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



little or no hiimus and nitrogen. It is, however, rich in phosphoric acid and 

 lime and well supplied with potash. The soil is uniform in texture through- 

 out the twelve-foot depth and becomes only a little coarser at twelve feet. 

 The only changes visible in color and texture in the vertical wall are 

 merely those of the shell layers above noted. The soil from which these 

 samples were taken has never been cropped, but similar soil, with a good 

 water supply, produces very fine alfalfa. Very little alkali is present in 

 this soil. 



Soil Xo. 11. Fertile, alluvial loam from Hay^ard, California. Uniform 

 in texture for seven feet and then rapidly becoming quite coarse and re- 

 maining so down to a depth of twelve feet. This soil is very fertile, 

 producing good crops of cherries, walnuts, potatoes, and other agricultural 

 plants. It is well supplied with humus and nitrogen, judged by the 

 standard for soils of the arid region, throughout the twelve-foot depth. 

 The phosphoric acid, potash, and lime are also plentiful in all the soil layers. 

 The samples used in these investigations were obtained in a cherry orchard. 



AMMOXIFICATIOX IX SOIL COLUMNS 



Second only to the importance of soil bacteria in maintaining 

 the total nitrogen supply in soils is their power to supply con- 

 stantly available nitrogen to plants. The essential nature of 

 this important phase of the activities of soil organisms is in no 

 wise detracted from by the recent research which has made it 

 clear that some plants at least can take their nitrogen from the 

 soil in forms other than the nitrate. While many of them may 

 not absorb their nitrogen in the form of nitrates, it seems quite 

 certain that practically all of them must take their nitrogen in 

 forms much simpler than the proteid. This being undeniably 

 the case, some agency in the soil is necessary to accomplish the 

 transformation of the organic nitrogen (no matter what the 

 source of the latter to the soil may be) into a simpler, more 

 available, or more assimilable form. These agencies we have 

 found to be the various types of soil organisms which constitute 

 what we now designate by the term "ammonifying flora" of the 

 soil. 



TTith these statements admitted, it seems reasonable to sup- 

 pose that any increase in the acti\ities of the organisms, included 

 under this head, is a distinct advantage to the plant. Under our 

 climatic conditions, where, as above stated, the plant roots very 

 deeply, besides making a large lateral root-development, it is 

 necessarv to have the activities of the ammonifving organisms 



