Nitrogen Gas Loss from Polymer Coated and Polymer Sulfur Coated Urea.

Broadcast topdressing nitrogen fertilizer is a common application method for turf grass. While nitrogen (N) is essential to plant life, broadcast topdressing exposes applied N to potential significant gas loss via ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission. This gas loss is a financial dilemma which can lead to atmospheric pollution. Polymer coated urea (PCU) and polymer sulfur coated urea (PSCU) are control release fertilizers that engineered to release N over time to match plant demand and have demonstrated reduction of N gas loss. Evaluating N gas loss is regularly done through soil flux measurements, which can be inconsistent due to variability in sampling and escape of N gas. The objectives of this study were to increase precision and accuracy of atmospheric N gas measurement while evaluating the control release properties of PCU and PSCU. A semi enclosed system was created to capture all NH₃ volatilization and N₂O after fertilizer application. Gas capture and analysis via Photoacoustic Infrared Radar Spectroscopy (PAIRS) was done in a laboratory setting over 48 d. Fertilizer prills were surface applied to a Timpanogos Loam soil. Gases were collected every 1 h. Residual soil N was analyzed at the end of the study. Between 75-89% of the applied N was accounted for throughout the study. The PCU and PSCU both reduced cumulative NH₃ volatilization compared to uncoated urea. Polymer coated urea NH₃ volatilization was equal to the control during the 48 d period indicating, at these conditions, a near elimination of N gas loss through this fertilizer source. Polymer sulfur coated and PCU both contained over five times less soil NH₄-N than uncoated urea and no increase compared to the control, while the PCU NO₃-N pool was equal to uncoated urea and PSCU soil NO₃-N was greater than uncoated urea. This suggests that when applied uncoated urea floods the soil with NH₄-N, whereas PCU and PSCU release N approximately equal to the soil microbial activity. The reduced pool of NH₄-N in PCU and PSCU and associated reduction in NH₃ volatilization would suggest that the decreased time as NH₄-N reduces the applied fertilizer NH₃ gas loss. Further research must be done to completely understand control release N fertilizer gas properties within a living turfgrass system which would include plant N intake and variations in temperature, water, and plant and soil interactions.