July 26, 2021 at 3:15 p.m.
Managing drought-stressed corn silage
The ideal temperatures for corn are 86 degrees during the day and 50 degrees at night. Drought and heat stress are most likely to negatively impact corn’s yield potential during pollination and grain fill.
Drought impacts corn pollination in two ways. Silking begins with the ovules at the butt end of the ear and moves up the ear as the process continues. Because silks are mainly composed of water, drought can reduce the growth rate and emergence from the ear tip. Silk emergence may be delayed and miss the pollen, or silks may shrivel to the point where they are not receptive to pollination, resulting in completely barren ears. If moisture alleviates drought conditions during pollination, some ears may partially fill. Drought stress can also accelerate pollen shed, leading to increased potential for a lack of synchronization.
The leaves of water-stressed corn will usually curl, reducing photosynthesis and, subsequently, the amount of nutrients provided to developing kernels. Kernel abortion can occur when successful pollination is followed by drought or heat stress and is usually more frequent at the ear tip. Drought or heat stress is most likely to cause kernel abortion during the first two weeks after pollination. Aborted or poorly filled kernels will be small, shrunken and an off-white color.
Moisture is key in determining when to harvest drought-stressed corn for silage. A recommendation is 62% to 68% moisture. Corn harvested too wet will result in excessive seepage and very high acetic acid fermentations. Harvesting when too dry will compromise packing, restrict fermentation and lead to spoilage issues at feed out. If harvested at the correct moisture, drought-stressed corn silage will ferment well. Follow normal, good harvesting practices.
Visual estimates of moisture content are generally misleading and inaccurate. The plant may look dry but contain significant moisture in the stalk, and different soil conditions can cause significant moisture variation across fields. Moisture should be monitored closely because it can drop quickly in drought-stressed corn. If it rains when harvest is close or happening, check moisture content again as the plant is likely to pull up moisture if it’s alive.
Typically, drought stress affects corn silage yields more than quality. Drought-stressed corn will likely be higher in protein and some minerals and lower in starch (energy). Fiber content will be elevated in drought-stressed corn silage, but its digestibility is usually higher. Drought-stunted, low-grain corn silage tends to be less dense, so truck and silo capacities are often lower. Because of the lower grain content, drought-stressed corn will be less responsive to kernel processing. Get a forage test when feeding drought-stressed corn silage so rations can be effectively adjusted.
Elevated nitrate concentrations are common in drought-stressed corn crops. The potential for high nitrate levels is greatest in young plants, especially their stalks, and in heavily manured fields receiving high nitrogen application. The potential is generally greatest for three to four days following a drought-ending rain but can be a problem at any time. Nitrate testing is cheap and should be used regularly on questionable feeds.
Leaving a 12-inch stubble in the field can reduce nitrates, but it will also reduce yields and may not be desirable unless a forage test confirms the presence of high levels of nitrates. Ensiling can reduce nitrate concentrations by 30% to 60%; grazing and green-chopping drought-stressed corn is not recommended.
High nitrates can contribute to animal feed problems and deadly silo gas, so be especially cautious when filling silos with drought-stressed crops. Silo gas is produced when nitrates are converted to nitrogen dioxide during the first four to five days after silo filling. Because it is heavier than air, silo gas can form in the silo and escape down the unloading chute into the barn. Silo gas is dangerous to both cattle and humans, causing severe lung injury or death due to the formation of nitric acid in the lungs.
To avoid exposure to silo gases, close the door between the feed room and barn, ventilate the silo by running the blower for at least 30 minutes before entering the silo, and learn to recognize the bleach-like odor and yellow-orange color as signals of silo gas. Never work alone. Be sure someone is around and able to quickly call 911 if exposure occurs. Caution should be taken in less confined spaces such as bags, bunkers and piles as silo gases can be present here as well.
Harvesting corn silage from plants that produce little or no grain is a cost-effective way to source forages and may be an opportunity to procure acres intended for corn grain. Engage in proactive conversations with neighboring crop farms to seek out additional acres needed to fulfill corn silage requirements.
The varied conditions of this year’s corn crop will make pricing corn silage difficult. Consider harvesting and hauling costs as well as the moisture content when pricing corn silage. Work with your nutritionist to determine the maximum price you can afford to pay given the other forage and non-forage options available.
Barry Visser is a nutritionist for Vita Plus.