Growing Crops on Arable Land
Arable fields lie undisturbed all winter, but as spring arrives they come to life. The farmer busies himself with tractor and plough, and intrepid insects, birds and other animals prepare to take their chances in this risky environment.
At the beginning of spring the farmer brings his tractor for the first time in the year to the arable fields. All through winter the land has been left alone, and the heavy machinery has stayed in the shed. Since the soil is far wetter in winter than it is in summer, no farmer can risk the damage heavy vehicles inflict by reducing soaking wet soil to useless, compacted mud.
As the days grow longer, the warmth of the sun gradually dries out the land. The water evaporates from the surface, and at the same time runs off the soil into the drains and ditches, which carry it away, lowering the level of water in the ground (the water table). If the soil is light and sandy, it dries relatively fast, but if it contains a greater amount of clay it has a denser consistency, and dries out more slowly. By the time the clay soils are dry enough to work, the season may be well advanced. Each farmer has to know his land and carefully assess the best time for starting work on it.
As the soil dries, it warms up. Then overwintered cereals (sown the previous autumn) begin to grow vigorously, pushing new roots into the drained and aerated earth. The new growth loosens the soil around the tiny stems, and one of the first jobs for the tractor may be to haul a roller over the young crop, firming and pressing the soil; this helps to prevent excess evaporation during the warm days that lie ahead. Crushing the young foliage also encourages the formation of extra shoots, and may result in a higher yield.
In modern farming, autumn sowing is more widespread than it used to be. Wheat is the only crop that was traditionally sown in autumn, and autumn sown wheat (winter wheat) is the kind that is usually seen today. In recent years, however, high yielding winter varieties of barley have also become very popular. This change has been made possible only by the widespread use of chemical weedkillers. As soon as the previous harvest has been gathered in, the stubble is burnt and then Paraquat, a weedkiller that destroys growing plants of any kind, is liberally applied. After sowing, the crop is treated as it grows with selective weedkillers. These destroy only broadleaved plants and do no harm to the crop.
One consequence of the use of selective weedkillers is that the more colourful species of weeds are much less common in arable fields than they used to be; in their place, couch grass, blackgrass and wild oat have increased. These plants have long, narrow leaves, similar to those of the cereals; any weedkiller that destroys them would have an equally deadly effect on the growing corn. The same applies to the `volunteers’ — unplanned offspring of the previous season’s crop. The darker green colour of wheat is a common sight in a field of winter barley, for the ear of wheat often breaks apart and scatters its grain during harvesting. One of the main reasons for stubble burning in autumn is to destroy this grain and keep the succeeding crop relatively pure.
The traditional system of spring sowing is based on entirely different principles. Instead of relying on chemical weedkillers, the farmer ploughs and harrows the land repeatedly in autumn. This causes the majority of the weed seeds in the ground to germinate and seedlings begin to grow, only to be buried and killed the next time the harrow or plough is used. The ploughshares also tear apart and destroy the perennial roots of couch grass, bindweed and creeping thistle. The land is then left to weather over the winter. The heavy clods are broken down by frost and rain, and by spring the bare soil is in the soft, friable state most suitable for crumbling and smoothing down to make a seed bed.
As soon as the land is dry enough, the farmer sets to work with the harrow, stirring up the top layers and crumbling them to the required tilth (fineness of consistency). In the process, a large number of soil-dwelling grubs are turned up, including click beetle larvae (wireworms) and the larvae of cockchafers and craneflies. Big populations of these insects can do substantial damage to growing crops, and the farmer has reason to be thankful to the gulls, lapwings and rooks which descend on the disturbed earth to feast on the unwelcome grubs.
Going for the main chance
Fluttering and hopping after the tractor, the birds demonstrate a way of life that is the key to success for all species of plants and animals in the arable field — opportunism. In the surrounding hedgerows and woods, spring is a regular and predictable phenomenon; these habitats are comparatively rich in plant and animal species, and their communities experience little change in conditions from year to year. In the field, however, the character of the season is determined every year by the farmer, by the machinery and materials at his disposal, and by such changing factors as the state of the market and agricultural fashions. The wild plants and animals must fit in where they can. Only the most resilient, prolific or adaptable can survive on ploughland over a long period. In the short term, the field plays host to a succession of visitors or temporary residents, which make the most of every lull in activity or, in the case of the birds following the harrow, turn the disruption to their own advantage.
While lapwings and gulls foraging for grubs are welcome, pigeons coming for the seed are a pest. The seed corn also attracts other, more stealthy raiders: wood mice and field voles emerge at night to carry it off to their burrows.
Within a few days of sowing, the seed germinates and a faint haze of green spreads over the dark earth. As the young plants grow, they make a succulent meal for a variety of grazing animals. Near large areas of woodland, for instance, the crop may be at risk from herds of deer. Despite their size, however, deer are less of a problem than rabbits. Before myxomatosis devastated the rabbit population in the 1950s, farmers reckoned it a waste of time trying to grow crops in fields adjoining woodland. As soon as the seedlings emerged from the ground, the rabbits appeared on the field and nibbled them down to the roots. Even now, although much reduced in numbers, rabbits can cause considerable damage.
As the season advances, ears begin to form on the winter corn, and the farmer applies a top dressing of nitrogen to encourage the growth of the grain. Applied too early, the fertiliser merely makes the stalks of the corn grow longer, and increases the risk of the crop being knocked flat by bad weather. So the farmer carefully monitors the stages of growth, while keeping a sharp eye out for signs of pests or disease. At one time a variety of precautionary pesticide sprays were applied in the spring. This is now out of fashion, partly because of the expense and partly because repeated blanket application simply gives rise to new strains of pests, capable of resisting the effects of the spray. This can render the chemicals obsolete within a few years. The modern farmer sprays only when absolutely necessary.
Some of the visitors to the fields may be tempted to stay. The partridge, picking its way sedately between the corn stems in search of slugs and insects, may decide to nest amid the growing crop. It shares with the harvest mouse and the skylark a taste for the open fields that can lead to disaster: all these creatures are liable to fall victim to the blades of the combine harvester.