The green world of plants and trees, source of life
for all the Earth's inhabitants, rich in the promise of abundance, yet dependent on two things: sun and soil. The subsoil and above it the skin of topsoil. Seemingly lifeless, yet within it, the penetrating eye
discovers a hidden world. Here are the ultimate particles of soil, rock coated with organic humus, separated by pockets of air and water. Within live the soil's
smallest inhabitants, the bacteria. So tiny, that in a teaspoonful of soil, they outnumber
the population of the Earth. Among them the nitrogen-fixing bacteria, organisms able to convert
the nitrogen of the air into chemicals needed for plant life. Their food, the ever-branching fungi, forming a mass of living tissue
in the soil. Feeding on these bacteria and holding them in check are countless larger
microscopic creatures. Larger again, the enchytraeids, minute worms. Springtails, wingless insects little changed in 300 million years. Above ground, the snail forages for its food, but returns to a fixed home in the soil. And there the earthworm tunnels its way, passing the soil through its body and so helping to aerate and fertilise it. Big and small, these creatures are in balance
with one another. Eating, fighting, dying, being born, in numbers beyond human comprehension. With the growth of intensive farming, man has upset this balance. For in the crop roots
which shoot everywhere down into the soil, he has provided a rich diet
for a host of pests. Among the most destructive of soil pests is the cabbage root fly, whose larvae inflict wounds
which damage the roots as well as exposing them to disease. Result: crop loss of cabbage, cauliflower, turnip, and other plants of the brassica family. Wireworms, tough-skinned and agile, bore through the soil, chewing off small roots as they go, tunnelling into large ones. Thus they live for three to five years in the top six inches of the soil. Result: widespread damage to root crops, cereals, vegetables, flowers. Where the crop
is not completely destroyed, it is often so damaged
as to be almost valueless. Cutworms, like most soil pests, are larval forms of insects
which live above ground. Their various species attack
almost every kind of crop, though the adult moth is harmless. Here, more than half a potato crop
has been destroyed. The cutworms have eaten the plants
just above ground level and have dragged parts of them
back into their burrows. White grubs are among
the most voracious of all these pests. They stay underground
for three years or more, chewing away whole root systems before emerging as adult cockchafers. Result: here an entire potato crop destroyed. Cereals, nursery stock, in fact most cultivated crops are attacked by the white grub. On a badly infested field, most of the plants are dead or dying. In the tropics, the banana weevil passes its whole life in the rootstock as larva, pupa, and adult beetle. Result: with the root system destroyed, the plant sickens and the fruit dies. Until recent times, farmers and agronomists were mystified by an unseen pest which stunted growth
and thus reduced yield. The magnifier sometimes showed
tiny cysts clinging to the root. Only beneath the microscope
was the culprit revealed: the eelworm, a nematode, of which more than 100 species scattered all over the world are parasitic
and destructive to plant life. Their mouths contain a sharp spear, which they can shoot out
to pierce the tender roots of plants. Result: abnormal growth and distortion of the root system
of many crops, secondary infections borne by bacteria, viruses and moulds. In the United States alone, damage estimated at $400 million a year. Here in Venezuela, a colony of leaf-cutting ants
has attacked a citrus tree. Within a few hours,
they will have stripped it of every leaf. The soldier ants carving the leaves
with their formidable jaws, the workers carrying loads
many times their own weight, combine in a task force thousands strong to drag the foliage back to their nest. Below ground, the leaves are chewed up
by the worker ants, and on them a tasty fungus has grown. This fungus garden feeds the whole colony and, at its head, the queen, who may live for a decade and mother countless millions of ants. The nests,
interconnected by underground tunnels, may spread across an acre or more
of fertile ground, denying it to human cultivation. Most of the life beneath the soil
is beneficial to man. What is harmful can only be attacked on the basis of a sure knowledge. Here on the famous Broadbalk field
at Rothamsted, studies in soil science,
begun a century ago, are still in progress. Samples of young wheat plants
are being collected and examined in the laboratory. By dissection of the plant, a count is made of the larvae
of the wheat bulb fly, which may do more than a million pounds
