Pneumatic Grain Drills.

This type of drill is suitable for drilling a wide range of seeds at relatively high forward speeds. Both trailed and mounted versions are made, with working widths of 2.5-8 m in common use.

Although the seed metering mechanism, usually a fluted roller, is land-wheel driven on most drills, on some it is driven by a hydraulic motor. Seed is supplied from the hopper at a controlled rate to a venturi where it enters an air stream from a fan driven by either the power take-off or a hydraulic motor and blown to a distributor head. This distributes an equal amount of seed to the seed tubes, which deliver it to the coulters. Hydraulic rams are used to control sowing depth. (Fig. 23)

Wide pneumatic drills sometimes have two hoppers with separate metering units which supply seed to the air distribution system. Another type of pneumatic grain drill has indi­vidual fluted roller feed mechanisms for each row or pair of rows, depending on model, and the metered seed is introduced to a flow of air from the fan and transported through the seed tubes to the coulters.

Seed rate is altered by adjusting the metering unit with a lever or handle. The air blast fan must run at the recommended speed for effi­cient operation. Some drills have an electronic control box which can vary the seed rate while on the move. This device has applications when using yield maps produced from the combine at harvest time. The control box may also have flashing lights to monitor seed level in the hopper, airflow and drive to the feed mechanisms.

Figure 23. The path of the seed in a pneumatic grain drill.

Tramlines.

It is useless to deposit seeds where no plants can grow. Therefore, it makes sense to provide for unsown tramlines there, where the wheel tracks for top dressing of fertilizer and pesticides will be. These are unsown rows which provide wheel­ings for spraying and fertiliser spreading after the crop has emerged. This technique, used by many farmers, avoids the tractor wheels damag­ing the growing crop and ensures accurate joining of bouts when using a sprayer or ferti­liser spreader. This applies to closely spaced crops such as small cereals and rape, which do not yield in wheel tracks. With widely spaced crops the row spacing can be arranged such that these wheel tracks just fit into the interrow area. Tramlines are usually 12, 18 or 20 m apart, depending on the working width of the farm sprayer and fertiliser spreader. Some farmers use 24 m tramlines.

Tramlines can improve the precision of fertilizer and pesticide distribution, since driving deviations are minimized. The yield depression caused by the tramlines propor­tionally can be decreased by wide working widths of the top dressing machines. There­fore, the top dressing operations should be carried out with multiple working widths of sowing.

There are two basic types of tramline equip­ment. Earlier versions had manual controls and relied on the tractor driver to remember to turn off the feed mechanisms at the proper time for the two rows which form the tramlines.

Automatic tramlining depends on an elec­tronic control box in the cab. One model gives the driver a choice of between one and six bouts before making the next set of tramlines.

The control unit is operated by the automatic marker changeover mechanism. It receives sig­nals from the markers and, after the pre-set number of bouts is completed, the tramliner solenoid shuts off the feed mechanism to the two rows which form the tramline. Seed tubes are closed off on pneumatic drills. An over-ride switch is provided for use if the markers have to be raised during the bout to clear blocked coulters.

Arranging of tramlines with bulk metering is possible by closing the respective seed gates of the hopper, by locking the respective seed rollers, or, for air seeders with central feeding, by closing the respective tube inlets at the circular deflector plate. Shifting of tramlines is done either by hand within the tractor cabin or automatically while turning at the headlands in an adjusted sequence.

Figure 24. Pneumatic grain drill feed mechanism.

Figure 25. The layout of a pneumatic grain drill with a front hopper. A fan blows the seed to the drill coulters attached to a power harrow on the rear linkage.

Markers. Drill wheelings are sometimes used by the driver to help achieve accurate joins between bouts, but markers provide a more accurate guide. Some tractor drivers use a marker disc or tine to cut a shallow guide furrow for the tractor front wheel on the next bout. Others prefer to join drill bouts by following a guide furrow central to the tractor. The marking furrow may be made with a tine or disc which, with a few exceptions where a rope or lever is used, is raised and lowered hydraulically. The marker arm is telescopic so that the distance between the disc or tine and the outer coulter can be altered to suit the wheel track width of the tractor.

To set drill markers refer to Figure 26 and follow this method: measure the distance from the centre of the tractor front wheel to the outside coulter on the drill (distance A); measure the row spacing (distance B).

