SOIL REACTION

Soil reaction.

   Soil reaction can be determined by measure of concentration of H+ and OH- where the soil can be determined as acidity, alkalinity or neutral soil. Soil that are acidic are said to have an acidic reaction and soil that are alkal said to have an alkaline reaction.

                                                                 

When there more H ions than OH ions in the soil solution then the soil is acidic. If there are more concentration of OH than H in the soil solution then the soil is basic. If the conctration of H and OH are equal in the soil solution then the soil is neutral.

                    The source of OH ions in the soil.
OH ions in the soil are added as a result of some reactions which release OH ions into the soil solution.
      Examples of these reactions include;
         H2O + ca[soil colloids particles] > H[soil colloids particles] + can+ + 2OH-

When reaction like this take place, the formed OH formed added to the soil solution

                   The source of H ions in the soil
There three source of H ions in the soil.
      I) Insoluable acid which may be present in the soil solution.
      ii) The alminium ions which adsorbed on the soil colloidal particles
     iii) The H ions that are adsorbed on the soil colloids.

                                                           SOIL PH
 The PH of soil is simply the negative logarithm of the H ions concentration of the soil solution. The soil reaction is expressed in terms of PH.

                                                               

             EFFECTS OF RAINFALL ON SOIL PH 

     Soil acidity occurs in place where there high amount of rainfall per year. The high amount of rainfall wash away exchangeable bases from upper parts of the soil to the bottom layer.

     The washing away exchangeable bases from top layer of soil to bottom layer is called leaching. As exchangeable bases are washed away leave the upper layer of soil with high concentration of H hence soil become acidic.

     On other hand basic soil occurs on the area where there is low annual rainfall. In the areas with low annual rainfall there some salts such as magnesium, calcium and sodium carbonate favor the formation of OH ions in the soil. As result the concentration of OH ions became high and soil become basic.