Rice Response and Ammonia Volatilization from Experimental Zinc Sulfate-Coated Ureas Containing Urease Inhibitors

Laboratory studies have shown that treating urea with low concentration of NBPT prior to coating can minimize ammonia loss. There is limited field research on the ammonia volatility potential of nutrient-coated urea fertilizers containing urease inhibitors. A two-year study was conducted to determine the ammonia loss and rice response to surface-broadcast urea, urea treated with N-(n-butyl) thiophosphoric triamide (NBPT), and five formulations of experimental zinc sulfate-coated urea (ZSCU) fertilizers with or without urease inhibitors. The ammonia volatilization and yield trials were analyzed as randomized complete block design. The nitrogen (N) treatments for the ammonia loss trial were applied at a rate of 134 kg N ha-1 and ammonia loss was monitored for 15 days using a semi-open static chamber. A yield trial was set up adjacent to the ammonia loss trial with N applied at 67 kg N ha-1 and134 kg N ha-1. In 2014, ammonia loss from urea (15.4%) was greater than ZSCU fertilizer with NBPT and urea treated with 0.9 g kg-1 NBPT (2.6 – 10.0%). The ammonia loss from urea (23.5%) in 2015 was greater than the other N treatments (4.1 – 18.4%). Among the various formulations of experimental ZSCU fertilizers, only the ones where urea was treated with 0.6 g kg-1 NBPT prior to coating with 1.7 g B kg-1 and ZnSO4 were effective in reducing cumulative ammonia loss as urea treated with 0.9 g kg-1 NBPT. The N treatments did not increase grain yield when compared to urea in 2014. In 2015, the NBPT-treated urea had greater grain yields than the other N treatments, which were not different from each other. Application of urea treated with 0.6 g kg-1NBPT prior to coating with 1.7 g B kg-1 and ZnSO4 is a reliable alternative to reduce ammonia loss from urea.