Liquid Nitrogen Fertilizers in Spring Wheat.

Spring wheat’s primary value is its quality, represented by high grain protein content. Thus, when evaluating use efficiency for spring wheat, combining yield and protein into protein yield, as proposed by Jackson (2001), makes sense because N is vital to both yield and protein production. Continuous advances in novel fertilizer technologies, and the active promotion of liquid products as more efficient, have renewed growers’ interest in liquid fertilizers.  Several foliar N fertilizers are currently available on the market. These products vary in analysis and can include N products or mixtures of N plus other macro and micro nutrients. Some of N foliar fertilizers include urea ammonium nitrate (UAN), liquid urea (LU), and highNRG-N. Many wheat growers in the Great Plains area are already using foliar products or considering including them in their nutrient management. These producers are in need of up-to-date and unbiased information about currently marketed foliar N fertilizers. This study aimed to answer the following questions: 1) Are liquid urea and highNRG-N agronomically and economically superior to UAN in improving spring wheat grain yield and protein content, and 2) What is the optimum dilution ratio of foliar fertilizers and the threshold at which spring wheat grain yield is reduced due to leaf burn. This study has been initiated in spring of 2012 and continued in 2013. The complete results for both growing seasons are summarized in this final report. Three experiments were established: two dryland - at WTARC (near Conrad, MT) and in a cooperating producer’s field (Jack Patton, Choteau County, MT), and one irrigated – at WARC (near Corvallis, MT) using Choteau spring wheat. Appropriate weed and pest management control were employed when necessary. Treatment structure is reported in Table 1. At seeding, urea was applied at 80 lb N ac^-1 to all treatments except for the unfertilized check plot.  At Feekes 5 growth stage (early tillering), 40 lb N ac^-1 was foliar applied utilizing an all-terrain vehicle (ATV)-mounted stream-bar equipped sprayer.  Three liquid N sources – urea ammonium nitrate (UAN), liquid urea (LU), and high NRG-N (HNRGN) and three dilution ratios of fertilizer%/water% - 100/0, 66/33, and 33/66 - were evaluated. The effects of N source and the dilution ratio (fertilizer/water) on N uptake, N use efficiency (NUE), spring wheat grain yield, and grain protein content and protein yield were assessed. The dilution ratio had no significant effect on grain yield, protein and other evaluated variables. Although the effect of product on grain yield was more pronounces in 2012, compared to 2013, in both growing seasons, HNRGN resulted in higher yields compared to UAN. At dryland locations, LU performed as well as HNRGN. At the irrigated location, there was little difference in yield associated with N product. In 2012, at WARC, lower yield but higher grain protein was observed with LU, compared to other N sources. Grain protein contents obtained in this study were excellent and ranged from 10.6% to 17.2%. Evaluation of product effect on protein yield and NUE allow us to assess how efficiently N products were taken up, assimilated and utilized to produce both grain yield and quality (protein). Protein yield is a valuable characteristic, especially for spring wheat in Montana. Protein yield was clearly higher with HNRGN at both dryland sites in 2012 and in 2013. Even where the differences were not statistically significant, over 30 lb ac^-1 advantage in protein yield accumulation was observed with HNRGN compared to UAN.      The effect of N source on NUE was very pronounces in favor of HNRGN at dryland locations in both growing seasons. The lowest NUE values were observed with UAN and LU produced intermediate results. The irrigated location had similar NUEs for all products, except for 2012, when LU resulted in lower (not statistically significant). Considering both agronomic and economic benefits, LU can be recommended as most appropriate liquid fertilizer N source for spring wheat production in Montana.