Management options for double crop soybeans

Information for double crop soybean producers to assess their crop and make important management decisions.

Planting double crop soybeans is not recommended in Michigan due to the risk associated with this practice. However, many producers tried it this year due to the early wheat harvest and high soybean price. With the growing season winding down, producers will need to decide if the double crop beans should be harvested as forage, harvested for grain or plowed down as a green manure crop.

The first step in making this decision is to determine the development stage of the beans. This is essential to predict if the beans will reach the R6 growth stage prior to the first killing frost. Soybeans that reach R6 prior to a killing frost are generally considered salvageable for grain.

When determining the growth stage, focus your attention on the upper four nodes on the main stem having unrolled leafs. Pick the most mature pod on the upper four nodes from plants at several locations in the field. If the seeds in the pods are 1/8 inch in diameter, the plants are at the R5 growth stage. If the seed in the most mature pods in the upper four nodes completely fills the pod cavities, the plants have reached the R6 growth stage. It typically takes 15 days for soybeans to progress from the R5 stage to the R6 stage. Late-planted soybeans will develop faster than this. so it may only take 10 to 12 days to go from R5 to R6. It will take another 10 to 12 days to reach R7 (one pod on the main stem has reached its mature color). At R7, the crop has reached physiological maturity and yield losses due to frost and freeze will be minimal.

The next step is to estimate the yield potential of the crop based on the plants per acre, pods per plant, seeds per pod and seed size. A worksheet for estimating soybean yields prior to harvest is available. Table 1 provides some estimated yields at various populations and pod counts.

Table 1. Estimated yields for double crop soybeans for various plant populations and pods per plant.


Pods per plant


10

20

30

Plants per acre

Estimated yield (bu/ac)

100,000

11

22

33

120,000

13

27

40

140,000

15

31

46

160,000

18

35

52

180,000

20

40

60

Assumptions: An average of two beans per pod and an average seed size of 3,000 seeds per pound.

If the yield potential is greater than 15 bushels per acre and the crop will be at or beyond the R6 growth stage at the time of a killing frost, the crop should be harvested for grain. Please see the Michigan State University Extension article on Harvesting, handling and storing frost-damaged soybeans.

If the beans will not reach the R6 growth stage prior to a killing frost or the yield potential is less than 15 bushels per acre, the crop should be harvested for forage. Assess marketing or feeding options for the soybean forage before making this decision. Additional information on harvesting soybeans for forage is available in the MSU Extension article Harvesting drought-stressed soybeans for forage.

If selling or feeding the immature or low-yielding soybeans as forage is not a viable option, the crop can serve as a cover crop or it can be incorporated into the soil when time and soil conditions permit. In either case, a significant nitrogen credit can be applied toward the 2013 corn crop. A rough estimate of the credit is 20 to 40 pounds of nitrogen per acre.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.

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