When forage stocks are low, warm-season grasses offer a solution to quickly beef-up your forage supply. Sorghum, sudangrass and sorghum-sudangrass hybrids provide good alternative forage options because they grow fast and are low-maintenance.
“For warm-season grasses, it’s important to plant a little later when the soil temp is at least 60°F but ideally 65°F — usually a few weeks after corn,” says Renato Schmidt, forage products specialist at Lallemand Animal Nutrition. “These grasses can also be an emergency crop. If we have extreme weather that delays planting like in 2019, the sorghum family can make the most out of the summer months and quickly provide another forage option at harvest.”
The sorghum family requires less water to grow and is more resistant to drought. Avoid planting in wet soils or low-lying areas. These crops also have lower soil fertility requirements compared to corn, especially for nitrogen. Sorghum crops are typically grown in drier areas, like Kansas, Texas, Colorado and Oklahoma, but they can also grow well in the Midwest, given the right soil conditions.
The nutrient value of warm-season grasses is a little lower than corn. In terms of feeding or energy value, it's about 85% of corn. However, they do contain a similar protein content, making them a good feed ingredient for heifers or pregnant heifers. They can be blended with high-quality haylage or another byproduct that's rich in protein.
Several traits are recommended to aid in forage management and quality:
- Brown midrib (BMR) — contains low lignin content, making it highly digestible
- Dry stalk — reduced crop moisture, requiring less dry time
- Male sterility— eliminates the reproductive phase, making it easier to manage multiple cuts
- Dwarfing — results in less stalk and more leaf area, but still comparable yield mass to taller sorghums
- Photoperiod sensitive — remains in a vegetative state most of the season (or until the day length is less than 12 h) rather than switching to the reproductive phase, therefore growing significantly more biomass
Monitor Nitrogen Intake
As mentioned earlier, the sorghum family requires less nitrogen than corn. High nitrogen availability can cause potential issues with nitrate accumulation. This is more likely to occur during stress conditions — like drought or physical damage to the plant, especially to the leaves.
“Nitrate accumulation happens when the plant suddenly starts pulling up nitrates from the soil and doesn't have the capacity in the leaves to convert these nitrates to protein. Nitrates can accumulate quickly and can poison animals,” explains Schmidt. “If you think you're going to have issues, raise the cutting bar — because the nitrates accumulate in the bottom part of the plant — or send a sample for analysis. It's a simple, inexpensive analysis that can offer a baseline of nitrate levels.”
If you plan to graze, monitor for prussic acid poisoning in young plants (under 18 inches in height). Do not leave green chop in a cart or wagon overnight and plan to feed; the heat can increase toxicity in feed.
Harvest Tips for Warm-Season Grasses
- Use a conditioner to break and crush the stems to wilt.
- If harvesting a single cut, process the berries similar to processing corn. Exposing the berries increases starch digestibility. Otherwise due to their hard shell, they may pass right through the animal and any energy they contain will be lost.
- Use an inoculant to kickstart the process. If the silage needs to be moved or has a history of stability issues during feed out, a Lactobacillus buchneri inoculant is recommended.
- Make a first cut for sudangrass is about 40 to 45 days after planting, depending on growing conditions, or at about 40” in height. Plan to cut and wilt again in mid-to-late September or hold until mid-to-late October and wait for a frost to remove some of the moisture. Ideally, target at least 32% dry matter for ensiling.
“The other option is to skip the July cut and do a single cutting in either September or October. You will harvest almost twice the tonnage, but expect to lose in terms of quality,” says Schmidt.
Headline photo showing plots with multiple harvest (left side) vs single harvest (right side) courtesy of Matt Akins, University of Wisconsin
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