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It’s harvest time but soils are wet or the crop may be delayed or drying down slowly and you need to decide whether to leave the crop in the field to dry down or harvest the crop at higher moisture than you’d like. Some things to consider include: the cost of drying grain for storage, risks associated with leaving the crop in the field to dry down, combine adjustments to harvest high moisture crops; reduced grain quality and storability, dealing with soil compaction, and managing variable moisture grain in the storage bin.1
Delayed maturity of corn (late planting, cool growing season, or wet soil conditions) can translate into slow drydown of mature corn grain. Temperature and humidity influence the rate of drydown, which declines quickly in late September and October (Table 1).2 Wetter grain at harvest increases the need for artificially drying of grain and increased production costs.
The longer corn is in the field, the risk of lodging, stalk and ear diseases, or reduced grain quality increases. Higher grain moisture and ear rot damage can increase the amount of fine materials in the bin, which can interfere with aeration or be a source of disease, mold, or toxins associated with ear rot.
The most important factor in handling high-moisture corn at harvest is getting the combine set up right:3
To keep wet grain going into storage from heating and losing quality, run the aeration fan continuously whenever grain exceeds 18% moisture and grain temperature is above 50°F.4 The length of time corn can be kept under temperature and moisture content before it losses ½% dry matter (the maximum loss to maintain current market grade) is shown in Table 2. General rules of thumb for the shelf life of corn are as follows: the shelf life is reduced by half for every 2% increase in moisture content over 16% and for every 10F increase in temperature over 50°F. Soybeans in storage tend to act like corn that is 2% greater in moisture content (Table 2).5 Adjust equipment to minimize the degradation of wet grain quality:6,7
Combine settings. Balance the need for aggressive shelling action to get small kernels off the cob against the extra kernel damage that is caused by aggressive shelling. Balance the need for aggressive cleaning to remove chaff and small particles against yield losses that occur when small, light kernels are blown out of the combine.
Manage fines and chaff. Fine particles and chaff affect airflow and increase mold problems in storage. Consider cleaning grain to remove fines and chaff, "core" bins to pull fines out of the center, or make sure that fines and chaff are uniformly distributed throughout the storage bin rather than being concentrated in certain areas (under the fill spout, for example).
Table 1. Field drying rates for corn in Minnesota.Coulter, J. 2008. Maturity, frost, and harvest moisture considerations for corn. University of Minnesota.
Table 2. Maximum storage time in months for shelled corn, soybean at various grain moistures.*Based on 0.5% maximum dry matter loss - calculated on the basis of USDA research at Iowa State University. Wilcke, W. and Wyatt, G 2002. Grain storage tips. University of Minnesota.
Dry grain uniformly. Check the grain moisture content of every load of corn and reset dryer controls based on changing moisture levels. Make sure that the moisture content of dried corn is low enough for safe storage (15% for winter storage, 14% for storage into spring and summer, 13% for storage a year or longer) and consider reducing these moisture levels by about a percentage point for corn that is immature, frost-damaged, or low test weight.
Dry corn gently. High drying temperatures can result in lower test weight and in more cracked and broken kernels. Natural-air drying (no heat) gives better test weight and less kernel damage than gas-fired drying. Use slow cooling methods after gas-fired drying to minimize quality problems.
Aerate stored grain to 20° to 30°F for winter storage.
Check stored grain frequently so that you can quickly address minor spoilage problems before they become costly problems.
When harvest has to proceed in wet fields, soil compaction and smearing can be a concern.Some guidelines for managing soil compaction during a wet harvest include:8
Sources: 1Nielsen, R.L. 2015. Information resources for challenging crop harvest conditions. Purdue University. 2Coulter, J. 2008. Maturity, frost, and harvest moisture considerations for corn. University of Minnesota. 3Digman, M. Combine considerations for a wet corn harvest. University of Wisconsin.4Dorn, T.L. Managing high moisture, stored grain through winter. University of Nebraska. 5Stahl, L. 2014. Storing, drying, and handling wet soybeans. University of Minnesota Crop News. 6Wilcke, W. and Wyatt, G 2002. Grain storage tips. University of Minnesota. 7Wilcke, B. 2004. Drying, handling, & storing wet, immature, & frost-damaged corn. University of Minnesota. 8Arriaga, F., and Luck, B. 2016. Guidelines for soil compaction management during a wet harvest season. University of Wisconsin. 171009153143