observable effect upon nitrogen concentrations in the tile 

 drainage. Agricultural records collected by the Department 

 show that many tile systems were fertilized heavily over 

 the years but discharged effluent relatively low in nitrogen. 



A study of agricultural practices revealed that irrigation 

 was the only agricultural practice that greatly influenced 

 changes in nitrogen concentrations . Immediate decreases in 

 nitrogen levels were observed in drainage from many tiled 

 rice fields during flooding. Drainage from one large tile 

 system decreased from 63 rag/l in the winter to 7 mg/l in the 

 summer. Nitrogen concentrations fluctuated in drainage from 

 other tiled crops during irrigation but generally decreased 

 during the summer months. Denitrif ication and dilution are 

 highly suspected as the reasons for summer decreases in 

 nitrogen concentrations . 



Levels and Sources 



The level of nitrogen concentrations was found to be most 

 related to location and type of soil (physiographic position 

 and soil series). Drainage from tile systems occupying 

 recent or older alluvial fans generally was higher in 

 nitrogen than drainage from tile systems located in basin or 

 basin rim physiographic positions. Nitrogen concentrations, 

 however, were much higher in drainage from tile systems 

 located in alluvial fans of the central area than drainage 

 from systems located in similar fans of the two northern 

 areas. These differences led to a close look at the 

 individual soil series as a source of nitrogen in the 

 drainage . 



The highest concentrations of nitrogen (about ^5 nig/l) 

 occurred in drainage from the Panoche family group (Panhill, 

 Panoche, and Lost Hills soil series) of the central area. 

 Nitrogen levels were roughly 10.0 mg/l in drainage from the 

 Sorrento family of soils (Sorrento, Rincon, and Ambrose soil 

 series), and other nonrelated basin and basin rim soils. 



Soil investigations were conducted by the Department at 

 44 sites along the west side of the San Joaquin Valley. 

 Virgin as well as irrigated sites were sought to evaluate 

 the variation in concentrations of nitrogen in the soil 

 profiles. Nitrate-nitrogen was found in all virgin soil 

 profiles sampled. The highest concentrations (saturation 

 extracts) were found in soil samples taken from virgin 

 profiles of Panoche and related soil series in the central 

 area. All virgin sites of Panoche and related soils 

 averaged about 97 mg/l in the 3- to 10-foot tile zone 

 (ranging from 8 to 23H mg/l). 



