1914] Loughridge: Humus and Nitrogen in California Soil Columns 179 



DISTEIBUTION OF HUMUS DOWNWARD IN 

 CALIFORNIA SOILS 



A very marked characteristic of the soils of California is their 

 great depth, as exemplified in the uniformity of color through 

 a depth of several feet, their good texture, affording easy pene- 

 tration of plant roots often to depths of twenty and even sixty 

 feet below the surface, abundant food available for plant use 

 throughout these depths, an absence of any well-defined subsoil 

 except at a depth of several feet below the surface, the absence 

 of any compact clay substratum differing from the surface foot, 

 and the presence of humus to a depth of as much as ten or more 

 feet. In each of these particulars the soils of California differ 

 from those of the humid states east of the Rocky Mountains, and 

 because of this the methods of culture are different, and in the 

 applications of phosphate fertilizers to the soil it is only with 

 great difficulty that they can be made to reach the feeding roots 

 of plants. 



There are several striking facts regarding the humus itself 

 in the soils of California which deserve mention and which 

 distinguish them from the soils of the humid region of the 

 eastern states, one of which has but recently been brought out 

 in the examinations that are being made of the one hundred and 

 more typical twelve-foot columns from the chief agricultural 

 divisions of the state. These facts are : first, the small percentage 

 of humus in the first foot of all California soils as compared 

 with the much higher percentages found in eastern soils ; second, 

 the distribution of the humus downward to depths of twelve and 

 more feet in upland soils, the total amount being usually greater 

 than that of the eastern soils; and tlurd, the rather higher 

 percentage of humus-nitrogen in the upper three feet, and the 

 distribution of the humus-nitrogen throughout the twelve feet, 

 thus giving the soil in the arid region a higher total of humus- 

 nitrogen than is found in the humid soils. 



Bacterial Activity in the Soil. — Another highly important 

 advantage possessed by California in her soils is the fact recently 

 brought out by Professor C. B. Lipman of this station in his 

 paper, "The Distribution and Activities of Bacteria in Soils of 

 the Arid Region ' ' :^ 



5 Univ. Calif. Publ. Agr. Sci., vol. 1, no. 1, pp. 17, 20. 



