As the summer comes to an end, farmers are geared up for corn silage harvest. Greater than average seasonal rainfall this summer has allowed for plentiful corn growth, but the lack of rainfall in the last few weeks has brought on several reports of hastened corn silage dry down and caused some growers in the southern portion of Pennsylvania to begin chopping in the past week.
Extension Agronomist Jessica Williamson reminds us monitoring corn moisture during this time in the season is crucial, as the moisture at which silage is stored according the storage structure is one of the key factors in properly ensiled forage. The appropriate moisture helps to ensure proper fermentation, which will aid in the guarantee of high quality and minimize losses due to seepage and mold.
Corn silage samples collected on two different dates by Alyssa Collins, Director of the Southeast Agricultural Research & Extension Center in Landisville and Assistant Professor at Penn State show variability in relative maturities of corn, which can be magnified by variability in hybrids. On August 24 a 106 day corn planted on May 12 had 72% moisture, a 109 day corn had 62% moisture and a 113 day corn had 68% moisture.
Waiting too long to harvest could result in too dry of silage for proper fermentation. With the quick dry down rates that are occurring currently due to weather, closely monitoring your corn is critical. According to the Penn State Agronomy Guide, corn silage should be harvested when whole plant moisture reaches 55 to 68%. For conventional upright silos, optimum moisture should be 63 to 68%; bunker silos – 65 to 68%; oxygen-limiting silos – 55 to 60%; and ag bags – 63 to 68% moisture.
Knowing the average expected dry down rate per day for corn silage is 0.5 to 0.6% will help to aid in determining proper harvest timing when moisture becomes close to optimal; however, the dry down rate varies by hybrid, and dry weather conditions further quickens the loss of moisture and could cause 0.7-0.9% dry down on a daily basis.
Although not perfectly accurate, a quick field test for estimating corn moisture levels can be done by breaking an ear in half and looking closely at the bottom half of the kernels. When the separation, or “milk line”, is 1Ž4 of the way down the kernel, moisture is approximately 70%. As the milk line reaches to approximately 1Ž2 of the way down the kernel, the moisture is approximately 65%. For a more accurate measurement of whole plant moisture, take a few plants at dent stage and run them through a chopper or lawn mower, allowing for all the plant parts to be thoroughly mixed together. Then use a Koster tester or a microwave to determine plant moisture by first weighing the wet sample, then slowly heating while continually stopping and stirring until the sample is completely dry. The difference in the weights of the wet and dry sample will indicate the moisture level of the silage. For more detailed instructions on using the microwave to determine moisture content, check the publication “Determining Forage Moisture Content with a Microwave Oven”.