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Fluid Journal : Spring 2017
8 The Fluid Journal Spring 2017 Methodology Information from several projects will be used to highlight corn production response and economic optimum N rate (EONR) with various sidedress and in- season (mid- to late-vegetative stages) applications. Traditional sidedress/split N is the application of partial N before or at planting, with the remainder applied as a sidedress before corn becomes too tall for sidedress equipment. Either can be a planned sidedressing or rate based on soil nitrate testing. Examples of such research include Woli et al. (2014) with anhydrous ammonia, and other projects currently under way. Enhanced in- season sidedress/split N is typically the application of the majority of N based on plant N sensing and application at mid-to-late vegetative growth stages, the application possible with high-clearance equipment. Examples of such research include Ruiz Diaz et al. (2008) Barker et al. (2012), and Barker and Sawyer (2016). N Application Timing Traditional Split/Sidedress. Anhydrous ammonia is a common N source used for corn production in Iowa, being about half of the fertilizer N consumed. Fall application is historically less effcient than spring application. A study conducted in central Iowa for three years found exactly that, with late fall application 6% lower yield and 54 lb N/acre higher EONR (Figure 1). This potential for lower yield and higher N rate need is why farmers are encouraged to apply anhydrous ammonia in late fall (cold soil temperatures) and to consider a nitrifcation inhibitor. An all spring preplant and a split/sidedress (20 lb/ acre ammonium nitrate at planting and the remaining N as anhydrous ammonia sidedress) had the same yield and EONR (144 lb N/acre preplant and 147 lb/acre split/sidedress). At four site-years in 2015 with sidedress N applied at the V5-V8 stages (Table 1, Nashua, Kanawha, Lewis, Crawfordsville), the mean yield at the economic optimum N rate (YEONR) was 210 bu/acre with all N applied preplant and 213 bu/acre with split/sidedress application. The economic optimum N rate (EONR) was 126 lb N/acre with preplant N and 130 lb N/acre with split/ sidedress N. For the other sites in 2015 and 2014 (Table 1), the initial N was Table 1. Economic optimum N rate (EONR, 0.10 N:corn price ratio) and corn yield at the EONR (YEONR) for several sites in Iowa with all N preplant or at-planting and split/sidedress with 40-50 lb N/acre preplant or at-planting and the remainder sidedress (approximately V4 or V9 growth stages depending on the study) (projects in progress, J. Sawyer, D. Barker, J. Hall, and J. Lundvall, 2015). Fig. 1. Corn yield response and economic optimum N rate (EONR, 0.10 $/lb N:$/bu corn price ratio) with fall, spring preplant, and spring split/sidedress (V2-V4 growth stage) anhydrous ammonia with a site each year in central Iowa (2007-2009). Clarion-Nicollet-Webster soils with corn following soybeans (Woli et al., 2014). applied at planting and the sidedress N at V9. The mean YEONR was 206 bu/acre with at-planting N and 205 bu/ acre with the split /sidedress. The mean EONR was 137 lb N/acre with at-planting N and 134 lb N/acre with the split/sidedress. Across all 2014 and 2015 sites, the mean YEONR was 208 bu/acre with pre- or at-planting application and 209 bu/acresplit/sidedress. The EONR was the same at 132 lb N/acre. Interestingly, with both sidedress timings (approximately V4 or V9 growth stages), the EONR was not lower with the split sidedress application compared to