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2013 Projects: Potassium and Sulfur for Alfalfa

Soil can supply large amounts of potassium (K) but producers and agricultural advisors are reluctant to eliminate K use for large K consumers like alfalfa fearing reduced yield and/or winter kill. In addition, sulfur (S) deposition rates have drastically decreased over the past 10 years and recent on-farm trials show a yield response to S addition, possibly due to the role S plays in N fixation by alfalfa. Both K and S are macronutrients essential for crop growth. Producers wanted to know: (1) whether S and K applied with manure in corn years is sufficient to bridge alfalfa years in rotations; and (2) what tools to use to reliably identify if extra S or K are needed. For K management, three approaches are commonly used: (1) K removal, (2) soil test K, and (3) K saturation-based methods.

For S management, recent NY farm trials resulted in the calibration of a new soil test for S; tissue testing was effective in identifying S and micronutrient deficient sites as well.

Recommendations for K for alfalfa can vary from 0 to 145 lbs K2O so side-by-side studies are needed to determine impact of K addition on crop yield, stand survivability, and forage quality. Recommendations for S are 20-30 lbs S/acre for S deficient sites. Once a new Cornell sulfur test was calibrated for alfalfa, we evaluated 50 alfalfa fields (across the state; two fields per farm) for potassium (K) and sulfur (S) status through both tissue testing and soil testing at 3rd cutting for two years (2012 and 2013 growing seasons). Farmers were invited to submit yield, tissue and soil data for two fields, ideally one field for which a S or K deficiency might be expected, and one for which a deficiency in either macronutrient is unlikely.

This project was funded by Northeast Sustainable Agriculture Research and Extension (NESARE) and the New York Farm Viability Institute.

If you would like to receive more information, have suggestions for furture modules, or have questions, contact Quirine Ketterings (qmk2@cornell.edu or 607-255-3061). You can also write to: Quirine Ketterings, Nutrient Management Spear Program, Department of Animal Science, Cornell University, 323 Morrison Hall, Ithaca NY 14853.