Effect of elemental sulfur, gypsum, and elemental sulfur coated fertilizers, on the availability of sulfur to rice

Rice crops throughout the world are becoming increasingly affected by sulfur ( S) deficiency as the use of S-free fertilizers increases. Sulfur additions, as coatings, to fertilizers such as urea ( U), di-ammonium phosphate ( DAP), mono-ammonium phosphate ( MAP), and triple superphosphate ( TSP) offer a way to introduce S back into these fertilizers. Five S sources ( elemental sulfur ( ES), sulfur coated urea ( SU), sulfur coated DAP ( SDAP), sulfur coated TSP ( STSP), gypsum, and a - S control, were applied to rice under two water regimes ( flooded and non-flooded) and with two placements ( surface and deep applications). The treatments were combined as surface non-flooded ( SNF), surface flooded ( SF), and deep flooded ( DF). Sulfur was applied at the rate of 10 kg/ha to S-35 labelled soil. At maturity of the grain, straw, and roots were analyzed for total S and S-35. Sulfur application increased grain yield and all sources were equally effective under all three conditions ( SNF, SF, DF), except gypsum, which was not different from the control under SF and DF conditions. Total S content and fertilizer S content in the grain and straw were not different between S sources. Elemental S and SU resulted in the highest recovery of fertilizer S in the plant ( 47% and 46% respectively) followed by SDAP, STSP, and gypsum. Recovery of fertilizer S was lower under SNF conditions compared with SF and DF. Release of S from SU was highest when applied on the surface under flooded conditions, compared with other coated fertilizers.