122 NATURE AND PROPERTIES OF SOILS 



in any soil tends to facilitate ease in drainage and to encour- 

 ;iL r <' good aeration. These two conditions are of course neces- 

 sary for the promotion of soil sanitation. Root extension and 

 bacterial activity are thus increased. It is of especial impor- 

 tance that the splitting-up of the organic matter shall take 

 place in the presence of plenty of oxygen, in order that toxic 

 compounds may not be generated and that products highly 

 favorable to plant growth should be formed. 



The soil organic matter, however, functions in other ways 

 than those strictly physical and chemical. Its degradation 

 products may serve as nutrients for higher plants. Bacteria 

 and other soil organisms are also furnished a source of energy 

 thereby and the production of carbon dioxide is much in- 

 creased. This carbon dioxide, as well as the organic acids 

 generated, tends to raise the capacity of the soil-water as 

 a solvent, and thus the amount of mineral material available 

 to the crop is greatly increased. The general effect of organic 

 matter, then, is to better the soil as a foothold for plants, and 

 to increase either directly or indirectly the available nutri- 

 ent supply for the crop. i 

 \f 65. Maintenance of soil organic matter. 1 — fhe mainte- 

 nance of a proper supply of organic matter in a soil is a ques- 

 tion of great practical importance, as productivity is gov- 

 erned very largely by the organic content of the soiL| This 

 maintenance of the soil organic matter depends on two factors : 

 (1) the source of supply and methods of addition; and (2) 

 the promotion of proper soil conditions in order that the 



1 Snyder, H., Effect of the Rotation of Crops upon the Humus Content 

 and the Fertility of Soils; Minn. Agr. Exp. Sta. Bui. 53, June, 

 1897. The Production of Humus in Soils; Minn. Agr. Exp. Sta., Bui. 

 89, Jan., 1905. Morse, F. W., Humus in New Hampshire Soils; N. H. 

 Agr. Exp. Sta., Bui. 138, June, 1908. Hopkins, C. G., Phosphorus and 

 Humus in Relation to Illinois Soils; 111. Agr. Exp. Sta., Circ. 116. Feb., 

 1908. Thatcher, E. W., Tlie Nitrogen and Humus Problem of Dry 

 Farming; Wash. Agr. Exp. Sta., Bui. 105, June, 1912. Fippin, E. O., 

 Nature, Effects and Maintenance of Humus in the Soil; Cornell Reading 

 Course for the Farm, Vol. Ill, No. 50, Oct., 1913. Loughridge, R. H., 

 Humus of California Soils; Calif. Agr. Exp. Sta., Bui. 242, Jan., 1914. 



