1914] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 199 



of seven feet; the other which appears in the table of analyses 

 is from the Henderson orchard and twelve feet in depth. 



On the west side of the valley another narrow black adobe 

 belt reaches along the base of the hills from west of Tracy into 

 jMerced County on the south. It is represented by a column of 

 ten feet taken three miles west of Tracy. 



Still another belt of black land, not so clayey as the others, 

 though containing from 12 to 14 per cent of clay, lies three miles 

 west of Tulare ; a column was taken from it. 



It is a matter of much surprise that these clay soils with their 

 very black color should have so small a percentage of humus, 

 the maximum of which is but 1.2 per cent, found in the soil 

 from Porterville. We would naturally anticipate finding fully 

 10 per cent, and yet in the Tracy soil there is less than 1 per 

 cent. It is evident that the necessary conditions of moisture 

 and warmth for the humification of the vegetable material are 

 not present in these very close, compact clays. The Porterville 

 soil is subjected to irrigation several times annually, while that 

 from Tracy is not, and this may account for the larger amount 

 of humus in the former. In the Stockton column the humus is 

 found to the full depth of twelve feet, while in the others it was 

 found only in the upper six feet. 



The nitrogen content of the Stockton soil is good in the upper 

 foot and fair for the three feet, the humus itself being rich in 

 nitrogen, but in the other columns it is quite low and suggests 

 the need of an additional nitrogen supply, either through green- 

 manuring or artificial fertilization. 



Reddish Clay Lands. — A prominent and wide region of lands 

 of this character occupies a large part of the eastern side of the 

 valley : it is narrow on the north in San Joaquin, Stanislaus, 

 ]\Ierced, and IMadera counties, and on the south in Tulare and 

 Kern, but quite wide in Fresno County. It is the southern exten- 

 sion of the belt of "bedrock" lands of Sacramento Valley. It 

 is largely characterized by a rocky hardpan of cemented gravel 

 and grit, with thicknesses of an inch to as much as twelve inches 

 and even more, occurring at depths of from two to six or eight 

 feet below the surface. When it occurs near the surface the 

 hardpan gives rise to a rolling or hogwallow feature. An excel- 



