What is Sunn Hemp?
Sunn Hemp, a tropical legume, is used in many tropical countries as the number one soil builder and cover crop for reclaiming poor land.There are millions of acres of this crop grown in other countries. Brazil calls it their number one soil builder. Sunn hemp is originally from India and has been grown since the dawn of agriculture. It has been grown as a green manure, livestock feed for forage, hay, and for non-wood fiber.
In 1931 USDA proclaimed sunn hemp excellent for building the soil. Since that time the use of sunn hemp in the US was almost unheard of. It has only been in the past few years that knowledge and benefits of this plant have taken root in the U.S.
Sunn hemp is a tropical legume whose claim to fame is that, 60 days from planting, it is typically over six feet tall, adds 120 pounds of Nitrogen to the soil, 10 pounds of residual Phosphorus and 80 pounds of residual Potash transfers from the subsoil to the topsoil, supplies four tons of organic matter, is a great soil builder, as well as increasing drought tolerance and yield and cash value of the next crop.
All livestock and wildlife thrive on sunn hemp. The leaves of sunn hemp are 30 percent protein. We have not found yet anything that eats vegetation that does not thrive on sunn hemp.
Sunn hemp is not an invasive weed. In fact, it smothers out 99.9 % of all weeds and is allelopathic to Palmer Amaranth. The sunn hemp will not flower and go to seed until the days start getting shorter (mid September in Alabama). There is not enough time for those seeds to mature in our area after flowering.
Sunn hemp is resistant to root-knot and Reiniform nematodes. Root-knot and reiniform nematodes are a major pest in South Alabama agriculture, and root-knot nematodes are a pest in almost every home garden in South Alabama. Gardeners could plant their spring crop and then in June, July, or August plant the sunn hemp.
Sunn Hemp Before Wheat
A Golden Opportunity: Harvest Corn—Follow with Sunn Hemp—and then Wheat
One of the major keys of cover crops is finding the window of opportunity that fits your farm. Placing Sunn Hemp right after corn harvest is a golden opportunity. This window may be tight for many farmers as the Sunn Hemp should be planted by August 25. Sunn Hemp is day-length sensitive. Sunn Hemp planted after Aug. 25 will only get 2 - 3 feet tall. Some cover crop growers are harvesting their corn in the afternoon and then planting a few acres of Sunn Hemp early the next morning. Waiting until the entire corn crop is harvested may narrow or even close the window of opportunity.
Sunn Hemp in 60 days is typically 6 feet tall and, being a legume, provides 100 lbs. of Nitrogen and brings up 20 lbs. of Phosphorus and 80 lbs. of Potash from the subsoil. It also produces four tons of organic matter as well as suppressing nematodes and weeds. It is excellent, particularly on suppressing Palmer Amaranth.
A golden opportunity is to fit Sunn Hemp after corn but before wheat. Wheat responds very well to Sunn Hemp and the Nitrogen and other benefits that it provides. Some wheat growers are producing their best wheat following Sunn Hemp. They are reducing the Nitrogen by 1/3 - 1/2 of their normal rates.