6. Retell the text ‘ Structure of soil’:

TEXT 7 CHEMICAL CONDITIONS OF SOIL

Soils can be acid, alkaline, or neutral. The amounts of acid and alkali in a soil influence the biological and chemical processes that take place there. Highly acid or alkaline soils can harm many plants. Neutral soils support most of the biological and chemical processes, including the process by which green plants obtain many nutrients. This process is called cation exchange. Many nutrients and other elements dissolve in the soil solution, forming positively charged particles called cations. The negatively charged clay and humus attract some cations and prevent them from being leached (washed away) from the topsoil by drainage waters. The solution that remains in the soil contains other cations. Nutrient cations on the clay and humus and those in the soil solution change places with nonnutrient cations that are on roots. The roots can then absorb the nutrients.

I. Study the following words:

Acid, alkaline, neutral, influence, take place, harm, neutral soils, including, obtain, cation, exchange, dissolve, soil solution, charged, humus, leach, remain, roots, absorb.

II. Give antonyms of the following words:

Harm, include, attract, positively, drainage, solution, nutrient, change, solve, absorb.

III. Make up your own sentences with words given above in exercise 2:

IV. What chemical conditions of soil do you know?

TEXT 8 HOW SOILS ARE CLASSIFIED

Pedologists classify soils according to the characteristics of a polypedon. The Soil Survey Staff of the United States Department of Agriculture uses a system that consists of 10 orders (groups) of soils. They are alfisols, aridisols, entisols, histosols, inceptisosl, mollisols, oxisols, spodosols, ultisols, and vertisols.

Alfisols develop under forest and grasslands in humid climates. Some agricultural soils are alfisols.

Aridosols occur in dry regions and contain small amounts of organic matter. Desert soils are ardisols.

Entisols show little development. They resemble the parent material and occur in many climates.

Histosols are organic soils. They form in water saturated environments, including swamps and bogs.

Inceptisols are only slightly developed. They are more common in subhumid and humid climates, but also occur in most other kinds of climates.

Mollisols develop in prairie regions. They have thick, organically rich topsoils.

Oxisols are the most chemically weathered soils. They have a reddish color and occur in tropical regions.

Spodosols contain iron, aluminum, and organic matter in their B horizons. They form in humid climates.

Ultisols occur in warm, humid climates. They are moist, well-developed, acid soils.

Vertisols form in subhumid and arid warm climates. They develop wide, deep cracks during dry seasons.

I. Study the following words:

Polypedon, staff, agriculture, consist, alfisols, aridisols, entisols, histosols, inceptisols, mollisols, oxisols, spodosols, ultisols, vertisols, humid, grassland, occur, swamp, bog, reddish, moist, crack.