Producers have been asking about the idea of early soybean planting in northern Minnesota as soybean production pushed further north.
Soybean acreage has dramatically increased with better yielding varieties and the introduction of glyphosate-tolerant soybean.
To answer the question "How early do we dare plant soybeans in northwest Minnesota?" University of Minnesota Extension carried out a five year (2006-2010) research project with grant funding from the Minnesota Soybean Research & Promotion Council.
We found that with soybean following sugarbeet in a rotation, the soil is dry enough to facilitate early planting, and that early planting could increase dry matter accumulation and the number of nodes and branches on the plant.
These factors ultimately lead to increased yields. The drawback to early planting was the risk of spring frost killing the soybean crop if seeded too early.
The research took place in Crookston over five growing seasons, and included weekly planting of two soybean varieties with relative maturities of 00.9 and 0.4 planted on eight consecutive weeks. Planting started as soon as the soil was fit in the spring, which ranged from April 10 in 2010 to April 26 in 2009 with an average first planting date of April 19. Planting continued for 10 weeks in 2010.
Each year, we collected data on these factors: days from planting to emergence, hourly soil temperature, hourly air temperature, population, dry matter yield, oil percentage, protein percentage, moisture and grain yield.
Early planting increased the dry matter yield and number of nodes and branches per plant; however, this did not always translate into increased yield. Yield results were variable for very early planting (April 10 to May 15), with yield penalties of 0-5 percent or up to 3 bushels per acre.
Average yield penalties for very late planting (late May to early June) averaged 5-26 percent or 3-16 bushels per acre. Populations were not significantly impacted by early planting and delayed emergence. There was a 1.1-percent increase in oil content and a 0.7-percent decrease in protein content with early versus late planting of soybean.
The main environmental factor contributing to whether the early or the late relative maturity out yielded each other was related to the amount of precipitation received in August. A dry August favored the early relative maturity soybean. Freezing temperatures were not encountered in any of the five years of the trials.
The recent trends of a more sub-tropical climate extending further north into Minnesota place the odds more favorable for early planting to be successful. Pushing the planting window ahead to April 21 versus May 10-15 for the Crookston region may result in only a 10-percent chance that the air temperature will drop below 28 degrees at soybean emergence.
When environmental factors are favorable (soil temperature and moisture), northern soybean producers should be ready to capitalize on them even if the calendar has not turned the page to May.
The research results from these trials can be found on the University of Minnesota Northwest Research and Outreach Center website at: http://
z.umn.edu/2vv under the section "On-Farm Cropping Trials Northwest and West Central Minnesota."
For more educational information and tools, visit www.soybeans.umn.edu. The website is a cooperative effort among the University of Minnesota, University of Minnesota Extension, and the Minnesota Soybean Research and Promotion Council. More Extension information about other commodity crops can be found at www.extension.umn.edu/