of damage a year in England alone. From the sample,
an aggregate figure is calculated: half a million larvae per acre. For different insects,
different methods of sampling. This soil core contains wireworms. The samples, several to the acre,
are placed in trays. The trays are heated. And the wireworms, struggling to escape, rise to the surface
where they are easily counted. Two wireworms per core sample indicate a million wireworms per acre. Yet after more than a century of study, our knowledge of the soil
is far from complete. Visit the world's agricultural centres, and you will find the scientist
investigating not only the pests, but the entire fauna of the soil. You may discover him
in Darwin's footsteps, tracking the earthworm to its burrow, for there is still much to learn
about what it eats and where it breeds. He may have to rear some insects
in controlled conditions so as to have enough of them
for his experiments. Or you may find him setting up
a tank of hot water linked by a copper bar to a tank of ice, making a temperature gradient
between hot and cold. On this bar, he is placing mites to see where they gather
in greatest numbers, for they will move to the place
where they are most comfortable and thus tell him what soil temperatures
they like best. Without accurate knowledge
of the lifecycle of pests, their effective control is impossible. Even the commonest of soil pests may have to be kept under observation. It is mid-May, and the pupae of the cabbage root fly
lie buried in the soil. The previous winter's severity will determine just when
they emerge as flies, so they are observed from day to day
in the laboratory. The flies are harmless to the crop, but the appearance of the eggs
on plant or ground must be watched for. A week or so later, the larvae will hatch out
and start to feed on the roots. It is then that they must be attacked. Otherwise, above ground, the damaged plants wilt and die. It's very important to time
the attack on soil pests exactly. Here in Holland, agronomists keep watch
for the appearance of eggs, in readiness to alert farmers through the national broadcasting system. Time to alert the radio. Anke... Cabbage root fly eggs
were found in Huizen. Please mark it on the map. A message from
the Plant Protection Service. The first cabbage flies have appeared
in the south and southwest of the country. The first eggs have been found. The traditional answer
to an outbreak of soil pest was to change to a new crop or allow a field to remain fallow. Then after a few years
plant the old crop again. Today, crop rotation is still
an accepted method of combatting soil pests. Certain pests,
which lie not too deep in the soil, are destroyed
by the normal tools of cultivation. Sometimes, special tractor attachments
are used against white grubs, which are mutilated by the blades or die from exposure to the hot sun. But the most effective method
of killing soil pests on a large scale is to use chemicals
to penetrate into the soil. The search for new chemicals is going forward all over the world. Each new compound
is thoroughly tested in advance to make sure that it has no ill effect
on plant growth. The aim: to give the farmer even more efficient and economical means of control. When the research and testing are done, another team of experts comes into play to spread the knowledge
of how chemicals can best be applied. It takes only the simplest equipment
for the Venezuelan farmer to rid his fields of the once-triumphant colonies of ants. The poison acts swiftly
on skin and stomach alike. With the death of the queen, the life source of the whole colony
has been destroyed. Insecticides may be applied
in many different ways, depending on the crop
that needs protection. Diluted with water,
they may be delivered in sprays, as here around cabbage seedlings. Here against the banana weevil. Dusted onto strawberry plants
with a portable two-stroke motor. Applied with sand onto cabbages. Mixed with bran against cutworms. And increasingly,
coated on the seeds themselves, putting the insecticides
where they are needed most. Against the microscopic nematodes, highly effective fumigants
can be injected. On larger farms, these pesticides, whether fumigants or sprays, can be applied by multiple-nozzle,
tractor-drawn equipment. At last, the soil pests are beginning
to yield to scientific attack. Across the world, the bare, stunted acres can be transformed into rich harvests. Yet today, one quarter of all the world's foodstuffs is lost to plant pests and diseases, enough to make good the diet of the two-thirds of mankind
still underfed. Each year that the crops are gathered in, the world has
35 million more mouths to feed. By the century's end, its population may be double. This is the challenge to the farmer and to all whose concern
is the living soil.
