The Effect of pH of Soils on Micro-organisms
The pH of soils affects the growth activity of soil microorganisms. For example, bacteria and actinomycetes are known to function properly at pH above 5.5, while fungi and sulfur-oxidizers function in an acid medium.
The most favorable pH range for microbes responsible for organic matter mineralization and hence N-, P- and S- availability is between 5.5 – 7.5.
At low pH values, therefore, such process as nitrification and nitrogen fixation is reduced. High soil acidity restricts the microfauna population.
A common example here is the earthworm population which is depressed under low pH (high acidity), thereby reducing the mixing of surface litter with soil.
Under those circumstances, the rate of organic matter decomposition is reduced.
Effect on Disease Pathogens
Soil pH affects some disease pathogens. An increase in soil pH had been known to favor potato scab disease which is controlled by the application of elemental sulphur.
Read Also: Roles of Microorganisms in Organic Matter Transformation
Maintenance of Ionic Balance
Soil acidity especially hydrogen ion concentration, (H+) has some buffering effect in maintaining ionic balance in the soil. If the leaching of cations is greater than those of anions in the soil there are net negative charges. H+ is released from exchange sites to soil solution to maintain the ionic balance.
Effect of pH on Soil Physical Conditions
Soil structure is most easily affected by soil pH. In soils with pH 8.5 sodium, Na+ causes dispersion of soil colloids resulting in physical problems. The dispersed clay particles plug soil pores.
Similarly, under extreme conditions of alkalinity colloidal materials could move to subsoil where they could precipitate from hardpan.
Air and water movement become impeded and plant root growth and penetration into the soil consequently become difficult.
Under very acid conditions deficiency of Ca may affect soil structure. Saline soils could result from using salty water for irrigation.
Read Also: Sources, Composition, Decomposition, and Mineralization of Soil Organic Matter and Soil Organisms
