The pH value of some sandy soils are below 5. May I know the causes of these low pH values of soil. What are the impacts of this on the environment?
Well, Discussion, may help.
Experiments carried out by scientists on soil gas samples in multiple locations have proven that the molecular pressure of carbon dioxide in soil air is usually higher than the air pressure on the surface of the earth and ranges between (0.1-0.001) atmosphere and the reason for the difference in carbon dioxide pressure is the difference In temperature, humidity conditions, microbial activity, susceptibility to organic matter and the effect of soil composition on the diffusion of gases.
Carbon dioxide reacts with water results in a change of acidity. For example, if the molecular pressure of carbon dioxide is (0.1) atmosphere and the water temperature is between (2-0) ° C, the pH ranges between (4.2 - 4.5) and this is less than the acidity of rainwater. The interaction of free oxygen with iron minerals is another source of acidity, knowing that the biochemical and hydro-chemical processes are also able to increase acidity in this zone and the hydrogen ion resulting from these reactions plays an important role in weathering minerals. As for the organic acids formed in this range, some of them have an important role in soil development, including what contributes to the processes of transporting insoluble components down towards the water level.
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In addition, soil may contain inorganic sulphate and or organic matter with combined sulphur. During microbial oxidation in an-aerobic condition( in absence of oxygen), these sulphur compounds may be reduced to hydrogen sulfide which also contributes acidity to the soil.
In addition to the already mentioned leaching processes, if the soil has been cropped or if pasture has been grazed, and the crops/animals removed, then there is a net depletion not only of elements such as N, but importantly too of cations such as Ca, which are replaced by protons pumped out by plant roots to maintain charge balance.
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