A traditional sickle mower cuts hay with sharp triangular blades mounted on a bar that moves back and forth. Disc mowers, more recently on the farm machinery market, use rapidly spinning sharp discs mounted on a bar.
Expense and Power
The initial cost of disc mowers is 20 to 30 percent higher than sickle mowers, and they cost more to operate.
It takes more power to run a disc mower, so a larger tractor is necessary. A small tractor can run a disc mower; and a sickle mower requires about 30 per cent less horsepower than a disc mower.
Quality of Cut
The disc mowers yield a ragged cut, which in some cases encourages plant diseases in the stubble. Disc mowers do better if the crop is thick, wet or is lodged (fallen over), but the impact cutting of the disc can damage the crowns of plants.
Sickle mowers are slower, but give a cleaner cut.
Early models of disc mowers were expensive to maintain because the failure of the gearbox of one disc meant trouble for the other discs. Manufactures now isolate the gear boxes, and the repair bills are less of a burden.
If you hit a major obstruction in the field, the disc mower will still likely cost more to repair than a sickle mower. The chief headache and expense of running a sickle mower lies in replacing the blades that are occasionally knocked off by rocks or other hard objects.
A disc mower can cut at a higher ground speed than a sickle mower, pushing easily through molehills and hay that is wet, tangled or fallen over. If you have a lot of acres to cut or have to cut under tough conditions, the disc mower might be best for you.
If you harvest your hay two or three times in a growing season, you'll want it to regrow quickly after you cut it. The clean cut of a sickle, which is rather like scissors, does less damage to the plants that need to grow again.
The disc mower seems the more likely choice for a grower with a powerful tractor, large acreage and substantial budget; the sickle mower may be better for the farmer with a small tractor and more modest fields.