Fundamentals of Soil Science (1+1)

Introduction

The physical properties of a soil play an important role in determining its suitability for crop production. These properties depend on the amount, size, shape, arrangement and mineral composition of its particles. These properties also depend on organic matter content and pore spaces.

• The plant support, root penetration, drainage, aeration, retention of moisture and plant nutrients are linked with the physical condition of the soil.
• Some important physical properties of soils are soil texture, structure, density, porosity, colour, consistence and soil water.

Soil Texture
Soil texture refers to relative proportion of mechanical / soil separates below 2 mm in diameter (viz. sand, silt and clay).
Three size classes are particularly important:

1. Sand (size as in beach sand)
2. Silt (size like talc/talcum powder)
3. Clay (small particles which stick together, like modeling clay)

• The determination of various sized particles (sand, silt and clay) helps in understanding various soil properties e.g. water retention, cation exchange capacity, soil workability, erodibility etc.
• The information about particle size analysis is also of utmost importance for judicious nutrient and water management.

Particle size classification:

S.No.	USDA Classification		International Soil Science Society classification
	Separate	Particle Diameter (mm)	Separate	Particle Diameter (mm)
1	Very coarse sand	2.0 - 1.0	Coarse sand	2.0 ‑ 0.2
2	Coarse sand	1.0 - 0.5	Fine sand	0.2 ‑ 0.02
3	Medium sand	0.5 – 0.25	Silt	0.02 ‑ 0.002
4	Fine sand	0.25 – 0.1	Clay	< 0.002
5	Very fine sand	0.1 - 0.05
6	Silt	0.05 ‑ 0.002
7	Clay	< 0.002