There is
nearly eleven times more lime in arid than in humid soils.
Conditions of aridity favor strongly the formation of lime, and
since there is very little leaching of the soil by rainfall, the
lime accumulates in the soil.
The presence of large quantities of lime in arid soils has a number
of distinct advantages, among which the following are most
important: (1) It prevents the sour condition frequently present in
humid climates, where much organic material is incorporated with the
soil. (2) When other conditions are favorable, it encourages
bacterial life which, as is now a well-known fact, is an important
factor in developing and maintaining soil fertility. (3) By somewhat
subtle chemical changes it makes the relatively small percentages of
other plant-foods notably phosphoric acid and potash, more available
for plant growth. (4) It aids to convert rapidly organic matter into
humus which represents the main portion of the nitrogen content of
the soil.
Of course, an excess of lime in the soil may be hurtful, though less
so in arid than in humid regions. Some authors state that from 8 to
20 per cent of calcium carbonate makes a soil unfitted for plant
growth.
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