field area. Considerable time was spent for field explora- 

 tion before sites were selected for the in-field moisture 

 sampling. 



Field Comparisons . During I966, a cooperative investigation 

 between the Department of Water Resources, the Environmental 

 Protection Agency (EPA) (then the Federal Water Quality 

 Administration), and the University of California at Davis 

 was conducted in the Firebaugh area. Soil samples were 

 collected from several fields and samples were analyzed for 

 nitrates and other minerals. These investigations revealed 

 moderate concentrations of nitrogen in the saturation 

 extracts collected from three irrigated Panoche soils. 

 Nitrogen concentrations in the tile drainage were much 

 higher, as shown by comparison in Table 24. 



TABLE 24 



NITROGEN CONCENTRATIONS IN SATURATION EXTRACTS AND 

 DRAINAGE FROM THREE TILED FIELDS OF THE PANOCHE SERIES 



1966 



Concentrations of NO^-N (mg/lj 



Field 

 Code 



Saturation Extracts ; Tile Drainageji/ 

 Profile -Ranged"; Average"!/; 195b; 1967; 19b»: 195^ 



FBH 5056 

 FBH 4045 

 FBH 3236 



4-22 

 2-34 

 7-30 



10 



7 



14 



50 37 

 31 19 

 44 39 



49 

 28 



44 



54 

 4/ 



1/ Weighted annual concentrations. 



?/ Range of concentrations between different sites. 



3"/ Average nitrogen in tile zone, depth-weighted. 



^/ Not sampled. 



Nitrogen concentrations observed in the tile drainage during 

 June and July, the months during which soil samples were 

 collected, were not too different from the annual averages 

 shown by the data for the whole year (I966). Data from 

 subsequent investigations of tile drainage (1967-69) showed 

 that nitrogen concentrations varied to some degree but never 

 reached the levels observed in the saturation extracts. 



Field investigations by the then FV/QA showed that soil moisture 

 extracted by in-field samplers contained higher nitrogen 

 concentrations than did tile drainage, in three out of four 

 fields studied. Soil moisture samples were obtained by means 



77 



