Soil Forming Factors

 A. Passive soil-forming factors               B. Active soil-forming factors

(i) Parent material                                            (i) Climate

(ii) Relief or topography                                 (ii) Vegetation and organisms(biosphere)

(iii) Time       

                

                                          Soil – the end product of soil-forming factors
 

A. Passive soil-forming factors

1. Parent material

Parent material is that mass (alluvium, colluviums, aeolian/loess, glacial-till) from which the soil has formed.

2. Relief or topography

•  The topography refers to the differences in elevation of the land surface.
•  On level topographic positions, almost the entire water received through rain percolates through the soil. Under these conditions, the soil formed may be considered representative of the regional climate. They have normal solum with distinct horizons.
• The soils on steep slopes are shallow, stony, and have weakly developed profiles with less distinct horizons.

3 Time

• Soil formation is a very slow process requiring thousands of years to develop a mature pedon. The period taken by a given soil from the stage of weathered rock (i.e. regolith) up to the stage of maturity is considered time.
• By matured soils, we mean soils with fully developed horizons. In soil formation nature works slowly. It has been reported that it takes hundreds of years to develop an inch of soil.

B. Active soil-forming factors

(1) Climate – It influences soil formation through (i) precipitation and (ii) temperature

(i) Precipitation: Precipitation is the most important among the climatic factors. As it percolates and moves from one part of the parent material to another, it carries with it substances in solution as well as in suspension.

(ii) Temperature: High temperature favors rapid decomposition of organic matter and increases microbial activities in the soil- In the tropical regions, the rate of weathering proceeds three times faster than in temperate regions and nine times faster than in the arctic.

(2) Biosphere (vegetation and organisms)

Vegetation controls the erosion. It facilitates percolation and drainage and brings greater dissolution of minerals. Organisms cause constant mixing within the soil profile. Their role as soil formers is related to humification and mineralization