August 14, 2007

EAST LANSING, MICH.-- The droughty summer weather might make corn fields look dry enough to harvest for silage, but looks can be deceiving and farmers should take time to test for whole plant moisture levels before they begin chopping

“The question comes up of when to harvest corn for silage that has gone through drought stress,” says Herb Bucholtz, MSU professor of dairy nutrition and animal science. “The answer is no different than when trying to harvest normal corn for silage.”

Corn silage should be harvested when the whole plant dry matter is between 30 and 35 percent for ideal mircrobial activity. Dry matter content is important for the bacterial fermentation that takes place in the silage process.

“If it's drier than that, you will not get as good fermentation, material will not store as well, may spoil and you may get a decrease in the digestibility,” said Bucholtz.

While a field full of curled-leaved stalks might look dry enough, the plants themselves might still harbor moisture, and an accurate test is needed. To test corn moisture levels, producers should select and chop 15 to 20 plants from various parts of the field. They should test those plants using either a Koster moisture tester or a scale and a microwave oven. Directions for the proper testing procedure are available from any county MSU Extension office.

Once the moisture content begins decreasing, farmers should monitor the fields every few days in order to gauge the drying rate begin to predict when to harvest.

“That rate of drydown on corn plants will differ from field to field, farm to farm and variety to variety,” Bucholtz points out. “The producer has to monitor conditions for their individual farm–they can't even count on doing what their neighbors are doing.”

High plant nitrate levels are a concern with drought stressed corn. Normally, corn plants process nitrates into harmless proteins, but drought stressed plants don't have enough moisture to carry out the conversion. Experts recommend waiting two weeks after rainfall before harvesting drought-stressed corn or forage crops, allowing time for the recovering crops to convert the nitrates into usable proteins.

“Timing is everything,” said Ken Rauscher, Pesticide and Plant Pest Management Division director, Michigan Department of Agriculture. “Delaying the harvest of drought stressed corn, especially if the crop has been rained on, reduces the risk of nitrate toxicity to animals.”

And though farmers might be tempted to harvest corn higher off the ground than normal, in order to lower nitrate levels, the normal four to six inch-level should be maintained to avoid unnecessarily losing yield.

Nitrates are potentially toxic to cattle. Feeding green chopped corn plants, grazing them or feeding unfermented corn silage or sorghum sudan is not recommended. After the ensiled material has undergone three to four weeks fermentation, the nitrate levels will be reduced. If producers are concerned about nitrate levels in their silage, they may submit samples for testing at the MSU Plant Diagnostic Laboratory.

After the silage sits in storage following fermentation, it needs to age. Bucholtz recommends letting it sit for three to four months, if possible, to enhance digestibility.

For more information about pre-harvest corn testing, contact your county MSU Extension office or MSU’s Plant Diagnostic Laboratory's Web site.

MSU offers a number of resources for farmers who are dealing with drought issues. Fact sheets related to drought and forage crops can be found on the MSU Beef Team web page. Resources on corn and other crops can be found on the Crop Advisory Team Alert site.

Further contact information: Laura Probyn, MSU ANR Communications, 517-432-1555 x171