Potassium (K) Fertilization of Alfalfa: How Much Do We Really Need?.

Record high potash prices combined with record low milk prices in the past couple of years caused dairy producers to question the need for K application on common field crops in New York State. Two studies were initiated to determine the impact of K application on alfalfa (Medicago sativa L.) yield and soil test K over time. In the first experiment, initiated in 2007, a K rate study was superimposed on 2nd year alfalfa plots using 5 annual rates (0, 93, 186, 286 and 375 kg/ha of K2O, up to 1 1/3 times estimated crop removal) and continued through the 5th year of the stand. Averaged over the alfalfa years, the annual yield without K addition amounted to 9.0 Mg/ha, consistent with the yield potential for the soil type. Yields did not increase with K and stand composition was not impacted either. Potassium addition did increase tissue K and soil test K over time. These results primarily reflect the soils ability to resupply K after significant amounts of crop removal. In the second study, K treatments (0 versus 235 kg/ha K2O in four replications) were established in 30 alfalfa-grass fields of varying soil test K levels. Potash was applied after first cutting in 2010 and 2011 and dry matter yields will be determined through 1st cutting in 2012. Preliminary results of this study will be presented as well.