Evaluation of Ammonia Volatilization and Zinc Nutrition of Experimental Zinc Sulfate Coated Urea Fertilizers in a Drill-seeded Delayed Flood Rice Production System

Approaches in controlling nitrogen (N) loss from preflood fertilizer applications in delayed flood rice (Oryza stiva) production in the mid-southern U.S.A. typically involves treating urea with urease inhibitors like N-(n-butyl) thiophosphoric triamide (NBPT). Limited research exists on managing N utilizing the combined effects of treating urea with a urease inhibitor and subsequently adding a physical zinc (Zn) sulfate coating. Zinc deficiency is also a major soil fertility constraint in flooded rice production. The objectives of this study were to: (i) determine the ammonia volatilization potential of experimental zinc sulfate coated urea (ZSCU) fertilizers on four rice soils in a controlled environment, (ii) quantify ammonia volatilization losses from surface broadcast experimental ZSCU fertilizers under field conditions, (iii) evaluate the effect of experimental ZSCU fertilizer use as an N source in rice production, and (iv) evaluate experimental ZSCU fertilizer as a Zn fertilizer source in rice production. Experimental ZSCU fertilizers used in the controlled environment study and field trial included; RCO3, RCO2, RCO5, RCO1, RCO4, RCO1S and RCO4S. To evaluate ZSCU as a Zn source, five preplant and four preflood Zn fertilizer treatment combinations were evaluated alongside the control and the recommended practice of applying granular Zn sulfate. In comparison to urea, application of experimental ZSCU and urea treated with NBPT in the controlled experiment reduced ammonia loss 14 – 81 and 27 – 64%, respectively, across all soils. Cumulative ammonia loss from RCO4 and RCO4S was comparable to the NBPT-urea at a rate of 0.9 g NBPT kg-1 (w/w). Cumulative ammonia losses from the field trial ranged from 3.1–15.1 and 5.4 –22.5% in 2014 and 2015, respectively. Cumulative ammonia loss from ZSCU fertilizers was significantly lower than urea but greater than urea treated with NBPT in both years. Urea treated with NBPT out yielded all other N fertilizers in 2015. Experimental ZSCU fertilizers, particularly those containing B and NBPT, did reduce ammonia volatilization in soils susceptible to ammonia volatilization; however, the effect in controlling ammonia volatilization did not result in increased rice yield. The experimental ZSCU was similar to surface broadcast Zn sulfate alone, despite the improved distribution when applying similar rates.