Double-crop soybean recommendations

By Dr. Laura Lindsey and Eric Richer, CCA, Adapted from C.O.R.N. 19-2021

Wheat harvest is rapidly approaching, and with relatively high soybean prices, we anticipate many growers will be interested in double-cropping soybean after wheat. According to the U.S. drought monitor (https://droughtmonitor.unl.edu/), areas bordering Michigan are abnormally dry, but throughout the rest of the state, soil moisture is good. Early wheat harvest, high soybean prices, and adequate soil moisture make double-crop soybean an attractive option in 2021.

The two primary requirements for successful double-cropping are: 1) adequate time to produce the soybean crop and 2) adequate water. In Ohio south of I-70, double-crop soybean production is common as there is generally adequate time to produce soybean; however, yield can be variable depending on soil moisture and rainfall. In Clark County Ohio, we’ve had double-crop soybean yield averages of 50 bushels per acre, but as low as 21 bushel per acre when water was limiting. North of I-70, double-crop soybean is less common but occurs when the wheat harvest is early and/or when soybean prices are high. Table 1 shows full-season soybean yield compared to double-crop soybean yield in a three-year study conducted at the Northwest Agricultural Research Station in Wood County. In Wood County, we’ve had double-crop soybean yield as high as 57 bushels per acre in 2018 and as low as 12 bushels per acre in 2016 (2016 was a hot and dry year.)

Table 1. Full-season soybean yield compared to double-crop soybean yield at the Northwest Agricultural Research Station in Wood County.

 Full-season soybean yieldDouble-crop soybean yield
201649 bu/acre

 

(planted May 25)

12 bu/acre

 

(planted July 1)

201761 bu/acre

 

(planted May 6)

29 bu/acre

 

(planted July 6)

201862 bu/acre

 

(planted May 24)

57 bu/acre

 

(planted July 5)

AVERAGE57 bu/acre33 bu/acre

Cultural practices, such as row spacing, seeding rate, and relative maturity, may be adjusted to help maximize soybean yield in the double-crop system.

Row spacing

Double-crop soybean should be produced in narrow rows at 7.5- or 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.

Double-Crop Soybeans, photo credit: OARDC

Seeding rate 

The harvest population for mid-to-late-June planting should be between 130,000 to 150,000 plants per acre. The harvest population for early-July planting should be greater than 180,000 plants per acre. Harvest plant population is a function of seeding rate, quality of the planter operation, and seed germination percentage and depends on soil moisture conditions, seed-soil contact, and disease pressure. Generally, seeding rates between 200,000 to 250,000 seeds per acre result in these targeted harvest plant populations.

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 greater for late planting. When planting soybeans late, the latest maturing variety that will reach physiological maturity before the first killing frost is recommended (Table 2). This selection allows 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 2. Recommended relative maturity (RM) ranges for soybean varieties planted in June and July in northern, central, and southern Ohio.

 Planting DateSuitable RM
Northern OhioJune 1-153.2-3.8
June 15-303.1-3.5
July 1-103.0-3.3
Central OhioJune 1-153.4-4.0
June 15-303.3-3.7
July 1-103.2-3.5
Southern OhioJune 1-153.6-4.2
June 15-303.5-3.9
July 1-103.4-3.7

Straw removal  

Finally, while straw removal may delay double-crop soybean planting a day or more, it will improve soybean emergence and add value to the wheat enterprise.  Removing the straw will improve the planter or drill’s ability to provide good seed-to-soil contact without hair pinning (when straw gets trapped in the seeding trench, increasing air spaces) and improve soybean emergence.  Straw yields in Ohio range from 1.2 to 1.8 tons per acre. This tonnage creates additional value for a wheat enterprise but will remove approximately $14-15 per acre of phosphorus and potassium value (Ohio Enterprise Budgets).

In summary, factors like an anticipated early wheat harvest and higher than normal soybean prices create a logical opportunity for double cropping soybean in Ohio this year.  Producers who chose to double-crop should plant as soon as possible after wheat/straw harvest and are encouraged to follow these cultural practices: use narrow rows, increase seeding rates, use a relative maturity suitable to their region and consider removing straw.  Happy double-cropping!

 

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