Combining hemp for seed
Combining hemp provides a special challenge to both the combine and the operator. In tall varieties, large quantities of plant material are put through the combine. Hemp straw contains very tough fibres that tend to wind around moving parts. Fine fibres work into bearings, causing friction that can lead to bearing breakdown and combustion. These factors cause heavy machinery wear, high maintenance costs and a great deal of time loss and frustration on the part of the operator. Early grain varieties such as Fedora 19, FIN314 and Fasamo are shorter and easier to combine.
Industrial hemp seed is harvested when the seed begins to shatter. At this optimum harvest time, about 70% of the seeds are ripe and about 22-30% moisture. Later combining results in increased grain losses due to shattering, bird damage and lower quality grain. Mature fibres tend to wrap more tenaciously around moving parts on the combine.
Raising the cutting blade to about 1 metre (40 in.), or as high as the header will cut effectively, reduces the amount of material entering the combine. With shorter varieties use a “closer to normal” header position. The header knife must be kept sharp at all times to minimize winding of fibres on the sickle bar. Replacing the slatted feeder conveyor with a belt helps reduce the amount of fibre that winds on the feeder shaft. Exterior rotating shafts and pulleys that may come in contact with stalks should be protected when harvesting taller varieties.
Proper setting of the combine improves the yield and quality of the grain and reduces wear on the combine. Experiment with ground speed, concave openings, air and cylinder speeds. The following settings are suggested for conventional combines: cylinder speed at 250 rpm, fan speed at 1070 rpm, 1/8-inch sieve and 3/8-inch chaffer, concave set tight. Run feeder housing chain loose in the corn position and close the pre-cleaner. Lower the beater grate, remove the curtains and install a speed-up kit for the beaters. Individual combine operators might find different settings work for their machines. Rotary combines seem to be less satisfactory for harvesting hemp grain because of a tendency to plug more readily.
Reported grain yields in Ontario have ranged from 300 to 1300 kg/ha at 12% moisture, after harvesting and cleaning. Higher yields may be possible as varieties and production technology improve.
Some “volunteer” hemp will likely appear in the fall or spring following the hemp crop. These plants are illegal and must be destroyed before being discovered by local drug enforcement authorities. Thorough cultivation or seedbed preparation is effective.