the Soil is the thin, fragile layer of a loose material covering rocky breeds on the most part of a terrestrial land.
In 2001 in the world lived about 6 billion persons. The area of a terrestrial land makes about 149 million in km 2 , t. With. On a share of each of us it is necessary about 2,5 hectares of the earth.
However almost 70% of a land cannot be used for agriculture. Them concern: caps of polar ices, the frozen ground, abrupt for these purposes abrupt and rocky mountains, deserts and the territories covered with naked rocks or too thin layer of earth for cultivation. Two thirds of remained 30% suit only for vypasa cattle. Thus, only on 10% of a terrestrial surface it is possible to grow up agricultural crops.
So, in 2001 on each of us it was necessary on the average 0,25 hectares of arable lands. Experts consider that 0,5-0,7 hectares are necessary for manufacture of present volume of a foodstuff in the western countries on the person.
Quality of the earth
Though it is possible to grow up plants a method gidroponiki - in water - unique reliable way of reception of the big crops is cultivation in soil.
The soil structure includes three basic elements: a ground, or fragments of radical spreading breed, gumus (the decayed rests of plants or animals) and live organisms, including zemlerojushchih animals, such as hearts, and also bacteria and the fungi decomposing organic substances. The soil is a friable formation. About the two fifth volume of the majority of kinds of soils occupy the emptiness filled with air or water. Their thickness fluctuates from several centimetres to several metres, thus the most fertile top layer of earth has no more than 25 sm at thickness. Besides, in different kinds of soils the different maintenance of water and the nutrients used by plants.
Some cultures grow in certain soil is better. So, wheat prefers fertile clay soil, barley is better for growing up in easier, sandy, and an optimum variant for a potato is the powerful layer of limy soil with the big maintenance of organic chemistry. There are the cultures well growing in different soils, and farmers can change soil structure, adding izvest, chemical and organic fertilizers.
The Bias of a surface of the earth influences its quality. If to remove a primary vegetative cover in places with an abrupt bias, the soil there is quickly washed away together with the roots of plants keeping it on a place. And it is more difficult to farmers to use agricultural machinery on slopes. One of the major factors influencing quality of soil, the climate is. Acts of nature - the drought, flooding, a strong wind, a frost and hailstones - can ruin a crop.
the Best earths - plains with a thick layer of a fertile soil in regions with favorable environmental conditions. In densely populated areas where few arable grounds, under crops should be used and inclined grounds. For this purpose apply a traditional method - on slopes do steps, or terraces. Terrasirovanie slows down a soil erosion, but manages very expensively.
For crops the first-rate quality earth as plant growing brings in to farmers the highest incomes is taken away. The quality of the earth, the above the risk connected with a possible poor harvest or a soil erosion is worse. There, where agriculture becomes unprofitable, the earth should be used either for vypasa, or for afforestations.
the land tenure Organization
With growth of the population of a planet loading increases by the earth in the course of reception of a foodstuff also.
In densely populated areas the big sites of the fertile earth are occupied by growing cities, promploshchadkami, automobile and railways, airdromes. In their territory there are big areas degraded and abandoned lands.
Quality of an arable land depends on its use. On formation of a soil layer millenia leave, and to destroy it it is possible for some years at not enough solicitous attitude. Two primary factors negatively affect soil: pollution and erosion.
Sometimes application of a considerable quantity of fertilizers reduces ability of bacteria to decompose an organic material of soil and to make nutrients necessary for plants. Pesticides are harmful to all useful organisms.
Failures as it happens in 1986 in the former USSR as a result of explosion and a fire on the Chernobyl atomic power station when there was an emission in atmosphere of the radioactive substances which have got then in soil can be the Reason of pollution of soils. The wind has carried radiation on huge territory. The animals who have suffered from radioactive infection, it was necessary to destroy.
In some countries industrial wastes dump directly on a ground, and the rests of poisonous metals ruin soil bacteria. Such toxic metal as aluminium is a basic element of clay minerals. Usually it is there in chemically connected condition and is safe for bacteria and plants. But the acid rains which are dropping out as a result of pollution of rain water by products of exhausts of cars, emissions of factories and power stations, liberate aluminium that harms to soil microorganisms and local plants.
the Soil erosion
It is the most serious form of degradation of soil. It is not necessary to confuse the soil erosion caused by the thriftless relation to the earth, to the natural.
