Evaluation of Ammonia Volatilization and Yield Potential of Experimental Zinc Sulfate Coated Urea Fertilizers in Rice Production.

Minimizing ammonia (NH₃) volatilization in rice fields averts potential economic and environmental losses. Enhanced efficiency fertilizers have been at the forefront in reducing ammonia volatilization. The potential synergic effect of using n-butyl thiophosphoric triamide (NBPT) on urea combined with a zinc sulfate coating has not been evaluated. The objective of this study was to evaluate ammonia volatilization and rice grain yield response of several zinc sulfate coated urea fertilizers. A two year field study was conducted with 8 and 10 nitrogen sources in 2014 and 2015, respectively. The nitrogen sources examined in 2014 were: urea, NBPT treated urea and five zinc sulfate coated urea fertilizers (ZSCU); ZSCU, ZSCU+.1% B, ZSCU+.17%B, ZSCU+.1%B+0.03% NBPT, ZSCU+.17%B+0.03%NBPT. In 2015, NBPT percentage in ZSCU was increased from 0.03%to 0.06% and a calcium shell coating was added as two additional N sources. Nitrogen was applied in the volatilization trials at a rate of 135 kg N ha^-1. Ammonia volatilization losses from fields were monitored over a 14 day period with semi-open static chambers. In the yield trials, N fertilizers were applied at two rates, 68 and 135 kg N ha^-1­­­. Cumulative NH₃ losses from fertilized plots ranged from 3.1 - 15.1 and 5.4 - 22.5 % in 2014 and 2015, respectively. Cumulative NH₃ loss from ZSCU fertilizers was significantly lower than urea but greater than NBPT-urea in both years. In 2014, there was no significant difference in rice grain yield among fertilizers sources at each application rate. However, in 2015, NBPT treated urea out yielded the other nitrogen fertilizers regardless of application rate.