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Fluid Journal : Fall 2017
10 The Fluid Journal Fall 2017 Dr. Miller is affiliate professor of soil and crop sciences at the Soil and Crop Sciences Department at Colorado State University in Fort Collins, CO. Table 10. Corn leaf nutrient DRIS norms. Nutrient Ratio 1 Average Stdev N:P 9.03 2.14 N:K 1.46 0.43 N:Mg 14.1 4.1 N:S 11.9 2.2 K:Mg 9.6 3.6 1 Ratios based on research of Elwali et al. 1985. Table 11. Cluster comparisons of corn GS R1 ear leaf K, K:Mg and yield over five years, 112 sites. Year Low K Cluster 123 High K Cluster Delta Yield K (%) K:Mg K (%) K:Mg (bu/ac) 2011 1.77* 5.9* 2.64 11.1 40.9* 2012 1.52* 3.2 1.91 6.7 58.1* 2013 1.67 3.0* 1.95 8.3 34.5 2014 1.60* 4.7* 2.17 10.1 48.2* 2015 - - - - - 2016 1.50* 3.6* 2.93 14.3 45.6 1 Ear leaf K, Mg and yield measurements for 112 sites, 4-8 reps per site, across seven states. 2 Cluster analysis of five lowest and highest ear leaf K, 16 to 32 sites. Number of sites per year, yearly dependent. 3 Cluster means within a year followed by (*) are significant at the 0.05 level. + Kac or N + KKCl increased grain yield over the check at these sites, but only over N alone at the Linden, WI site, at an average of 10 bu ac-1 , non significantly. In 2016, the site in Byron, IL showed a 17.1 bu ac-1 response to top-dress 100 lbs ac-1 K2SO4 but no response to side-dress Kac at 50 or 100 lbs ac-1 applied at GS V3-V4 (Table 8). Yield response to K2SO4 may have been to either K or S at the site, although ear leaf analysis of the check plots showed S well within the sufficiency range, whereas leaf K was 1.08%. K observation study. Beginning in 2011 and through 2014, corn leaf R1-R2 analysis data have been collected from research check plots at 76 sites across six Midwestern states where K fertility studies have been conducted. In 2016 this study was expanded to include 48 sites where data were collected on soil analysis, ear leaf nutrients, and stalk nutrients at maturity, population, and grain yield, based on four replications within grower fields across the Midwest from which 32 sites with complete data sets were selected. This datum set is extensive and full analysis is pending. Select data on leaf analysis and grain yield are discussed. Using this database of 32 sites across 5 Midwestern states, cluster analysis comparisons contrasting eight sites with the lowest ear leaf K values and the eight with the highest were conducted (Table 9). Cluster results showed consistent mean leaf N value differences between clusters and, as expected, statistically significant differences in mean leaf K, along with elevated mean leaf Mg for the low K cluster. Large differences were noted in mean leaf N:K, K:Mg, and N:Mg ratios, with the low leaf K cluster having macro nutrient ratios outside corn DRIS optimum ranges as defined by Elwali, et al, 1985 (see Table 10). Most significant was that low ear leaf K clusters had significantly lower mean yield by 48.2 bu ac-1 . Further analysis of low vs. high ear leaf K clusters for 2011-2014 indicates that lower grain yields are associated with lower leaf K and that K:Mg ratios are consistently lower with K deficiencies in ear leaves (see Table 11). Over the five years, cluster analysis shows that sites with low ear leaf K and K:Mg ratios <6.0 have averaged 45.5 bu ac-1 lower yields relative to clusters which have K and K:Mg ratios falling within optimum ranges. These results show a strong interaction of corn ear leaf K and Mg for corn at growth stage R1-R2, and when K deficiencies <1.9% occur there is a subsequent increase in ear-leaf Mg, resulting in lower K:Mg and N:Mg ratios. Based on DRIS ratios the relationship of N, K, and Mg is best shown in the theorized diagram (Figure 3) where the optimum ratios are achieved at the center of the triangle. With the onset of K deficiencies and subsequent increased Mg uptake, ratios of K:Mg and N:Mg shift to the lower right, and results in a consequent impact on grain yield. Although these results are preliminary, observation analysis of five years of field data shows a strong relationship between ear leaf K nutrition and grain yield. Summing up Results of the population study show optimum yields are obtained with planted populations of 32K-36K plants ac-1 based on 30 inch rows in the Midwest. Higher populations resulted in a reduced number of plants with ears and decreased yields. Grain yield response to population and side-dress N was site specific in 2015, with only a response to the VN treatment at the Sutherland, IA site and responses at the Wellington, CO site. 2016 results showed grain yield responses to both N and K at the Linden, WI site. Grain yield response to K source studies indicate site and product specific differences across four site years of research. Interactions with N were noted, and the average response to sidedressed K was 10 to 12 bu ac-1 . Observational data analysis of corn ear leaf tissue nutrients, based on check plots established in grower fields from 2011 to 2016, indicate leaf K levels <1.9% are indicative of lower yields and that, with K deficiencies, corn leaves showed increased Mg accumulations resulting in lower K:Mg ratios and substantially lower grain yields. Establishing N, K, Mg DRIS ratio norms is an effective tool in diagnosing corn K deficiencies and addressing K fertility management of corn. Further research is needed to develop predictive models of corn K nutrition based on soil test methods and weather variables.