The Natural soil erosion is a slow continuous process, simultaneously with which the new soil layer is formed. Scientists have counted up that one square metre of the earth disappears as a result of natural erosion for 30 thousand years.
And irrational use of the earth can accelerate so erosion process that for some decades huge territories remain without a soil layer. The first settlers in America so mercilessly maintained the earth that for 100 years have ruined 20% of arable lands.
In some developing countries (such as Colombia in the South America, Lesotho, Malawi and Swaziland in a southern part of Africa) the situation is even worse. Here more than 75% of the suitable earths for processing have seriously suffered as a result of irrational use.
As there is a soil erosion
The Soil erosion can be caused an exhaustion of the earth or excessive vypasom cattle. An earth exhaustion - result of cultivation on it of the same culture for a number of years without replenishment of the maintenance of nutrients in soil by application of fertilizers. It leads to decrease in fertility of soil, and, hence, and volume of crops. Connectivity of the soil becoming sensitive to erosion also worsens. Vybivanie pastures occurs at vypase too big livestock of cattle on one ground. These herds eat away and tread a grass and plants faster, than they grow, reserving the naked earth.
Erosion Process passes in two stages. In the beginning coherent clods of the earth break up to separate particles which then watch off or carried away by a wind.
In areas with plentiful rains of a drop bombard a ground surface. Usually plants take basically this blow up, but there where there is no vegetation, the rain bangs on the bared earth, lifting soil particles in air and rejecting them on distance to 1,5 m.
Besides, force of blow of rain drops condenses a ground, and it becomes covered by a firm crust. It complicates infiltration of a rain moisture in soil and spreading breed, as a result bolshee the quantity of water flows on an earth surface.
This water (named scientists a superficial drain) picks up inconsistent particles of soil and carries away them in streams and the rivers. As a result at the bottom of the rivers often settles a fertile soil large quantity that, besides, leads to a shallowing rusel and to flooding.
This kind of erosion takes place, when the rain washes off a thin layer of a surface of soil. At an early stage plane erosion is difficult for finding out. But later farmers notice that their crops grow scanty, the earth loses fertility. Even more harm erosion, characteristic, mainly, for districts with a bias where superficial drains gather in streams puts ovrazhnaja. After strong rains these streams turn to the streams cutting deep ditches (ravines) in the earth.
The Ravines, which depth can reach from 20 to 50 m, are often formed there where water flows on small deepenings (to furrows, skotoprogonam, kolejam).
In droughty and mainly flat areas the main originator of a soil erosion is the wind. Shaft are formed of the friable, bared ground and dunes. Turning to a fine dust, the earth is transferred by a wind on the big distances. So, owing to excessively intensive agriculture the considerable part of soil of Great Plains (USA) has appeared at the bottom of Atlantic ocean.
the Climate and erosion
In 1970 and 1980th hunger raged in Africa in area saheli - the zone of droughty steppes lasting from the east on the West in northern part of continent to the south from Sahara - the biggest desert in the world. In 1950th of rains in this district dropped out more usual, and the area of pastures has increased. Inhabitants of the located to the south and densely occupied zone of savannas located to the south (tropical steppes) began to get over in sahel. The cattle has started to pit excessively pastures, and people cut down trees and bushes on fire wood.
In 1970 and 1980th a number of droughts, and vegetation saheli took place could not be restored more in the necessary volume any more. Strong winds blew off and disseminated the naked earth, causing a strong soil erosion. The cattle was lost, and people starved, as earlier droughty steppes have turned to desert as a result of the process named desertification. It, possibly, has not occurred, if on the eve of droughts was not excessive vypasa cattle.
Plans for the future
The Tragedy in saheli has reminded in time us that the soil has a limit. Considering growth of the population of the Earth, farmers should master the agrotechnical receptions, allowing to avoid the worst consequences of a soil erosion.
Scientific researches also should help is better to use fertilizers and insektitsidy, in the past harming to soil, and artificial companions of the Earth can serve for tracking the agriculture organisation all over the world.