Class 7 Soil Notes for exams

Class 7 Soil Notes for exams. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

SOIL NOTES

The word soil is derived from a Latin word solum meaning ground. It is a stratified mixture of inorganic and organic materials, both of which are products of decomposition. Inorganic component of soil i.e. mineral constituents are derived from the soil forming rocks, by fragmentation or weathering. Weathering of rocks takes place by two methods:

● Physical weathering - It is due to the action of rain, wind and temperature.

● Biological weathering of rocks - This is due to growth of lichens and mosses on the rocks. The organic component of the soil is formed either by microbial decomposition of dead remains of plants (litter) or animals, or through metabolic activities of living organism present in the soil. Thus the formation of soil takes place by interaction between the physical and biological components.

Soil can be defined as the uppermostcrust of earth, which is mixed with organic material and in which animals, and microorganisms live and plants grow.

Components of soil

● Inorganic material derived from parent (material) rocks

● Organic material derived from dead and decayed materials

● Biological system - such as bacteria, fungi, algae, protozoa and other soil animals such as nematodes, earthworms etc.

The air and water occupying the pores between the soil particles, which are loosly packed

Soil and food production

● Loamy soil has about 30-50% silt and 20% less than clay particles.

● Sand contains rock particles with diameter in range 0.125-2.0mm.

● Clay has soil particles whose size is less than 2-4 mm in diameter.

● Silt soil is composed of particles whose diameter ranges from 1/256-1/16mm.

 Soil Profile:

A soil consists of three horizontal layers. They are true soil at the top, sub soil and bedrock. Each horizon is different from other by its own physical and chemical composition and organic contents produced during the process of soil formation.

Soil Texture:

Soil is the medium for plant growth, it provides anchorage to plants.

● Soil provides nutrients, both major and minor, to plants for their growth and development. Thus, it circulates the nutrients into biological system by means of mineral weathering.

● Soil harbors the microorganisms such as bacteria and fungi, which fix the free atmospheric nitrogen into soil (nitrogen fixation) and at the same time, some of the fungi also fix phosphorus (mycorrahage).

Soil texture refers to the mixture of different soil particles grading from coarse into fine grades of gravel, sand, silt and clay. Soils with a large proportion of sand grains are called Sandy Soils. Clayey Soils have a large proportion of clay particles and a little of sand, and soils, with fairly equal proportions of sand, silt and clay are called loams.

Fertile Soil

Fertility of the soil is nothing but ability to nourish the plant life with required nutrients. The fertility of soil decreases when crop is grown in the same land repeatedly. Another cause of reduction of fertility of soil is soil erosion. Soil erosion refers to physical removal of soil particles from their original place and transportation to some other places. Soil fertility can be prolonged both by the human efforts (application of manures, bio-fertilizers, chemical fertilizers to soil of crop fields etc.) and natural processes.

Soil Formation:

Soil is a stratified mixture of organic and inorganic materials and both are decomposed products. The organic matter are derived from plant and animal life as well as moisture and air, while the inorganic matter is supplemented by parent rocks, topography and time which are considered as passive agents. The factors supplementing organic matter are called active agents.

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