COMPARISON OF AMMONIUM-SULFATE AND UREA AS NITROGEN-SOURCES IN RICE PRODUCTION

Wetland rice agriculture is the major anthropogenic source of methane, an important greenhouse gas. Methane emissions are less when ammonium sulfate (AS) rather than urea is the nitrogen (N) source. However, an agronomic advantage of AS over urea has not been established The obje ctives of this study were: (i) to compare the effectiveness of AS, ure a, and urea plus elemental sulfur (S) as sources of N in flooded rice culture, (ii) to compare fertilizer recovery of each source of N from application at preflood (PF) and panicle initiation (PI), and (iii) to determine if there is a response to S by rice grown on a soil with a less than optimum level of available S. 'Cypress' rice was drill-seede d in a Crowley silt loam soil (fine, montmorillonitic, thermic Typic A lbaqualf) of 7.25 to 10.75 mg S kg(-l). Ammonium sulfate, urea, or ure a plus S was applied in split applications of 101 kg N ha(-1) PF and 5 0 kg N ha(-1) PI. Microplots with retainers and N-15-labeled N were us ed. Unlabeled N was used in field plots. Microplots were harvested at 50% heading, while field plots were harvested at maturity. Dry matter and total N accumulation at 50% heading and at maturity were similar r egardless of N source. Grain dry matter yields were 8.54, 8.47, and 8. 79 Mg ha(-1) for AS, urea, and urea plus S treatments, respectively. G reater N recovery was generally found from N application at PI than at PF, but this was not reflected by an increase in grain yield. No resp onse to S was detected, although grain yields were slightly higher whe n S-containing fertilizers were used. Ammonium sulfate and urea were e qually effective for flooded rice production in Louisiana.