Potassium Sources for Soybeans

Little Ontario research has been done on soybean K needs. The relative chloride (Cl) sensitivity of Ontario cultivars has not been tested. The objectives of this project were to determine whether Cl or Mg applied with K fertilizers influence soybean response to K and to determine whether Ontario soybean varieties differ in response to K and sources of K.

As in 1998, differences among K sources were small and subtle on the five soybean varieties evaluated. In 1999, sulfate sources tended to promote oil and depress protein, relative to Cl sources. Seed diseases, including Alternaria, Phomopsis, Diaporthe, Fusarium, Cladosporium, and others, tended to decline with addition of K fertilizers of any source. In the clay loam soil used in 1999, K sources had no effect on seedling emergence. The two years of research have not identified a clear preference for one source of K over another, but suggest that the most direct role of K on the soybean crop was in reducing seed diseases. ON-18