nitrate-nitrogen at two sites of west side soils durinc 

 collection of soil material for its lysimeter studies (22). 

 The initial leachate collected from the lysimeters filled 

 with Oxalis and Panoche soils ranged respectively from 

 564 to 4,515 mg/l nitrate-nitrogen. These high concentra- 

 tions were attributed to disturbances and aeration resulting 

 in rapid nitrification of organic matter. After leaching, 

 the nitrogen concentrations reached static levels of 

 25 mg/l for Panoche and 226 mg/l for Oxalis, which were 

 very close to the concentrations observed in the initial 

 soil -water extracts taken at the time the soil was removed 

 from the field. Further investigations of soil nitrogen by 

 USER in the SLUSA revealed variable concentrations of 

 nitrogen in irrigated soil profiles. Thirteen sites were 

 sampled in four transects across the Valley; five holes 

 were bored at each site to depths of 40 feet in some cases. 

 The range and average nitrogen concentration for the tile 

 zone (3 to 10 feet) at each site are given in Table 27. 



TABLE 27 



NITRATE-NITROGEN CONCENTRATIONS IN 

 IRRIGATED WEST SIDE SOILS INVESTIGATED BY USER 



Site; 

 No. 



Soil Series and Type 



;Sat. % 



Range of 

 NO3-N in 

 ;Soil Profiles; 

 (mg/l)2/ 



Avg. NO3-N in 



Soil Profiles 



(mg/l) 



1 Oxalis silty clay 



2 Lethent silty clay 



3 Panoche clay loam 



4 Panoche silty clay 



5 Oxalis clay _ / 



6 Lethent clay 2*^ 



7 Levis silty clay 



8 Oxalis silty clay 



9 Panoche silty clay 



10 Lost Hills silty clay 



11 Panoche clay loam 



12 Panoche silty clay 



13 Oxalis silty clay 



1/ Average saturation percentage. 



^/ Range of NOo-N by depth between sites 



3/ Soil was sampled to 5 feet only. 



81 



