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Fluid Journal : Fall 2017
8 The Fluid Journal Fall 2017 check; N 40 lbs/ac-1; 50 lbs ac-1 K; 40 lbsac-1ofN+50lbsac-1K;VNrate and VN +50 lbs ac-1 K as a fluid using a spoke wheel injector system at a depth of 3 inches, 3 inches each side of the row. N source was urea and the K source was K acetate (Kac). Sub plot treatments were randomized within each population main plot, with six replications. For 2016, sidedress treatments consisted of N rates of 0, 50 lbs ac-1 and 50 lbs ac-1 +50 lbs K as K acetate with six replications. Soils were sampled preplant at five depth increments to 18 inches, along with in-season corn tissue samples at R1 to R2. Crop grain yield, harvest population, moisture, and test weight data were collected at harvest. Soils were evaluated for pH NO3-N, M3-P, M3-K, CEC, Cl, using the Iowa State University moist soil test K method at Solum Laboratories, Ames, IA. Corn tissues were analyzed for N, P, K, Ca, Mg, S, Zn, Mn, Cu, B and nutrient ratios by Sure-Tech labs, Indianapolis IN. All sites were machine harvested. K source study. An additional study was conducted in 2015 and 2016 to assess sidedress K application methods using a spoke wheel injector with treatments of: a check plot: (1) check treatment; (2) 50 lbs ac-1 KCl-K2SO4; (3) 100 lbs ac-1 KCL-K2SO4 (4) 50 lbs ac-1 K acetate; and (5) preplant top dress K2SO4 in 2016. Treatments were randomized complete block with six replications on sites with an established corn population of 32K plants ac-1 . Ear leaf tissue nutrients R1-R2, crop grain yield, harvest population, moisture, and test weight data were collected. K observation study. In 2016, forty-eight observation sites were established in growers’ fields across six states for the purpose of assessing the impact of soil K and crop nutrition on grain yield. Each site consisted of four check plots each 15 x 40 feet and data collected on soil fertility (pH, P, cations, SOM, CEC, Zn-DTPA), soil nutrient stratification, V2-V4 population, R1-R2 ear leaf nutrients, stalk nutrients, harvest population, and hand harvested for grain yield. Results Population NxK study. The 2015 plant population study showed optimum grain yields were obtained Table 8. Impact of side dress and top dress K on grain yield for Byron, IL 2016. Treatment 123 Grain Yield (bu ac-1) Mean Stdev Check 225.3 11.8 50 Kac – Spoke Wheel 222.7 7.8 100 Kac – Spoke Wheel 220.1 14.7 100 K2SO4 Top Dress 242.5* 13.7 1 Soil Test K levels by site: 132 ppm, respectively. 2 Fertilizer application: top dress dry pre-emergence over row; spoke wheel side dressed V3-V4 rates lbs ac-1 . 3 Column means followed by (*) are significant at the 0.05 level from the check treatment (7 reps). for planted populations between 32K and 38K plants per acre for three of the four locations (Figure 1). The Farmer City Illinois site was impacted by post emergence herbicide drift and, as a result, grain yields for the 44K planted population were reduced. The Wellington, CO site, which had planted populations of 34K, 41K and 48K plants per acre, had reduced yields associated with delayed early season irrigation and high spatial heterogeneity associated with previous treatments from research studies conducted in 2012. Population main plot CVs were 14%, 16%, and 21% respectively, with grain yields for the check plots ranging from 112 to 183 bu/ac for the 48K plants ac-1 population across the six plots. The Linden, WI site in 2016 showed yield optimum at a planted population 38K plants ac-1 at 255.4 bu ac-1 , which had a harvest ear population of 34,800 plants ac-1 (Figure 2). Observations of the 2015 corn population study showed higher plant populations resulted in an increasing percentage of plants not bearing ears. At the Sutherland, IA and Dodgevlle, WI sites, a planted population of 26K plants ac-1 resulted in a 1.7% to 2.0% reduction, respectively, across the two sites in plant-bearing ears, whereas the 44K plants ac-1 population resulted in 7.5% to 3.4% reduction in plant-bearing ears (Table 1). Similar results were noted for the Farmers City site, however crusting at emergence greatly reduced stand counts by V3. Population in 2015 had no impact on grain yield for the 26K and 44K plant populations by sidedress N and K fertilizer applications at growth stage V3 to V4 at the Sutherland, IA Figure 2. Impact of corn population on mean grain yield for Wisconsin site 2016 Figure 1. Impact of corn population on mean grain yield for four sites 2015.