EFFECT OF PLACEMENT AND SOURCE OF SULFUR IN FLOODED AND NON-FLOODED RICE CROPPING SYSTEMS

Many rice-growing areas in developing countries are becoming S deficient. A glasshouse experiment was conducted to study the effect of water regimes in successive crops (nonflooded:non-flooded, flooded:flooded and flooded:non-flooded), surface (S) and deep (D) placement of sulfur fertilizer and S sources (elemental S (E) and sulfate S (S)) on the growth of rice. A soil of granitic origin was used and S-35-labelled sulfur fertilizers were used to investigate S uptake by plants and the dynamics of S in soils. Among the sulfur sources, surface-applied gypsum produced the highest total yield, which was 83.6 g pot(-1) under flooded conditions. Total yields under flooded conditions were ranked in order SS > SE > DS > DE > control. In the first crop, the highest S-35 recovery in the plant was 67.8% from the non-flooded SE, compared with 51.7% in the DE treatment. Deep-placed elemental S (DE) became more effective than SS and SE for the subsequent rice crop, both in terms of plant dry-matter yield and fertilizer S-35 content. The highest S-35 recovery in the second crop was 29.5% in the previous DE treatment in the flooded: non-flooded system. This compares with 7.5% in the SS treatment in the same cropping system.