USA
October 7, 2021
Let’s talk about a crop that can grow in inhospitable environments and still provide numerous benefits. It can increase soil organic matter and provide lots of nitrogen. It suppresses plant parasitic nematodes and improves soil health.
Yes, sunn hemp is a superhero in the plant world. And it is a powerful solution to many agricultural challenges related to degradation of natural resources and food security.
Sunn hemp growing in Brazil. This leguminous crop has multiple uses: cover crops, biofuels and more. Credit: Antonio Luis Santi
Sunn hemp (Crotalaria juncea L.) is a legume commonly used as a cover crop for southern and sub-tropical and tropical farming systems. It has recently been more adopted in the Midwestern United States cropping systems.
Sunn hemp is not in the same family as industrial hemp; that is a Cannabis specie, a non-hallucinogenic plant “cousin” of marijuana.
Sunn hemp is a tall, shrubby plant – and can reach up to nine feet high! It’s an annual crop that creates a lot of biomass, along with well-developed root systems. It’s deep-yellow flowers produce tiny seeds – so tiny that one pound can contain over 15,000 seeds!
Sunn hemp can grow to be as tall at nine feet tall above ground. Shown here, a test plot at Kansas State University. Credit: Carlos B. Pires
Originally from India, sunn hemp has been widely used as green manure and livestock feed in Brazil, Paraguay, and Bangladesh. Other potential uses for sunn hemp are non-wood fiber, oil, and as an alternative biofuel crop.
Because it is a legume, sunn hemp pulls atmospheric nitrogen and puts it into the soil – a process called nitrogen fixation. This leaves the soil with more nitrogen (a necessary nutrient for crops) than before the sunn hemp was grown.
Sunn hemp is a legume. Its roots are colonized by a bacteria called Rhizobium. These bacteria pull nitrogen from the air after becoming established inside the root nodules in a process called nitrogen fixation. Credit: Carlos B. Pires
Farmers only need 8 to 12 weeks of frost-free growth conditions to receive the benefits of sunn hemp. Ideally, farmers would then plant a small grain crops, like wheat, to use the symbiotically produced nitrogen in the soil. Planting another crop after sunn hemp may reduce the need for synthetic nitrogen fertilizers, which can be lost to the atmosphere as nitrous oxide or even leached as nitrate to groundwater.
Sunn hemp has been extensively used as a soil improvement crop. Its enormous potential to produce biomass and fix nitrogen is crucial to build up soil organic matter and sequester carbon.
Sunn hemp plant in Kansas. The extensive root systems of sunn hemp improve soil structure and allow water to infiltrate. Above ground, the plants can grow to nine feet tall, creating biomass for future use. Credit: Thomas Roth
When used as a cover crop, sunn hemp can reduce soil erosion and conserve soil moisture. The large root systems break up soil, which increases water infiltration, and because it’s a legume, it boosts soil microbial community composition.
Sunn hemp can be used as a forage crop – and has the potential to fill an important gap in annual summer grazing. Its hardiness, productivity, and palatability make it an option worth considering for farmers looking to build their soil and grow their livestock.
Answered by Carlos B. Pires, Kansas State University
Read more about a researcher using sunn hemp in Florida.
About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.
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