The capacities of these soil materials to fix P, Mo, S, and B are influenced by liming. A cid mineral soils at pH 5.0 and lower often contain appreciable amounts of Al and Mn in the soil solution which are detrimental to plant growth. Optimum growth and efficient use of fertilizer nutrients in acid soils require the addition of lime to eliminate the toxic effects of Al, H and Mn. Soils of humid regions usually contain little weatherable Ca and Mg minerals. Removal by crops Calcium and magnesium composition of some crops.
Acidity is reduced by the volatilization and denitrification of nitrogen.
For example, under flooded soil conditions when the residual nitrates in the soil are denitrified, the soil pH value will increase. Nitrate fertilizers containing a basic cation such as Ca, K, or Na will also increase the soil pH value. The hydrogen will cause clay particles to break down, further releasing more toxic aluminum. This is the type of acidity caused by organic matter and bound Al. Exchangeable Aluminum and Basic Cations Soil chemists have defined exchangeable cations in acid soils as those cations extracted with a neutral unbuffered salt solution.