Harvesting Drought - Stressed Corn for Corn Silage

We have experienced drought-stricken corn throughout much of the Northeast & Eastern Midwest this crop year. Now it is time to harvest. How do we manage it from here to feed-out? Valuable nutrients remain to be salvaged for feeding purposes, and while yields may be reduced, the plants can still be harvested and utilized with some additional attention.

Corn that has been stressed all summer due to drought may have few, if any ears, and usually will have a lower energy value - 65 to 85% of normal corn silage. Drought-stricken corn silage typically has a higher protein content than normal silage. However, most of this protein is found in the plant rather than in the grain, making it more easily degradable in the rumen. As a result, NPN or non-protein nitrogen supplementation does not work as well when compared to normal silage. It becomes especially important to supplement drought corn with a natural protein source.

The dry matter content of droughty silage must be in the normal range (60 to 70% moisture, depending on storage unit) to make good silage, because normal silage packing and removal of oxygen must occur for complete and thorough fermentation to occur.

Some growers may be tempted to graze or green chop stressed corn. This is not recommended because the risk of nitrate-nitrite toxicity is too great. Nitrates accumulate in the plant only if there is a large amount of nitrate in the soil and something interferes with normal plant growth, such as drought. A good shower on drought-stricken plants will cause the plant to absorb soil nitrates quickly.

If the corn is fed to animals soon afterward, toxicity can occur. Ruminants consuming nitrates reduce them to nitrites, which are absorbed and can be toxic. Moderate levels of nitrite can be tolerated, but high concentrations overwhelm the animal’s system, causing a decreased ability of the blood to carry oxygen.

Symptoms of nitrite toxicity include increased pulse rate, quickened respiration, heavy breathing, muscle trembling, weakness, staggered gait, blindness, and even death. If the blood is sampled, it will be a chocolate brown color rather than bright red.

Drought-stricken corn plants should be analyzed for nitrites. Laboratory analyses may be reported in several ways. You can calculate nitrate nitrogen by:

Nitrate (NO3) x .23	=	Nitrate Nitrogen
Potassium Nitrate (KNO3) x .14	=	Nitrate Nitrogen
Sodium Nitrate (NaNO3) x .16	=	Nitrate Nitrogen

An excellent way to reduce the nitrate level in plants is to ensile them. One-third to two-thirds of the nitrates may be eliminated/converted to ammonia during the ensiling process, which can be utilized by the rumen bacteria. Wait three weeks after ensiling before feeding the silage so that the fermentation process can be completed. The amount of moisture in the plant will affect the length of fermentation. Corn ensiled at less than 55% moisture will undergo less fermentation and minimal nitrates will be converted. Dry corn doesn’t pack well. Air is trapped, which causes heating and molding to occur, instead of proper fermentation.

An additional way to reduce the nitrate levels is to harvest the corn a little higher from the ground than normal, because the lower third of the stalk contains the highest concentration of nitrates.

Nitrogen dioxide comes from nitrate-nitrogen during fermentation. Most of the gases are produced 3-4 days after filling the silo, but the actual production of gases begins within 2 hours. Concentrations of 25 ppm are invisible and can’t be smelled. Do not enter a tower silo without first running the blower for at least 10 to 15 minutes. Follow this procedure for at least the first 2-3 weeks after filling.

In summary, if these precautions are followed, they will help lower nitrate levels in the plant and reduce feeding problems in the ration.

Drought-stressed silage is not necessarily a totally lost or failed crop when managed with the correct handling techniques.