Double Cropping Soybeans

Some Ontario soybean producers are considering the feasibility of double cropping soybeans after cereals. Over the past few years, cereal harvests have been early and late season growing conditions have been excellent. However, there has been relatively little research conducted in Ontario to determine best management practices for double cropped soybeans.

Risks

Dry conditions during mid-summer seeding can be a challenge in plant establishment. The biggest difficultly to double cropping soybeans is the risk of an early fall frost. If temperatures fall low enough, the soybean plant will shut down. If this frost occurs before seeds have been formed in the pods, there is nothing to harvest.

Figures 1. Planting soybeans into winter barley stubble took place on July 11, 2012 in very dry conditions near Mitchell.

Figure 1 - Planting soybeans into winter barley stubble took place on July 11, 2012 in very dry conditions near Mitchell.

2012 Trials

In order to provide useful recommendations for double cropping soybeans in Ontario, an OMAFRA project was undertaken to test management practices to increase the likelihood of a successful crop. The initial study was to determine optimum seeding rates for double crop success (100,000, 200,000 and 300,000 seeds per acre) and to test the appropriate maturity (variety) to seed. Each of these treatments were randomized and replicated three times at a field scale in three separate trial locations.

In 2012, trials were planted at three locations, two in Perth County near Mitchell, and one in Middlesex County, near Lucan. The Bornholm site was planted on July 11 after winter barley. The other two sites were planted on July 23 and 24 after winter wheat (Figure 1). There was a slight delay at the two later planted sites because of the need to remove straw. As a result, only the early-planted Bornholm site, planted July 11, made it to yield and was harvested November 23. The other two sites did not make enough yield to warrant combining due to an early October frost.

At the site that was harvested, two varieties were planted. Variety A had a CHU rating of 2,650 or a relative maturity of 0.4. Variety B had a CHU rating of 2750 or a relative maturity of 0.8. Variety A was approximately 100 CHU "shorter" than an adapted variety for the planting area. Only Variety A was used in the seeding rate experiment. The results are in Table 1.

Table 1 - Double Crop Yield for Variety A at Various Seeding Rates (2012, 1 Site)

Treatment Average Yield (bu/ac) Yield Advantage (bu/ac)
Variety A (100 000 seeds)
18.0
-
Variety A (200 000 seeds)
20.6
2.6
Variety A (300 000 seeds)
23.4
5.4

As the results show, by increasing the number of seeds planted, yield was increased substantially. This trend relates well to other seeding rate trials conducted in the past. In this study, by increasing the seeding rate from 100,000 seeds/acre to 300,000 seeds/acre, yield was increased by 5.4 bushels per acre.

Variety B was an adapted soybean variety for the area, versus the shorter day Variety A (100 CHU less). In this case, there was little yield difference between the two varieties. In future trials, a larger CHU difference will be compared to assess any possible yield gains from planting shorter maturing varieties.

Frost Damage

Figures 1 and 2 illustrate the risk that has always limited the number of double crop soybean acres in Ontario. The past year provided an opportunity to try double cropping because of the early cereal harvest. However, an early October frost was enough to kill the crop, so that there was no yield in some cases. The later the soybeans are planted, the higher the risk of crop failure due to frost.

Figures 2: A soybean plant killed by frost, the beans were planted July 23 and frost occurred in early October.

Figure 2 - A soybean plant killed by frost, the beans were planted July 23 and frost occurred in early October.

Figure 3: Soybean seed in the pod was not fully developed at the time of the killing frost

Figure 3 - Soybean seed in the pod was not fully developed at the time of the killing frost.

Bottom Line

The initial findings of this study show that higher seeding rates will increase soybean yields when double cropping, which parallels other seeding rate findings. The most critical component of double crop success is seeding immediately after cereals are harvested. Any delays due to straw removal, can lead to a complete crop loss and zero return on investment due to a killing frost.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca