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Fluid Journal : Spring 2015
13 The Fluid Journal Spring 2015 delayed mineralization, induced by the drought, decreased the response to fertilizer N, which can be noted with the average yield range of each location being less than 1 Mg ha-1. Test weight, for the first time during the evaluation of the study, was significantly impacted by treatment. It is important to note that harvest was delayed at both locations due to rain, and because of that, overall test weight was negatively impacted. The test weight results from 2013 are a good summation of the overall study (Figures 4 and 5). At Lahoma, the N rate of 6.7 kg N ha-1 had a significantly greater test weight than the 26.8 kg N ha-1, while at LCB the 26.8 kg N ha-1 rate was a significantly greater test weight than the 6.7 kg N ha-1 treatment. A final result of the 2013 crop year showed that at Lahoma CoRoN treatments resulted in significantly greater test weights than UAN, 56 and 54.6 respectively. Yet at LBC, while there was no significant difference, the average test weight of UAN treatments was 54.4 and the average test weight of CoRoN treatments was 53.9. Take home Regardless of the source rate or late season environment--flag leaf and beyond--applications never positively impacted yield and therefore should not be recommended as such. However, the FL and PA application did, at times, impact grain protein, test weight, flour yield, mix tolerance, mix time, and loaf volume. What variable was impacted, and to what degree, was not consistent across treatment or environments. The confounding result of the 2013 crop year test weights is a perfect example. The application of N post-anthesis did impact these variables more often than did flag leaf application. The source of the PA application was seldom significant, indicating that the cheaper source, UAN, was just as effective if not more so as the low salt controlled- release source, CoRoN. The greatest take-home may be that if the field is properly fertilized to reach maximum yield potential, an economical return on late-season N applications is unlikely. Currently, work is being performed to estimate the impact of these late-season N applications in situations where N is limiting. Figure 3. The deviation from 2000 to 2014 average of percent relative humidity for the Lahoma Research Station in 2011, 2012, and 2013. Figure 4. At Lahoma, the N rate of 6.7 kg N ha-1 had a significantly greater test weight than the 26.8 kg N ha-1. Figure 5. At LBC the 26.8 kg N ha-1 rate was significantly greater test weight than the 6.7 kg N ha-1 treatment. Dr. Arnall is associate professor, Dr. Seaborn is supervisor and research chemist, Dr. Mullock is soil fertility agriculturalist, and Mr. Burgess is M.S. student in charge of project at Oklahoma State University.