Source: Penn State Extension

By Delbert Voight, Agronomist

This year has changed the game when it comes to double cropping soybeans. Typically as July progresses after small grain harvest growers no-till soybeans. The late timing this year might be an issue for other re-crop forages after small grains, however, with continued rains and ideal planting conditions many growers will continue to plant. I have seen fields planted directly after barley that did emerge almost immediately with the rains. We have ample moisture in the soil right now and it appears that some is in the forecast.

It takes about 90 days for soybeans to develop pods and dry seed, so if we get an average frost we need to be planting beans by July 15-Aug. 1 in Pennsylvania to be in the window for harvest based on average frost-free dates. The Pennsylvania Average First Frost date map indicates that some areas frost about Nov. 1 in Pennsylvania, so those areas could still plant soybeans. Here are some other considerations.

  1. Plan to establish at least 180,000 plants per acre, so to achieve that a minimum planted population of 200,000 is recommended for double-crop soybeans prior to July 5, after which 220,000 plants per acre might be in order to ensure ideal canopy cover.
  2. Plant narrow rows. 15- and 7-inch or narrower rows are preferred. There is less time for the soybeans to gain height to pod, so the narrow rows allows for more beans to grow at higher populations.
  3. If the field has visible weeds, do a burndown to ensure weed competition is kept to a minimum.
  4. Set a realistic economic target. Traditional double crop yields of 30 bushels per acre is not out of the question (we typically see about a 50% response the first week of July) and at $9-per-bushel soybeans, there is some but not a lot of room to spend input costs over and above what’s needed to make the crop. This simple table to the right best illustrates the impact of planting date.
    Approximate yield response of
    soybean to changes in planting date.
    Date Percent of Full Yield Potential
    May 10 100%
    May 20 98%
    May 30 95%
    June 10 88%
    June 20 76%
    June 30 70%
    July 10 60%
  5. Be aware that the potential for an early frost is possible, and if forage is needed consider management for a forage use of the soybean. If the goal is forage supply, then perhaps sorghum sudangrass or another annual crop may be a better selection.
  6. Maturity considerations. There has been talk about moving to a shorter maturity. Past experience in this area would suggest full-season maturities for double crops may out-yield short-season maturities. Our double-crop soybeans planted with full maturity over the last several years have matured with no problems in the fall. Last season, which was also a wet season, our Lancaster Double-Crop Soybean Trials averaged 54 bushels per acre planted on June 24 at 220,000 plants per acre. To view the maturity and varieties please visit Pennsylvania Soybean Performance Test 2014. 

Dave Holshour from Virginia Tech related the impact of maturity on delayed planting. For April and May plantings, a 3-day delay in planting resulted in a 1-day delay in maturity. For example, planting 30 days late would cause a 10-day maturity delay. However, in the June and July plantings, a 5-day delay in planting resulted in only a 1-day difference in maturity.

Most important is to plant a maturity group that would grow as long as possible in the vegetative state to gain height before flowering, which allows for an adequate canopy for maximum yield and still mature before a frost.

Finally, Penn State agronomist Greg Roth and I are looking at other parameters for double-crop soybeans that might prove useful in the future to further add yield to this late-plant timing. We are revisiting row width, date of planting, growth regulators, seed treatments and other practices to ensure recommendations stay curent. Stay tuned for more information as the Mid-Atlantic begins to focus on double-crop timing.