Find in Text 4 English equivalents for the following words and expressions and memorize them.

1) достаточное количество

2) недостаточное количество

3) потребности растений

4) самое важное средство

5) удобрения

6) токсичность

7) удобрение (как процесс)

8) орошение

9) обработка земли (рыхление земли)

10) древесина (лесоматериалы)

11) контроль за сельхоз вредителями

12) эрозия

13) высокий урожай

14) засушливые районы

15) однородный состав

16) грунтовые воды

17) сброс отходов

Translate the text from English into Russian.

TEXT 4

Diffusion is the movement of nutrients in soil water that results from a concentration gradient. Diffusion of ions occurs whether or not water is moving. When an insufficient amount of nutrients is moved to the root surface via mass flow, diffusion plays an important role. Whether or not plants will be supplied a sufficient amount of a nutrient also depends on the amount needed. Calcium is rarely deficient for plant growth, partially because plants' needs are low. As a consequence, these needs are usually amply satisfied by the movement of calcium to roots by mass flow. The same is generally true for magnesium and sulfur. The concentration of nitrogen in the soil solution tends to be higher than that for calcium, but because of the high plant demand for nitrogen, about 20 percent of the nitrogen that plants absorb is moved to root surfaces by diffusion. Diffusion is the most important means by which phosphorus and potassium are transported to root surfaces, because of the combined effects of concentration in the soil solution and plant demands.

Mass flow can move a large amount of nutrients rapidly, whereas diffusion moves a small amount of nutrients very slowly. Mass flow and diffusion have a limited ability to move phosphorus and potassium to roots in order to satisfy the needs of crops, and this limitation partly explains why a large amount of phosphorus and potassium is added to soils in fertilizers. Conversely, the large amounts of calcium and magnesium that are moved to root surfaces, relative to crop plant needs, account for the small amount of calcium and magnesium that is added to soils in fertilizers.

Summary Statement

The available nutrients and available water are the nutrients and water that roots can absorb. The absorption of nutrients and water by roots is dependent on the surface area-density (cm 2/cm3 ) of roots. Mathematically: uptake = availability x surface area-density

SOIL FERTILITY AND SOIL PRODUCTIVITY

Soil fertility is defined as the ability of a soil to supply essential elements for plant growth without a toxic concentration of any element. Soil fertility refers to only one aspect of plant growth the adequacy, toxicity, and balance of plant nutrients. An assessment of soil fertility can be made with a series of chemical tests.

Soil productivity is the soil's capacity to produce a certain yield of crops or other plants with optimum management. For example, the productivity of a soil for cotton production is commonly expressed as kilos, or bales of cotton per acre, or hectare, when using an optimum management system. The optimum management system specifies such factors as planting date, fertilization, irrigation schedule, tillage, cropping sequence, and pest control. Soil scientists determine soil productivity ratings of soils for various crops by measuring yields (including tree growth or timber production) over a period of time for those production uses that are currently relevant. Included in the measurement of soil productivity are the influence of weather and the nature and aspect of slope, which greatly affects water runoff and erosion. Thus, soil productivity is an expression of all the factors, soil and nonsoil, that influence crop yields.

For a soil to produce high yields, it must be fertile for the crops grown. It does not follow, however, that a fertile soil will produce high yields. High yields or high soil productivity depends on optimum management systems. Many fertile soils exist in arid regions but, within management systems that do not include irrigation, these soils are unproductive for corn or rice.

SUMMARY

The concept of soil as a medium for plant growth is an ancient concept and dates back to at least the beginning of agriculture. The concept emphasizes the soil's role in the growth of plants. Important aspects of the soil as a medium for plant growth are: (1) the role of the soil in supplying plants with growth factors, (2) the development and distribution of roots in soils, and (3) the movement of nutrients, water, and air to root surfaces for absorption. Soils are productive in terms of their ability to produce plants.

The concept of soil as a medium for plant growth views the soil as a material of fairly uniform composition. This is entirely satisfactory when plants are grown in containers that contain a soil mix. Plants found in fields and forests, however, are growing in soils that are not uniform. Differences in the properties between topsoil and subsoil layers affect water and nutrient absorption. It is natural for soils in fields and forests to be composed of horizontal layers that have different properties, so it is also important that agriculturists and foresters consider soils as natural bodies. This concept is also useful for persons involved in the building of engineering structures, solving environment problems such as nitrate pollution of groundwater, and using the soil for waste disposal. The soil as a natural body is considered in the next chapter.

(H.D. Foth, Fundamentals of Soil Science)

Answer the questions.

1) What is diffusion?

2) What is soil fertility?

3) What is soil productivity?

4) What factors should be taken into account in terms of any soil management?

5) How do soil scientists measure soil productivity?

6) What is important for soil to produce high yields?