Role of Physical Properties of Soil

After reading this article you will learn about the role of physical properties of soil:- 1. Role of Texture 2. Role of Structure 3. Role of Soil Density 4. Role of Porosity 5. Role of Soil Consistence 6. Role of Soil Colour 7. Role of Soil Temperature.

1. Role of Texture:

Texture has good effect on management and productivity of soil. Sandy soils are of open character, usually loose and friable. Such type of the texture is easy to handle in tillage operations. Sand facilitates drainage and aeration. It allows rapid evaporation and percolation.

Sandy soils have very little water-holding capacity. Such soils cannot stand drought and are unsuitable for dry farming. In sandy soil, few crops can be grown such as potato, groundnut and cucumbers.

Clay particles play a very important role in soil fertility. Clayey soils are difficult to till and require much skill in handling. When moist clayey soils are exceedingly sticky and when dry, become very hard and difficult to break. They have fine pores, and they are poor in drainage and aeration.

They have a high water-holding capacity and poor percolation which usually results in water-logging. They are generally very fertile soils, in respect of plant nutrients content. Rice, jute, sugarcane can be grown in this soil very successfully.

Silt is a very valuable constituent of the soil. Good loamy soils contain about 30 to -50 per cent silt. An ideal loam may be defined as a mixture of sand, silt and clay particles which exhibits light and heavy properties in about equal proportions.

In drainage, absorption of water, water-holding capacity they are intermediate between sandy soils and clayey soils. Tillage operations are best adapted to this class of soil. In loam soil good tilth is obtained easily. They are practically suited to every kind of crop such as wheat, maize, pulses, oilseeds, potato, groundnut, vegetables, rice, sugarcane etc.

2. Role of Structure:

Soil structure influences the amount and nature of porosity. Structure controls the amount of water and air present in the soil. Not only are the amount of water and air dependent on soil structure, but their movement and circulation are also controlled by soil structure. It effects tillage practices. Structure also controls run-off and erosion.

Platy structure normally hinders free drainage whereas sphere-like structure (granular and crumby) helps in drainage. The best structure for favourable physical properties of soils are crumby and granular. This type of structure provides optimum infiltration, water-holding capacity, aeration and drainage.

Activities of soil microorganism and supply of nutrients are good. Mostly rice is grown by puddling the soil. The puddling destroys all clods and peds, resulting in a structure less mass. Preparation of good tilth for the seed bed for the next crop is difficult in the puddled soil.

3. Role of Soil Density:

The bulk density varies with the total pore space present in the soil and gives a good estimate of the porosity of soil. Generally, soils with low bulk densities have favourable physical conditions, whereas those with high bulk densities exhibit poor physical conditions.

Soils which have a loose structure (crumby) have a lower bulk density than soils having compact (platy) structure. Bulk density also helps to determine the weight of the soils.

4. Role of Porosity:

Porosity of the soil greatly helps to judge the moisture movement within the soil. Macro pores allow readily movement of air and water. It does not hold water under normal condition. In contrast, micro pores can hold more water and restrict the movement of air and water in the soil.

Thus, in sandy soil, in-spite of the low total porosity, the movement of air and water is surprisingly rapid because of the dominance of the macro pore spaces.

Fine-textured (clay) soils allow relatively slow air and water movement despite the large amount of total pore space (total porosity). Therefore, the size of the individual pore spaces rather than their combined volume is the important consideration.

The loosening of fine-textured soils promotes aeration not so much by increasing the total pore space as by raising the proportion of the macro pores. For ideal conditions of aeration, permeability and water retention, a soil should have about an equal amount of macro and micro pores.

Porosity of a soil is easily changed. Any operation that reduces aggregation and decreases the amount of organic matter in the soil, decreases pore space.

5. Role of Soil Consistence:

Consistence of soil depends on the texture, nature and amount of inorganic and organic colloids, structure, and especially the moisture content of soil. With decreasing moisture content, in general, the soils lose their stickiness and plasticity and become friable and soft and finally when dry become hard and coherent. Optimum soil consistence increases the water-holding capacity and plant food material. Thus, increasing the fertility of soil.

6. Role of Soil Colour:

Soil colour is indirectly related with soil fertility:

(a) Relation of soil colour with temperature: Directly the soil colour influences soil temperature to some extent. The dark-coloured soils absorb more heat than light-coloured soils.

(b) Relation of soil colour with organic matter. Organic matter imparts black to dark grey tinges. More quantity of organic matter content improves the soil structure.

(c) Relation of the soil colour with drainage. Bluish and greenish colours of soil indicate water-logging. Need of drainage can be determined by the colour variations in the soil.

(d) Relation of soil colour with parent material. Soil colour may indicate their origin from parent rock material.

7. Role of Soil Temperature:

There are following effects of soil temperature on fertility of soil and plant growth:

(a) Effect of soil-temperature on soil microorganism:

A certain amount of heat is necessary for the proper functioning of microorganism in the soil. Soil temperature controls the rate of microbiological process involved in mineralization of nitrogen, composition of organic matter, nitrogen-fixation etc.

There is lowest microbiological activity where soil temperature is below 5-C and above 54-C. Optimum temperature for microbiological activity is between 25-35—C.

(b) Effect of soil-temperature on the decomposition of soil-organic matter:

Organic matter decomposition depends on microbial process and microorganism activity is related with temperature. The higher the temperature, the more rapid is the decomposition.

(c) Effect of soil-temperature on absorption of soil water:

Very low and very high temperature affects the absorption of soil water by the roots of plant.

(d) Effect of soil-temperature on nutrients availability:

Soil temperature influences the various chemical reactions that take place in the soil. The solubility of food nutrients and their availability are considerably influenced by soil temperature.

(e) Effect of soil-temperature on seed germination:

Soil temperature is one of the important factors that influences germination of seeds. The temperatures at which different seed fail to germinate or germinate very slowly. If it is too high, seed may be injured.

(f) Effect of soil-temperature on plant growth:

The growing plant requires a certain amount of heat right from the seed germination up to the stage where the plant reaches maturity. During plant growth physiological processes are influenced by temperature.

(g) Effect of soil-temperature on soil formation:

Process of weathering and soil development are accelerated where there is an increase in soil-temperature.

(h) Effect of soil-temperature on physical properties:

Soil temperature indirectly influences soil structure.

(i) Effect of soil-temperature on plant diseases:

Development of disease are also related with soil-temperature.