Biological Papers- 203 



SOILS AND BACTERIA.* 



By Lyman C. Wooster. Ph. D., State Normal School, Emporia. 



OWING to the inexact forms of statement used by many writers, 

 most people believe that plants use as foods certain minerals 

 found in soils, while animals eat organic materials found in plants 

 and other animals. Any one who knows aught of the needs of 

 plants and animals and of the nature of foods knows that plants 

 and animals must both have for their tissues and activities starch, 

 sugar, oils, and proteids ; and that no plant, except a few bacteria, 

 can get energy and tissue foods directly from the mineral world. 

 Water, carbon dioxid, potassium and sodium nitrates, ammonia 

 in some form, sodium chlorid, calcium sulfate (gypsum), magne- 

 sium sulfate (epsom salts), calcium phosphate and some soluble 

 compound of iron are merely the crude materials out of which 

 green plants, in the presence of sunlight or the light of the electric 

 arc, build their foods, such as starch, oil, and the proteids. The 

 minerals named above are crude food materials, and are foods in 

 no other sense; but their presence in soils is as necessary to com- 

 plex plants as are brick, mortar and lumber to the house-builder. 



The amount of these crude food materials used by a crop of 

 wheat, for example, is surprisingly large. From a single farm of 

 160 acres, where exclusive wheat farming is followed, there is an 

 annual waste of fertility equivalent to 28,500 pounds of nitrogen, 

 5000 pounds of potash, 3000 pounds of phosphoric acid, and 1600 

 pounds of lime. Unless these minerals are returned to the soil, 

 the land must continue to diminish in productiveness till it finally 

 becomes barren. This was the fate of the old tobacco plantations 

 of old Virginia, and is soon, certainly within fifty years, to be the 

 result of continuous wheat cropping in Kansas without the use of 

 fertilizers. 



The humus and bacteria of the soil are most directly concerned 

 with its nitrogen content, and it is to these elements of fertility 

 that I wish to address myself. 



It is very unfortunate for the farmer that no cultivated plant 

 can use uncombined nitrogen as a crude food material, for the at- 

 mosphere is four-fifths nitrogen. The nitrogen used by plants 



• In preparing this paper I have freely used the observations and experiments described in 

 two standard works, "Bacteria," by Geo. Newman, published by G. P. Putnam's Sons, and 

 "Physics of Agriculture," by F. H. King, published by author, Madison, Wis., together with my 

 own personal observations and experiences. These have served as the bases of the inductions, 

 -which I trust will be of some service to the farmers of our state.— l. c. w. 



