180 University of California Publications in Agricultural Sciences [Vol. 1 



. . . that soils of the arid region at all depths studied show ammonifying 

 powers, which are, however, generally most vigorous in the first six or 

 eight feet. In one case ammonificatiou was noted in soil from a depth 

 of fifteen feet, or adjoining the water-table. ... As for nitrification my 

 data present again features of striking interest. They go to prove that 

 nitrate formation, like ammonification, goes on at much greater depths 

 in soils of the arid than in soils of the humid region. . . . That nitrifica- 

 tion is found commonly down to a depth of five or six feet in soils of the 

 arid region. In one case soil from an eight-foot depth showed a vigorous 

 nitrifying power. 



Professor Lipman's observations greatly emphasize the im- 

 portance of having the roots of the various crops utilize the 

 food-supplies at their command at depths of many feet ; for not 

 only is there a nitrogen supply, but our investigations on the 

 soil columns show that the amount of available phosphoric acid 

 and of potash is large at depths of twelve and more feet. 



DISTRIBUTION OF HUMUS AND HUMUS-NITROGEN IN 

 SOIL COLUMNS FROM EACH AGRICULTURAL 



REGION 



The agricultural regions of the state comprise the Sacramento 

 and San Joaquin valleys, forming together the central Great 

 Valley, the foothills lying on the western slope of the Sierra 

 Nevada, the many Coast Range valleys and low hills among the 

 mountain ranges along the western side of the state, the South- 

 ern California valleys and the low hills, the desert plain, which 

 is being brought under cultivation by the development and use 

 of irrigation water, and the northeastern lava-bed valleys. 



As the object of this investigation was chiefly to ascertain the 

 extent to which humus was found in the lower depths of the 

 soils, the soil columns were taken only from those regions whose 

 soils are many feet in depth. The number of columns obtained 

 was 110 from thirty-seven counties, each column intended to 

 represent a characteristic type of land in its particular region. 

 There are, of course, very many small valleys and minor soil 

 regions that have not been included in this investigation. The 

 columns have been placed in vertical frames against the walls 

 of the lecture room of Budd Hall at the University of California, 

 arranged and labelled according to the respective agricultural 

 regions. Each soil occupies an eight-ounce bottle and the 



