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. The October 7th, 2021 Sustainable, Secure Food Blog explores more this plant that can grow in inhospitable environments yet still provide numerous ecological benefits.
According to blogger Carlos Pires, sunn hemp 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.
It 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!
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.
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 grains crop, like wheat, to use the symbiotically produced nitrogen. 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.
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. Foraging needs to be stopped if seedpods are formed. This is because the seeds have a low concentration of a toxin.