Soil consists of mineral particles, organic matter and pores. Mineral particles originate from
subsoil and rock, which gets crushed to smaller and smaller pieces through physical and chemical
weathering processes.
The mineral soil particles are divided into four groups according to their size:
Gravel and stones: particles larger than 2 millimetres
Sand: particles from 0.05 to 2 millimetres; they can be felt between the fingers
Silt: particles from 0.002 to 0.05 millimetres
Clay: particles smaller than 0.002 millimetres
The difference between sand, silt and clay is not visible to the naked eye. Still it is important to
distinguish between them, as the properties of the soil is very much dependent on the composition
of the different particle sizes. Soils having equal amounts of clay, silt and sand are ideal
for agricultural use. Such a soil is called loam.
Mineral particles contain nutrients which are slowly released in the process of weathering.
Plant roots and some micro-organisms can actively dissolve nutrients from mineral particles
and use them for their growth. The plants need minerals to build up organic matter and for
physiological processes.
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