60 Agricultural Chemistry. 



liost plant, there are bacteria in the soil which use free nitrogen, 

 but which do not grow in union with the higher plants. These 

 bacteria are found in most soils and are said to possess this power 

 when the supply of carbonaceous matter in the soil is plentiful. 

 Indeed, some years ago, such organisms under the name of 

 "alinite" were prepared for sale, but the success attending their 

 use was doubtful and their manufacture has ceased. 



It is thought that the fertility and richness in nitrogen of 

 forest or prairie soil is largely due to the activity of such or- 

 ganisms, which would find suitable conditions for growth in the 

 large quantity of organic carbonaceous matter contained in such 

 soils. At present it is impossible to say whether the nitrogen 

 added to the soil in this way is of any considerable amount. 



Gases in a soil. The spaces between the particles of soil, be- 

 sides containing a certain amount of moisture, are usually occu- 

 pied by air. Because of the chemical changes going on in the 

 soil this air becomes robbed of its oxygen, and enriched with 

 carbon dioxide. This air is not stagnant but undergoes constant 

 renewal by diffusion from the air above. 



The gases drawn from the soil at different times will be found 

 to vary in composition ; the oxygen may be anywhere from 10 to 

 20 per cent, the carbon dioxide from 1 to 10 per cent, while the 

 nitrogen usually differs very little in amount from that in the 

 atmosphere, that is, about 78 per cent. The amount of carbon 

 dioxide is greater and of oxygen less during the summer and 

 autumn than in the winter or spring. The higher temperature 

 in the soil during summer and autumn favors chemical decom- 

 position, with greater production of carbon dioxide. 



Tillage and drainage. The operations of tillage and drainage 

 serve in many important ways to make the conditions for plant 

 life more favorable and to increase the amount of plant food 

 which is at the disposal of the crop. 



By tillage the surface soil is pulverized and brought into a 

 loose, open condition. Large lumps are broken into small par- 

 ticles and the fine tilth thus obtained, allows a rapid extension 



