Sept. 10, 2010

Still waiting for soybeans to mature? Consider harvesting corn with stalk rot now to get a jump on harvest and reduce field losses.

Stalk rots have been reported in many Nebraska corn fields and farmers and crop consultants have been advised to scout fields and when stalk rot is widespread, harvest the mature crop early to avoid losses. (See these CropWatch stories: Corn Disease Update: Scout for Stalk Rots in Corn and Ear Rots May be a Problem Again This Year, Minimize Losses.)

Harvesting high moisture corn in September to prevent field losses requires planning, preparation, and prioritizing.

• First, get your grain bins and harvesting equipment ready for harvest, drying, and storage before placing any grain in the bin. (See Ensure Quality Grain Storage by Starting with Clean Equipment, Bins in the Aug. 27 CropWatch.)
   
• Second, ensure the grain is dry enough to store safely. Corn should be at 15% moisture or below for long-term storage without aeration during the colder months of the year (November- March).
   
• Third, cool the grain mass to reduce mold and insect activity. The rate grain quality deteriorates depends on the moisture content and the grain temperature. The goal for corn is to reduce moisture to 15% moisture and cool it to 30°F for long-term storage.

Predicting Shelf Life of Stored Grain

Shelf life is defined as the time grain can be stored — with periodic aeration to maintain uniform temperature in the grain mass — before it loses one-half of one percent of its dry matter. This is considered the maximum dry matter loss you can suffer and still maintain the original market grade. 

At a given grain moisture content, shelf life is about half as long for each 10°F increase in temperature. At a given temperature, the shelf life is about half as long for each two percentage point increase in moisture content.

Estimating Drying Time for Corn and Soybeans

The time required to dry grain in a bin is a function of

• the ambient air properties —  temperature and relative humidity (RH),
• the airflow rate (cubic feet per minute per bushel (cfm/bu), and
• whether supplemental heat is added to the air stream used to dry the grain and the magnitude of the heat rise if used.

The following Excel worksheets estimate the time (days) to dry corn to the recommended 15% moisture and soybeans to 13% moisture assuming a range of initial grain moisture contents and ambient air temperatures and relative humidity conditions

• Drying Time for Binned Soybeans & Corn Using Natural Air -- Two Excel worksheets that show the estimated time to dry soybeans and corn using natural (unheated) air, assuming 1.0 cfm/bu airflow.
• Drying Times for Binned Corn Using Heated Air -- Two Excel worksheets showing the estimated time to dry corn with a wide range of initial moisture contents using heated air, assuming 1.0 cfm/bu airflow

Note how air temperature affects drying time. Harvesting and drying corn in September while waiting for soybeans to mature and dry down not only gives you a jump start on harvest, it can actually cut the electricity cost for fan operation.

If using natural air drying, the estimated time to dry corn from 21% to 15% at 60°F and 50% relative humidity is 20.6 days whereas it takes 29.9 days to dry from 21% to 15% at 40°F and 50% relative hudmidity. This is a 32% time savings when starting at 60°F compared to 40°F air temperature assuming 50% relative humidity in both cases.

Stated differently, assuming relative humidity stays the same, the grain would have to field dry about 2 percentage points by the time the average air temperature hits 40°F in order for the hours of fan operation to be roughly equivalent between the two scenarios.

Tom Dorn
Extension Educator, Lancaster County