Are your soybeans short? Are they still yellow? Are they behind? If so, you are not alone. Conditions have been much less than perfect for soybean production in the Red River Valley – especially the northern Valley. Crookston has seen 829 Growing Degree Days (April 29 – July 18). This represents only 74% of the heat collected in an “average” year. When one adds the excess rainfall that has been seen across the region, there is no wonder that some soybeans are far behind normal.

Maximizing soybean yields in the Red River Valley requires strong early season growth and a normal to late first frost. If these two criteria are met, other factors such as midseason rainfall, midseason temperatures, soil fertility, and pest control affect final yields to a relatively small extent. A soybean plant/crop requires a very large and healthy root system to support water and mineral uptake through the season. Developing such a root system requires three things: a warm soil; a soil profile that is moist, but not waterlogged; and a good supply of energy from the aboveground portion of the plant (this requires light and heat).

To help put some numbers to this issue of delayed development of a soybean crop, I am including a figure from the Southwest Research and Outreach Center at Lamberton. Although this is not Red River Valley data, per se, I do believe that it fits reasonably well with yield responses seen in the Valley. This figure shows yield responses to planting date across 16 years. The data is based on yield as a percent of the maximum yielding date for any particular year. It shows that yield potentials begin to drop at planting dates beyond the third week in May. It also shows that planting dates around the third week in June result in a 50% yield potential.

How does this relate to slow developing soybeans in the Red River Valley? It may indicate that a soybean crop that is thee weeks behind normal development at this date, might still achieve a 65-75% yield. However, soybean fields that are a month behind probably fall into the 50% yield potential category.

So, where does this put us for yield potentials for this year? Certainly, the top was taken off of yield potentials in many fields; however, there is some good news. First, warm temperatures this past week helped move the crop along and helped to remove some of the excess soil moisture to allow deeper rooting. Second, August weather patterns can have a significant impact on soybean yields. Consistent warm/sunny days and warm nights over the next eight weeks could turn this crop around. While these slow developing fields will not set yield records, there is a chance for reasonable yields across the valley.

Seth Naeve: Extension Agronomist—Soybeans