative plots increased by 0.7 to 0.9 t/ha or greater while those from the residual plots decreased to about 0.1-0.3 t/ha. Generally, with cumulative applications and average over rates and seasons, there was no difference in grain yield due to phosphate sources. But during later seasons, yields from HR_RP were higher than for RP and TSP, in that order. Seasonal variations may have played a part in masking certain trend due to sources. Soil analysis showed that fertilized plots showed higher available P than unfertilized plots. The soils taken after Season 11 showed that the residual plots had only marginally lower availabel P than the cumulative plots, despite not receiving phosphate fertilizer for the last five seasons. Grain N content showed higher value with phosphate applications.
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