Alfalfa production is a key component of livestock production in Tennessee. Alfalfa has the ability to take up luxury amounts of potassium, which can lead to high plant tissue K concentrations and lower concentrations of other nutrients. The objectives of this research were to determine 1) whether Tennessee K recommendations for alfalfa were sufficient and accurate, and 2) if splitting K applications impacted alfalfa yield.

Alfalfa (Cropland Consistency 4.10RR) was established in Springfield, TN in spring 2012 on a Staser loam soil (Fine-loamy, mixed, active, thermic Cumulic Hapludolls). Soil test values were determined with Mehlich-1 using ICAP. Soil test K was low throughout the study. Phosphorus (134 kg P2O5 ha-1) and Boron (1.12 kg B ha-1) were applied each spring at green-up. The experimental design was a Latin square split-plot design, with four fertilizer K rates (0, 67, 134, and 269 kg K2O ha-1) as the main plots and two timings (one application at green-up or split applications) as the split-plots. From 2012 to 2014, alfalfa was harvested in approximately 30-day intervals with a Carter Harvester (Carter Mfg. Co., Inc., Brookston, IN). Harvests took place in July, August, and September in 2012, May, June, July, and September in 2013, and May, June, July, August, and September in 2014. Soil measurements included pH, buffer pH, Mehlich-1 P, K, Ca, Mg, Zn, Mn, and B, and crop measurements included dry matter yield, tissue K content, and K removal. Alfalfa tissue analysis was determined by nitric acid digestion and Inductively Coupled Plasma (ICP) spectrometry analysis of the diluted digest. Tissue K content and K removal are not available for the September harvest in 2014.