Drought-stressed forage requires special care

August 14, 2007|by JEFF SEMLER

Even with the recent rains, many parts of the region are experiencing drought conditions. And even though many folks have been harvesting silage, here are some guidelines for dealing with this situation adapted from "Management of Drought Stressed Corn for Silage," by Dr. Limin Kung Jr., at the University of Delaware.

Drought-stressed corn should be harvested at the same dry matter (DM) for normal corn: 32-35 percent DM. Determining whole plant dry matter or moisture is critical because visual assessments can be very inaccurate. Many plants that look dry contain a significant amount of moisture in the stalk. Use of a microwave oven or Koster Moisture Tester is recommended. Under hot dry conditions, plants may dry down at 1-2 points per day. Ensiling corn at less than 28-30 percent DM will result in excess nutrient runoff and extremely acidic silages. Harvesting corn too dry (greater than 40 percent DM) restricts fermentation, reduces the loss of nitrates, results in forage that is difficult to pack, and can result in excessive spoilage and poor bunk stability.


Chop forage at a theoretical setting of three-eighths to three-quarters of an inch if harvested at the optimum DM. If you have already missed the optimum dry matter for harvest and the plants are very dry, (more than 40 percent DM) consider chopping your forage finer to improve packing (but remember you will have to balance the TMR for adequate effective fiber during feedout).

If the forage is not well eared, mechanical processing may not be needed. Process if the amount and maturity of the kernels warrants it.

As always, filling fast, packing tight and sealing immediately will help to ensure a good fermentation. Be sure to have adequate tractor weight on the pile, as drier forages are more difficult to pack. Allow silage to ferment for at least three to four weeks (longer would be preferable) prior to feeding and gradually introduce new silage to animals.

Silage additives for drought-stressed corn

Homolactic acid bacteria (microbial inoculants): Severely drought-stressed corn forage may contain lower numbers of naturally occurring lactic acid bacteria and may need some help during fermentation. If forage is in the normal range for DM, consider using a homolactic acid bacteria. Some strains of Lactobacillus plantarum may help with the reduction in nitrates.

Heterolactic acid bacteria (Lactobacillus buchneri): Drought stressed corn silage often has a high sugar content and can be highly prone to spoilage when exposed to air. Lactobacillus buchneri is an organism that safely produces acetic acid, which reduces aerobic spoilage organisms and improves bunk life.

Buffered propionic acid-based preservatives: Silage additives based on buffered propionic acid may be an acceptable additive for drought-stressed forage, especially if the DM percent of the whole plant is high, greater than 38 to 40 percent. Addition of 2 to 4 pounds of such products per ton of wet forage can improve aerobic stability of the silage and reduce DM losses in the silo and during feedout. Higher application rates will increase the probability of effectiveness. Although this may seem costly, such preservation easily pays for itself by preventing drops in intake and milk production that would occur if cows were fed spoiled silage.

Water: Water can be added to increase the moisture level of overly dry forage, but the amounts needed to have a substantial impact are large. For example, to decrease the dry matter of forage at 50 percent to 45 percent, one would have to add 200 pounds of water per ton of forage. In addition, added water can cause run off problems, as it is not absorbed efficiently by the forage mass.

Sugars/molasses: Drought stressed corn forage usually contains moderately high concentrations of fermentable sugars. Thus, the addition of molasses or other fermentable substrates is usually not warranted if the forage is harvested at the proper DM content.

Non protein nitrogen additives: Non protein nitrogen (NPN) additives (urea and anhydrous ammonia) should not be used on very dry, drought-stressed forages.

Nitrate poisoning from drought-stressed forages

Many plants can accumulate nitrate under stressful conditions (excessive fertilization or water stress from rain after a drought). Sunflowers, corn, wheat, barley, rape, bromegrass, and sweet clover are some of the more common plants that can accumulate high levels of nitrates. High nitrates cause toxicity because once they are absorbed into the blood stream, they are converted to nitrites that bind to hemoglobin and reduce the oxygen carrying capacity of the blood. Acute poisoning can be observed within six hours of forage consumption and is characterized by dark-brown blood, labored breathing, tremors, and weakness. The following information is primarily aimed at the management of drought-stressed corn silage, but general concepts are valid for other forages as well.

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