Baldwin County Extension Office
302A Byrne Street
Bay Minette, AL 36507
Telephone (251) 937-7176 or
928-0860/943-5611 ext. 2222
FAX (251) 937-7285
Regional Extension Agent/Agronomic Crops
December 1, 2009
Sunn Hemp - a New Cover Crop for Alabama
Russell Hendrix in Fruitdale, Washington County, Alabama is the producer conducting the “On Farm Sunn Hemp Demonstration and Research” project for Southwest Alabama. Sunn hemp is used in many tropical countries as the number one 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 being a tropical plant grows only in the summer here. Brazil’s second soil builder is the “Tillage Radish”. There are over 350,000 acres of the tillage radish in Brazil.
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. It is also excellent for deer and goats.
Sunn hemp is a good source of Nitrogen. It is a tropical legume so as it grows it produces Nitrogen. Then when the crop dies it releases Nitrogen back into the soil for the next crop. Over the summer sunn hemp in favorable conditions may grow ten to twelve feet tall and release 200 pounds of Nitrogen back into the soil.
In Hendrix’s experiment the sunn hemp was planted on August 10, 2009. A good fit for sunn hemp in South Alabama would be to plant sunn hemp following a corn crop. This is why it was planted on August 10th. On October 6, 2009 sixty days after planting the sunn hemp was sampled. It was air dried for 10 days and weighed in order to calculate the amount of organic matter and nitrogen the sunn hemp would add to the soil. Hendrix’s sunn hemp in 60 days was 6 feet tall and produced 7,840 pounds (3.92 tons) of organic matter and 118 pounds of Nitrogen.
A good rotation in South Alabama would be corn, Sunn hemp and then wheat. This would allow the sunn hemp to rebuild the soil and supply the Nitrogen for the following wheat crop.
In Hendrix’s experiment no diseases or insects were noticed to affect the sunn hemp. It appears to smuther out most if not all other weeds including pig weed and nutsedge. This crop may prove very beneficial in ridding land of unwanted weeds and pests. Hendrix’s experiment also included attracting deer. The deer enjoyed eating the leaves of sunn hemp until the crop grew around 3 feet tall. The leaves of sunn hemp are 30 % protein. From that point on the deer did not damage the crop, but still enjoyed walking in it.
Sunn hemp is resistant to root-knot and Reiniform nematodes. This is another major factor for growing this crop. 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. Sunn hemp would be a tremendous benefit in reducing nematode populations in almost every home garden in our area. Gardeners could plant their spring crop and then in July or August plant the sunn hemp.
Cultural Practices: The recommended seeding rate is 50 pounds per acre. Seed costs are now around $3.00 per pound so growers might experiment with lower rates, even 25 pound per acre. Seed can be broadcast and covered about ½ to 1 inch deep or drilled in.
Sunn hemp will grow on poor soil with a pH of from 5 to 7.5. It will grow on sandy or clay soils, just not too hard packed clay. The soil does need to be fairly well drained. It will need zero Nitrogen, but will grow better if ample Phosphorus and Potash are in or added to the soil.
Sunn hemp is fairly drought tolerant, but will grow better if it receives ample moisture. Sunn hemp may be planted any time after there is no danger of frost in the spring and will die again at first frost in the fall.
The plant grows very fast and in about 60 days will be 6 feet tall or taller. This is a good time to mow the sunn hemp about 10-12 inches high and let it ratoon or regrow again. If allowed to get too tall and old the stems will become tough and fibrous and will not decompose rapidly. If the plants are too tough they will also cause problems the following year when you are trying to prepare your soil and plant.
Sunn hemp is a day length sensitive crop. It will grow any time during the summer, however it will not flower and go to seed until the days start getting shorter (late September here). So the plants do not reproduce mature seed in our area. The only place the seed will grow in the U.S. is South Florida, South Texas, Puerto Rica and Hawaii. Therefore seed is fairly expensive for large acre conditions.
Research has been conducted in the U.S. since the1930’s. Even then it was reported for its excellent soil conditioning benefits. Research is presently being conducted in Hawaii, South Carolina, Florida and Auburn University. Dr. Jorge Mosjidis is the plant breeder at Auburn working with sunn hemp. He is concentrating on breeding varieties that will produce seed here in the Southeast. The major purpose of this is to decrease the seed costs so growers could use this cover crop on a large scale. His varieties are probably two years from being commercially available.
Seed supply here in the U.S. is limited and is rather expensive. It is too late to plant seed this year, however, there may be a small supply of seed that growers could purchase to experiment with and home gardeners could afford for their smaller gardens next season. The seed supplier for Alabama is Tucker Farm Center (251-267-3104) in Frisco City.
Russell Hendrix’s On Farm Experiment will include the “Tillage Radish”. Hendrix mowed and then disked the sunn hemp on October 10 and then planted the “Tillage Radish” on October 15, 2009. The radish will benefit from the Nitrogen and soil improvements provided by the sunn hemp and then will provide a winter blanket for the soil and will greatly improve the soil condition, replenish Nitrogen to the soil and help to control the nematodes. This field will have been greatly improved for whatever crop Hendrix decides to plant next spring.
Russell Hendrix in Washington County is the producer conducting the "On Farm Sunn Hemp Experiment" for Southwest Alabama. Photo taken six weeks after the sunn hemp was planted.
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