Summer annuals can double as stockpiles

As haymakers tackle first cutting and grazing livestock relish in lush pastures, it may seem a bit early to think about seeding summer annuals, let alone harvesting them. But having a plan for these forages will help farmers use them more efficiently — even if it’s a Plan B.

In the latest episode of the “Productive Pastures Podcast,” Carson Roberts, the state forage specialist with the University of Missouri Extension, and Jeff Jackson, an alfalfa and forage specialist with Croplan, discussed stockpiling sorghum-sudangrass for fall and winter grazing. They agreed that stockpiling may not be the primary intention for sorghum-sudangrass, but it can serve as a good emergency forage option, especially if late-season feed supplies run low.

Roberts conducted research on different hybrids of stockpiled sorghum-sudangrass to observe how yield and quality changed over time. He admitted that he expected dismal results, but was surprised that, on average, the stockpiled forage maintained total digestible nutrients (TDN) and crude protein (CP) levels that could be sufficient for pregnant dry cows. Of course, the key to this system is harvesting sorghum-sudangrass at least once during the growing season so it stays in a vegetative state until plants experience a hard freeze.

“The freeze essentially locks that quality in,” Roberts said. “All of those compounds are still in the plant, the plant doesn’t senesce, and [those nutrients] aren’t sent to the roots or put into a seedhead. Even though it’s brown doesn’t mean the quality changes,” he added.

According to his data, stockpiled brown midrib (BMR) sorghum-sudangrass with the brachytic trait averaged 7% CP. Following this, BMR sorghum-sudangrass without the brachytic trait and conventional hybrids averaged 6% and 5% CP, respectively. Nonetheless, in many cases, providing a protein supplement in stockpiled pasture may be necessary.

Roberts said dry matter yield declined at approximately the same rate across all types of sorghum-sudangrass. On average, yield dropped 12% from November to December, and it fell another 50% from December to January. Therefore, he suggested grazing sorghum-sudangrass first in a stockpile system, then move cattle to other stockpiled forages like tall fescue.

Leaves and stems

Roberts broke down the differences between BMR sorghum-sudangrass with the brachytic trait and conventional hybrids to further analyze CP content. In his experiment, the former type of plants were 43% leaves and 57% stem. Conventional sorghum-sudangrass was 19% leaves and 81% stem.

“If you look at them, you’d say they were different plants,” Roberts said. “One is all stemmy and it has skinny leaves on it, and the other one is pretty much half leaf.”

The stems on both brachytic and conventional sorghum-sudangrass were less than 3% CP, whereas plant leaves contained between 9% and 10% CP. The difference in forage quality comes from the variable leaf-to-stem ratios.

“If you plant a conventional hybrid, it’s going to be equivalent to cornstalks. If you have to plant something that has been improved in any way, it’s going to be maintenance quality,” Roberts said. Regardless of the hybrid, Roberts encouraged farmers to strip graze stockpiled sorghum-sudangrass so animals utilize all parts of the plant instead of just selecting for leaves.

Seeding options

In closing, Roberts and Jackson offered a few alternative options for planting sorghum-sudangrass. They suggested no-tilling it into a tall fescue field can be successful — but it depends on several factors. For instance, tall fescue must be grazed down and on the tail-end of its spring growth curve so it doesn’t compete with sorghum-sudangrass seedlings when it starts to regrow. Soil conditions matter, too.

“The relationship between soil moisture and how aggressive that fescue is growing makes a big difference,” Jackson said.

Additionally, the specialists agreed that sorghum-sudangrass can also be interseeded into a dwindling alfalfa stand after first cutting. By second cutting, the summer annual should be well established, and by third cutting, it could comprise the lion’s share of total forage yield.

“We can really improve the tonnage in an alfalfa field that is getting a little bit tired by putting some sorghum-sudangrass with it,” Jackson said.

Sorghum-sudangrass can also be seeded behind alfalfa that is terminated after first cutting. Roberts suggested this can reduce the risk of nitrate toxicity in sorghum-sudangrass because of the way alfalfa fixes nitrogen and slowly releases the nutrient to the soil.