Nitrogen losses and the production of nitrogen gas corre- 

 sponded to increases in soil moisture above Hi percent . He 

 also found that nitrogen losses in tile drainage from the 

 field only amounted to 1.5 percent of the 246 pounds per 

 acre applied. Decreases in nitrate were associated with 

 increases in depth and proximity of the water table. Inves- 

 tigations conducted by the then Federal Water Quality Admin- 

 istration (FW(^) in cooperation with the Department of Water 

 Resources showed similar denitrification in saturated 

 Panoche loam and Tulare loam soils of 0.54 percent and 

 0.62 percent per hour, respectively. 



In several tile systems investigated for dissolved oxygen, 

 the lowest concentrations were observed in drainage from 

 rice fields. Fields having more than one crop had the 

 highest levels, followed by fields in which cotton and beans 

 were grown. Ranges and averages are presented in Table 14. 



TABLE 14 



DISSOLVED OXYGEN CONCENTRATIONS 

 IN TILE DRAINAGE FROM VARIOUS CROPS 



Crop 



Number 



of 

 Systems 



Dissolved Ox ygen (ppm) 



MsLXimum : Minimum ; Average 



Dilution . Dilution was also mentioned as a cause of low 

 nitrogen in heavily irrigated crops. The decrease in 

 nitrogen due to dilution is somewhat substantiated in that 

 nitrogen levels are the lowest during peak irrigation and 

 nearly always approach the preirrigation concentrations. 

 Also, TDS levels decreased simultaneously with nitrogen 

 concentrations in drainage from many individual systems 

 where discharges remained high in the summer months. 

 Figures 10 and 11 illustrate the reactions of TDS to irriga- 

 tion and their correlations to nutrients. A decrease in 

 TDS and nutrients (nitrogen and phosphorus) along with an 

 increase in discharge was observed in the composited 

 drainage from the entire study sirea (Figure 12). This 

 decrease is presumed to be caused partly by dilution and 



57 



