Nitrate values in soil -water extracts were averaged, 

 converted to nitrogen, and divided by the average saturation 

 percentage to bring the values close to those of saturation 

 extracts . The highest concentrations were found at one site 

 of the Oxalis soil series; nitrogen averaged 206 mg/l in the 

 tile zone. All other Oxalis sites had low to moderate 

 concentrations. The next highest concentration was found 

 at a site of Lost Hills series; nitrogen levels averaged 

 109 mg/l. Only moderate concentrations of nitrogen were 

 found in the Panoche series; average concentrations ranged 

 from 5 to 35 mg/l at the five sites sampled. These soil 

 nitrogen values were slightly lower than those found in 

 saturation extracts of irrigated Panoche soils by the 

 Department . 



If the sites sampled by USER are representative of the soils 

 in the SLUSA, then future drainage from this area could 

 possibly be higher in nitrogen than from the Gustine-Mendota 

 area. All the Oxalis sites sampled from that area averaged 

 6H mg/l, a value that is much higher than the values indi- 

 cated in tile drainage or soil samples collected from the 

 basin rim soils of the Gustine-Mendota area. If the 13 

 sites investigated by USER are weighted by the number of 

 borings at each site, the average is 37 mg/l (Table 28), 

 close to the two-year average from tile systems in the 

 Gustine-Mendota area. 



TABLE 28 



NITRATE -NITROGEN CONCENTRATIONS FOR 

 DIFFERENT SOIL SERIES INVESTIGATED BI USSR 



Soil ; No. of ; NQ^-N (m g/ l) 



Series ; Borings ; Profile Range!/ ; Average 



4 - 228 109 



- 482 64 



- 195 19 



1-22 8 



4-9 6 



Weighted Grand Average^./ 27 



1/ Maximum and minimum observed within all 



profiles sampled. 

 2/ Weighted by number of borings. 



82 



