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Fluid Journal : Fluid Journal 2005-2007
Early Spring 2006 Fluid Journal 2 areas of the Northern Great Plains. The unpredictability of rainfall, combined with very small rainfall events, is such that producers are looking at approaches like post-emergent N applications where all the fertilizer does not have to be applied at the time of seeding. While adopting new approaches, it is important that we understand the risks of post-emergent N applications. A new development in this regard is the GreenSeeker®, an active sensor that has the potential of increasing NUE. Technologies like the GreenSeeker sense crop needs for additional N, which then can be applied at variable rates. The objective of this study was to look at different proportions of N fertilizer applied during the seeding operation and the balance applied as UAN in a surface dribble at three different growth stages. Response at seeding Spring wheat. An overall response to N fertilizer was observed at the Indian Head Research Farm in 2004 (Figure 1). The grain yields were higher where some starter N was applied at seeding (with the balance applied as a surface dribble band) than when all the N was applied as a surface dribble band. Even adding just 33 percent of the total N fertilizer requirements at the time of seeding, with the balance applied post-emergence, resulted in yields similar to application of all the N fertilizer at the time of seeding. However, the dry year of 2003 showed us that applying 33 percent of all the N fertilizer at seeding was not enough. In 2004, where no N fertilizer was applied at seeding and all the N was applied post-emergence, the yields were better when applied at the 3-leaf stage than at the 1- or 5-leaf stages. This may simply reflect better rainfall immediately after seeding. Canola. There was a grain yield response to N fertilizer for the Indian Head trial in 2004 (Figure 2). In addition, we also observed a wheel traffic effect with all application timings of post- emergent N applications, with the largest effect occurring at the last two application dates. In order to correct for this effect, comparisons of treatment means were made to corresponding means associated with the wheel traffic effect at a particular growth stage. The treatment where all the fertilizer was applied at seeding was not significantly different versus where 33, 50, and 67 percent of the fertilizer N was applied at seeding and the balance at the 6-leaf stage. When all the N was applied postemergent, the yields were inferior to the other N treatments. This means that some N is required at seeding but the exact amount will vary with years and agro-ecological zone. As with the results for spring wheat, applying some starter N at the time of seeding was better overall than applying all the N post-emergence. Adding 33 to 67 percent or more of the N fertilizer requirements at seeding, combined with the two earliest dates of postemergent application, was capable of protecting grain yields. Conclusions • Based on the results of 2004 and the observations of 2003, some starter N needs to be applied at the time of seeding in order to protect yield potential and minimize the risks associated with post-emergent N applications • The best proportion of starter N to post-emergent N will be dictated by the agro-ecological zone in question but should be at least 33 percent, preferably more. Applying at least 50 to 60 percent of the fertilizer needs at time of seeding would greatly reduce the risks associated with post-emergent N applications • In the drier zones, more starter N will be required and in the wetter zones, less may be required. Dr. Lafond, Dr. Brandt, Dr. May, and Dr. Grant are research scientists with Agriculture and Agri-Food Canada, and Dr. Johnston is the northern Great Plains director with the Potash and Phosphate Institute of Canada. Figure 2. The effect of N timing and starter N levels on yield (average bu/A) of canola when N is applied post-emergent at the 6-leaf stage.
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