AGRONOMY 39 



it may work a positive injury by either causing 

 an unnecessary waste of nitrogen, or, in the case 

 of rich soils, it may supply too much nitrate, 

 and thus produce a rank growth of leaves in- 

 stead of fruit. 



In Great Britain, nitrification goes on in the 

 soil until the late autumn ; but the rate depends 

 upon the nature of the soil. In old soils, 

 nitrification does not go on rapidly enough to 

 furnish the necessary nitrogen ; but in a new 

 soil, nitrification is liable to go on too rapidly. 

 Deep digging and thorough cultivation of orchards 

 and gardens aid nitrification, and render the humus 

 available as plant-food. The addition of lime aids 

 nitrification, and prevents the formation of sour or 

 acid land. Good drainage is also necessary to 

 nitrification in the soil. In water-logged soils 

 humus does not decompose naturally, but peat 

 is produced on account of the absence of oxygen. 



Humus is a means by which water is retained 

 in a soil — and this property is of great value in 

 times of drought. In sandy soils, humus also 

 assists in the rise of sub -soil water to the roots 

 of trees and other plants. 



The humus of the soil is increased by the 

 use of well-prepared farmyard manures. Humus 

 also aids in rendering the insoluble mineral 



