Alfalfa Response to Potassium Rate and Timing of Application.

Alfalfa is a high-quality forage crop grown by Tennessee farmers primarily as a feed source for horses and dairy cattle.  While alfalfa can be a high-yielding forage crop, it requires attention and proper nutrient management to perform optimally.  Potassium is an important nutrient to alfalfa growth, development, and maintenance of a strong stand.  University of Tennessee (UT) recommendations for K fertilization of alfalfa are currently 213-269 kilograms K₂O per hectare for medium to low testing soils, respectively.  A three-year study was conducted in Springfield, Tennessee to refine UT recommendations for K in alfalfa.  Alfalfa was established on a Staser loam (Cumulic Hapludoll), which tested low in soil K throughout the study.  Phosphorus and boron were applied at UT recommended rates (134 kg P₂O₅/ha and 1.12 kg B/ha) each spring at green-up.  K was applied at rates of 0, 67, 134, and 269 kg K₂O/ha each year.  Each rate was applied in full each spring at green-up, and rates other than zero were also split to study effect of application timing.  The 67 kg K₂O/ha split treatment received half of its K₂O at green-up and half after the first harvest.  The 134 and 269 kg K₂O/ha split treatments broke the K₂O requirement into four applications, at green-up and after each harvest.  Alfalfa was harvested four times per year, at about 30 day intervals.  Yield and tissue K content were measured.  The results of this research will help refine UT recommendations to alfalfa growers across the state.