Potassium Sources for Soybeans

The objectives of this project are: 1) to determine whether chloride (Cl^–) or magnesium (Mg) applied with potassium (K) fertilizers influences soybean yield and quality and 2) to determine whether Ontario soybean cultivars differ in response to sources of K. The project is being carried out with financial support from the Ontario Agri Business Association.

For the first two years, the experiment was conducted on the same plots each time. The growing season was far more favorable for soybeans in 2000 than in 1999. While soybeans did not respond to any K source in 1999, all sources of K increased yield in 2000 by about 12 percent.

In the third year, 2001, with treatments applied to new plots, a cultivar by source interaction was detected for the first time. Sulfate of potash magnesia (K₂SO₄·2MgSO₄) increased the yield of two cultivars by 15 to 17 percent, while reducing the yield of the other two cultivars by 8 to 10 percent. In both 2000 and 2001, K also increased seed size and sugar content and slightly decreased protein content. Potassium decreased incidence of disease in 1999 and 2001, but had little effect in 2000. Researchers concluded that soybeans following soybeans need substantially more K than soybeans following corn. ON-18