From an agricultural standpoint, the soil may be defined as that portion of the land surface adapted to the support and growth of crop plants. It is a system of many components, mineral and organic, and contains living organisms. The material remnants and detritus of nearly all if not all activities on the solid portion of the earth’s surface find their way to the soil, and by various transporting agencies, especially water and wind, are carried from soil to soil.
The number and the relative proportions of the various components vary quite widely in different soils. Moreover, every component of the soil is continually involved in processes of change.
Therefore each soil is a dynamic system, with a complex summation of properties consequently it is highly individuated ; no two soils can be expected to be exactly alike, nor any one particular soil to remain just the same from time to time, either in crop producing power or response to cultural methods. Each soil must be regarded as distinct, with its own properties ; but these properties are continually being modified as a result of activities within the soil as well as by natural and artificial agencies from without.