Minnesota Corn: Harvest Faces Weather Challenges

The development of Minnesota’s corn crop is highly variable this year, due to numerous weather challenges and wide ranges in both planting dates and hybrid relative maturities. The rain and snow this week added even more challenges, requiring corn growers to prioritize fields for harvest and to make difficult grain-drying and storage decisions. There are several important points to consider when making these decisions.

Did the corn reach maturity before a killing frost?

Corn physiological maturity is often determined when a black layer is formed at the kernel tip. At this point, kernels have reached maximum dry matter accumulation and grain moisture will typically range from 28 to 35%. If corn is not mature before being killed by frost, a black layer will form prematurely, but grain moisture will often be greater than 35%.

Yield, test weight and quality impacts

Dr. Mark Licht at Iowa State University provides the following guidelines for corn grain loss due to frost: Grain yield decreases more the earlier a killing frost occurs (ranges from 12% in late dent up to 41% at beginning dent stage). Yield losses are also less when only leaves are killed (ranges from 6% in late dent up to 27% at beginning dent stage).

Test weight can also be impacted. The minimum test weight for No. 1 yellow corn in the U.S. is 56 pounds/bushel and 54 pounds/bushel for No. 2 yellow corn. Frost-damaged corn can be expected to have a test weight in the lower 50’s to 40’s. Lighter test weight grain can be more susceptible to breakage as well as handling and storage issues.

More fines can be generated in handling, which can hinder air flow in the bin. Although frost-damaged corn can have lower grain protein and digestibility, animal feed is a good outlet for this grain due to the potential for dockage at the elevator and quality issues that hinder the ability to store the grain safely for an extended period of time.

Drying and storage impacts

Grain moisture of frost-injured corn is deceptively low because the outer portion of the kernel dries quicker than the interior. Often grain moisture will be 1 to 2 percentage points higher than many grain moisture meters will indicate. Newer 150 mhz units used by many elevators will be more accurate.

Frost-killed corn should be dried 1 to 2 percentage points lower than the typical 14 to 15% moisture content, and cooled as quickly as possible. It will take more energy per unit of moisture removed to dry frost-damaged corn. Note that storage life drops rapidly as corn test weight falls below 53 pounds/bushel.

What can be expected for drydown in the field?

The degree of drydown in the field depends on several factors:

  • Maturity of the corn when it was frost-damaged or killed
  • Hybrid
  • Moisture content
  • Air temperature
  • Relative humidity
  • Solar radiation
  • Wind speed

Field drying normally is more economical than mechanical drying until mid to late October in Minnesota, while mechanical high-temperature drying is more economical than field drying after that, according to Dr. Ken Hellevang, Extension Engineer at North Dakota State University.

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Corn standing in the field may dry about 2.5 percentage points per week in Minnesota during October, assuming normal weather conditions, and about 1 percentage point per week during November. Corn at 35% moisture content on Oct. 11 might be expected to dry to about 27% by Nov. 1 and about 22% by Dec. 1, according to Dr. Hellevang. Therefore, corn moisture content at harvest likely will be in the mid-20% range this year.

Dr. Hellevang recently outlined additional corn drying and fan speed recommendations for the higher moisture corn we are dealing with this year in his article: Expect High Moisture Corn at Harvest.

Stalk quality

Note that stalk quality is always a concern when leaving corn in the field to dry. Corn that was subject to environmental stress earlier in the growing season, such as too little or too much water, poor root development due to compaction, or nutrient deficiency, may lodge more easily and should be prioritized for earlier harvest. Corn with poor stalk quality due to insect and or disease pressure should also be targeted for earlier harvest.


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