Some years, soybean producers must plant at a later-than-optimal date. Fortunately, you can still achieve adequate yields.
Here, we share strategies for soil conditions, seeding rates, planting dates, maturity selection and other factors for success with late-planted soybeans.
Soil temperature and conditions
Wet soils
While it’s important to plant soybeans as soon as possible, avoid the temptation of planting when soils are too wet.
Soil conditions at and after planting usually influence how successfully the crop establishes. Pulling implements and the planter through, or driving on, wet soil can cause soil compaction and smearing.
Smearing and soil compaction
When a planter’s double-disc openers cut through wet, heavy soil, sidewall smearing can occur. This results in compacted soil around the seed that’s difficult for seedling roots to penetrate.
Seed furrows can also open up after heavy soil dries when planting in wet conditions. This leads to poor seed-to-soil contact and poor stand establishment.
To limit soil compaction, keep axle loads under ten tons and properly maintain tire air pressure. This helps the soil, plus it will help your tractor run more efficiently and with less slippage.
On wet soils, use the lightest tractor that can get the job done.
Ideal planting conditions
Soybean has delicate seed, so it benefits when planted about 1.5 inches deep, modestly firmed into the seed furrow, covered by relatively loose soil and into soils that are 60 to 70 degrees Fahrenheit.
Planting in cool and wet conditions
If you plant in marginal conditions, soybean emergence can almost be eliminated due to even modest soil crusting and the lack of oxygen in saturated soils. This is why it’s important to pay attention to the five-day forecast prior to planting.
In some fields, growers may need two planting dates: One for the majority of the field when it is dry enough, followed by a second planting date to fill in the remaining low areas after they have sufficiently dried.
Planting in cool and wet conditions may lead to poor germination and seedling diseases such as Pythium. Extended cold and rainy periods after planting magnify these problems.
Seeding rates
University of Minnesota Extension research indicates that, under ideal conditions, southern Minnesota producers should plant about 140,000 live seeds per acre (Table 1).
More guidance on Minnesota soybean seeding rates
Producers in central and northwestern Minnesota need increased seeding rates.
Soybeans grown there require harvest stands of approximately 125,000 to 150,000 plants per acre to maximize yields. This is likely due to shorter-statured soybeans with fewer total nodes, which these regions often produce.
More guidance on Minnesota soybean seeding rates
Table 1: Minnesota seeding rate recommendations by maturity group
| Maturity group | Maturity group |
|---|---|
| Group II soybeans | 140,000 live seeds per acre |
| Group I soybeans | 150,000 live seeds per acre |
| Group 0 soybeans | 160,000 live seeds per acre |
| Group 00 soybeans | 170,000 live seeds per acre |
Late planting: Strategies for success
Early-May plantings usually result in maximum yields, while delayed planting results in yield loss (Table 2).
Research shows a 2 percent yield loss on May 10, a 3 percent yield loss on May 15 and a 6 percent yield loss on May 20 (or 94 percent of normal yield).
Table 2: How planting date affects soybean yield
| Planting date | Yield loss | Yield potential |
|---|---|---|
| May 1 | 0% | 100% |
| May 5 | 1% | 99% |
| May 10 | 2% | 98% |
| May 15 | 3% | 97% |
| May 20 | 6% | 94% |
| May 25 | 9% | 91% |
| May 30 | 13% | 87% |
| June 4 | 18% | 82% |
| June 9 | 24% | 76% |
| June 14 | 30% | 70% |
June planting
Yield potential drops quickly as planting is delayed through June, according to soybean planting date trials conducted in Lamberton between 1998 and 2004.
Planting soybeans around June 1 will provide about 85 percent of a maximum theoretical yield, but if you plant on July 1, you can expect yields to be about 50 percent of those of early-planted soybeans.
This relatively linear decrease in yield potential through June indicates you’d lose around 1 percent (or about 0.5 bushels per acre) of the soybean yield potential each day you delay planting.
Adjust soybean maturities when planting after about June 10.
At this point, plant a soybean variety with a relative maturity (RM) rating of 0.5 units shorter than your original soybeans. For instance, if you live in central Minnesota and originally planted a RM 1.7 variety, by about June 10 switch to an early group I soybean (such as a RM 1.2).
If replanting in late June, switch to a variety that is one full maturity unit shorter than you’d normally plant.
The only caveat is producers who normally plant very long-season varieties would need to make the switch earlier. Likewise, producers who normally plant short-season varieties can hold with their current varieties a bit longer.
Soybean trials examining how planting date, row spacing and population interact in southern Minnesota have shown that producers do not need to alter row spacing and population when planting soybeans at later-than-optimal dates.
While narrow rows produced larger yields in the late-planted fields, this advantage was no larger than with early-planted soybeans. Similarly, increased seeding rates did not preferentially benefit later-planted soybeans.
Soybean does not require deep planting for proper root development.
However, continue closely monitoring soybean planting depth so seeds are placed on top of the moisture and will have ample access to moisture prior to emergence. This helps establish a uniform stand.
Hicks, D.R. & Naeve, S.L. (2018). Soybean damage and replanting.
Reviewed in 2018