Potassium Rate and Timing of Application to Optimize Bermudagrass Hay Yield and K Content.

A six year K rate and timing study was conducted on a Staser silt loam (Cumulic Hapludoll) on the Highland Rim approximately 30 miles north of Nashville (N 36° 28’ and W 86° 50’, elevation 217 m). Maintaining yield of Vaughn's hybrid bermudagrass (Cynodon dactylon) hay involves annual fertilization with a potassium containing fertilizer.  The high annual yields associated with this forage and removal of the hay for sale or use elsewhere on the farm quickly depletes soil test levels of potassium, to the low range, at economically feasible rates of K application. When all K is applied at greenup, forage K levels may often be higher than that desired for some animal consumption needs and may decrease to deficient or near deficient levels for hay production by the end of the harvest season.   potassium levels in the forage and thus removal increased with rates of fertilization.  The grass was established during 2005 and measurements began in 2006.  Four harvests were obtained in all but 2007.  Data obtained during 2007 were not used as only 2 harvests were achieved because of drought.   No increase in soil test levels of potassium were measured during any year or at any rate of fertilization in this experiment. No beneficial effects on yield or K content of the forage were achieved with split appications of K. Fitting a linear plateau model to annual total average hay yields at each rate summed over harvest dates  (5years data) suggests that a yearly appication of 149 kg K₂O/ha at greenup is adequate to maximize annual forage yield.  Average annual forage yields declined during the time period of the experiment (2006-11).