representing the major soil series and physiographic posi- 

 tions were sampled in an area extending from Tracy south 

 along the west side to Lost Hills. Forty-five sites were 

 sampled to a depth of 10 feet or more; samples were collected 

 at incremental depths not exceeding 3 feet . Virgin sites 

 were sought to obtain the quantity of nitixigen in the soil 

 before irrigation. Several dry-farmed and irrigated sites 

 were also sampled. 



R anges and Magnitudes 



Nitrogen concentrations within individual profiles varied 

 considerably between sites and with depth; leaching was 

 apparent at the surface of nearly all virgin profiles sampled, 



Table 20 is a virgin profile of the Panhill series and is an 

 example of the variability of nitrogen by depth. The distri- 

 bution of nitrogen throughout the profile is typical of 

 similar virgin sites and other related soil profiles investi- 

 gated in the area. As the example shows, nitrogen in the 

 first foot or more has been leached. An inverse condition 

 was found for many irrigated soils which were fertilized. 

 Therefore, for this study only the samples from 3 to 10 feet 

 were considered representative of nitrogen in the tile zone. 

 (Tile laterals are normally Installed at depths between 

 6 and 9 feet.) This was done to make the most accurate 

 assessment of the average nitrogen conditions in the soil 

 profile. 



TABLE 20 



EXTRACT ANALYSIS OF A VIRGIN ALLUVIAL SOIL 

 ON THE WEST SIDE OF THE SAN JOAQUIN VALLEY 



777 TT TTT r~I 7 :Saturation: ECxlO^ : NOo-N 

 Site .Depth Range. Texture ! percentage: of Extract; (mg/l) 



N-6 0-1.5 loam 42.8 515 l8.0 

 (Panhill 



Series) 2.5 - 4.0 sandy clay 43.6 5.270 83.5 



loam 



4.8 - 5.7 fine sandy 32.8 6,575 257.0 

 loam 



6.5 - 8.2 loam 37.6 6,240 242.0 



9.2 -10.4 fine sandy 32.6 5.985 208.0 

 loam 



71 



