Observation Analysis of Soil Edaphic Factors on Corn Leaf Potassium in the Midwest.

Increasingly over the past fifteen years low soil test potassium (K) in the Midwest has been noted in the agricultural testing industry and maize ear leaf analysis has shown K deficiencies (< 1.90 %) range from 15 -55% in Indiana in the past 10 years. Observational analysis of maize ear leaves at growth stage R1-R2 across 132 Midwest sites across six states over six years show K deficiencies are consistently associated with elevated Mg levels. Cluster analysis comparisons of sites with sufficient leaf K (> 2.2%) and deficient sites (K < 1.9%) show grain yield differences which range from 2.3 - 3.9 Mg ha-1, averaging 3.0 Mg ha-1. Low leaf K clusters were associated with low K:Mg ratios (< 6) and low N:Mg ratios (<10). Low leaf K levels were correlated with low stalk K content at black layer. Soil analysis results indicate no significant differences in ear leaf K clusters for soil test Mehlich 3 K whereas differences were noted in soil K base saturation ratio, with lower ratios having both lower leaf and stalk K concentrations. A negative relationship was noted for CEC and SOM with leaf K. Optimum corn yields were observed when ear leaf K contents exceeded 2.2%, leaf N > 2.9% and harvest populations were > 76,000 plants ha-1.