Drought has become more of a reality in recent years for the normally water-blessed Midwest – and elsewhere in the U.S. Even though drought is not an annual event, widespread and season-long extended dry stretches during mid-summer to late summer have caused considerable crop loss for forage growers and reduced forage and grain inventories for livestock producers.
In addition to yield reductions in water-limited environments, there is often a quality penalty such as reduced starch content or the presence of molds and mycotoxins, making forages more costly to feed.
Today, several tools can help maximize forage production and quality in water-limited growing environments.
Forage species differ
Of the major U.S. forage species, corn, sorghum and sudangrass have the lowest water requirements, while alfalfa and grass species need much more in terms of the water per ton of forage produced.
Short-term water shortages generally have the least impact on alfalfa and grasses since they are deep-rooted plants that accumulate biomass in direct proportion to the amount of water available.
Seed crops like corn and sorghum require a specific amount of water to reach the seed-producing and filling stages.
Interruptions of water supply during the critical flowering and grain-fill growth stages can lead to very high yield reductions (Table 1).
However, both sorghum and corn can recover from short-term drought stress and produce forage, even though it may be at a reduced yield.
Extended periods of drought, coupled with high temperatures, severely slow plant growth and lead to extreme yield reduction or death.
In recent years, producers have been feeding corn silage at high inclusion rates in dairy and livestock rations.
This is partially due to the high yield potential of corn silage relative to alfalfa or grass crops, as well as the energy value of corn silage with high starch content.
Improved corn genetics helps growers produce more consistent, high-quality forage for livestock operations.
Genetic gains for corn in water-limited environments
Over the last two decades, considerable gains have been made in the ability of corn genetics to withstand stressful growing environments.
Drought-tolerance levels achieved in today’s best hybrids stand in stark contrast to hybrids of just 20 years ago.
Many corn growers and researchers estimate that if today’s hybrids had been grown during the 1988 drought, corn yields could have easily been double what they were.
Under drought stress, today’s best drought-tolerant hybrids often yield within 75 to 80 percent of their average yield in low-stress environments.
Research has shown that several key characteristics of corn hybrids are important for maximizing performance in drought conditions.
Corn plants bred with well-structured root systems are capable of accessing scarce water resources. Hybrids with insect and disease resistance help keep plants healthy and growing vigorously.
Recent drought events have proven the value of corn rootworm-protected and corn borer-protected genetics in reducing yield losses in water-limited fields.
Hybrids with strong silking characteristics under drought exhibit less yield loss by maintaining synchronization of pollen shed and silking during this critical period.
Finally, corn hybrids showing yield stability across multiple environments, including those with moisture stress, are an important indicator of improved drought tolerance.
Breeding for improved drought tolerance
Considerable resources have been devoted to breeding and characterizing hybrids for improved performance under drought-stress environments. Various seed companies have developed screening programs to evaluate drought tolerance in their corn products.
Choosing a corn silage or grain hybrid with improved performance under water-limited conditions starts by selecting the products adapted to your area with high drought-tolerance scores.
Other hybrid traits should always be considered in selecting a product, regardless of the hybrid’s drought rating or the drought risk in your field.
Crop management in drought-prone environments
A variety of crop-management practices can help maximize forage production during drought events. In addition to choosing the best genetics for drought tolerance, growers may need to adjust planting rates or dates to maximize performance.
Ensuring good insect and disease protection encourages vigorous growth and helps avoid drought-related losses.
Optimum fertility and weed-free fields also help the corn crop capture limited water resources. Finally, where limited irrigation water is available, timing of water applications is critical to avoid more severe losses.
Forage quality changes with drought
Forage energy per acre is maximized in low-stress, high-yield environments for corn, as well as the other forage crops.
When faced with dry periods and drought stress, forage quality changes can occur in several ways.
For corn, one significant change is the reduced accumulation of starch in the form of grain.
Drought can result in corn silage with little to no starch or grain, depending on stress at pollination and subsequent kernel abortion. Energy is partitioned more into sugar and fiber in the stalk and leaves than into the grain.
Fiber digestibility also changes, depending on growing conditions during stalk development.
Figure 1 shows a Michigan study that compares fiber digestibility (NDFd-24hr) in various growing environments.
In this study, the best fiber digestibility was produced when plants grew under moderate to high heat and dry conditions.
Studies conducted by Michigan State University indicate that severely stressed corn (short plants with essentially no ears) still had a feeding value of approximately 70 percent of normal corn silage due to the highly digestible fiber and sugar content.
Due to the potential variability, it is important to analyze droughty corn silage for dry matter, NDF, NDF digestibility, sugar, starch and nitrates (percentage NO3 or ppm NO3-N) and to consider segregating storage based on fields that may have relatively higher feed value.
Drought can lead to several anti-quality factors as well. Drought-stressed grain is more prone to the growth of mold and yeast.
In the most severe situations, some molds can produce mycotoxins, which are injurious to cattle. Drought-stressed corn silage with high sugar content can result in aerobically unstable feed (feed heats on feedout) after ensiling.
Readily available carbohydrates like sugar fuel the growth of yeast and other organisms; this leads to heating and spoilage.
Drought-stressed corn silage should be carefully ensiled. Good silo management starts by harvesting at the correct moisture level and chop length, enabling proper packing density and air exclusion in the silo.
Next, use a research-proven L. buchneri inoculant to help ensure efficient and proper fermentation, along with providing aerobic stability on feedout.
Finally, test the silage prior to feeding to make sure it does not contain high levels of nitrates or mycotoxins and is safe to feed.
In recent years, forage growers and livestock producers have frequently commented that they “never expected this kind of corn silage yield based on this summer’s drought conditions.”
Comments like this indicate that the seed industry has raised the bar on drought tolerance, helping everyone reduce risk and increase profitability. FG
Daniel Wiersma
Livestock Information Manager
DuPont Pioneer
