Acreages Monitored . The number of acres tiled was not 

 determined for the systems sampled from 1959 to 1963. 

 During 1966 approximately 1,5^5 acres were sampled In the 

 Gustine-Mendota area. Table 5 presents a summary of acre- 

 ages devoted to agricultural subsurface drainage systems and 

 acres sampled for nutrients within the major tiled areas of 

 the San Joaquin Valley in I967 and I968. 



TABLE 5 



ACREAGE* TILED AND ACREAGE SAMPLED 

 FOR NUTRIENTS IN MAJOR TILED AREAS 



♦Acreages vere estimated from scaled drawings on U.S.G.S. quad sheets 

 {l/h mile of interceptor line was assumed to drain Uo acres). 



A few tile systems lying outside the major tiled areas were 

 also sampled. Acreages representing these systems are shown 

 separately in Table 5. 



Tile acreage sampled increased from 1967 to 1968, due to the 

 addition of two new tile systems to the monitoring progreun; 

 also, several of the systems being sampled were expanded. 

 About 53 percent less acreage was monitored in 1969 than in 

 1968, due to a reduction in the program. 



Table 6 summarizes the number of tile systems and acres 

 sampled in I968 within different physiographic positions and 

 soil series. These tile systems are located within the major 

 tiled areas of the Valley and are the ones that were inten- 

 sively sajnpled. Acreages of isolated or satellite tile 

 drainage systems within specific positions or soils were not 

 determined . 



33 



