The best known and most universal driven tillage machine is the rotary cultivator (Fig. 5), whose use ranges from primary and secondary tillage in conventional systems to minimum tillage and use in paddy field rice cropping. This machine performs primary and secondary tillage in one pass, even on difficult soils, while on sandy soils with little structure and internal cohesion, the use of the rotary cultivator can be problematic. An advantage of the machine is that organic matter is disintegrated and mixed into the whole worked area of soil. A problem can be that soil over the whole worked area is cut into very small clods, which can cause encrustation and erosion and, under wet conditions, smear at the bottom of the worked area may occur. A possibility to lessen these problems and reduce energy consumption is to reduce the rotor speed, but then it may happen that the seedbed is not sufficiently fine. The rotary harrow can be used for minimum tillage, too. Certain machines perform seeding either by using a seeder bar right behind the rotor so that the seedlings are put into the soil at working depth or on the plane created by the roller and covered by that portion of soil which is going over the roller (Fig. 5). Thus, only the seedbed zone or a slightly deeper soil area is loosened.
Rotary cultivators, made in various widths from 1 m for compact tractors up to about 5 m for tractors up to 185 kW (250 hp), have a series of ‘U’ shaped blades attached in a spiral around a horizontal rotor shaft. They are power take-off driven and mounted on the three-point linkage. Small rotary cultivators use the 540 rpm shaft but the wider models have a high power requirement and the 1,000 rpm shaft is normally used.
Plate 6. Mounted rotary cultivator. The overload slip clutch springs can be seen below the top link bracket. Drive from the gearbox is transmitted to the rotor by a heavy chain running in an oil bath. Working depth is controlled by skids at each side of the machine.
The drive arrangement is through a gearbox and chain drive to the rotor. An overload slip clutch is built into the drive and the rotor speed can be varied by using different pairs of driving gears. (Fig. 6) Some of the larger rotary cultivators have a gear lever to select any one of six or more rotor speeds. The blades are arranged in a scroll pattern (Fig. 7) around the rotor to put a constant load on the tractor power shaft. The soil is thrown against a hinged flap at the back of the cultivator blades; this helps to shatter the clods.
Figure 7. The blades are arranged in a scroll pattern on the rotor of a rotary cultivator.
Heavy duty tines on a separate toolbar hitched between the tractor and cultivator can be used to break up the subsoil, and a crumbier roll can be fitted at the rear to consolidate the cultivated soil.
Adjustments.Tilth three adjustments can be made to vary the type of tilth produced:
1. The rotor speed can be varied by choosing a different gear ratio in the cultivator gearbox (Fig. 8). A fast rotor speed gives a fine tilth.
Figure 8. One type of gearbox used to change rotor speed on a rotary cultivator.
2. The tractor forward speed, changed through the gearbox with the power shaft speed maintained at 540 rpm. A low forward gear will give a fine tilth.
3. The hinged flap behind the machine gives a fine tilth when lowered. The tilth will be very coarse with the shield raised.
Plate 9. This rotary cultivator has drive shafts from a central gearbox to gear drives at both sides of the machine. The knife blades are for tough soils with many stones and for incorporating straw.
Working depth.Adjusted with a wheel. Depth of trailed models is controlled with an external ram on the machine. A skid is sometimes fitted to prevent the cultivator going too deep, especially if the depth wheel drops into a low place.
• Stubble cleaning.
• Seedbed work, especially for root crops. A spiked rotor can be used for seedbed making. (Fig. 10)
• Cutting up weeds and crop residues.
• Land reclamation work and around headlands.
Plate 10. A spike rotor can be used to prepare seedbeds with a rotary cultivator.