By Charles Wortmann, Ismail Dweikat
In Nebraska, hemp grown for fiber or grain will more closely match existing cropping systems than hemp grown for CBD. Fiber hemp could increase diversity for current rotations, but may offer some challenges, given no pesticides are currently labeled for pest management.
Varieties of hemp, whose stems are used for fiber, bio-fuel, or other products, grow to 6-7 feet in height, providing the desired long fibers for industrial processing. Varieties such as Futura 75, Futura 77, and Fanola have had some validation for Nebraska conditions. Hemp varieties should be certified as having <0.3% THC. Earlier maturing varieties may be preferred for grain production, and in some instances, they may be desired for both grain and fiber harvest. Fiber yield is likely to be less with earlier-maturity varieties than later-maturity varieties because cellulose concentration and yield increase as the season progresses. Hemp production for fiber is likely to be more competitive at higher latitudes while production for grain is more appropriate for lower latitudes due to photoperiod sensitivity. Male plants die off during the season and monoecious female varieties are generally preferred for industrial hemp production.
Grain production may be optimized with no more than 150,000 plants per acre and sowing 20 to 30 lb/ac of seed. Fiber production may be best when planting in row spacings of less than 12 inches with about 300,000 plants per acre (15-30 plants per square foot; 35-55 lb/ac of seed). High plant density results in tall plants capable of producing longer fibers. Hemp can be sown with a grain drill such as used for wheat. The seed weight has been estimated at 15,000 to 27,000 seed per pound (1000 kernel weight of 18-22 grams; the seed will be smaller for monoecious varieties). The seed is fragile and can be damaged during planting. With air planters, the fan speed should be set at low.
In Europe, fiber yields were not increased by having more than 182,000 plants per acre and this plant density resulted in better quality fiber than with higher plant densities. Hemp plant stands are likely to self-thin as more vigorous plants suppress the less vigorous, such as the male plants. Seed placement should be ½ to ¾ inch deep; some recommend seeding at more than a 1-inch depth in dry soil. Emergence is likely three to five days after spring planting. Hemp is more tolerant of low soil temperature at planting than corn and while seedlings can be killed by an early frost, hemp survived a 24o F temperature in May in Canada.
Fertilizer recommendations have not been determined for Nebraska. Penn State University has recommended 150 lb/ac N, 30 lb/ac P2O5 and 20 lb/ac K2O. In a series of trials in Europe, mean fiber yield did not increase with when nitrogen was increased from 90 lb/ac to 140 lb/ac; however, in another set of trials conducted in the Netherlands, fiber yield increase as the N rate was increased to 180 lb/ac. In Alberta Canada, grain yield peaked with 110 lb/ac N and fiber yield peaked with 80 lb/ac N. The optimal P and K rates will depend on soil test values.
Weed, Disease, and Insect Management
No herbicides or other pesticides are labeled for hemp in the US. Weed suppression with narrow rows, high plant density, and tall plants is important for fiber production. If planted in rows, inter-row cultivation may be needed for early weed control. Hemp can be planted no-till following a burn-down application of herbicide.
There is potential for disease and insect pest problems but information and recommendations are lacking for Nebraska and other states. No pesticides are labeled for hemp in the US. Therefore, rotation of hemp with other crops may an important component of integrated insect and disease management for hemp production. Hemp may benefit other crops in rotation such as through suppression of weeds and some nematode species by hemp. In Alberta, gray mold has been a problem and rotation with canola was found to increase sclerotinia.
Grain should be harvested when shattering begins. The rest of the plant will still be green and about 70% of the seed will be mature. The grain water content may be 22-30%. Grain combines can be used for grain harvest and some have suggested settings similar to those used for grain sorghum. The long stems can challenge combine harvest so some have placed PVC pipe around moving parts to reduce wrapping.
As with any grain crop, the proper harvesting, processing, transportation, and storage are critical to prevent spoilage and ensure the highest value for the harvested grain. Hemp grain is thin-walled and fragile, requiring care in harvest, storage, and transport. Grain should be dried immediately after harvest to less than 10% moisture.
Hemp is cut for fiber production between early bloom and seed set when the lower leaves of female plants begin to yellow. It is left in the field for up to five weeks for retting, a decomposition process that breaks the bonds between the outer long bast fibers and the inner shorter hurd fibers. The hemp is then raked into windrows two or three times for drying and to remove leaves. When dry, the windrows are baled and the bales are transported for processing to remove and separate the bast and hurd fibers. Bast fiber concentration is highest in the "bark" of the stem while high lignin but shorter hurd fibers dominate in the rest of the stem. Therefore, wider diameter stems are preferred.
Hemp Production Budgets
For information on budgeting for hemp grain and fiber production, see worksheets from Pennsylvania State University. A Cornell University publication has estimated mean values of production to be about $800 per acre for fiber alone, $1100 per acre for grain alone, and $1360 per acre for grain plus fiber. With a land charge of just $101 per acre, they estimated production costs of $458 to $546 per acre. Production in Canada and Europe has been highly mechanized with labor demands per acre similar to that of other agronomic crops, except for weed control and harvest operations which require relatively more time for hemp.
Source : unl.edu