Deep boring investigations conducted by soil scientists of 

 the Agricultural Research Service (ARS) also revealed high 

 levels of nitrogen (up to 225 nng/l) in Panoche soil profiles 

 along the west side of the San Joaquin Valley. Further 

 investigations by ARS showed very high concentrations of 

 nitrogen in parent materials of the Panoche soils. Average 

 nitrogen concentrations of the various parent material strata 

 ranged up to 2,000 mg/l in 1:1 soil-water extracts. 



Irrigated sites of different soil series contained less 

 nitrogen in the soil than virgin sites of the same series. 

 Eleven irrigated sites of Panoche soils averaged 37 mg/l — 

 60 mg/l less than the virgin Panoche soils . Nitrogen concen- 

 trations in samples collected from five irrigated Panoche 

 sites (25 borings) in the Federal San Luis Unit Service Area 

 (SLUSA) by the United States Bureau of Reclamation (USBR) 

 averaged 19 mg/l overall and ranged from 5 to 35 rag/l 

 between sites. Although these concentrations were somewhat 

 lower than those found by DWR, one site of the Lost Hills 

 series (which is closely related to the Panoche series) had 

 the highest average concentration found (109 mg/l). 



Alluvial fan soils of the two northern areas appear to 

 contain less nitrogen than those of the central area. Much 

 lower concentrations were found in samples collected from 

 the Sorrento and related soil series. Nitrogen levels 

 averaged 25 mg/l and ranged from 2 to 59 mg/l for the five 

 sites sampled. 



All of the basin rim soils investigated were irrigated. 

 Average nitrate-nitrogen levels ranged from 1 mg/l to 171 mg/l 

 and averaged about 37 mg/l. Out of the eight basin rim sites 

 sampled, two contained high levels of nitrogen (more than 

 100 mg/l). The other six were low (less than 5 mg/l). 

 Higher concentrations were found by USBR in some of the 

 irrigated soils of the Federal San Luis Unit Service Area. 

 The Oxalis series, which comprises the major portion of the 

 basin rim soils in the airea, averaged 64 mg/l for the four 

 sites investigated and ranged from 5 to 206 mg/l between 

 sites. The other basin rim soils in the area averaged less 

 than 10 mg/l nitrate-nitrogen for the 3- to 10-foot tile zone. 



Comparisons were made between the nitrogen observed in tile 

 drainage and that found in field moisture samples (porous 

 cups) and soil samples (saturation extracts) collected from 

 the same tiled fields. The compsurisons showed that in three 

 out of four cases nitrogen was higher in the field moisture 

 samples than in tile drainage from the same field. Satura- 

 tion extracts prepared from soil samples were, however, about 

 30 to Ho percent lower than the average concentrations found 

 in the tile drainage. 



