By Jerry Clark
With soybean prices struggling to move upward over the past several months, every soybean in the field needs to make it to the bin. Of course, the reality is, not all beans will get to reside in the bin and will unfortunately spend the winter in the field or get gobbled up by some form of wildlife.
A few timely management decisions can help reduce the number of soybeans left in the field. One of the most important decisions is when to pull the trigger to harvest the beans. Maturity will vary greatly from variety to variety and from maturity group to maturity group. Soybeans are considered mature when 95% of the leaves have dropped and 95% of the pods have turned the mature color, usually gray or brown. Maturity can sometimes be difficult to determine, as issues such as green stem or diseases can accelerate or mask the level of maturity.
Soybean seed moisture changes very little, remaining near 60% during the de-greening period and entering senescence. As the pods turn to mature color at the beginning of maturity stage (R7), seed dry matter accumulation is complete, and seed moisture rapidly decreases. One Iowa State University study determined that during the first 12 days after maturity, the average drydown rate was 3.2% per day, which is about five times faster than that of corn. After that period, the drydown rate significantly slows down or stops completely, stabilizing at about 13% moisture.
Paying attention to when the soybean crop reaches maturity can help farmers schedule harvest activities. Under average weather conditions, soybeans will reach 13% moisture in about 12 days following maturity. However, if weather conditions are conducive, grain drydown can be achieved in as early as nine days after maturity. Thirteen percent moisture is often the target for harvest of soybeans and for them to be stored long term.
Minimize harvest losses
Numerous tests of soybean combine losses show that up to 12% of the soybean crop is lost during harvest. Harvesting losses cannot be reduced to zero, but they can be reduced to about 5%. Harvesting soybeans at 13% and minimizing shatter and field losses to less than 5% is the goal. What happens to losses if the soybean crop gets too dry? A University of Wisconsin three-year study determined that by delaying harvest by two, four, and six weeks, field losses increased to an average of 9%, with as much as 19% loss.
Combines can be operated to reduce losses without affecting the harvesting rate. Consider shatter losses of 2% acceptable, as more than 80% of the machine loss usually occurs at the gathering unit. The height of the cutter bar directly impacts what beans get into the bin. Make sure that knife sections, guards, wear plates and hold-down clips are in good condition and properly adjusted.
Ground speed and reel speed also play a major factor in shatter and field loss. Use a reel speed about 25% faster than ground speed. The reel axle should be 6 to 12 inches ahead of the cutter bar. Reel bats should leave beans just as they are cut. Reel depth should be just enough to control the beans.
Controlling field losses will allow more soybeans to make it into the bin, take some of the sting out of dealing with low prices and force wildlife to feed somewhere else.
Clark is the Chippewa County, Wis., Extension agriculture agent.