Effect Of Polymer Coated Urea On N Leaching and Potato Yield.

We measured NO₃-N leaching under a combination of irrigation and nitrogen practices on an Entisol in Citra, FL to determine the contribution of different management programs on reducing N loss from potato production. Treatments consisted of three nitrogen management programs (soluble N at 224 kg ha^-1 N from a urea-ammonium nitrate mixture, or 224 or 168 kg ha^-1 N from polymer-coated urea) and three sprinkler applied irrigation treatments (maintaining soil moisture at field capacity with daily irrigation at 125% ET or 100% ET, or maintaining soil moisture between 50 and 75% field capacity) and were arranged in a completely randomized design with three replicates. For the soluble-N treatment, 10% of the N was applied immediately prior to planting, with the remainder evenly split at plant emergence and 44 days after planting. 100% of the polymer-coated urea was incorporated in the bed immediately prior to planting. Nitrate-N leaching loads were calculated from leachate volume and N concentrations in the leachate. Both polymer-coated urea treatments had significantly lower NO₃-N leaching than the soluble N treatment, with polymer-coated urea at 168 kg ha^-1 resulting in the lowest N loss and no differences in yield among treatments. While polymer-coated urea reduced N loss and maintained potato yield, there are still perceived economic barriers that prevent the widespread adoption of controlled-release technologies in Florida potato production systems. However, cost analysis of the fertilizer programs showed that reduced N rates can offset the high cost of polymer-coated urea without reducing yield.