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Hemp grows best on rich and fertile, neutral or slightly well-drained clay-loam or silt-loam soils in which the subsoil is fairly retentive of moisture. Although hemp makes heavy nutrient demands on the soil, research conducted at Canadian experimental farms during the 1930s showed that hemp takes less from the soil than wheat or corn when taking into account that up to 70 per cent of the nutrients absorbed by the plants are resumed to the soil, in particular with the large numbers of falling leaves and through the retting process. Cleaning or mechanical stripping of the leaves and flowers in the field also allows for maximum nutrient recycling. However, prior to the nutrient recycling, hemp extracts more nutrients per hectare than grain crops, removing about two to three times as much nitrogen, three to six times as much phosphorus, and 10 to 22 times as much potassium per hectare, owing to fast biomass production.
Therefore, to achieve an optimum hemp yield, at least twice as much nutrient must be available in an easily assimilable form as will finally be removed from the soil by the leaf-free harvest. Fertilizer rates vary depending on soil type. end use of the plant and crop rotation. A three-year, but preferably a four-year rotation, such as cereals, clover for green manure, com, hemp and then back to cereals is recommended to help maintain soil fertility.
Harvesting of hemp for high quality fibre occurs as soon as the mop is in flower. Harvesting for seed production and fibre occurs four to six weeks after powering, however the fibre will be of poorer quality because of lignification of the best fibres making it stiff and coarse. If the goal is maximum stem yield, the implication for fibre hemp breeders is clearly to breed late- or non-flowering cultivars.
A lapse of nearly 60 years in the development of hemp harvesting equipment in North America requires some innovative ideas. Equipment developed for other fibre crops, such as Kenaf, may be used for hemp with minor modifications.. Attempts at using sickle mowers, haybines and round balers have been used with some success depending on she end use of the hemp stalk. Requirements for chopped stalk by the pulp and paper and fibreboard industry would allow the use of these types of equipment.
Harvesting hemp for the long best fibre for the cordage and textile industries requires the fibre to be undamaged negating the use of haybines and balers. To ensure the long best fibres are undamaged a resting process is required.
This is the process of decomposition by bacteria and moulds by which the pectin that binds the fibre and the non-fibrous portion of the stalk is broken down. Once the binding agent is broken down, the fibre and the stalk are easily separated. There are several different resting procedures that can be used.
Dew resting is the traditional method induced by frequent rains and dews. After the hemp stalk is cut, it is spread evenly on the ground to allow decomposition of the pecan. There is a fine line between resting and rotting. if continued wet weather prevents the straw in the fiend from being lifted at the proper fume, it becomes over-retted and is of little value. Without the proper equipment dew resting is labour intensive. n may take one to two weeks if she weather Is warm and humid, but usually four to five weeks are required. The resting process is followed by a period of drying and the bunches are then stored for further processing. The fibre from dew rested hemp is light brown in colour and rather coarse. It is used primarily for twine' cordage and fine paper.
Water retting: Bundles of hemp are submerged in clear water low in calcium and chlorides allowing bacterial activity to break down the pecan. The average retting period is seven to 10 days after which rested bundles are then rinsed, washed, sun-dried and stored for fibre extraction. Although water resting is more costly than dew retting, the fibre is of a higher quality. It can be combed one or more times, refined, dyed, spun and woven into whatever extent is required for cable, rope, string, thread, cloth, clothing, linen, etc.
Warm water retting is similar to water rotting but the hemp is soaked for 24 hours then new water is added and brought to an elevated temperature for about two to three days. A very uniform, dean fibre is produced
Green retting: As the name implies, green stalks are mechanically processed to separate the fibre from the stalk The high quality fibre can be refined for the textile for the textile industry while the remaining stalk can be used in the paper and fibreboard industries.
Chemical retting: Hemp stalks are placed in a processing tank where chemical agents are used to dissolve the pectin. By maintaining a constant processing temperature the resting time can be reduced to 48 hours while producing a very high quality fibre.
After the retting process the hemp fibre and the stalk are loosely held together and must be decorticated, scutched, hackled and combed to remove the remaining pieces of stalk, broken fibres and extraneous material. Mechanical decortication equipment can be used in conjunction with turbine scutchers to separate the fibre and the nonfibrous portion of the stalk Inventors and implement companies are working together developing machinery to harvest and process hemp for the textile, paper, fibreboard and seed industries.
In 1916, USDA predicted a papermaking future for nonfibrous portions of the hemp stalk Extraction of the fibre from the hemp stalks results in a second highly useful byproduct called hurds. The lignin content of the hurds is lower than in wood, of offering better opportunities for non chlorine bleaching or the production of unbleached pulp. The hurds, about 45 per cent cellulose, 35 per cent hemicellulose and 20 per cent lignin, can be used to produce a variety of products rayon, fuel, cellophane, food additives, industrial fabrication materials and paper products. Before 1883, about 75 to 90 per cent of the worlds paper was manufactured from hemp best fibre. In 1989, 92 per cent of the virgin fibre used to manufacture paper came from wood, the remaining eight per cent was from annual crops «over residues. As world paper consumption increases by about four per cent annually, interest in hemp as a potential law material for paper production has been revived since hemp can produce more paper per hectare than 20-year-old trees Archer prominent end-use for hemp is industrial fabrication. Hemp fibres and hurds are an excellent natural material used in the manufacturing of lumber, plywood, particleboard or composite constructor material.
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