CH. iv] Weather 57 



The effect of iveather on the soil 



While climate plays a great part in determining the 

 general character of the soil the weather is responsible 

 for tolerably wide variations exhibited from year to 

 year. 



There are at least five ways in which the weather or 

 seasonal effects operate: 



1. High rainfall tends to wash out two very useful 

 constituents, calcium carbonate and nitrates, both of 

 which must be replaced or the soil loses fertility. For- 

 tunately other useful substances are absorbed by the 

 soil and are therefore less liable to be lost. 



2. High rainfall has an adverse physical effect and 

 spoils 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 plant life are finally beneficial 

 to bacterial activity (p. 46), and lead to an increased 

 production of plant food. 



5. Frost has a beneficial effect on tilth. 



These factors of course all intermingle in their action, 

 but their general effects may be summed up briefly. 



The nitrates formed during spring and 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; conse- 

 quently a mild spring following on a hard winter is 



