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College of Food, Agricultural, and Environmental Sciences


Harvesting Corn for Silage A Tough Decision

August 19, 2002

OTTAWA, Ohio - Harvesting corn for grain or for forage may be one of the toughest decisions some Ohio growers are facing this season.

At a time when growers may have been giving up on their crop, scattered rainfall and cooler temperatures arrived during pollination -- a critical time in a corn plant's development that ultimately determines yield potential. Pollination during unfavorable weather conditions can lead to a reduced kernel set, where the ears of corn are partially filled, or can even be completely empty.

In northwest Ohio, where the majority of the state's corn crop is suffering from drought stress, stunted growth and insect pressure, poor pollination may have made the decision to chop the corn easy for growers.

But with new life breathed into the crop, many farmers are now torn: should they harvest for silage or should they hold out for the grain? They were hoping Ohio State University Extension agronomists could help them answer that during an Extension meeting for harvesting drought-stressed crops held recently at the American Legion Hall in Ottawa, Ohio.

"It could go either way right now," said Ed Lentz, an Ohio State University Extension district agronomist based in Findlay, Ohio. "Growers may see 100 bushels per acre to 120 bushels per acre in the western half of the state. Some places may even see 150 bushels per acre. It's been a difficult growing season for us and it's still only the third quarter. We still have the fourth quarter to go." Lentz, like other Ohio State Extension agronomists, has been singing the same tune all season: too much rain in the spring and not enough this summer. The result is a combination of poor root and ear development.

Many corn plants throughout northwest Ohio are on the ground, the victim of shallow root systems that couldn't support the plants when high winds recently blew through the area.

Additionally, ear development may not meet expectations to produce high yields.

"Losing rows on the ear is the fastest way to drop yield estimates," said Lentz. "We like to see 18 to 22 rows on the ear. Twelve to 14 rows knock yields back pretty quickly and we may have a lot of 12-row corn out there. Plants that don't have an ear on them by now will remain blank or not mature in time if an ear appears later." Growers who are considering harvesting their corn for forage should decide quickly. The more the corn ears develop, the more energy is transferred from the leaves to the kernels, reducing the nutrient value of the crop for feed.

Bill Weiss, an Ohio State animal science researcher, said that the energy level in drought-damaged corn is generally five percent to 10 percent less per pound than normal corn silage. Drought-stressed silage is lower in starch and higher in fiber and protein.

"Drought-damaged corn silage is higher in protein than normal corn silage because there is not as much of an ear. There's more leaf and a shorter stalk, so it makes for good cow silage," said Steve Boyles, an Ohio State Extension beef cattle specialist.

The determining factor when to chop corn for silage is the crop's dry matter content, said Weiss, who is with the Ohio Agricultural Research and Development Center in Wooster, Ohio. The wetter the corn, the slower the fermentation process, increasing the risk of nitrate toxicity in the feed and the leaching of nutrients animals need.

"As corn reaches dry matter content of 35 percent, a grower needs to make a decision of whether or not to chop the corn. An ideal dry matter content is 32 percent to 38 percent," said Weiss. "If the dry matter content is too low, you'll get bad fermentation. If it's too high, you'll get heat damage, mold development and a shorter bunk life." To accurately determine dry matter content, it is important for a grower to gather a representative sample size of the corn stalk he is measuring, said Weiss.

"Don't let the dryness of leaves deceive you into thinking the whole plant is dry. The stalks are going to be wetter than the leaves," said Weiss. "Also, plants without ears at the same stage of maturity are wetter than plants with ears. You have to test the crop, you can't just base it on looks." An efficient procedure growers can use to weigh overall moisture content is to use a microwave oven to dry a corn stalk, then use a series of equations to calculate the percent moisture. The process is outlined in Ohio State Extension fact sheet AGF-004-90 located on Ohioline at

High nitrate concentrations are a concern in drought-stressed corn. "Nitrate is taken up from the soil, but is not yet metabolized in the plant. It just concentrates in the lower portion of the plant," said Maurice Eastridge, an Ohio State Extension dairy specialist.

Eastridge said that when livestock consume feed with high nitrates, the nitrate is converted to nitrite, absorbed across the rumen wall and competes with oxygen.

"So in essence, the animal begins to suffocate because there is not enough oxygen in the bloodstream," he said. "Normally what would happen is bacteria break down the nitrate to nitrogen and the bacteria in the rumen utilize it in protein synthesis." Corn fermented in silos for up to two weeks can reduce nitrate concentrations by as much as 60 percent. Nitrate-nitrogen concentrations .1 percent or less of dry matter is considered safe; between .1 percent and .2 percent is low risk; between .2 percent and .35 percent is considered high risk and anything over .35 percent is toxic.

Soybeans can also be harvested for forage, but like corn, farmers must make the decision quickly to chop the plants for silage.

"Farmers will want to chop soybeans for forage before the beans have a chance to develop and take nutrients out of the leaves," said Lentz. Additionally, once oil is present in the seeds, it decreases the natural population of bacteria required for fermentation in the silo.

Lentz said many soybean fields throughout northwest Ohio have reached a stage of maximum growth potential, and the number of beans and bean size is now dependent upon rainfall amount.

"The crop has reached its maximum potential and any stresses the plants encounter now will just diminish that potential," said Lentz. "We don't expect a bumper crop, but we could have some 40 bushel-fields out there, so it's a tough decision for the farmer. Any plants that won't produce beans are a viable forage option."

Candace Pollock
Bill Weiss, Maurice Eastridge, Ed Lentz