Coulters

Suffolk (Fig.20).This has a cast iron shoe which cuts a narrow furrow for the seed. Its shape helps to keep a straight and even depth furrow. Suffolk coulters do not block easily and are not affected by stony land. There are no moving parts to lubricate but soil contact wears the bottom of the coulters rather quickly. Penetration can be difficult in hard ground. Suffolk coulters are suitable for sowing both root and cereal crops.

Ceramic tipped coulters with a life up to five times longer than steel are used on some Suffolk-type coulters.

Figure 20. Two types of drill coulter.

Disc coulters (Fig.20).are saucer shaped and cut a rather irregular depth furrow. Their cutting action helps with penetration and they work well in most soils. Stones can stick between the disc and its support and cause uneven wear. Different manufacturers use various types of disc. Some use double discs usually staggered in two or three rows across the drill. Others use a single serrated edge disc for added grip. Disc coulters are not suitable for drilling root crops.

Hoe coulters. (Fig.21)Their main use is for minimal seedbed techniques with a cultivator/drill com­bination. Hoe coulters can have various width shares usually with replaceable points, which are bolted to spring tine shanks and mounted in staggered rows across the full width of the drill. The coulters stir the soil and make a shallow furrow for the seed. The seed tubes from the feed mechanisms are attached to the back of the coulter tines.

Some drills have hinged flaps (see Figure 22) on the coulters to prevent soil blocking the seed outlet if the coulters are lowered when the drill is stationary or it is accidentally reversed while they are in the ground.

Figure 21. The tension spring on this Suffolk-type coulter maintains the correct sowing depth.

Figure 22. A Suffolk coulter with covering tines and a hinged flap which prevents soil blocking the coulters if the drill is reversed when they are in the ground.

Sowing depth. A regular sowing depth is important for even emergence of the seedlings. The coulters are carried on arms which pivot individually at the front of the drill. Sowing depth is altered by adjusting a depth limiting stop on the hydraulic ram used to raise and lower the coulters. A hand lever or screw adjuster is used to set coulter depth on some mechanical lift drills.

Compression springs above or tension springs below the coulter arms are used to set the coulters at the correct depth in the soil. The spring pressure is adjusted to suit soil con­ditions with the most pressure required on com­pacted ground. Some minimal tillage and plain grain drills have hydraulic rams to increase or decrease the working depth of the coulters.

Row width. Row widths of 180 mm (7 in) are traditional for cereal crops but drills with coulter spacings from 90 to 150 mm (ЗУ2-6 in), depending the preference of the farmer, are in current use. Some single-pass cultivator drills with pneu­matic seeding have wider row widths. One model has double disc coulters 240 mm (9Vi in) apart; another, with special coulters spaced at 500 mm, drills seed in wide bands giving the plants more room to grow.

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