440 SOILS: PROPERTIES AND MANAGEMENT 



plays a part in the solution of iron. The lower fungi and 

 the algae precipitate iron from solution as iron oxide-. 



363. Decomposition of non-nitrogenous organic matter. 

 — The organic matter commonly decomposed in soils 

 contains a large proportion of compounds containing no 

 nitrogen. Many non-nitrogenous substances decompose 

 rather rapidly, and the organic nitrogen disappears less 

 rapidly than the carbon, hydrogen, and oxygen of organic 

 bodies. 



Humus always contains a higher percentage of nitrogen 

 than do the plants from which it is formed. 



The non-nitrogenous substances consist of cellulose and 

 allied compounds forming the cell walls of plants, and the 

 carbohydrates, organic acids, fats, and the like, contained 

 in them. The dissolution of cellulose is brought about 

 by the action of the enzyme cytase secreted by a number 

 of fungi, and is also probably accomplished by the Bacillus 

 amylobacter, but whether through the secretion of an 

 enzyme is not known. Other bacteria have been reported 

 to secrete a cytase that acts on certain constituents of the 

 cell wall. It is probable that numerous organisms capa- 

 ble of fermenting cellulose and allied substances exist in 

 the soil, accomplishing this decomposition through the 

 production of cytase. 



The effect of cytase on cellulose and other fiber is to 

 hydrolyze it with the formation of sugar, as glucose, 

 mannose, zylose, arabinose, and the like. 



Starch is converted into glucose by a ferment (diastase) 

 either present in the plant itself or possibly secreted by 

 fungi or bacteria. All the sugars are finally converted 

 into organic acids which may combine with mineral bases. 

 Distinct organisms have been isolated that can utilize 

 for their development formates, acetates, propionates, 



