It’s that time of year again when the combines thresh, yield monitors blink, weigh wagons weigh, and calculators calculate to determine yields and coffee shop bragging rights.  The cool growing season has pushed harvest later than normal, which complicates life on the farm at a number of levels.  For one thing, harvested grain moisture will be higher resulting in increased grain drying costs and lower returns.  A wet crop also means that things like test weight, wet corn price, and shrink will be out of normal harvest year ranges.  Finally, what are the consequences, if any, of simply leaving the crop in the field over winter to dry? 

     Most extension agents receive a number of phone calls each fall  with requests to convert wet bushels to dry bushels or estimate the number of bushels that would fit in a given bin, silo, or wagon.  To begin, let's start with the concept of a "bushel."  A bushel is a volumetric measurement.  Specifically, a volume bushel is the equivalent of 1.244 cubic feet.  Test weight is a measure of the weight of grain (usually expressed in pounds) per volume bushel.  Each different type of grain has a standard bushel weight at a specific moisture content.   

     Perhaps the most important relationship to understand is between grain moisture and test weight.  As kernel moisture decreases, grain test weight increases.  When grain dries it also shrinks and becomes denser, allowing for more kernels to "pack" into a volume bushel.  Additionally, dry corn is naturally more slippery, or slick, which tends to allow for better packing.  For example, corn at 28% moisture will have a test weight that is about 4 pounds lower than the same corn dried to 15.5% moisture.  It doesn’t matter whether the drying is done naturally in the field or artificially in a bin.  In 2009, it's certain that corn will come off the field wetter than most years.  Expect lower test weights from the moisture factor alone. 

     Another important factor when dealing with wet corn is shrink.  This is the weight loss that occurs to corn during a mechanical drying process.  The shrink factor is usually cited as the percentage weight loss for each point of moisture removed.  When considering water weight loss only, the shrink factor is constant for any given final moisture [determined by dividing 100 by (100 minus the percent final moisture)].  For example, the shrink factor for a final moisture of 15 percent is 1.176.  Total water loss for corn dried from 25 percent down to 15 percent would then be 11.76 percent (10 points removed x 1.176). 

     The other factor that goes into determining total shrink is handling loss.  There will typically always be some weight loss to corn after it is dried that is not fully accounted for by water loss alone.  Actual handling loss will vary from one operation to another but should be less than 1 percent of the total weight loss.  Typically, handling loss increases as initial grain moisture increases.  

     To avoid higher drying costs, low test weights, and large shrink reductions, some producers may contemplate leaving the crop in the field to dry through part or all of the winter.  Wisconsin research has shown the outcome to such a strategy can be highly variable.  When snow accumulations are heavy, the crop can essentially be lost.  Further, if stalk quality has deteriorated, the ability of corn to stand through winter (snow or not) is not very great.  Generally speaking, little grain dry down occurs after the end of November and this typically makes leaving corn in the field through winter a risky and unprofitable choice.