1914] Loughridge: Humus and Nitrogen in California Soil Columns 257 



as that of the San Joaquin or Southern California, and the 

 amount of organic nitrogen in the soil is below the 0.05 per cent 

 regarded as necessary for fertility. 



Southern California. — The soils of the valleys of Southern 

 California represented by the composite of twenty-five columns 

 have about the same humus content in the first foot and in the 

 upper three feet as was found in similar parts of the columns 

 from the Sacramento Valley and the foothills, but are far behind 

 those of the Coast Range valleys. The humus is well distributed 

 downward to twelve feet, and as with the Sacramento soils 

 affords an excellent and large feeding area for plant roots; every 

 encouragement should be given crops to take advantage of this 

 by sending their roots deep into this fertile soil mass. The upper 

 three feet contains a little less than one-half of the total humus. 



The humus of the first foot is too low for the maintenance of 

 good physical condition and careful attention should, as a rule, 

 be given to the turning under of green crops and the humification 

 of the same. 



The humus in the upper three feet contains 5.74 per cent of 

 nitrogen, but this gives only the small amount of 0.03 per cent to 

 the soil : this is equivalent to about 1200 pounds per acre-foot, 

 which under the influence of bacteria gradually becomes available 

 for plants. 



"^Desert" Plains. — The desert lands represented by a com- 

 posite of five columns from the valleys of Imperial, Coachella, 

 Owens River, and Mojave River are very low in humus in their 

 upper several feet, as is to be expected from the meagerness of 

 the natural humus-forming vegetation. One-half of the humus is 

 held in the upper five feet instead of in three, as is the case with 

 other regions. The presence of so much humus in the twelfth 

 foot is a matter of some surprise, for the lands seem usually 

 quite deficient in natural moisture other than hygroscopic for 

 hundreds of feet in depth. The amount of humus in the twelfth 

 foot is one-half that of the first foot. The humus of the upper 

 three feet contains but 4.97 per cent of nitrogen, which gives but 

 0.01 per cent of organic nitrogen in the soil : this is equivalent 

 to about four hundred pounds per acre-foot, which is very little. 



Lava-hed Region. — The valley lands of the Lava-bed region 



