agricultural writers.

"Thus the more we cultivate, the more we hasten the nitrification,
oxidation, or destruction of the organic matter or humus of the
soil. Where the soil is well supplied with decaying organic matter,
we rarely need to cultivate in a humid section like this, except for
the purpose of killing weeds.

"The presence of carbonates in the soil is essential for
nitrification, because the bacteria will not continue the process in
the presence of their own product. Nitrification ceases if the
nitrous or nitric acid remains as such; but, in the presence of
carbonates such as calcium carbonate (ordinary limestone) or the
double carbonate of magnesium and calcium (magnesian limestone, or
dolomite), the nitrous acid or nitric acid is converted into a
neutral salt of calcium or magnesium, one of these atoms taking the
place of two hydrogen atoms and forming, say, calcium nitrate:
Ca(NO3)2. At the same time the hydrogen atoms take the place of the
calcium in limestone ( CaC03), and form carbonic acid (H2CO3), which
at once decomposes into water (H2O) and carbon dioxid (CO2), which
thus escapes as a gas into the air or remains in the pores of the
soil.

"The fact that nitrification will not proceed in the presence of
acid reminds us that only a certain degree of acidity can be
developed in sour milk. Here the lactic acid bacteria produce the
acid from milk sugar, but the process stops when about seven-tenths
of one per cent. of lactic acid has developed. If some basic
substance, such as lime, is then added, the acid is neutralized and
the fermentation again proceeds.