For the third year in a row, soybean planting is being seriously delayed by weather in Minnesota. Like with the previous couple of years, it’s a slow-go across most of the state.
On Monday, May 20th, the USDA Minnesota Crop Progress Report indicated that 22% of Minnesota’s soybean crop was planted, four days behind 2018 and eleven days behind the five-year average.
Averages being what they are, many parts of the state report that the rate of soybean planting has been highly variable depending on rain patterns and soil conditions. For example, soybean and corn planting are significantly behind in southwestern and western Minnesota, but close to normal for northwestern Minnesota.
While south central Minnesota growers have made good progress to date for corn planting, soybean planting has lagged due to spring tillage and fertilizer applications. Many areas of southeastern and eastern Minnesota have received excessive rainfall in May which was also complicated by colder than normal weather resulting in less than ideal planting conditions.
Yield penalty with delayed planting
Without beating around the bush, how much yield are we losing with these delays? Last year reaffirmed that we can have good yield with delayed planting, but remember that 2018 came with record high early-season temperatures that pushed the crop along. Coupled with late first frosts, we dodged a bullet. Let’s hope for the same in ’19.
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Our best dataset on soybean yield response to delayed planting comes from Lamberton, where Bruce Potter and Steve Quiring have been conducting date-of-planting trials since 1988. Much of the variation in yield response comes from conditions after planting – as noted above – but on average, yields tend to decline very little after mid-May planting (see Figure 1).
By June 1 planting, we can expect yields of around 90% of the potential based on planting date alone. The yield curve tends to drop off in June with an overall daily decline of about 1% per day from June 1 through 30. Early June daily losses are less than 1%, and daily declines later in the month are greater than 1%.
Farmer-reported yields support this research. Farmers in south central Minnesota reported a 0.4 bushel per day decline in yields from late April planting through early June planting.
Managing soybean maturities
So, how should later planted soybeans be managed? The first question asked is always about soybean maturities (MG) and switching varieties. Conventional wisdom states that we should not switch until June 10. The only caveat here is the starting point. Farmers that have chosen very long soybean MGs for their area should consider switching a bit earlier. Those with short MG seed need not be concerned until late June.
We conducted a study of soybean MGs and planting dates at St. Paul and three sites (Arlington, Hancock, and Spooner) in Wisconsin in 2014-2016. MG 1.5 lines were planted at all sites. Northern sites included some earlier MGs and southern sites included some longer MGs. Figure 2 shows the yield response of MG 1.5 lines relative to the highest-yielding MG*Planting date combination at each site. Little yield was lost with planting delayed until June 1, but significant losses occurred with planting thereafter.
Figure 3 shows the yield responses for the longest soybean maturities chosen for each site (MG 2.5s in the South and 1.5s in the North). One can see that early planting and long MGs tended to result in maximum yields. Yield declines due to late planting were greater with long MG lines, but only due to a higher starting point. July 1 planted lines differed little between the common MG 1.5s and the longest lines chosen at each site.
The same data are presented in one figure here (Figure 4). Notice that maximum yields are only attained with the combination of the longest maturing soybean varieties and early planting. When planting late, there is little potential for higher yield based on MG selection. Long MG lines offer little potential for increased yields when planted late, and downside risks of planting long MG lines are likely smaller than conventional wisdom prescribes.
How about seeding rate? In a recent blog post, Adjust your seeding rate, but not your maturity group for late May planted soybean , Dr. Shawn Conlely provides some valuable data on seeding rate by population work in Iowa, Wisconsin, and South Dakota in studies planted in late May and June. Yield responses to population were not dissimilar to what we see with early seeding, with yields reaching a maxiumum at 140-160k (the highest rate tested).
Because the response was relatively flat, additional seed beyond 100k did not pay (at $65 per 140k, and $7 grain), economically.
So, what’s a farmer to do?
Even with delayed planting, maximum yields will be attained at higher seeding rates and maximum economic returns will likely occcur at much lower rates. The good news is that there is really no wrong answer here and that gives farmers a lot of flexibility based on their own situations. Optimistic farmers planning on improved markets and significant Market Facilitation Payments (MFPs) should hold with their planned seeding rates, and might be happy with earlier canopy closure with slightly increased seeding rates.
Pessimistic farmers and those significantly strapped for operating capital, or those stretching seed to cover some abandoned corn acres, could cut soybean seeding rates slightly and likely be happy with their cost savings. However, be aware that thin soybean stands will be more susceptible to environmental hazards such as crusting, sand-blasting, and hail, and are always more susceptible to late-season weed pressure.
Here are some of my don’t do’s
- Don’t panic. We’ll get this crop in the ground. We are past our optimal planting window, but there is still time for a terrific crop.
- Don’t make big changes. For the most part, follow your normal BMPs for soybeans.
- Don’t switch varieties for inferior genetics. You’ve carefully selected high-yielding lines for your farm, don’t throw that away. Genetic differences may be significantly larger than maturity effects.
- Don’t forget to manage weeds. This may mean waiting to do your tillage, or being sure that you can get your pre-emergence spray down, but don’t lose sight of this when trying to get beans in the ground.