Wet weather has kept many farmers (and us) out of the field. According to the USDA National Agricultural Statistics Service, as of May 15, 10% of the soybean acres were planted. At the same time last year, 46% of soybean planting was complete. On average, in Ohio, the majority of soybean acres are planted mid to late May (Table 1). Although, it is not uncommon for soybean planting to creep into June. In general, we don’t recommend altering soybean management until planting in June. Below are some guidelines to consider if planting soybeans in June.
Row spacing. Regardless of planting date, we recommend planting soybean in narrow rows (7.5 to 15 inches). The goal is to have row widths narrow enough for soybean canopy closure by the time flowering occurs in late June/early July. This becomes even more important as soybean planting is delayed. The later in the growing season soybeans are planted, the greater the yield increase due to narrow rows.
Seeding rate. If planting soybean during the first half of June, a seeding rate of 200,000 to 225,000 seeds/acre is recommended. At a seeding rate of 200,000-225,000 seeds/acre, the final stand should be adequate to maximize yield (see Figure).
Relative maturity. Relative maturity has little effect on yield when planting during the first three weeks of May. During the first half of June, a four-day delay in planting delays physiological maturity about one day. As planting is delayed, yield potential goes down, and there is concern about whether late maturing varieties will mature before frost. When planting late, the rule of thumb is to plant the latest-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 the plants to grow vegetatively as long as possible to produce nodes where pods can form before vegetative growth is slowed due to flowering and pod formation. Table 5-4 from the Ohio Agronomy Guide gives the recommended soybean relative maturities for June and July planting dates. With these recommended relative maturities, soybeans should not get damaged by frost occurring at the normal time.