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  Physical properties of soil:
 

 

Some important physical properties of soil related to the growing of crops include


 

 

Soil micro-organisms show maximum growth and activity at optimum soil temperature range. All crops practically slow down their growth below the temperature of about 90C and above the temperature of about 500 C.


Texture:

Soil texture refers to the relative amounts of inorganic particles, that is, sand, silt and clay. While sand grains are large and coarse and clay particles are very fine and smooth, silt particles are intermediate.



Structure

Soil structure refers to the way in which soil particles are grouped or bound together to form lumps or aggregates. There are two main types of soil structure, single grained and compound structure.
The structure of soil can be changed, modified and improved or damaged depending on the various soil management practices adopted like tillage, manuring, liming, rotation of crops, irrigation, drainage etc.


Density

The density of soil that is weight per unit volume can be expressed in two ways viz; the density of ‘solid’ (particle density), particles of the soil and the density of the ‘whole’ (Bulk density) soil that is inclusive of pore space. Generally soils with low bulk density have better physical condition than those with higher bulk densities. Texture and structure of a soil, its total pore space and organic matter content are all related to bulk densities.


Porosity

In between the particles there are empty spaces which are occupied by air and water and are termed as pore spaces. Pore spaces between the aggregates of soil particles are macro-pores and those between the individual particles of the aggregates are micro-pores. The percentage of macro pores is more in sandy soils these soils never remain water logged and allow water to percolate down so rapidly that their moisture content is very low,crops suffer due to shortage of soil moisture. The percentage of micro pore is more in clayey or fine texture soils. In this soil water logging condition causes adverse effect on respiration of roots and bacterial activities. A proper balance between the macro and micro pores can be maintain by timely cultivation and addition of organic matter so as to that crop neither suffers from shortage of excess of water.


Soil consistence

It is a combination of properties that determine the resistance of the dry soil to crushing or pulverising action by implements and when wet its ability to be moulded or changed in shape. All soils have cohesive and adhesive properties. Sandy soils have these properties to a much lesser degree than fine texture clay soils. A good tilth soil has both the macro and micro pores in more or less equal proportion, ensures adequate retention of water and also free drainage of excess water. The effect of such physical condition of soil on germination of seed and growth of plant is very beneficial.


Colour

Soils have various shades of black, yellow, red and gray colours useful in soil classification. Parent material e.g. red sandstone, organic mater, presence of certain minerals e.g. titanium compounds imparts darker colour, hematite give red colour, limonite-yellow colour, predominance of silica or lime. Soil colour is indirectly helpful in indicating many other properties of soils e.g. a dark brown or black coloured soil indicates its high organic matter content and fertility. A red or yellowish soil shows good aeration and proper drainage. A white or black colour due to accumulation of certain salts of alkali indicates deterioration of soil fertility and its unsuitability for normal growth of many crops.


Soil temperature and plant growth

The biological processes for nutrient transformations and nutrient availability are controlled by soil temperature and soil moisture. Soil temperature has a profound influence on seed germination, root and shoot growth, and nutrient uptake and crop growth. Seeds do not germinate below or above a certain range of temperature but Micro-organisms functioning in the soil are very active while a certain range of temperature, which is about 270 to 320C. It is necessary to know whether the soil temperature is helpful to the activities of plants and micro-organisms and the temperature could be suitably controlled and modified. The various factors that control the soil temperature are soil moisture, soil colour, slope of the land, vegetative cover and general tilth of the soil. Soil temperature can be controlled by regulating soil moisture, proper soil management practices viz. good drainage, proper mulch, good crumby structure, addition of sufficient organic matter help in keeping the soil sufficiently warm and help in the chemical and biological activities in the soil.

 

 

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