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Corn and Soybean Planting when it is Cold and Wet

By Jeff Coulter, Seth Naeve, and Dave Nicolai

Unseasonably cold temperatures, wet conditions, and potentially snow are impacting corn and soybean planting in much of the Upper Midwest. The regional climate service partnership between the National Oceanic and Atmospheric Administration and U.S. Department of Agriculture released the following weather briefing for the Upper Midwest on April 27, 2017:
  • Overall weather predictions:
    • Freezing temperatures in some freeze-sensitive areas during the next 2 weeks.
    • Cool air and soil temperatures, along with rain and/or snow are possible through the next 2 weeks.
  • Temperature outlook for May 3-9:
    • Odds favor below-normal air temperatures.
    • Odds slightly favor much-below-normal air temperatures.
    • Greatest chances in the western Great Lakes to Upper Midwest.
  • Precipitation outlook for May 3-9:
    • Odds favor above-normal precipitation.
    • Greatest chances in the Great Lakes to Mississippi River Valley.

Corn planting – Factors for success

Soil conditions

Avoid tillage and planting when soils are wet. In general, a field is ready for seedbed preparation when soil in the depth of tillage crumbles when squeezed. Pre-plant tillage when soils are wet can create a cloddy seedbed that reduces seed-to-soil contact. Achieving excellent seed-to-soil contact is essential for rapid and uniform imbibition of moisture by seeds and uniform emergence. Tillage when soils are wet can also create a compacted layer below the depth of tillage that can restrict root development.

Sidewall compaction occurs when planter disc openers cut through wet fine-textured soil, resulting in compacted soil around the seed that is difficult for nodal roots to penetrate. In addition, seed furrows can open after planting in such conditions, resulting in poor seed-to-soil contact.

Planting depth

A planting depth of 2 inches is optimal for corn in most situations in Minnesota. Shallow placement of seed increases the risk of poor nodal root establishment. High planting speeds that result in bounce of planter units and shallow placement of some seeds should be avoided, as this can cause variable emergence and hinder nodal root development.

Planting date

In years like 2017 when few growing degree days are accumulated during late April and the first half of May, maximum corn yield can still be obtained when planting occurs by mid-May. In most cases, corn yield in Minnesota is reduced when planting is delayed beyond mid-May. If planting is delayed beyond the third week in May, switching late-maturity hybrids to earlier-maturity hybrids reduces the risk of corn freezing in the fall before it has reached maturity.

Soil temperature

Germination of corn requires that seeds imbibe 30 percent of their weight in water and that soil temperature be 50°F or warmer. More time between planting and emergence increases the potential for stand establishment problems, since imbibition of water by seed is not influenced by soil temperature. Risk of stand establishment problems is reduced if soil in the seed zone has reached or is near 50°F at planting and is expected to warm.

Soybean planting – Factors for success

Weather and soil conditions

Avoid planting with extreme cold and wet weather in the near-term forecast. The lack of oxygen in saturated soils and the formation of a soil crust of even modest strength can almost eliminate soybean emergence. Therefore, it is important to pay attention to the 5-day forecast prior to planting. Planting in cool and wet conditions may lead to poor germination and seedling diseases caused by pathogens such as Pythium. These problems are magnified by extended cold and rainy periods after planting.

Planting date

Planting soybean in Minnesota on May 10 results in only a 2% yield loss, on average, compared to a 3% yield loss for May 15 and a 6% yield loss for May 20:
Planting date Yield loss Yield potential
percent (%) % of maximum
May 1 0 100
May 5 1 99
May 10 2 98
May 15 3 97
May 20 6
May 25 9 91
May 30 13 87
June 4 18 82
June 9 24 76
June 14 30 70

Soybean maturity

Recent planting date research at the University of Minnesota supports the historical planting date data shown above; however, we have found that soybean maturity affects the rate of yield loss somewhat. Planting very full-season varieties (+0.5 MG) for a location will tend to produce greater overall yields, but only when those soybeans are planted by the first week of May. By mid-May, any yield advantage of longer-than-adapted varieties is lost. Likewise, a somewhat shorter-season variety (-0.5MG) can be planted through the end of May with little yield penalty; however, the yield potential of short-season varieties is lower than those of adapted or longer-than-adapted lines.

Again, yield penalties throughout May depend on the soybean maturity. Long-season varieties have a greater yield potential, but tend to have a greater yield penalty related to late planting. Short-season varieties will yield less than long-season varieties when planted early, but yield similarly when planted in mid- to late-May.

While we hope that farmers will not be held out of the field for long, it’s important to keep the maturity switching recommendations in mind. The standard University of Minnesota guideline is that soybean maturities should not be adjusted until June 10. Soybean producers who start with very long-season soybeans, should consider switching by June 1. Those who plant short-season soybean varieties can hold their maturities until late-June.

More educational resources are available at Extension's CropProduction website.
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