As small grains are harvested across the state, here are some management considerations for double-crop soybean production:
Relative Maturity. Relative maturity (RM) has little effect on yield when soybeans are planted during the first three weeks of May. However, the effect of RM can be larger for late planting.
When planting soybean late, the latest maturing variety that will reach physiological maturity before the first killing frost is recommended (Table 1). This is to allow the soybean 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 1. Recommended relative maturity (RM) ranges for soybean varieties planted in June and July in northern, central, and southern Ohio.
|Planting Date||Suitable RM|
|Northern Ohio||June 1-15||3.2-3.8|
|Central Ohio||June 1-15||3.4-4.0|
|Southern Ohio||June 1-15||3.6-4.2|
Figure 1. Partial economic return by seeding rate for double-crop soybean planted in Clark County, Ohio.
Row Spacing. Double crop soybeans should be produced in narrow rows- 7.5 to 15-inch row spacing. The later in the growing season soybeans are planted, the greater the yield increase due to narrow rows. Soybeans grown in narrow rows produce more grain because they capture more sunlight energy, which drives photosynthesis.
Seeding Rate. Harvest population for mid- to late June plantings should be between 130,000 to 150,000 plants/acre. Harvest population for early July plantings should be greater than 180,000 plants/acre.
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Harvest plant population is a function of seeding rate, quality of the planter operation, and seed germination percentage. It depends on such things as soil moisture conditions, seed-soil contact, and disease pressure.
Figure 1 shows the partial economic return by seeding rate (grain price of $9.44/bu and seed cost of $0.43/1000 seeds) for double-crop soybean planted in Clark County, Ohio. In June, the optimum seeding rate was >250,000 seeds/acre, while in July, the optimum seeding rate was 213,000 seeds/acre.
The average harvest population for soybean planted in June at 250,000 seeds/acre was 143,000 plants/acre (57% of the seeding rate) due to heavy rainfall after planting. The average population for soybean planted in July at 250,000 seeds/acre was 204,000 plants/acre (82% of the seeding rate).
For additional information on double-crop soybean see here.