Researchers at the University of Wyoming (UW) are studying sunn hemp as a potential forage crop for producers in the state. This tropical legume, unrelated to industrial hemp and cannabis, is known to perform well under hot growing conditions and add nitrogen into the system. 

UW Assistant Professor of Agronomy and Cropping Systems Carrie Eberle, based at the James C. Hageman Sustainable Agriculture Research and Extension Center in Lingle, is spearheading research to understand the best way for Wyoming producers to utilize sunn hemp in their rotations or plant as an emergency forage crop. 

Sunn hemp potential

According to Eberle, sunn hemp is a short-day crop, meaning the plant does not reliably flower while getting 12 or more hours of sunshine each day. 

“This means in Wyoming, sunn hemp should not go into its reproductive phase,” Eberle notes. “This is really important and a benefit of the crop because it means we are not worried about the crop setting seed and being problematic as a weed or becoming an invasive species.”

Additionally, Eberle shares this is beneficial to producers as the quality of the crop, in terms of nutritive value, can be maintained through the growth phase. 

“I am also interested in sunn hemp in Wyoming because it is relatively drought tolerant,” she says. “It can grow with as little as 10 inches of moisture. This crop is tolerant to dry conditions, has a deep taproot and doesn’t require a lot of water.”

Eberle continues, “It is also adapted to low-quality growing conditions, including poor soil health with low organic matter, low fertility and low pH. These are conditions this crop tends to do very well in and is a potential for producers in Wyoming to grow in some of our less than ideal conditions which, even in an irrigated system, don’t have to delegate much water to.” 

She explains all of these traits make sunn hemp appealing in terms of fitting into a Wyoming crop rotation. 

Crop uses

“In the U.S., sunn hemp has primarily been used as a green manure cover crop,” Eberle explains. “Because it’s a legume, it has a rapid growth rate – growing up to four feet in two months. This makes sunn hemp a good cover crop with a lot of biomass and up to 120 pounds of nitrogen fixed per acre.” 

Internationally, sunn hemp is also used as a fiber crop in many regions to make ropes, paper and other fiber products. The crop was previously used in the U.S. for fiber, but is not commonly used today. 

Eberle’s main focus for growing sunn hemp in Wyoming is the ability for the crop to be utilized as a forage crop. 

“There are a lot of cattle, sheep and other livestock in Wyoming,” she says. “Oftentimes, producers are looking for high-quality feed alternatives.” 

Traditionally, Eberle adds, producers use alfalfa in ration over a grass mixture because of the increased protein content. Similar to alfalfa, sunn hemp is a legume, but the greatest difference is alfalfa is a perennial crop producers can get multiple cuttings from, while sunn hemp is a short-season crop. 

“Sunn hemp is potentially very beneficial as a short-season substitute in a rotation, as a rescue crop or as an emergency crop to get into the ground quickly when producers know they are going to be short on feed for the year,” she says. “The big question is, how good of a forage crop it will be in Wyoming?” 

Studying sunn hemp 

According to Eberle, some studies have shown sunn hemp contains 15 to 25 percent crude protein, depending on growing conditions, harvest and management practices. Curious to see if sunn hemp holds this quality under Wyoming growing conditions, Eberle and her team of researchers studied the effect of planting dates and varied water supply on plant growth and quality. 

“2017 was a dry year, and plants in the rain-fed system showed a good rate of growth early on, but it flattened out – the lack of water caused the crop to be stunted,” she says. “However, in 2018, rain-fed plant growth early in the season was slow, but the plants took off during the last 30 days of the growing season to reach around four feet of height by 60 days after plating.” 

She continues, “Irrigated plants experienced quick, steady growth. In both years, the late-June planted crops were able to use a growth advantage to reach taller heights faster than earlier planted sunn hemp.” 

While Eberle shares planting dates did not have a significant effect on biomass produced in each season, the difference in water system may have impacted yield. In drought conditions, the 2017 rain-fed group averaged 1,308 pounds of biomass per acre, while the 2018 rain-fed group averaged 2,951 pounds of biomass per acre. Irrigated crops in 2017 and 2018 produced around 2,200 pounds per acre. 

Forage crop potential

“The critical component of this study is the feed value to livestock,” Eberle states. “If producers want to be able to grow this crop in a rotation and get the rotational benefits of a legume, but also be able to use it as a supplemental feed for livestock, we have to know if it is actually a high-quality feed.” 

The study compared critical feed components such as crude protein, acid detergent fiber (ADF), neutral detergent fiber (NDF) and total digestible nutrients (TDN) from their sunn hemp crop to a good-quality alfalfa. 

She continues, “Across the board, regardless of planting date and irrigation system, we were able to maintain a nice, high quality of the sunn hemp feed. This is really encouraging, as this crop was tested under ideal circumstances, even if there is a slight decrease in under normal growing conditions, there is good potential for sunn hemp to be a quality forage in Wyoming.” 

Overall, Eberle’s study shows initial growth of sunn hemp is slow in the first 30 days, meaning producers might have to nurse the crop and will need good weed control, or explore crop mixes such as seeding with teff grass or sudangrass to help the crop in the beginning. Additionally, the crop can provide one to two tons of forage per acre within 60 days of planting, and feed quality is equal to that of good-quality alfalfa.