Sorghum, sorghum-sudan or sudangrass: Which is right for me? -

For the rest of this article I’ll refer to these collectively as “sorghums” unless discussing a specific one.

Research and Acquisitions Manager / Western Forage Resource

During the summer months, cool-season grasses and legumes don’t grow as well at this time of year, which can be a challenge, especially on a grazing operation. These sorghum summer annuals grow quickly, are very high quality and require only modest amounts of moisture and fertilizer.

Which should I plant?

The answer to this question largely revolves around how you plan to harvest the forage. Forage sorghum is best if you are after a single huge silage cut. Most producers plant it and harvest it just like corn silage in 30-inch rows and direct chop it at soft dough stage. Heads ripen from the top down, so evaluate seeds from the middle of the head to determine soft dough stage.

Moisture at this maturity will typically be just under 70 percent, which is perfect for sorghum. The regrowth of forage sorghum is the slowest of the three, and generally we don’t plan on a second harvest.

If you need to make dry hay, by far the best member of the family is sudangrass. Sudangrass stems are finer than the other two and in humid environments it is the only one that will dry down enough in a reasonable time to bale.

Sudangrass exhibits the quickest regrowth of the three and therefore is very useful in grazing situations as well.

The most common member of this family is a cross between the other two types: sorghum-sudan. Sorghum-sudan is larger stemmed that sudangrass, making it unsuitable for hay in all but the most arid climates.

Its regrowth is intermediate between sorghum and sudangrass but most growers will get at least two harvests in a 75- to 80-day growing window. It is suitable for grazing, baleage or silage but not recommended for dry hay in humid climates.

Planting sorghums

The most common question we get about these crops is, “How late can I plant?” By the time you read this, optimum planting time will be right around the corner, or even past for some folks in the deep South.

While the answer varies with geography, if your soil temperature is not at least 60°F, these seeds will not germinate well, and 65°F soil temperatures are even better.

For most folks, sorghums are planted well after corn planting is done; often times about the same time as first-cutting hay is coming off. However, sorghum-sudans and sudangrasses are typically ready for a first harvest in 45 to 60 days, and a second harvest in 30 to 40 days in warm conditions. So they can still contribute huge amounts of forage in the summer months.

In answering the question of how late you can plant, forage sorghums typically need at least 90 days of growth, and sorghum-sudan and sudangrass need about 40 good growing days for each harvest.

Good growing days for sorghum are above 60°F, especially at night. So if you are 100°F degrees in the daytime but 40°F at night, your crop will grow significantly slower. And if you get a frost, it will often kill these crops or certainly set them back drastically.

For most of the country, these crops can be planted through late July and still give enough forage to offset planting and production costs.

Special traits

BMR
Several exciting traits are used in the sorghum family to make them better forage crops for targeted uses – the most common is the brown mid-rib trait (BMR). Just as in corn, the brown mid-rib trait results in higher forage quality due to lower lignin content in the plants and higher fiber digestibility.

Lower lignin in plants can lead to problems with standability but this is not as common with sorghum as it is with BMR corn. Sorghum stalks are very dense, not pithy like corn stalks.

If the forage is intended for anything other than cows at maintenance, the BMR trait is needed to help provide as much energy from the forage as possible.

Brachytic dwarf
To deal with standability issues, the industry has come out with another trait known as brachytic dwarf plants. They have the same number of leaves as a full-height plant, but the distance between nodes has been reduced. This results in a drastically shorter plant and somewhat decreased tonnage, although the decrease is not as drastic as you might think.

Most producers are willing to give up just a bit of tonnage to avoid the crop lodging anyway, but multiple trials over the past years indicate the yield loss is minimal.

In multi-cut crops like sorghum-sudan and sudangrass, there really is no yield drag at all if at least three cuttings are taken. For graziers and custom choppers, brachytic dwarf sorghum-sudans and sudangrasses give the added benefit of being able to withstand cuts at 3 inches instead of the 6- to 8-inch heights we recommend for conventional height products.

The reason is that sorghum plants grow best if at least two nodes are left after harvest. In a full-height plant, the second node is often about 6 inches above the ground. In these dwarf plants, the second node is often less than 3 inches above the ground, allowing for quick regrowth even at low-residual heights.

Photo-period sensitive
Photo-period sensitive sorghums grow for long periods of time without going reproductive. In these plants, heading is not initiated until they experience about 12 hours and 20 minutes of sunlight per day, which is going to be fairly late in the fall, depending on latitude. This trait also gives long harvest windows, because you don’t have to rush harvest due to grain development.

Male sterile
These plants do not produce pollen, so unless pollen from another source blows in, there will not be any grain production. These plants have obvious uses in any “grass-fed” market where grains are not allowed to be fed to livestock.

Dry stalk
The least utilized trait that is gaining popularity is the so-called “dry stalk” trait. Sorghum plants are high in sugar and like most high-sugar plants, they are high in water content as well. Plants with this dry stalk trait will be several percentage points lower in water compared to conventional types at boot stage.

Note that this trait really isn’t expressed until the crop hits boot stage, so if you are cutting at 30 inches tall, no matter the growth stage, this trait may be of little benefit.

Currently this trait is most popular with the single-cut forage sorghum crops. Having this trait gives some assurance that a low enough moisture can be obtained for directly chopping the silage crop.

We see this trait used especially in more northern areas where there aren’t as many warm days to grow these crops. Another alternative in the north is to let the forage sorghum grow until a frost, at which point it will dry down. The risk with this approach is that often the whole weather pattern turns and you can’t get in to harvest the crop.

Note that in general, forage sorghum can be harvested wetter than corn silage. Moisture percentages in the high 60s is ideal, but don’t worry about something in the low 70s; chop at 1-inch length and there will be almost no juicing of a sorghum silage crop at 72 percent moisture.

One detail to note is that the above-mentioned traits are all derived from conventional breeding and therefore are not GMOs. So organic producers or others who may want to avoid GMOs can use these hybrids on their farms.

As you assess your forage inventory going into this summer, consider planting one of these members of the sorghum family. Talk to your local extension agent or seed dealer to determine which type is best for you and if any of the special traits would be beneficial for your operation.