Analysis of WICST Cropping System-5 Alfalfa K Fertilization Trial

After approximately 15 years, several plots in the organic dairy rotation (CS5; corn-oats/alfalfa-alfalfa) of WICST have soil test K (STK) levels that have decreased to the optimum level or below so alfalfa yield may be limited. This is despite manure applications in 2 out of 3 years of this rotation. Potassium sulfate (K2SO4) is an organically approved fertilizer that should increase K availability to alfalfa. Some organic advocates suggest that organically managed soils may be more efficient in making nutrients available to plants than traditional soil tests predict. Since our plots have been managed organically since 1990, we felt that the system was at or near equilibrium. In 2005 and 2006, we superimposed a potassium study on the alfalfa production phase of CS5 to determine if we should start applying K to these organic plots.

Authors: Jon Baldock, Janet Hedtcke, Joshua Posner