Among sunnhemp's many uses are the following: green manure, nitrogen fixation, weed suppression, livestock forage, and pest control. Farmers in Tanzania have found tillage easier in fields where sunnhemp has been grown and incorporated into the soil, due to improved soil texture. These farmers can plow their fields before the rains, giving crops the benefit of the full rainy season, improving their chances of a successful harvest. Sunnhemp's deep root system aerates the soil and increases water infiltration. The deep roots also retard soil erosion.
Nitrogen fixing rhizobium associated with these roots, fix atmospheric nitrogen normally unavailable to plants. Professor M. P. Salema of Sokoine University of Agriculture, Morogoro, has isolated superior kinds of rhizobium for improved nodulation on sunnhemp. By innoculating their seeds with the rhizobium farmers can now increase their production.
Nitrogen that has been fixed by the soil rhizobium is made available to crops by composting sunnhemp or turning it into the soil in situ. The organic matter added to the soil also improves soil moisture retention and texture. Cut sunnhemp can be used as a mulch to suppress weed growth and to control erosion. Ultimately the sunnhemp mulch will decompose, adding nitrogen to the soil to benefit succeeding crops. Sunnhemp's low carbon to nitrogen ratio causes it to decompose readily, quickly adding nutrients to the soil. Sunnhemp, unlike most nitrogen fixing legumes, performs well on poor and acidic soils. For this reason farmers in Tanzania have used sunnhemp to revitalize weedy or infertile fields
In addition to its soil improving qualities, sunnhemp also controls weeds. Under appropriate conditions sunnhemp establishes quickly and grows abundantly, thus out competing weeds. If planted densely, sunnhemp prevents weed growth in the first year, and reduces subsequent weed growth for the following 1-3 years. Sunnhemp can out compete couch grass (Digitaria sp) but not blackjack (Bidens pilosa). Over the course of 3 years sunnhemp eventually out competes stargrass (Cynodon sp) in paddies.
The same rapid, abundant growth that out competes weeds also controls erosion. Planting sunnhemp between crops, both spatially and temporally, maintains a continuous plant cover which stabilizes the soil and breaks the impact of rain drops. Since sunnhemp is drought tolerant, it is able to protect the soil when rains begin again.
According to farmers' observations, sunnhemp controls nematodes which attack tomatos. Farmers plant sunnhemp about four months before planting the tomatos. Cut the sunnhemp and dig it in to the soil one month before planting the tomatoes or when the sunnhemp is about one meter high. Sunnhemp also hosts a beneficiall insect, the earwig. Earwigs enter stem borer tunnels in search of larvae. Occasionally they climb the foliage to prey on leaffolder larvae. Earwigs can consume 20-30 prey daily, and live 3-5 months. Farmers in Tanzania have noticed few harmful insects in fields where sunnhemp is intercropped with maize.
Farmers in Tanzania have discovered several successful management techniques for growing sunnhemp in association with their food crops. Some farmers plant single stands of sunnhemp before and after maize when chemical fertilizer is unatainable. Although an extra plowing is required to plant the sunnhemp, weeding is reduced, and maize yields are higher. Other farmers sow sunnhemp along with maize, and incorporate it into the soil when it nears the height of the maize.
Farmers who rotate sunnhemp with maize or sorghum plow the sunnhemp under at flowering. At this stage the sunnhemp has accumulated near to maximum amounts of nitrogen, and the biomass is still succulent enough for fast decomposition and release of nutrients. In very poor soils sunnhemp improves soil fertility most when the mature plant, including the seeds, are incorporated into the soil.
Sunnhemp can also be used in a rotational planting schedule along with rice and beans. Sunnhemp is planted in the rice fields at the time of the first rice weeding. The sunnhemp is still short when the rice is ready for harvest. After harvesting the rice, sunnhemp covers the field, and is plowed in before planting beans. Farmers in Tanzania have found these method quite effective in controlling weeds. A later issue will feature a community where Sunnhemp is used as a fertilizer, and its seeds are valued as a cash crop.
For more information, or to order a copy contact:
Fr. Gerold Rupper, O.S.B.
Sunnhemp Seed Bank
Bos 1, Peramiho Tanzania