Kona Coffee and Hemp and Biosustainability
Sunn Hemp (Crotalaria juncea) is a native of India that has received recognition as a coveted green manure and cover crop. As a legume, it possesses the nitrogen-fixing properties that make it a valuable green manure which can be grown in a field and then mowed and plowed into the soil before rotating to a cash crop.
Sunn Hemp
The Kona Coffee Belt, on the volcanic slopes of Mauna Loa, is not an area where “plowing” green manure into the rocky soil, is practical. However, composted Sunn Hemp can be applied to the soil surface around the base of the coffee trees, where each ton of dry hemp yields up to 51 lbs of Nitrogen!
That fact becomes exciting when converted into equivalent bags of fertilizer required to supply the same amount of Nitrogen, (for example: 20 bags of a commonly used product). Without Nitrogen, plants cannot grow.
Sunn Hemp is grown on Patrick Farm, specifically for the purpose of composting it into a high fiber, high nitrogen fertilizing mulch that can be applied around the base of the coffee trees , where it gradually decomposes and mixes into the soil. The mulch acts as a weed suppressant around the coffee tree as it breaks down, and helps conserve water.
Flowering Sunn Hemp
Four crops of Sunn Hemp are planted, harvested and composted in our fields each year. A small portion of the crop is allowed to flower and develop seed for replanting. The bulk of the crop is cut off just above the soil, leaving the roots, with their nitrogen fixing nodules, in the soil. The leafy stalks are placed around the coffee trees where they mulch aerobically. The hemp is best harvested before flowering has occurred, and the plants become so fibrous, that they are difficult to cut with a weed whacker. Three months after planting, by broadcast, the sunn hemp has reached approximately waist high, and the first flowers are starting to appear. At this stage the hemp is cut and placed on the ground around the coffee trees, and then the reseeding is repeated.
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MCSORLEY, R. 1999. Host suitability of potential cover crops for root-knot nematodes. Supplement to the Journal of Nematology 31: 619-623
ROTAR, P. P., and R. J. JOY. 1983. ‘Tropic Sun’ sunn hemp, Crotalaria juncea L. Research Extension Series 036. College of Tropical Agriculture and Human Resources, University of Hawaii. 7 pp.
REEVES, D. W., Z. MANSOER, and C. W. WOOD. 1996. Suitability of sunn hemp as an alternative legume cover crop. in Proceedings of the New Technology and Conservation Tillage 96 (7): 125-130. University of Tennessee Agricultural Experiment Station, Tennessee
Dempsey, J.M. 1975. Fiber Crops. The University Presses of Florida, Gainesville, FL
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