Feed management: Drought stressed corn silage
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It has been a dry year through many parts of the state. Several corn fields have suffered from drought stress conditions which arise multiple questions such as how to proceed at harvest or what precautions are needed when feed out begins? This article addresses some of the general questions around water stressed corn used for silage.
What impact should I expect from drought?
The influence of drought on the corn will be determined based on duration and timing. For the majority of farms in Michigan, corn is planted between early May and early June. If this was the case, most plants were silking around middle July to early August. According to the US Drought Monitor, this period is also when the major dry conditions were observed in Michigan. Silking is the most critical step in determining yield that is negatively affected by water stress. Research shows that water stress during silking reduced corn yield between 40-50 percent. However, even with poor ear development, the corn can still be a good quality feedstuff for cows. Research shows that although the concentration of starch decreases in a drought, the concentration of soluble sugars increase. Soluble sugars are essential to the fermentation process occurring in silage and are mostly captured as lactic acid. Under good rumen function, the lactic acid is absorbed and metabolized for energy, although starch concentration, which decreases energy, is still present in water stressed corn. Additionally, when harvesting earlier, producers should expect lower yields with increased digestibility, thereby providing a greater portion of the energy that is captured by the animal.
When should I harvest?
This is a valid concern. As previously mentioned, areas such as yield, digestibility and energy content are affected by drought stress. Many producers are drawn to chop when the corn begins to look dry, however you should “never judge a book by its cover” or never judge dry matter (DM) by the look of the plant. DM is often lower than what it appears, therefore, MSU Extension recommends that whole plant dry matter testing is still the best indicator to establish plant maturity and plan the harvest date. Independent of the drought conditions, always use 32-35 percent DM (68-65 percent moisture) as the determinant to harvest corn for silage stored in bunks or piles, and 35-38 percent DM (65-62 percent moisture) if store in bags or uprights.
What is the main issues or concerns at feed out?
Nitrate accumulations are the main concern when feeding drought stress corn. Nitrates will concentrate in the lower parts of the plant, therefore, MSU Extension recommends increasing cutting high on the plant to reduce nitrate concentration in the silage if drought stress was severe or is an important concern. Also, avoid chopping after a rain event as it increases the plant nitrate uptake. Although the fermentation process will reduce the concentration of nitrate, always sample and test feed samples to avoid any potential issues. If after testing, the concentration of nitrates is still a concern MSU Extension recommends meeting with your nutritionist to adjust feed out following feeding guidelines to mitigate the harmful effects of nitrates. For recommendations of feeding guidelines when nitrates concentration are a concern, refer to Table 2 of the following article.
How to adjust for variation while feeding?
Sometimes water stress is not equally distributed, even within the same field, as slope and other factors can affect it. Drought stressed corn potentially has a greater variation of DM through the bunk or pile. MSU Extension recommends testing feed DM often to ensure that adjustments are being made when silage is being fed out as greater variation is expected.
In summary, although yields and quality are affected, silage from drought stress corn can still be valuable to feed the dairy herd if precautions are taken to avoid or mitigate problems. For additional questions of information contact your local dairy or forage expert from Michigan State University Extension.
Additional resources
Corn silage refresher – Part 1: How to set your cutting date
