Strategies with Delayed Soybean Planting

Strategies with Delayed Soybean Planting

Strategies to use with delayed soybean planting
  • Relative maturity – may need to switch to shorter maturities
  • Row spacing – why narrow is usually better
  • Custom planting – finish planting sooner
  • Seeding rate – may or may not need to be adjusted

According to the USDA NASS June 10 crop report, soybean planting was 79% complete compared to the five-year average of 94% and last year’s 97%. In addition, lots of acres were planted into marginal conditions and may have poor stands needing to be replanted. With the delay in planting, agronomic practices such as relative maturity, row spacing, and seeding rate may need to be adjusted. The following are considerations when planting in the second half of June or into July. 

Relative Maturity

Compared to corn, we don’t need to make as drastic a change in soybean maturity groups (MG) compared to the normal for your area. Late-planted soybeans will typically require fewer days to reach maturity than earlier planting dates.

Table 1 shows the soybean growth and development model based on a 2003-2004 planting date study at Lincoln (average response of 14 varieties - 3.0 to 3.9 MG). Note the date that plants reached R8 or full maturity. In 2003, the mid-June planting date delayed maturity by seven days compared to the early May planting date. In 2004, mid-June planting delayed maturity by 22 days, even though the planting date was 50 days later. Because soybeans are photoperiod sensitive, flowering and development will be triggered by day length, resulting in similar maturity among planting dates, although earlier plantings will have more nodes and yield potential. 

Table 1. UNL soybean growth and development results from 2003 and 2004 at Lincoln, Nebr.
2003V1
Days after
planting
R8
Days after
planting
Date of R82004V1
Days after
planting
R8
Days after
planting
Date of R8
May 2 32 158 Oct. 7 April 28 26 146 Sept. 21
May 17 24 148 Oct. 12 May 16 23 126 Sept. 29
May 30 19 136 Oct. 13 June 2 17 130 Oct. 10
June 16 12 120 Oct. 14 June 17 17 118 Oct. 13

Results from a 2013 South Dakota State University variety trial reinforces these findings.  Maturity ratings on 55 varieties from 10 companies, ranging from 1.8 to 2.9 MG, was conducted at the Southeast Research Station in Beresford, SD. Study results showed the equation for days to maturity was:

Days to maturity from planting = 5.4*MG + 113 days. 

In 2013, switching from a 2.8 to a 1.8 MG reduced the time to maturity by only five days, when planting in mid-June as compared to late April. Changing maturity groups during this planting period did not make a large difference in maturity, something to consider if you were thinking about changing to a much earlier maturity group.

However, if planting after June 15, you may want to go with the earliest maturity group number recommended for your 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. Frost before maturity becomes a concern with late June or July plantings.

Screen shot from SoyWater showing an R7 date.
Figure 1. Screenshot of SoyWater showing R7 date.

One way to evaluate different maturity groups is to use SoyWater, http://hprcc-agron0.unl.edu/soywater/index.html. By entering your field location, planting date, and MG, SoyWater will give you a predicted maturity (Figure 1). When evaluating maturity, the key growth stage to be worried about is reaching R7, which is when one normal pod on the main stem has reached its mature pod color. Once plants reach this stage, metabolic traffic from the plant to the seed has ceased so a fall freeze is not going to affect the yield of wet but physiologically mature seeds. Keep in mind though that the dry down of the seeds from 60% moisture to a harvestable level will take longer given the cooler temperatures experienced later in the fall.

Based on information from SoyWater, Table 2 shows scenarios for three maturity groups (1.0 to 3.0) planted on five dates at Schuyler. Using 30 years of climate data, the average first 28°F freeze for Schuyler is October 14, with the earliest occurring on September 19 in 1991 and the latest on November 6 in 1998. With a June 15 planting date, the 3.0 MG should reach maturity well before the average first freeze. The shorter maturities reach R7 well before the average freeze, resulting in minimal to no freeze risk, but they will likely give up yield potential.

Table 2. SoyWater simulations for three maturity groups on five planting dates.
Planting DateDate of R7 1.0 MGDate of R7 2.0 MGDate of R7 3.0 MG
May 1 August 12 August 28 September 6
May 15 August 16 August 31 September 9
June 1 August 22 September 5 September 14
June 15 August 29 September 12 September 22
July 1 September 10 September 25 October 7

Row Spacing and Custom Planting

The next consideration is row spacing. With late planting, narrower row spacing is generally recommended. 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. 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.

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. When using a drill, 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 been 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.

If your operation does not own a narrow row planter or drill, there are now two strong considerations for custom planting. First, if there can be two or more planters operating at a time, your last acres will be planted sooner and take less of a yield hit, especially with additional rain delays in June (e.g., 5/8 bu/acre per day at 7 days = 4.3 bu/ac advantage). Second, you can capture the yield advantage of narrow rows. Regional studies have shown a 3-4 bushel/acre yield advantage to narrow row spacing (20 inches or less).

Seeding Rate

Many sources recommend increasing seeding rates by 10% after early June for both drilled and planted beans. We understand this line of thinking to attempt to improve canopy closure for yield and weed control by having more plants per acre, but there is some debate around this practice. An Iowa State study published by DeBruin and Pederson in 2008 did not find a seeding rate (75K, 125K, 175K, 225K) by planting date (late April, early May, late May, and early June) interaction for yield, indicating no need for increased seeding rates at later planting dates. In addition, given that there is a wide range of seeding rates planted across the state, a blanket statement of a 10% increase may not be appropriate. Growers will need to evaluate this recommendation based on their normal seeding rates and their planting equipment.  

It’s also important to be aware of crop insurance considerations and your options.

In summary, soybean producers still planting should be

  • considering reducing their maturity group no more than 0.5-1.0 compared to normal,
  • narrowing their row spacing, and
  • evaluating their seeding rates based on their situation.