USES AND CARE OF SOILS

Soils are used in a great variety of ways, agriculture being the leading soil use.

There has always been great variation in the quality of soils available for agriculture. In most instances, the better soils are used for crops, and the less suitable ones are kept for pastures or timberlands.

Properties that determine the agricultural quality of soils include: 1) ability to produce high crop yields under good management and careful handling; 2) the ease with which they can be used profitably; 3) the amount and kind of care they require. Good soils respond well to proper management, which involves correct cropping practices, use of fertilizers, and effective protection against damage. Without good care all cropland deteriorates with continuous use. The loss that results from improper care of good soils is greater than from improper care of poor soils, since the former are more valu­able. A good rotation system consists of adjusting the crop arrangement to the physical nature of the land and, same time, maintaining a balanced economic farming programme. Rotation implies the growing of more than one n a farm. In other words, rotation and diversification go in hand.

Since no two crops make identical demands on the soil, one crop may require excessive amounts of a given nutrient another crop may be able to supply. For example, legumes return nitrogen to the soil, but most other crops re-more nitrogen than the soil can normally supply. Thus a rotation programme involving clovers and other legumes combined with cotton, corn, small grains, and other heavy users of nitrogen may meet most nitrogen requirements. Crop rotation and associated diversification help improve the economic status of farming in many ways. Besides maintaining the soil in a good state of productivity, rotation and diversification help reduce the risks of economic losses from low yelds. Also, the income and the labour requirements are spread through the year instead of being seasonal in nature,as in the case of a single crop, such as wheat. Some phases of a well-ordered crop rotation programme are apt to succeed, if others fail. It is not necessary for all parts of the programme to show a financial profit; it is the overall result that counts. A soil-improving crop, for example, may not be economically profitable at the time it is grown, but its benefits may be clearly realized in future years.

Land use is a continuous operation. Farmers normally do it their land aside while they are restoring their soils; repair and improve them while the land is in use. The ways that soils are used, the length of time they remain productive, and the harvests they yield depend to a marked degree upon the care they receive.

Under careful and proper use soils may continue indefini­tely to produce good yields. It is improper use and lack of care that harm soils. Thus good care is of vital importance in prolonging the useful life of soils.

Improper use may result in the deterioration of soil struc­ture; several things may contribute to this deterioration, including: plowing when soil is too wet; failure to return organic matter; unwise use or lack of lime; neglecting to ro­tate crops. An even more serious and widespread kind of soil damage is the loss of essential plant nutrients. This may re­sult from continuous growing of the same crop and from fail­ing to fertilize it properly. Still another serious cause of depletion in most soils is known to be the loss of organic matter.

Most kinds of soil damage are related to each other in many ways. For example, organic deficiency is definitely a factor in soil erosion and in structural breakdown as well as in the deficiency of plant nutrients. Consequently, under­standing these relationships and properly evaluating them in a balanced farming programme make modern agriculture truly a scientific undertaking.

УПРАЖНЕНИЯ.

1. Найдите в тексте антонимы следующих слов и словосочетаний:

to succeed, economic loss, to raise, poor user, damage, to deplete the soil, dry soil, the latter

2. Объясните значение терминов: crop rotation, diversifi­cation. Скажите, в чем заключается связь между по­нятиями, обозначаемыми этими терминами.

3. Прочтите без словаря следующий текст и расскажите, какую информацию вы из него извлекли:

ROTATIONS.

A rotation is a succession of crops usually fixed in a cer­tain definite order. Nowadays rotations are not so fixed as before. To meet the changing conditions and the needs of the new crops can be introduced into rotations and changes made when and where needed, opposite of a rotation is to grow one crop year after year. It is known as monoculture and can lead to troubles, particularly disease. The one crop which can be grown in this way is grass; permanent grass, if farmed properly, can be productive for a long time.

FERTILIZATION.

In spite of the increasing use of synthetic fertilizers in agricultural practice and the subsequent raise of crop yields, it is found generally that, to maintain a high level of inherent, their use must be accompanied by periodic applications of bulky organic manure, either in the form of farm compost, or other organic by-product, either of the farm of certain industries.

The maintenance of high productivity depends on a number of factors; the soil must be in the optimum condition for crop growth and must be in a position to furnish both food and water; it must have a suitable reaction in the chemical sense, and it must contain no substances toxic to growth.

It must be physically amenable to cultivation, resistant to forces of erosion, and the micro-flora and micro-fauna must be of a character to ameliorate the general chemical and physical properties of the soil and the soil-plant relationship. Any substance which when added to the soil brings about an improvement in any one of those directions could be considered as a fertilizer or manure using the terms in their widest sense, and it is in connection with these indirect benefits that organic manures are of such great importance in fertilizer practice. As a source of plant food, farmyard manure contains all the important nutrients although their availability is variab­le. The potassium present is readily soluble and immediately available; the nitrogen is present in both available forms, and in compounds which only slowly break down; the phosphate compounds also decompose slowly. This is one reason why, for particular crops, applications of manure need to be supple­mented with dressings of inorganic fertilizers and in parti­cular with available phosphorus compounds. The less avail­able portions of the farmyard manure are slowly released and become of value to succeeding crops.

Whatever the type of soil, applications of manure can have a beneficial action upon the physical properties. Heavy soils can be made easier to work, and the aeration and drainage improved by means of the increased organic-matter content, whilst on sandy soils the moisture-holding capacity of the manure increases drought resistance, the binding effect of the organic matter controls erosion and the increased base-exchange capacity improves the power of the soil to retain plant nutrients. Soil colour will be darkened by the incorpo­ration of humus, with an increase in the heat-absorbing power.

If a crop is growing under conditions of a single nutrient deficiency, the addition of appropriate fertilizer will give an increase in yield, but increases so observed are not direct­ly proportional to the quantity of fertilizer used. As the rate of application increases, a given extra increment of fertilizer gives a smaller increase in crop until a maximum yield is reached. Beyond this figure further additions may either have no effect or may even do damage and cause crop reduction.

The growth responses following the provision of adequate supplies of two or more limiting nutrients are not necessarily the arithmetical sum of the separately obtained responses. Quite frequently it is found that the increase in yield of a crop when supplied with two different fertilizers is much greater than the sum of the individual yield increases; the two fertilizers are then said to have a positive interaction.

The use of compound or mixed fertilizers is increasing and possesses many advantages from a management point of view. Labour costs are considerably lowered by the reduction of the number of operations necessary, and frequently compounds can be obtained commercially containing the nutrients in concentrated form, thus reducing the quantity to be applied in any particular instance.

base-exchange capacity — емкость катионного обмена

УПРАЖНЕНИЯ

1. Найдите в тексте синонимы выделенных слов и словосочетаний:

To check erosion, decrease in yields, to keep high fertility, to break down, to add, especially, the following crop.

2. Выпишume из текста «Fertilization» все интернациональные слова и дайте их русские значения.

3.Прочтите без словаря следующий текст, разделите его на абзацы и озаглавьте каждый абзац: