SECTION I 

 SUMMARY AND CONCLUSIONS 



Summary 



Tile drainage systems in the San Joaquin Valley were inten- 

 sively monitored from I966 through I968. This report empha- 

 sizes nutrient data collected during that period. Nutrient 

 and soils data are also presented from investigations 

 conducted prior to I966, from other investigations during 

 the 1966 through I968 period, and from a continuing monitor- 

 ing program which was initiated in I969. 



Average Nitrogen (nitrate-nitrogen) Concentrations 



The nitrate ion (NO3) is the dominant nitrogen constituent 

 found in San Joaquin Valley tile drainage. The combined 

 amounts of ammonium (NH4), nitrite (NOg). and organic 

 nitrogen rarely exceed 1.0 milligram per liter (mg/l) in the 

 drainage regardless of the total levels found. All discus- 

 sions of nitrogen that follow in this report will be limited 

 to nitrate-nitrogen. 



Nitrogen averaged 19.3 mg/l in the combined drainage from 

 tile systems monitored on a regular basis from 1962 through 

 1969. During I968, forty-two tile systems were monitored 

 weekly for a full year in all of the major tiled areas. 

 During the same period a number of "isolated" and "satellite" 

 tile systems were also sampled monthly during most of the 

 year. The composite drainage from all of these systems 

 averaged 20 mg/l . 



Variations of Nitrogen Concentrations 



The average nitrogen concentration remained relatively 

 constant from year to year during the more intensive investi- 

 gations. During 1967 and I968, the annual averages were 

 18.6 mg/l and I9.9 mg/l, respectively. The annual average 

 for 1969 (19.^ mg/l) was only slightly less than that of 1968, 



The greatest long-term change in average nitrogen levels 

 appeared to occur between I962 and 1966 when the concentra- 

 tion decreased from 25. 1 mg/l to 18.6 mg/l, respectively. 

 This change occurred primarily because a larger number of low 

 nitrogen level tile systems were sampled in I966 that were 

 not included in the earlier investigations. 



