8o BACTERIA AND SOIL FERTILITY 



average lime content of 101.7 parts per million, whereas the 

 lake contains only 13.2 parts per million. 



Calcium Carbonate. — The loss of lime from a soil varies 

 with (i) the methods of agriculture, intense methods increasing 

 the loss; (2) the application of animal manures and green ma- 

 nures, which increases the bacterial activity and also the solubility 

 of the calcium carbonate; (3) the addition of commercial fer- 

 tilizers to a soil hasten the loss of calcium in drainage water. 



The numerous acids produced by bacteria react with limestone 

 rendering it soluble so it can be carried away in the drainage 

 waters. ^Therefore, the absolute amount lost varies with the 

 water reaching the soil as well as the composition of the soil. 

 Hall estimates that the annual loss from the Rothamsted soil 

 which contains about 3 per cent of limestone is from 800 to 

 1,000 pounds an acre annually, whereas in this country where 

 liming is necessary the farmers usually provide for a loss of 400 

 pounds an acre annually. 



Bacteria, by the liberation of carbon dioxid, may also pro- 

 duce small quantities of limestone. This enables many soils which 

 contain only very small quantities of lime to retain their neutral 

 reaction and continue to produce fair crops. This, however, is 

 not always the case, as is witnessed by the acid soils occurring 

 in many districts. 



Phosphorus. — Phosphorus occurs in the soil mainly in the 

 form of calcium, iron, or aluminum phosphate. Moreover, as 

 soluble phosphorus compounds are applied to a soil they are 

 changed to insoluble compounds. There are also small quantities 

 of organic compounds of phosphorus. All of these are only 

 slightly soluble, but bacteria act on the organic phosphorus com- 

 pounds and render the phosphorus available to plants. 



In this general process of decay the nitrogen passes through the 

 forms of ammonia, nitrous and nitric acid, and at the same time 

 the carbon passes into various acid compounds including the com- 

 plex humic and ulmic acids and the simpler acids — acetic, lactic, 

 and butyric. The final product of the carbon is carbon dioxid. 



