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 magnesium (Mg) applied with K fertilizers influences soybean response to K and to determine whether Ontario soybean varieties differ in response to K and sources of K.

In 2000, the experiment was conducted on the same plots as the previous year. The growing season was far more favorable for soybeans than in 1999. Yields were about 70 percent higher. All sources of K increased yield by about 12 percent, increased seed size and sugar content, and slightly decreased protein content. Varieties differed in how their oil content responded to K. Most of the varieties had increased oil content with any source of K, but one variety had lower oil content when K was supplied in sulfate (SO₄) form. In contrast to 1999, diseases were at higher levels, but were suppressed very little by K from any source. Results suggest that K needs of soybeans following soybeans differ substantially from those of soybeans following corn. ON-18