HORTICULTURAL SOILS. 
75 
One essential condition of the nitrification of organic matter 
is that it only takes place in a moist soil, sufficiently porous to 
admit air; hence the beneficial effect of mixing a certain pro¬ 
portion of sand, charcoal, or peat to soil composts for potting 
purposes, and the value of a sufficiency of crocks for drainage. 
It is also necessary that some chemical base should be present in 
the soil, with which the nitrates as they are formed can combine ; 
this condition is usually fulfilled by the presence of carbonate of 
lime (chalk), nitrate of lime being produced. In leaf moulds and 
peat moulds rich m humus the nitrification is sometimes 
rendered difficult by the lack of such a constituent, the alkali 
bases rendered soluble by nitrification get rapidly used up, and 
the soils in consequence become overcharged with acidity, to the 
injury of the growing plants. It is necessary in such cases to 
apply an antidote, which may be lime, chalk, or wood ashes; 
these substances tend to accelerate the nitrification in an extra¬ 
ordinary manner.] 
Temperature is another prime factor in determining the rate 
of oxidation and nitrification in organic materials and soils ; the 
activity of all living agents, whether animal or vegetable, being 
dependent on the occurrence of a favourable degree of heat, and 
being confined to certain specific ranges of temperature. 
Oxidation is consequently found to be far more rapid in summer 
than in winter, and much more energetic in hot climates than 
in cold; accordingly we find it more active in a conservatory 
than in the open garden. 
The nitrifying organisms in soils may be killed by severe 
drought. This may probably explain the fact of some plants 
suffering so terribly from insufficient watering at certain stages 
of their growth. For instance, the chrysanthemum never 
thoroughly recovers the ill-effects of excessive drought. 
Recent investigations have shown that the microderms are in 
greater or less numbers in all fertile soils, but are most active in 
soils under cultivation, teaching us the advantage of the frequent 
use of the hand-hoe and other implements of tillage in the open 
garden, and of a friable porous soil for potting purposes. The 
soil should have good capillary action, so that at all seasons it 
will as near as possible contain that amount of moisture which 
is present when ground digs well, because this is found to be the 
degree of moisture most desirable. Soils should also contain 
