Many of our customers find it profitable to double-crop soybeans. A reoccurring question many of our growers ask is, “What is the right population and which maturity should I plant?” As many of you know, many factors contribute to yield potential such as planting date, final stand populations, varietal selection, soil fertility, rain fall, planting conditions, etc.
According to Jim Beuerlein (now retired OSU Extension Specialist), “late planting reduces our cultural practice options for row spacing, seeding rate and variety maturity. For the last half of June, 225,000 to 250,000 seeds per acre are recommended, and in early July drop 250,000 to 275,000 seeds per acre.”
Soybeans are not like corn because they are photo period sensitive. The amount of daylight the plant receives triggers its reproductive cycle. The date and timing of physiological maturity are affected by day length and the stage of seed development in the uppermost pods on the plants. Relative maturity (RM) has little effect on yield for plantings made during the first three weeks of May but the effect can be large for late plantings. During the first half of June, a 4-day delay in planting delays physiological maturity about one day. In the last half of June it takes a 5-day planting delay to delay physiological maturity a day. As planting is delayed, yield potential decreases and there is concern about whether late maturing varieties will mature before a killing frost.
When planting late, the rule-of-thumb is to plant the latest possible maturing variety that will reach physiological maturity before the first killing frost. The reason for using late maturing varieties for late planting is to allow vegetative growth for as long as possible to produce nodes where pods can form before flowering and pod formation. Also, it is recommended to plant taller varieties that will allow for greater amounts of pods to form because more nodes equals more pods and more yield. So we need late maturing varieties that will mature before getting frosted but since we never know when the first frost will occur, we use a narrow maturity range that will not be damaged by frost occurring at the normal time.
Assuming normal weather and frost dates, varieties with the following relative maturity should mature before frost and produce maximum possible yields when planted on the dates indicated. Varieties with an earlier relative maturity will mature earlier but will produce reduced yields (C.O.R.N.).
Matt Hutcheson, CCA
Seed Consultants, Inc.