Richard Taylor, Extension Agronomist; rtaylor@udel.edu
I was asked this week about how fast corn dries down. The first question was about corn silage. Actual dry down rate varies depending on factors such as air temperature, solar radiation/day length (whether in August, early- or late-September, or October), hybrid, soil moisture levels, and a host of other factors. Most sources report an average drying rate of 0.5 percentage points per day during the month of September although the average rate by year has varied from 0.4 to 0.7 percent per day. If you look at the daily dry down rate within a given year, the rate varies tremendously from as little as 0% per day to as much as 1% in a given day. So for silage even though the average rate is 0.5% per day since making good silage is so dependent on having just the right amount of moisture so the silage will pack well and will ferment properly, you will need to watch your corn very carefully and do frequent checks to ensure the corn does not get too dry.
For grain, a number of factors impact the rate of dry down and these include weather, hybrid, maturity group, planting date, accumulated growing degree days or heat units, and husk and ear characteristics such as husk leaf number, thickness, and tightness of wrap and ear position (drop) and length protruding from husk. By far the most impact occurs with the type of weather we experience in any given fall. In years when the weather is cool and rainy, dry down will be very slow, perhaps less than 0.3% per day. In years where we have warm days, dry conditions, and plenty of sunlight, kernel dry down can reach 1% per day.
Dr. Bob Nielsen with Purdue University has studied the many factors involved in corn dry down and reports that the average daily dry down rate can range from about 0.8 percentage points per day for corn that nears black layer (physiological maturity) in late August to about 0.4 percentage points per day for corn that does not reach maturity until mid- to late-September. Although monitoring grain moisture loss is not quite as critical as with corn silage, we do know that harvest losses do increase as grain moisture falls below about 18 to 22%. With grain prices quite high, minimizing losses by harvesting when grain moisture is still slightly high can pay a healthy premium as can making adjustments to your combine to ensure the most efficient grain recovery possible.