After reading this article you will learn about the pore space in soil and factors affecting it.
Types of Pore Space in a Soil:
The pore space in a soil represents that part of the soil volume which has been occupied by air or water.
Pore space in a soil may be of the following three types:
(i) Macro pore space occurs between peds. They are more than 75 micron in diameter. Water and air rapidly pass through them. They are necessary for rapid drainage of the soil.
(ii) Mesopores are 75 to 30 microns in diameter. Relatively larger mesopores occur between the peds while relatively smaller ones occur within the peds. Mesopores are required for storage of water for crop growth.
(iii) Micro-pores are less than 30 microns in diameter. Water is held within the micro-pores tightly enough to be unavailable for plant growth.
Factors Affecting Pore Space Per cent of Soils:
Total and Micro-pore spaces of soils increase when the clay percentage increases i.e. their texture becomes finer. The microspores ices of clayey soils are much more than those of the sandy soils, because clay particles unite to form soil aggregate within which micro-pore space occur.
(ii) Organic matter:
Organic matter is decomposed by the soil microorganisms to form humus, which usually binds the soil particles to form aggregates. Besides this, humus also stimulates the growth of soil microorganisms, which mechanically bind the soil particles to form aggregates within which micro-pore spaces occur. Hence the micro and total pore spaces increase.
(iii) Nature of crops and cultivation:
Excessive cultivation of soils increases the oxidation of humus. Consequently, total and micro-pore spaces of soils are decreased if soils are more and more cultivated. Less cultivation is required for growing grasses, the roots of which bind the soil particles to form soil aggregates.
Crops like potato, maize etc. require the maximum amount of soil cultivation for soil aeration which increases the oxidation of humus. Hence grasses increase the percentage of pore space of the soil, whereas arable crops like maize, potato etc. decreases it.
(iv) Soil depth:
Since plant roots and organic matter occur more in surface soil then in sub-soil, so pore space per cent of the surface soil is usually much more than that of the sub-soil.