COMPOSITION AKD FERTILITY OF THE SOIL. 23 



pared, nor the stationary roots of plants be fed. It is in 

 the great change thus introduced into water-logged soils 

 by land drainage that its extraordinary power as a fer- 

 tilizing agency depends, to which reference is made in 

 another chapter. 



The relative fertility of a soil is further dependent on 

 the climate wherein it lies. Disregard of local conditions 

 as to rainfall, temperature, aspect, height above the sea, 

 and other necessary circumstances, may lead to very erro- 

 neous estimates of the value of soils. They may be the 

 same in composition and texture, and yet diifer greatly 

 in value. Nothing is more certain than that the amount 

 of rain, and the season of its descent, determine in a 

 great degree the nature of the husbandry of the place, 

 and the value of its soil for agriculture. The temperature 

 of the air in any particular locality has an important 

 bearing upon the actual productiveness of the soil, what- 

 ever may be its composition and texture, and however 

 propitiously the rain may fall upon it. Other things 

 being equal, we should expect that sheltered situations, 

 with a good southern aspect, would be those in which we 

 should find the capability of any given soil best exhibited. 

 But though soil and rain and duly-tempered warmth 

 favor us, these and many other considerations besides, 

 may fail to determine, in every case, whether this or that 

 plant may be grown within particular limits. That also 

 depends on the presence or absence of its proper food, 

 and it is here that art is available for meeting the defects 

 of nature. 



Causes of Barrenness. — They are of course the converse 

 of those of fertility. The soil may be empty, considered 

 as a storehouse of plant food, or locked up in stagnant 

 water, and thus incapable as a laboratory in which that 

 food is prepared. There are, however, special causes of 

 infertility. This may arise from the soil containing some- 



