Management of Potassium in a Hybrid Bermudagrass Hay System.

Maintaining yield of 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.  Even though fertilization with potassium occurs at high rates soil test levels still decline because of luxury consumption of potassium by the forage and subsequent removal of that forage from the field.  Current University of Tennessee annual recommendations for potassium fertilization of low testing soils is 214 kg K₂O/ ha.  At current fertilizer costs this amounts to an investment of about 106 USD per ha just for potassium amendments.  Evaluations of rates of K₂O needed to maintain satisfactory production have never been done under Tennessee growing conditions.  A study was established in 2006 at the Highland Rim Research and Education Center near Springfield, TN.  Plots are arranged in a 4X4 Latin square with 4 treatments of K₂O  ( 0, 53.5, 107, 214 kg K₂O/ha ) applied each spring.  Harvests were made at approximately 30 day intervals during the growing season.  Nitrogen was applied in the spring and after each harvest at a rate of 90 kg N/ha up to a maximum of 356 kg N/ha per year.  Two years of data strongly indicate that optimum forage yields can be obtained at a much lower rate of K₂O fertilization than is currently recommended by the University of Tennessee.  Potassium levels in the forage and thus removal increased with rates of fertilization.  No increase in soil test levels of potassium were measured at any rate of fertilization in this experiment.