Add A to В and position the marker this dis­tance from the outer coulter.

Figure 26. Setting drill markers

Using Grain Drills. Some trailed grain drills and mounted cultiva­tor/drill combinations are narrow enough to be towed or transported on the tractor hydraulic linkage from field to field. Wider drills may either be moved along the road with an end-towing kit or have hydraulically folded wing sections (Fig. 27). An end-towing kit has hydrauli­cally lowered wheels at one side of the drill and provision to attach a drawbar at the opposite side.

Many farmers buy their seed grain in big bags and use a forklift truck to carry them from a trailer and lift them over the drill to fill the grain hopper.

Figure 27. A wide direct drill with pneumatic feed hydraulically folded to 3.0 m for transport.

Some farmers drill three or four bouts around the headland before drilling the main part of the field. This ensures the coulters penetrate to the correct depth before the headlands are com­pacted when turning at the end of each bout. This technique provides a guide mark for lower­ing and lifting the drill into and out of work.

The headlands may be drilled last when the field is drilled with a direct drill or a combina­tion cultivator drill.

Calibration. The amount of seed sown per hectare can be calibrated or checked in the field or farmyard (Fig. 28). Some drills are linked to a computer in the tractor cab which can be used to check seeding rate while drilling is in progress and, if required, vary the rate to suit the soil conditions in various parts of the field.

Figure 28. The calibration trays on this drill fold down to collect the grain when checking the application rate.

Figure 29. In order to calibrate the seed and fertiliser on this drill, trays are under the feed mechanism housings while the gearbox is turned a set number of revolutions.

Settings for a wide range of crops and seed rates are given in the operator's manual for the drill. When it is set to the required rate a static calibration test can be made to check that the required quantity of seed will be sown at this setting (Fig. 29).

Fluted roller and studded roller force-feed drills with small-diameter driving wheels, as well as pneumatic drills with a mechanical metering system, can be calibrated in the bam with a crank handle which turns the feed mech­anisms or metering unit for a set number of turns, usually equivalent to sowing 1/25 hectare or 1/10 acre. The number of turns varies with the model and drilling width and this information is given in the instruction manual.

After setting the drill according to the instruc­tion book, to give the required seed rate, the crank handle is turned the required number of times with the drill in gear. The grain is col­lected in trays and weighed. This weight is multiplied by 25 for rate per hectare or by 10 for rate per acre to find the actual seed rate.

The feed mechanism on very wide drills is often in two parts with a separate drive to each half. Both must be checked to complete the cali­bration process.

Pneumatic seed drills can be calibrated by turning the feed mechanism a set number of times with a handle, the seed is collected and weighed. A simple calculation is used to find the seed rate in kg/ha. Drills with a feed mecha­nism driven hydraulically or by electric motor linked to an in-cab computer can be calibrated from the driving seat. When linked to a radar unit the computer maintains the pre-set seed rate. If it detects a change in tractor forward speed the computer automatically alters the speed of the motor driving the feed or metering mechanism to maintain the required seed rate.

Maintenance of grain drills. Check that the coulters, feed tubes and feed mechanisms are in good condition. Keep drive belts and chains at the correct tension.

Fertilizer is very corrosive. It should be cleaned out of the drill at the end of each day's work.

Clean the drill before storage, protect all bright parts from rust, replace broken parts and store under cover.

Seeder units

Mainly used for root crops and vegetables, seeder units have a feed mechanism which can be set to drill the seed at various spacings in the row. A number of units, usually between four and twelve, are attached to a tractor toolbar.

Seeder units consist of a frame on two wheels with a mechanical or vacuum feed mechanism, coulter, covering device and seed hopper. The rear wheel firms the soil after the seed has been covered. The feed mechanism may be driven in one of the following ways:

1. Individual drive by the seeder unit front wheel.

2. Master wheel drive with the toolbar land wheels driving the seed mechanisms through a gearbox and system of chains or vee-belts.

3. Individual electronically controlled electric motor drive to each unit. Varying the speed of the electric motors changes seed rate and seed spacing in the row.

Vacuum feed drills have a master wheel drive for the seed wheels and a power take­off driven fan.

Figure 30. Belt feed mechanism.

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