Impact of Maize Ear Leaf K and Macro-Nutrient Ratios on Grain Yield in the Midwest.

Results from seventy-six sites over four years of Midwest maize research show that ear leaves at growth stage VT-R1 with K levels < 2.0%, and with Mg:K ratios > 0.16 are indicative of lower yield potentials.  Cluster analysis across four years show the Mg:K ratio was more indicative of lower grain yields than leaf K alone.  For 2013 sites with Mg:K ratios exceeding 0.18 averaged 3520 kg/ha lower grain yield relative to sites with a ratios < 0.14.  In addition low N:Mg ratios were also noted on the lower yielding locations for 3 of the 4 years.  Soil test Mehlich K was a poor predictor of leaf K levels and yield levels for 2013 and 2014 over 34 locations.  These results support the premise that K deficiencies occurring during maize vegetative growth stages V5 - VT, which lead to lower ear leaf K levels at pollination, result in lower grain yields in the Midwest.