Comparison of Nitrogen Sources for Spring Wheat Production.

There is a growing interest in new fertilizer technologies among Montana growers, dealers and crop advisors.  Environmentally Smart Nitrogen (ESN) is a relatively new slow-release form of urea nitrogen (N) fertilizer contained within a proprietary polyurethane coating. The proposed benefits of ESN include increased grain yield and quality and higher fertilizer use efficiency. The objectives of this study were: 1) to evaluate ESN as a N fertilizer source for spring wheat production in comparison to conventional urea, and 2) to evaluate nitrogen use efficiency, and grain yield and protein response to these two fertilizer materials, alone and in combination. This study has been funded by Montana Fertilizer Tax Advisory Committee and initiated in 2011, and continued in 2012. Two dryland sites - Western Triangle Ag Research Center (WTARC, Conrad, MT) and Northwestern Agricultural Research Center (NWARC, Kalispell, MT) and one irrigated site - Western Agricultural Research Center (WARC, Corvallis, MT) were established for 2 consecutive growing seasons. Three sources - urea, ESN, and a 50%-50% urea-ESN blend were evaluated. Following yield-goal based recommendations for spring wheat, four N rates - 0, 50, 100, and 150 lbs N ac^-1 (at WTARC and WARC) and 0, 100, 200, and 300 lbs N ac^-1 (at NWARC) applied to hard red spring wheat at seeding were evaluated. Additionally, 2 topdress rates applied at Feekes 5 growth stage – 0 and 40 were lbs N ac^-1 assessed. At Feekes 5, crop canopy reflectance – Normalized Difference Vegetative Index (NDVI) was measured in each plot using the GreenSeeker (GS)(except for NWARC in 2011) and Pocket Sensor (PS) (except for WTARC in 2012) optical sensors as a means of assessing N status of the crop. At harvest grain yield and grain protein content were determined. The response of spring wheat to N sources and their rate of application were evaluated to develop N fertilizer application guidelines. Statistically significant effect of fertilizer N source on grain yield (independent of N rate) was observed at 2 of 6 site-years with no consistent trend among the site-years. At NWARC in 2011, the yield increased as: urea<blend<ESN, and at WARC in 2012, urea produced higher yields compared to blend and ESN. Grain yield response to both N applied at seeding and to topdress N was observed (P<0.05) at 5 of 6 site-years. In general, higher N rates applied at seeding resulted in significantly higher grain protein content at 5 of 6 site-years.  Grain protein content response to topdress N was evident at 3 of 6 site-years only. The crop reflectance measurements obtained with the two sensors were very consistent at 3 of 4 sites (where both GS and PS NDVI data were available). The GS and PS NDVI values were highly correlated with spring wheat grain yield at 3 of 5 site-years (P<0.0001). On the other hand, grain protein content was highly correlated with sensor measurements only at 1 of 5 site-years. This agrees with previous findings that, unlike grain protein content, yield potential can be accurately estimated mid-season using sensor-derived data. This study will be continued for one more growing season in 2013 at 3 locations.