Urea, Urea-ESN Blends, and ESN As N Sources for Wheat.

There is a growing interest in enhanced efficiency fertilizer (EEF) technologies among Montana growers, dealers and crop advisors.  This interest is mainly due to continuous efforts to improve the efficiency of fertilizers and to reduce environmental losses. Environmentally Smart Nitrogen (ESN) (44-0-0) is a form of polymer-coated nitrogen (N) fertilizer marketed as a slow-release product. Slow-release N products have been widely adopted in turf production and other high value crops such as ornamentals and vegetables (Keller, 2010). Several studies have illustrated that higher yields and better crop quality can be obtained using ESN compared to conventional urea (Gordon, 2008). This article summarizes the results from a 3-year-long study that tested the efficacy of ESN, in comparison to urea, for wheat production in Montana. The specific objectives of the study were: 1) to evaluate ESN as an N fertilizer source for spring wheat production in Montana in comparison to conventional urea, and 2) to evaluate N use efficiency (NUE), and grain yield and protein response to these two fertilizer materials, alone and in combination. The study was initiated in the spring of 2011, continued in 2012 and completed in 2013 growing season. Field trials were conducted at three locations in Montana: an irrigated site at Western Agricultural Research Center, near Corvallis, MT (WARC) and two dryland sites - one at North Western Agricultural Research Center, near Creston, MT (NWARC) and one at Western Triangle Agricultural Research Center, near Conrad, MT (WTARC). Plots were arranged in a split-plot design with N source (urea, ESN, and a 50:50 blend of urea and ESN) x N fertilizer rate (0, 50, 100, and 150 lb N ac^-1 at WTARC and 0, 100, 200, and 300 lb N ac^-1 at WARC and NWARC) as the main plot factor and topdress (0 or 40 lb N ac^-1) as the subplot factor. This study had enabled us to evaluate the N source effect on grain yield and protein content in a wide range of growing environments. Grain yield has varied from 30 to almost 100 bu ac^-1 between the site-years. Similarly, grain protein content has ranged from 11 to almost 18%. Spring wheat grain yield responded to preplant N application at 7 of 8 site-years, also higher grain protein content was achieved with preplant N application. No consistent trend in grain yield associated with N source was observed in this study: out of 8 site-years, urea resulted in higher yields at 3 site-years, ESN produced higher yields at 3 site-years, and the blend – at 2 site-years. No significant differences in grain protein content associated with N source were observed at most site-years, ESN and urea/ESN blend resulted in higher grain protein compared to urea alone at 3 of 6 site-years evaluated. Nitrogen uptake increased with increase in preplant N rates at 7 of 8 site-years; topdress N application increased N uptake in 5 of 8 site-years. The manufacturer’s general recommendation for utilization of ESN for spring wheat in Great Plains region is application of N as 100% ESN in the fall prior to seeding wheat the next spring. Another commonly recommended application scenario is a spring application as a blend (40-75% ESN + 25-60% urea). Our results showed that spring-applied ESN and urea/ESN blend performed as well, but not better than urea alone from the point of view of grain yield, protein content, N uptake or NUE in spring wheat in Montana. With ESN costing consistently more than urea per unit of N, and based on results of this 3-year study, we can recommend that wheat growers in the Northern Great Plains chose urea as their N source.