By Jim Specht, UNL Professor of Agronomy and Horticulture and Jenny Rees, UNL Extension Educator, University of Nebraska-Lincoln
This year has been another interesting one. With recent, much needed rains, soybean planting continues to be delayed. According to the USDA NASS crop report on May 28, soybean planting was 63% complete compared to the average of 79%. As we approach June, we have received questions regarding how agronomic practices should change — if at all — for late planting. The following are considerations when planting in June or July.
Several have asked if narrowing rows at this time of the year would be a good idea. Because the longest day of the year occurs on June 21, and all days get shorter after that, soybeans need as much sunlight as possible to make pods, seed, and yield. We like to see that canopy "green to the eye by the fourth of July" which may or may not be possible at this point. To close the canopy sooner, you may want to consider planting narrower than 30 inches. UNL research has shown that up to 5/8 bu/ac can be lost for every day after May 1 that planting is delayed. Thus, there is now a need to mitigate, to the degree still possible, the loss in the crop’s ability to capture all incoming sunlight from now on.
In Figure 1 DuPont Pioneer Agronomy Research summaries several University studies conducted between 1997 and 2009. Five studies compared drilled versus 30-inch rows and found an average 4.1 bu/ac yield increase in drilled rows. Six studies showed essentially no yield difference when comparing drilled rows to 15-inch planted rows. Six studies showed a 3.6 bu/ac yield advantage with 15-inch rows compared to 30-inch rows.
Cautions with Narrow Rows
While narrowing rows can help close the canopy quicker at this point, there are a few cautions to consider. In general, non-uniformity of seed depth placement and of seed-to-seed placement within the row is more of a concern with drills versus 15-inch or 30-inch planter units. Increasing seeding rates by 10% (potentially up to 20%) may be necessary to fill in gaps that occur. This may not be as much of a concern with newer precision planting drills. Also, narrowing rows can favor diseases such as sclerotinia stem rot (white mold of soybean) that like a humid, moist canopy. While sclerotinia has not a major issue in Nebraska, it has been observed in some fields; we would not recommend narrow rows if you have experienced a problem with white mold in your fields.
Generally, with late planting (after June 15) it is still best to stick with varieties that are in the maturity-adaptation range for the given region. You could go with the earliest maturity group (MG) number recommended for the given area, such as reducing your MG number by 0.5-1.0, but don’t try using a maturity group much shorter than that or you will sacrifice yield potential.
There have been some seed quality issues with soybean this year that have caused producers to look at seed in other maturity groups. Some producers have looked at later MG than that typically recommended for their area in order to get better seed. At this point in the season, that can present a risk for frost. We would instead recommend looking at the earlier end of the recommended MG for your area.
Increasing seeding rate by about 10% after early June for drilled and planted beans also can help achieve canopy closure.
It’s also important to be aware of crop insurance considerations and your options. For more on this, please see the CropWatch article, Late Planting Provisions for Multiple Peril Crop Insurance.
In summary, right now soybean producers should be considering narrowing their row spacings, increasing their seeding rates by 10%, and maintaining their current maturity group (or reducing it no more than 0.5-1.0).
If you're planting soybeans late, consider
- using narrow row spacings;
- increasing seeding rates by 10%; and
- maintaining your current maturity group (or reduce it by no more than 0.5-1.0).
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Figure 1. Average yield results from seven soybean row spacing studies published in the last 10 years. (Courtesy of DuPont Pioneer Agronomy Research)
Table 1. Locations, years and row spacings included in soybean row spacing studies summarized in Figure 1.