Sulfur Nutrition of Rice. III. A Comparison of Fertilizer Sources for Flooded Rice

Sulfur deficiency in rice (Oryza sativa L.) is becoming a more significant constraint to rice yields as the use of high analysis, low S‐containing fertilizers increases. There is a wide range of sulfatic fertilizers available and these have not been tested, to any degree, under flooded conditions. A pot experiment was conducted on a low fertility Paleudult soil to test the S‐supplying capacity of ammonium sulfate, gypsum, elemental S, and sulfur coated urea (SCU) applied at 30 kg S/ha to flooded rice. At 25 days after transplating (dat), fertilizer source had no significant effect on total top yield and S uptake was lower in the control, elemental S and SCU treatments. By 50 dat S deficiencies were evident in the control and SCU treatments where tiller number, yield, and % S levels were decreased. Sulfur uptake from SCU was not significantly different from the zero S control over the 113 day growing period. At maturity yields and S uptake were not significantly different between the gypsum, elemental S (100% <60 mesh), and ammonium sulfate sources. These results confirm the suitability of fine (100% <60 mesh) elemental S as a S source for rice, and show that S from SCU is not available to flooded rice at least in the first crop after application.