Synchronizing Nitrogen Application with Uptake Using Urease and Nitrification Inhibitors to Maximize Nitrogen Use in Forage Seed Stands in Northeastern Saskatchewan

Abstract

Management of nitrogen inputs in forage seed production systems continues to be a significant challenge for forage seed producers. Since the decline in availability of ammonium nitrate in western Canada, urea has become a widely used source of fertilizer nitrogen (N). However, the nitrogen use efficiency (NUE) of surface applied of urea can be low due to the lack of incorporation. Recently, so-called enhanced efficiency, or stabilized urea products incorporating urease and nitrification inhibitors have shown promise in reducing gaseous N losses and enhancing NUE. Thus, this study was initiated to examine the use of stabilized N products in forage seed production systems in northeastern Saskatchewan. Three stabilized urea products and two application strategies (fall vs. spring) were evaluated and compared to untreated urea. All treatments were applied at a rate of 100 kg N ha-1. The study evaluated two forage species: hybrid bromegrass (Bromus riparius Rehm. X Bromus inermis Leyss.) and timothy (Phleum pratense L.). The study was undertaken in four established commercial fields (two each of bromegrass and timothy) and was initiated in fall of 2012. Rates of N transformation, seed yield, biomass production, biomass quality, NUE, 1000-seed weight, and economic returns were evaluated over the 2013 growing season. The use of controlled release N products delayed fall N transformation in the bromegrass fields and increased seed yields by 14 to 22%. Spring applied treatments also proved effective at delaying N transformation, though their influence was less pronounced. Moreover, spring applied N treatments were generally associated with a yield reduction of 11 to 19%. In general, biomass quantity and quality, NUE, number of seed bearing tillers, 1000-seed weight and economic returns were not significantly influenced by the use of controlled release N products. In timothy, seed yield and biomass production were greatest when the N was spring applied; however, there were no significant differences between the stabilized and untreated urea products. Similar results also were observed for forage quality, NUE, number of seed bearing tillers, 1000-seed weight and economic return. The absence of consistent yield trends suggests that unless environmental conditions that promote high N loss are present, the utility of stabilized N products may be limited to that of a risk management tool.