At this time, predictions of nitrogen from future-drained 

 areas based on nitrogen in soil samples or field moisture 

 samples can be made only with additional field study and 

 extensive correlation to existing tile drainage. 



In summary, the one thing that can be said about tile 

 drainage is that its nitrogen content will vary greatly 

 between certain areas and also during the seasons. The 

 magnitude of variability depends basically upon three things: 

 (1) the particular kind of soil a tile system is associated 

 with and its physical location, (2) the irrigation pattern, 

 and (3) to a lesser extent, the type of crop being grown. 

 Although nitrogen levels from individual systems cannot be 

 accurately predicted from year to year, the Department is 

 reasonably certain that nitrogen levels in future drainage 

 can be predicted from the composite drainage of existing 

 tile systems in the San Joaquin Valley. 



Phosphorus (phosphate-phosphorus ) 



Phosphate (orthophosphate) is the major phosphorous constit- 

 uent found in tile drainage of the San Joaquin Valley. Very 

 low concentrations of organic phosphorus were found because 

 of the low organic content of the tile drainage. Laboratory 

 analyses revealed that concentrations of orthophosphate in 

 tile drainage were essentially the same as total plus organic 

 phosphorus. For this reason emphasis in this report is given 

 to orthophosphate, which is referred to as phosphorus. 



Phosphorous concentrations averaged 0.09 mg/l in drainage 

 composited from valley tile systems during 1962 to I969. 



According to the available data, there are no indications of 

 long-term changes in phosphorus. Phosphorus from the Tulare 

 Lake area averaged O.69 mg/l — seven times higher than 

 drainage from either of the two northern areas or the central 

 area. Concentrations averaged less than 0.1 mg/l in the 

 composited drainage from any one of these three areas. 



The high levels of phosphorus in drainage from the Tulare 

 Lake aj?ea eire suspected to be due to unusual source materials 

 contained in the soils. Analyses of the soils do not indicate 

 high concentrations of phosphorus, but there is an abundance 

 of phosphorous -bearing fresh water shells in the soil profiles 

 from that area. It is suspected that anaerobic conditions 

 exist in the saturated subsoils of the lakebed which create 

 an environment conducive for the release of phosphorus 

 from the shells and their related organic remains. 



