Water Management in Horticultural Crops (1+1)

Physical properties of soils

1. Colour

• Colour is one of the most useful and important characteristics for soil identification. Concentration of organic matter imparts a grey, black or dark-brown colour to the soil. Diffusion of iron oxides imparts red and yellow colour to the soil. Manganese dioxide and hydrated iron oxides may also contribute red colour. A light grey colour may indicate a very low content of organic matter and iron. Soil colour changes with moisture content.
2. Texture

• The size of particles comprising the soil determines its texture. The texture of a soil is perhaps its most nearly permanent characteristic. The texture commonly refers to the fineness or coarseness of soil as a whole as to the proportion of the particle groups of different sizes.
• The mineral particles of the soil differ widely in size and can be classified as follows:
Name of the particles	Size limits in mm	Distinguishable by naked eye
Gravel	Larger than 1	obviously
Sand	1 to 0.5	Easily
Silt	0.5 to 0.002	Barely
Clay	Less than 0.002	invissible


• The supply of water to plants is relatively more in soils of moderately fine texture than in those of coarse texture. The amount of water available to plants increases with the capacity of the soil to hold water in available form. The textural class and available water are presented in the table 1.
Table 1.Textural class and available water (cm/m)
Textural class	Available water
Sand	1.5
Loamy sand	7.4
Sandy loam	12.1
Loam	19.1
Silt loam	23.4
Silt	25.6
Sandy clay loam	20.9
Silty clay loam	20.4
Sandy clay	8.5
Silty clay	18
clay	15.6



3. Structure

• The capability of any soil for growth of plants and its response to management depends as much on its structure as on its fertility. The common types of soil structure are granular, prismatic, columnar, platy and laminar. Fine grained soils have granular structure and are desirable for irrigation as large voids provide space for circulation of air. From the standpoint of agriculture, permeability of soil to water, air and roots provided by favourable soil structure is important.
4.pH value

• pH value or hydrogen ion concentration is a measure of the intensity of acidity or alkalinity of a soil. Its value ranges from 0 to 14, of which 7 is neutral in the sense of chemical reaction. Below 7 the soil is acidic, above 7 it is alkaline.
5. Soil organic matter

• It has role on the physical properties of the soil. It improves infiltration rate and water holding capacity.