Soybean production has increased very rapidly in recent years. In 1939, Wisconsin grew only about 20,000 acres of soybeans for grain. This figure had increased to around 450,000 acres twenty years ago and is now at approximately 1.7 million acres. The average yield of soybeans in Wisconsin varies a great deal from year to year depending on growing conditions. The average yield in 1972 was about 28 bu/acre, which was the same as the average yield for 2003. Clearly, this average yield is far below yields of 70 to 90+ bu/acre commonly being reported in highly managed test plots.

Nutrient availability can be strongly influenced by soil pH and many of Wisconsin’s soils are natively acid, often requiring lime to raise the soil pH. Since many of Wisconsin’s soybeans are grown on soils with some degree of acidity, more information on the effect of soil pH on nutrient uptake and yield is needed. Earlier studies conducted at various Agricultural Research Stations in Wisconsin showed that a soil pH of at least 6.3 was required for optimum yields of soybeans. At the Marshfield location in 1984, a soil pH below 5.2 was very detrimental to soybean plant performance and top performance seen when the soil was limed to a pH of 6.3 (Fig. 1). A similar study conducted that same year in southern Wisconsin at the Arlington Research Station, showed that soybean yields may require a soil pH somewhat above 6.3 for optimum production.