In Alabama, dry weather sometimes severely stunts the growth of corn. Some producers who recognize they are not likely to produce any significant amount of corn grain often consider the possibility of harvesting corn as silage.
The forage quality of corn is good, whether drought-stressed or not. The crude protein content and sugar content of drought-stressed corn is likely to be higher than non-stressed corn, but the crude fiber and digestible fiber also may be higher than with normal corn silage.
The result is that on a dry matter basis, animal performance may be somewhat lower with drought-stressed than it would be on non-stressed corn, but the main impact on forage production by drought is reduced dry matter yield.
The idea of using what was intended to be a grain crop for forage can make sense in many situations. It actually is a better option to make silage from such corn than to use it for green chop or grazing. The primary reason for this is that the nitrate levels in drought-stressed corn are often dangerously high.
However, when corn is ensiled, the nitrate level will usually be reduced by at least 20 percent. This makes nitrate poisoning somewhat less likely. In addition, the highest concentration of nitrates is in the base of the cornstalks. Thus, when corn is harvested for silage, some of the plant part containing the highest concentrations of nitrates is not included in the chopped material harvested for silage.
One of the challenges associated with harvesting drought-stressed corn for silage is determining when the plants are at the proper moisture content. The correct moisture content to harvest corn for silage is the same for drought-stressed and normal corn. Normally, good preservation and storage will occur when corn chopped for silage is at 65 to 70 percent in horizontal (trench or bunker) silos, 60 to 70 percent in bags, 60 to 65 percent in upright silos and 50 to 60 percent in upright oxygen limiting structures.
For drought-stressed corn that has no ears or very poor ear development, the normal approaches to determine the proper harvest stage usually do not apply. Therefore, chopping some material and determining moisture content in a microwave oven or with a moisture tester is advisable.
Simply looking at plants and trying to assess the moisture content does not work well because even though some leaves are beginning to brown, there may be enough moisture in the stalks to cause the silage moisture to be too high. This results in poor fermentation and/or excessive seepage. On the other hand, if corn is too dry, packing and excessive oxygen may result in poor fermentation.
In some cases, it may be advisable to raise the cutter bar on the silage chopper when harvesting drought stressed corn, as this may result in more desirable moisture content for ensiling the forage. In addition, because stems contain higher levels of nitrates than leaves, a higher cutting height may reduce the likelihood of nitrate poisoning danger.
Dangers of nitrous oxide poisoning to humans is increased on drought-stressed corn because of the higher nitrate levels in corn plants. Thus, it is advisable to use extreme caution when filling silos, especially with drought-stressed plant material. Running the blower for 15 minutes or so is always a good idea before entering a silo, but especially when drought-stressed material is ensiled.
In some cases, the decision as to whether to harvest corn for silage may be influenced by the expected grain yield versus the expected silage yield.
A rule of thumb is that for drought-stressed corn, usually about 1 ton of silage per acre can be produced for each five bushels of corn grain that might have otherwise been produced. If there is no grain present, a rule of thumb is that about 1 ton of silage can be produced for each foot of plant height (excluding the tassel).
Making hay from corn usually does not work well. Corn plants are difficult to bale and are especially difficult to dry enough for storage as hay. Furthermore, curing corn plants for hay does not reduce nitrate levels, while the nitrate levels of corn silage are often reduced by as much as 35 to 50 percent.
If any forage is suspected of having potentially dangerous levels of nitrate, it makes sense to have the forage tested before feeding it to livestock.