Effect of Elemental Sulfur, Gypsum, and Elemental Sulfur Coated Fertilizers, on the Availability of Sulfur to Rice

Abstract

ABSTRACT 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 35S labelled soil. At maturity of the grain, straw, and roots were analyzed for total S and35S. 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.