438 



THE PRINCIPLES OF SOIL MANAGEMENT 



The process of decay gives rise to products, chiefly 

 carbon dioxid, that are solvents of mineral matter, and 

 leaves the nitrogen and ash constituents more or less 

 available for plant use. 



Oxygen is also necessary for the germination of seeds 

 and the growth of plant-roots. These phenomena, 

 although not involving the removal of large quantities 



of oxygen, are 

 yet entirely de- 

 pendent upon 

 its presence in 

 c o n s i de r a b 1 e 

 amounts. 



304. Carbon 

 dioxid. T h e 

 solvent action 

 of carbon dioxid 

 is its most im- 

 portant func- 

 tion in the soil. By its solvent action it prepares for 

 absorption by plant-roots most of the mineral substances 

 found in the soil. Although a weak acid when dissolved 

 in water its universal presence and continuous formation 

 during the growing season results in a large total effect. 

 Carbonic acid dissolves from the soil more or less 

 of all the nutrients required by plants. The amounts so 

 dissolved are appreciably greater than those dissolved 

 in pure water. The constant formation of carbon dioxid 

 by decomposition of organic matter keeps this solvent 

 continually in contact with the soil. 



Carbon dioxid serves a useful purpose in combining 



Fig. 117. Hand cultivator, or wheel hoe, with 

 attachments. 



