Field Drying Rates in Standing Corn

All but the latest planted corn has reached physiological maturity and is now drying to a harvestable moisture content in the field. The "black layer" has formed at the kernel tip of the cob and stops the flow of nutrients into the ear. Because the black layer creates a disconnect, all grain drying must occur from the corn kernel outward, through the husk, and into the atmosphere.

📸: BASF internal photograph 

The drying process is driven by the moisture gradient between the husk or kernel perimeter and the atmosphere. Warm temperatures reduce the relative humidity in the air adjacent to the corn ear, and the wind serves to remove the evaporating moisture from the proximity of the ear, keeping the gradient steep and increasing the rate of grain drying. There are a number of decisions to be made when it comes to harvest timing, including stalk integrity, ear drop potential, overall workload, and drying capacity.

📸: BASF Contributing Writer/Featuring Corn on left with no remaining green vegetation, and ears both upright and facing downward, while corn on the right has similar ear positioning but green foliage above the ear leaf. (Ears shown in the next picture.)

There are some visual clues about moisture content as corn begins to dry down. In addition, there are some tactile clues if you strip back the husks and attempt to remove the grain by hand. When the black layer forms, the moisture content of the grain is, on average, about 30%. The corn ear will have a noticeable moist feel, and the cob will not snap off the corn plant without a little bit of a fight. As drying continues, the grain is removed more easily from the cob, whether by hand on a small sample or as a combine rolls through the field.

As "free drying" occurs in the field, other forces may be at work that will reduce the amount of grain you harvest: ear drop, loss of stalk integrity, and excessive drying that promotes kernel shattering in the combine. Observations by scouting or even from the cab of the combine will inform you about your disease and insect issues that might have caused some harvest losses and trigger some thoughts about next year's crop protection measures.

📸: BASF Contributing Writer/Featuring two ears on the left that are from completely dry corn with either up or down ear orientation, while the ear on the right is from corn with green vegetation (moisture content shown). The same ears are shown on the right with the husks removed. 

📸: BASF Contributing Writer/Featuring harvested ears with a measured moisture content of grain.

Visual observation of the corn crop and corn ear position and color is only a very loose estimate of the maturity and moisture content of your grain. I visited a dozen or so fields all within a very small geographical area and harvested ears with differing husk "looks" and measured the moisture content of the grain. The very highest moisture content was for immature ears in the milk stage (R3). Shortly after the black layer forms, the husk will begin to turn color and eventually dry to a brittle feel as moisture content approaches 15%.

Warm, dry days with a little wind can drop corn grain moisture by 0.8%–1.0% per day, so pay attention to drying rates from the black layer (30%) to a harvestable moisture, keeping in mind your workload and the condition of your harvestable crop.

Coming next: Corn and soybean harvest timing and efficiency.

BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.