Ammonia Volatilization of Zinc Sulfate‐Coated and NBPT‐Treated Urea Fertilizers

Abstract

Core Ideas Combining Zn sulfate‐coated urea with low percent NBPT improved ammonia volatilization control in low pH soil when compared to the recommended NBPT application rate. Combining Zn sulfate‐coated urea with boron compounds provided ammonia volatility control. The inhibitory effect of urea coated with Zn sulfate alone on ammonia volatilization is influenced by soil properties. A study was conducted to determine ammonia loss from surface‐broadcast urea, urea treated with three rates of N‐(n‐butyl) thiophosphoric triamide (NBPT), and experimental zinc sulfate (ZnSO4)‐coated urea (ZSCU) fertilizers with or without urease inhibitors. Four trials were conducted in environmentally regulated boxes over a 14‐d period. Cumulative ammonia loss from urea was 13.98, 15.57, 23.07, and 27.74% of applied N for the Mowata, Crowley H, Crowley L, and Kinder soils, respectively. Cumulative ammonia loss from urea was greater than all rates of NBPT‐treated urea (5.57–13.35%) and ZSCU fertilizer containing urease inhibitors (2.63–11.50%) across soil types. The number of days after fertilization when the maximum rate of ammonia loss occurred increased with each incremental increase in NBPT rate for the Mowata and Crowley L soils, increased between the 0.3 and 0.6 g kg−1 NBPT rates for the Crowley H soil, and increased between the 0.6 and 0.9 g kg−1 NBPT rates for the Kinder soil. Only one of the experimental ZSCU fertilizers (zinc sulfate‐coated urea with boron and NBPT [ZUN]; Crowley H soil only) increased the number of days after fertilization when the maximum rate of ammonia loss occurred; however, the volatilization rate was lower than urea for all ZSCU fertilizers across soils. The ZUN and ZUC were the most effective ZSCU fertilizer in minimizing cumulative ammonia volatilization by 58 to 81%. The ZSCU fertilizers have the potential to reduce ammonia losses as compared to urea; however, ZSCU fertilizers with B and NBPT were the most effective.