The Role of Farm Machinery
Although crop production can in theory be controlled almost entirely by a mixture of chemicals — fertilisers, pesticides and weedkillers — most farmers still use large pieces of machinery in various stages of cultivation.
Farmers cultivate the land for four reasons: to clear crop debris, to incorporate manure, to kill weeds and to achieve a properly drained and aerated granular soil structure, or ‘filth’. Traditionally these objectives are attained by physical means. After the harvest the land is turned over by the plough; weeds, manure and rubbish are buried, and the resulting clods are then broken down by a variety of harrows and rollers, combined with the shattering effects of frost action and alternate wetting and drying.
The plough The principal implement of traditional cultivation is the plough. Designed to cut out a slice of soil and turn it over, it consists basically of a disc coulter — a vertical rotating blade which separates each slice from its neighbour, a share — a horizontal blade which undercuts it—and a curved mouldboard to lift and invert it.
The precise shape of the mouldboard determines the effect on the soil: the gleaming furrow slice, beloved of Victorian ploughmen and poets, came from the lea plough. This plough had a long, smoothly twisting mouldboard that preserved the slice in one piece and pressed it firmly against its predecessor to smother weeds. Most ploughs today have a more aggressively curved, or even slatted, mouldboard to break up the slice of earth and reduce the work required to produce a seedbed. Now that chemical weed control is available, the farmer’s main concern is to get the crop in the ground before the winter rains make cultivation impossible.
A single ploughing implement consists of between three and ten such plough bodies along a diagonal plough beam that is linked to the tractor’s hydraulic three-point mounting. By this mounting the plough is automatically raised and lowered to cope with ground irregularities, and the implement can be raised well clear of the ground to allow the driver to back right up to the hedge before starting the next furrow; had this mechanism not been widely adopted in the 1930s our hedges would have disappeared long ago.
Cultivators and harrows
The main function of the mouldboard plough is to bury crop remains and weeds, and to incorporate manure. It is therefore useful on, say, a dairy farm where feed barley and maize are often grown on fields which were previously well-manured grassland. To an intensive cereal grower its value is doubtful. Here the land is fertilised artificially and of the crop remains only the roots make a valuable contribution to the condition of the soil. Raw stubble takes time to decay and contains little goodness, so it is usually burnt. Having done this, many farmers leave the land much as it is, rather than turning it all over—at considerable expense—exposing the plant roots and risking the loss of plant nutrients by oxidisation.
This theory forms the basis of the technique known as minimum cultivation. In its extreme form it involves drilling the seed directly into undisturbed soil, but normally the ploughed surface is broken up by a tined cultivator or a disc harrow. This disrupts the crust that tends to form on arable land (which has a relatively poor vegetation cover and is easily ‘panned’ by heavy rain); and it disturbs annual weed seeds, encouraging them to sprout. They are then killed by spraying with a contact herbicide, such as paraquat, which burns off the foliage while leaving the roots intact. It does not penetrate the soil, and it may be that such chemical weed control has a less drastic effect on soil life than the wholesale disruption caused by traditional methods.
The disc harrow consists of a battery of circular blades that rotate as they are drawn over the ground. Originally designed to break up the clods created by ploughing, it has proved a most efficient and flexible cultivation tool. The blades are arranged in sets, angled to the direction of travel; the greater the angle, the deeper it bites, but a bigger tractor is needed to pull it.
The cultivator is a crude implement by comparison, being merely a number of strong tines bolted to a tractor-mounted toolbar. It is particularly effective on light, friable soil which shatters on impact, and is in fact a heavier version of the clod-shattering harrow which is found on every farm. This latter device is usually equipped with spring-loaded tines; drawn rapidly across land which has been previously disced or cultivated, its kicking action produces a rough seedbed ideal for a crop such as wheat. A finer seedbed may be achieved using a zig-zag harrow which has a number of prongs mounted in staggered formation on a light lattice frame. Themay be given by the Cambridge roll, consisting of a large number of freely rotating metal rings which produce a characteristic ridged effect on the land. Stones are pressed into the soil and the level surface which results helps in both establishing and harvesting the crop.
All this activity is naturally very time-consuming and it can lead to subsoil compaction. It is not uncommon, therefore, to see two or three different implements hitched in tandem. An alternative is to use a power harrow that has rotating tines and a powered, slatted crumbler-roller which prepares a seedbed in just one pass over the land.
Despite such precautions the continued passage of heavy machinery over the land eventually leads to compaction and drainage problems. A hard pan forms beneath the cultivation level, which must be broken up if the crop is to thrive. For this purpose the farmer uses a subsoiler, a steel wedge mounted at the foot of a vertical blade. Drawn through the subsoil by a powerful four-wheel drive tractor, it breaks up the hard pan and allows standing water to drain away.
Feeding and planting
Well-cultivated land is of little use if it lacks the necessary plant nutrients. The roots and foliage of weeds, ploughed-up grassland and crop remains are an important source of these, and so is animal manure, whether scattered by the animals themselves or by a muckspreader.
There is rarely enough animal manure produced on the farm to replace wholly the plant food removed from the soil by intensive cropping. Consequently every farmer uses manufactured fertiliser, normally in the form of dry granules which are scattered by a broadcaster. This is not a particularly accurate device: coverage may be incomplete or uneven and much fertiliser may end up in the ditch or under the hedge. There it is lost to the farmer and merely serves to upset the hedgerow ecology. One remedy is a pneumatic applicator which delivers the granules through a row of boom-mounted nozzles. Alternatively liquid fertiliser may be applied using a sprayer. This is less precise but more popular because it requires no specialist equipment.
Having fertilised and cultivated the land, the farmer is ready to sow the seed. This may be done using a broadcaster, but a seed drill is usually preferred. Essentially this is a number of tubes, arranged side-by-side, which deliver seed (and fertiliser if required) into slots opened by a corresponding set of light disc coulters or tines. Direct drilling into unbroken land requires a more heavily built machine, but the principle is identical. The seed is contained in a hopper spanning the full width of the implement and delivered automatically. For critical application the seed mechanism is designed to place seed accurately at predetermined intervals— a useful device in planting a regularly spaced crop.
Some crops, such as Brussels sprouts, are raised under glass and planted as seedlings, when they need careful handling. Fully automated mechanisms are complex and expensive and can only be justified by a big investment in the crop. Consequently in vegetable-growing areas it is still common to see semi-manual transplanters in action. These have several operators who travel on the back of the machine, feeding the plants between pairs of rotating rubber discs which transport them down to the opened furrow. Potatoes may be planted in much the same way.
Once the crop is in the ground, it must be maintained in good condition. This is a job for the sprayer, loaded with whatever pesticide, fungicide or selective herbicide is thought best to combat the latest scourge. Occasionally the job may be done from the air by a contractor; more commonly the equipment is hauled by a light tractor, travelling in the well-established wheel-tracks or ‘tramlines’ spaced to match the coverage of the spray-booms. The same system is used to provide a top-dressing of fertiliser, if required, by which time the farmer is already planning the forthcoming harvest.