Nitrous Oxide Gas Fluxes in a Potato Field Following Application of Urea and Coated Urea Fertilizers

Application of urea and other forms of nitrogen (N) fertilizer can generate atmospheric emissions of nitrous oxide (N₂O), which is a potent greenhouse gas. Field experiments were conducted on a loamy sand soil in Becker, Minnesota to evaluate the effects of soluble and coated forms of urea on N₂O fluxes in a potato field. The following treatments, all receiving a total of 270 kg/ha N were tested: 1) Conventional urea with split applications at emergence and 5 additional applications; 2) Polymer coated urea (ESN, 44-0-0, Agrium, Inc.); 3) Polymer coated urea (PCU, 42-0-0, Kingenta Co.); and 4) Sulfur coated urea (SCU, 35-0-0, Kingenta Co.). The coated urea treatments were applied 6 days prior to planting and then immediately incorporated. All treatments included 45 kg/ha N as diammonium phosphate at planting as part of the total N applied. Closed chambers were used to measure soil-to-atmosphere fluxes of N₂O on 25 dates from 27 April (one day after planting) through 14 September 2007. On each sampling date, measurements were made for one hour in 3-plot replicates of each treatment; each using paired gas-flux chambers with one chamber placed on the hill and the other in the inter-row. Flux of N₂O was estimated from the rate of increase in N₂O concentration within the chamber. The soluble urea treatment displayed a gradual increase in flux starting at 24 days after planting (DAP) and continued until reaching a maximum at 47 DAP. This increase appears to have been the result of a 110 kg/ha N application as soluble urea at 19 DAP. None of the other treatments displayed such an increase. Integration of the flux data across the entire sampling period resulted in estimates of 6.9, 5.2, 4.7, and 4.2 kg N₂O-N ha^-1 emitted from soluble urea, Agrium ESN, Kingenta PCU, and Kingenta SCU, respectively.