Wednesday, October 16, 2013

Harvesting very green corn for silage this season

Chad Lee and Carrie Knott, Extension Agronomists, University of Kentucky
Donna Amaral-Phillips, Extension Dairy Nutritionist, University of Kentucky

Farmers are chopping silage at the normal time on the calendar and commenting on the very green corn in the fields. Silage corn was planted late this spring and that delays corn development. The summer was cooler and cloudier than normal, which also delays corn development. Finally, there is a lot of biomass in the corn this year, so drydown may take a little longer. Corn chopping may need to be delayed several weeks this season to get corn to the proper moisture.

In some years, the very green corn would be an indication of high nitrate levels. Corn has grown well throughout most of this season, so nitrates are less likely to be a problem. However, testing for nitrates is always a good idea.

Corn used to be harvested based on the stage of maturity. However, moisture content is critical to proper ensiling. So, moisture content of the entire plant is the greatest factor needed to determine when to chop corn this year. Corn should be chopped for silage at about 60 to 70% moisture for bags and about 65 to 70% for bunkers. Moisture content at harvest is very important. Corn silage harvested too wet will not ferment correctly, resulting in a clostridial fermentation, and cattle may not want to consume the fermented product. A very quick method for assessing the plant moisture is grab a sample of chopped corn and squeeze it into a ball. If the ball falls apart slowly and no free juice is visible, then the corn should be about 60 to 70% moisture. If the ball holds together then the corn is probably too wet to chop. If the ball falls apart rapidly, then the corn is too dry for proper ensiling.

The ball test is gives you an idea of the moisture. Actual moisture can be tested with a microwave or Koster tester. With the microwave test, get a sample size of about 3 to 4 ounces (100 grams). Weigh it. This is the “fresh weight”. Spread the sample uniformly in a microwave, preferably on a microwave-safe dish. Place a cup of water in the microwave with the corn sample to prevent a fire. This is very important! Heat the sample for one or two minutes and weigh. Heat for 30 seconds and weigh. Repeat until two weigh recordings are similar. If the sample chars, then you should use the previous weight. The final weight is the dry weight. The percent moisture is calculated with the following equation:

[(fresh weight- dry weight)/fresh weight] x 100 = percent moisture

Once silage has fermented for at least three weeks, the fermented feed should be tested for its nutrient content before being fed to livestock. Depending on the stage of maturity of the corn plant at harvest, the amount of starch, sugars, and digestibility of the fiber in the plant may be different than fully mature corn silage. This corn silage can be fed to livestock but the differences in nutrient composition may change the amount and type of supplements recommended to be fed.

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