After reading this essay you will learn about the physical and chemical properties of soil.
Essay on the Physical Properties of Soil:
Physical properties include size of soil particles, soil structure, pore size and water holding capacity etc. The relative proportion of different sized soil mineral particles (sand, silt and clay) determines the soil texture.
The main three soil types are as under:
i. Sandy Soils:
Ploughing in these soils is very easy and these soils are generally considered as light soil. These soils contain significant amount of sand. When the moistened soil is rubbed between thumb and finger it feels gritty and does not stick to hand. When a ball of moistened soil in the hand is squeezed, it breaks with slight pressure.
Handmade balls of properly moistened soil fall apart easily. After application, the water leaches down quickly. Pore size of sandy soils is greater than clayey soils which results in higher infiltration rate of air and water in such soils.
ii. Clayey Soils:
Soil with clay content more than 40% is called as clayey soil. Irrigation/rain water takes long time to leach down. Ploughing of these soils under low moisture conditions leads to development of clods. Formation of wide cracks upon drying is the characteristic feature of these soils. Balls can be easily made by moist clayey soils. Water holding capacity of these soils is greater than sandy soils. Water stagnation is the main problem with these soils.
iii. Loamy Soils:
Characteristics of these soils are in between that of sandy and clayey soils. Soil structure, aeration, water movement, water holding capacity and nutrient content are optimum for crop cultivation. These soils are best suited for agriculture. When rubbed between thumb and fingers, it feels like powder.
Essay on the Chemical Properties of Soil:
Every soil has different chemical properties such as soil reaction (pH), electrical conductivity (EC), salt content, types of salts present etc.
Based on these chemical properties soils are classified as under:
i. Acidic Soils:
Acidity or basicity of soil is measured by pH. The pH range of 6.5 to 8.7 is considered normal for crop production. If pH is less than 7, soils are considered as acidic. These soils are generally found in areas receiving high rainfall, which is high enough to leach appreciable amount of exchangeable bases from the surface layer.
ii. Salt Affected Soils:
These soils contain some amount of soluble salts. However, under some circumstance when the concentration of salts in a soil is high enough, which adversely affects the crop growth, such soils are known as salt affected soils.
Based on types of salts present, pH and EC, the salt affected soils are classified into three groups:
a. Saline Soils:
Soils with higher concentration of sulphates and chlorides of calcium, magnesium, and potassium are known as saline soils. The pH of these soils is less than 8.7 and EC is more than 0.8 mmhos/cm. A powder white layer of soluble salts is developed on the soil surface upon drying after irrigation. Water stagnation is not a problem in these soils. In local language, these soils are also called as kallar, reh, thur or shora.
b. Alkali Soils:
Carbonates and bicarbonates of sodium are the main salts in alkali soil. The pH of alkali soils is greater than 8.5. Sodium gets attached to clay particles and deteriorates chemical and physical properties of soils. Infiltration rate of these soils is very low which causes water stagnation problem in these soils.
c. Saline-Alkali Soils:
The soils having higher concentration of sodium and soluble salts in it are called saline-alkali soils. So these soils have combined characteristics of saline and alkali soils. These soils have higher amount of sodium attached to clay particles and higher amount of soluble salts in it.