The Effect of Climate and Weather on the Soil. 11 
Thus there are at least five ways in which the weather or 
seasons affect a soil apart from the great climatic effects we 
have already studied : — 
1. High rainfall tends to wash out two very useful con- 
stituents, calcium carbonate and nitrates, both of which must 
be replaced or the soil loses fertility. Fortunately other 
useful substances are less liable to loss. 
2. High rainfall has an adverse physical effect, spoiling the 
tilth. 
3. In dry conditions there is less or no washing out of 
calcium carbonate or of nitrates, and hence less wastage of 
fertility. 
4. Drought, frost, hot sunshine, and other factors which 
are detrimental to life are finally beneficial to bacterial activity 
and lead to an increased production of plant food. 
5. Frost has a beneficial effect on tilth. 
These factors are of course all mixed up in their action, but 
the general effects may be summed up briefly. 
The nitrates formed during summer by bacterial action, 
and destined to serve as food for the next generation of plants, 
are readily washed out during a wet winter, but they remain 
safely locked up in the soil throughout a period of frost and 
snow when no leaching takes place. There they lie ready for 
use when spring awakens the young plant into activity, and in 
consequence a mild spring following on a hard winter is 
commonly a period of vigorous growth. This is well seen 
in Canada, where a remarkable development of vegetation 
takes place directly the weather is sufficiently warm. In part 
the result is due to the effectual cold storage of the plant food 
neither loss nor deterioration going on in frozen ground ; in 
part to the disintegration of the soil organic matter under the 
action of frost so that it becomes more easily assailable by soil 
bacteria, and partly to the improvement already mentioned in 
the amount of work the plant food makers can do. 
Another effect of a wholly different nature is also produced. 
Frost puffs up or lightens the soil ; it splits the hard clods and 
brings them down to a nice crumbly tilth well adapted for a 
seed bed. On the other hand, long continued wetness con- 
solidates the soil, makes it sticky and very unsuitable for 
seeds. Thus at the end of a mild wet winter the soil is poor 
in plant food because of the leaching that has gone on, its 
population of micro-organisms is very mixed because the 
susceptible harmful ones have not been depressed, and it is 
in a bad mechanical condition because the wetness has made 
the clay particles very sticky. On the other hand, at the end 
of a more severe winter when the land lay frostbound or 
covered with snow there is a good supply of plant food, all 
