Validation of Soil Test and Plant Tissue Potassium Recommendations for Soybean in North Carolina.

Validation of Soil Test and Plant Tissue Potassium Recommendations for Soybeanin North Carolina

Lauren Lintz, Carl Crozier, and David Hardy

ABSTRACT

Soybean covers the largest acreage for field crops in North Carolina accounting for an average of 1.6 million acres between 2010- 2015.  Increases average yield result in higher nutrient removals, particularly potassium (K).  Approximately 40% of the soil samples received by the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) in 2015 had low Mehlich 3 soil test K levels, resulting in recommendations of K₂O applications last validated in 1984.   K deficiency in soybean can result reduced leaf K levels, visual yellowing or necrosis, and decline in yield through reduction in seeds per pod, seed weight, and pods per plants.  Nine sites selected across NC with varying soil types considered to have low soil test K levels had replicated soil fertilization rates (0-200 lb. K₂O per acre) broadcast applied, plus a foliar treatment.  We will present data on changes in soil test K levels, as well as trifoliate leaf K concentrations sampled at V3, V5, R2, and R5 stages. Harvested yield response to changes in Mehlich 3 soil test K levels and plant tissue K concentrations will be used to evaluate soybean response to NCDA K fertilization recommendations.