1914] Lougliridge: Humus and Nitrogen in Calif ornia Soil Columns 207 



and had the former been more abundant the percentage given to 

 the soil would have been sufficient for needs of crops. 



Humus and Nitrogen in the Entire Column. — Humus was 

 found to occur to depths of ten or twelve feet in but thirteen of 

 the columns. In the brown land of Farmington and the alluvial 

 soil of Kings River it would clearly have been found at that depth 

 had the columns been taken to twelve feet. On the other hand, 

 in five of the ten-foot or twelve-foot columns humus was not 

 found in the lower four or five feet. The percentages diminished 

 downward from the first foot in all cases, in some instances very 

 sharply, and usually added but little to the combined percentage 

 of the upper three feet. The Farmington column with its 7.76 

 per cent of humus is the richest group (excepting the Stockton 

 marshes), followed by the Tracy loam and Tulare plains soils. 

 Twelve of the columns have higher total amounts of humus than 

 the average of several hundred soils of the humid region, and 

 doubtless the total amount of organic nitrogen in these soils is 

 also greater than that in the humid. 



The humus not only varies in its percentage of nitrogen in 

 each of the twenty-five localities from which the soils were taken, 

 but also in the several depths below the surface in each column. 

 It is poorest in the Tulare Lake bed and richest throughout the 

 column from Kearney Park, where each foot except the first 

 contains more than 10 per cent. It is only occasionally that 

 among other columns is there found a humus having as much as 

 10 per cent. The general average of all is but 6.22 per cent, a 

 figure too low to benefit the soil greatly except where the humus 

 content is above 1 per cent. 



The sandy loams of the plains which comprise the greater 

 part of the San Joaquin Valley and the red lands of the eastern 

 side of the valley are but slightly different in their general 

 averages of humus, the latter, because of the high percentages 

 in the Farmington clay, having slightly more throughout its 

 column. The surface soils are clearly in need of green-manure 

 crops that will supplement that humus already present. The 

 soils are liable to form surface crusts where there is so little 

 humus present, and require special care and treatment to prevent 

 injury. 



