Corn's Response to Potassium and Phosphorus.

Supplemental P and K fertilization is critical to sustain soil productivity and optimize corn (Zea mays L.) yield in the Mississippi Delta.  Currently, Mississippi State University utilizes the Lancaster extractant to determine soil nutrient availability.  As Mississippi producers have shifted to a more grain based production system the need for updating soil test correlation data bases has heightened.  Little to no data is available that correlates Mehlich-3 extractable nutrients to corn yield and/or tissue concentration in Mississippi.  Therefore, the objectives of this project where to correlate Lancaster and Mehlich-3 soil test P and K nutrient availability with corn nutritional status at VT and relative corn grain yield.  Since 2012 research has been established each year on production farms and research station locations with Mississippi.  Individual experiments were a randomized complete block design with five replications of the nutrient of interest (i.e. P or K).  Prior to fertilizer application, approximately 6 0-15 cm soil cores were collected from the unfertilized control in each replicate for soil test analysis. For each nutrient, five total P₂O₅ or K₂O rates were hand applied to individual plots.  For P trials, to date we have not observed a corn grain yield response to P.  Soil test values at the locations were experiments were established have ranged from medium to low based on current MSU recommendations.  For Potash response trials four out of seven trials have responded positively to application of K (p <0.10).  In general, on sites where responses to supplemental K₂O have been observed, mean corn grain yield increases have ranged from 1442 to 4578 kg ha^-1.  Soil test values for K responsive sites have ranged from 39 to 185 mg K kg^-1.