is quite dependent upon the amount of nitrogen present or 

 added, its form, the soil texture, the type of crop, and 

 the maturity of the crop. Dyer, et al (20), showed evidence 

 of nitrate leaching due to irrigation in comparisons of 

 irrigated and nonirrigated profiles of Panoche soils on the 

 west side of the San Joaquin Valley. Johnston, et al (21), 

 concluded that nitrogen and phosphorous levels in drainage 

 from west side tile systems correlated with fertilizer appli- 

 cation. However, as many or possibly even more investiga- 

 tions have shown that leaching of applied fertilizers is 

 negligible under certain conditions. Williford and Tucker 

 (22) reported very low recovery of tagged fertilizer (N^^) 

 in leachate collected from a series of lysimeters filled 

 with fine-textured west side soils which were cropped, 

 heavily fertilized, and irrigated routinely. The highest 

 percentage recovered was in leachate collected from Panoche 

 fine sandy loam, which was only 3-58 percent of the total 

 applied. Bower and Wilcox (23) reported that nitrogen 

 failed to increase in the upper Rio Grande from drainage 

 influence of three highly fertilized adjacent areas. In 

 this case, records of fertilization showed an increase from 

 a very low to a very high level over a 30-year period. The 

 absence of nitrates in the drainage was attributed more to 

 denltrification promoted by anaerobic conditions than to the 

 possibility of no significant leaching below the root zone. 



A pplied Nitrogen Versus Discharged Nitrogen . In several 

 cases, the nitrogen concentrations observed in tile drainage 

 from Individual systems seemed to correlate with the amounts 

 of fertilizers applied. However, high rates of fertiliza- 

 tion were recorded for many tiled fields having low levels 

 of nitrogen in the drainage. Fertilizer records obtained 

 over a ten-year period are compared in Table 15 to the 

 average nitrogen concentrations observed in subsurface 

 waters dischcLrged from major tiled areas. The yield of 

 nitrogen per acre was also determined for comparison to the 

 average fertilization rates. For the most part, no direct 

 correlations could be made during this study between the 

 quantity of nitrogen fertilizer applied and the concentra- 

 tions of nutrients in tile drainage. Only in the Gustine- 

 Mendota area did there appear to be a general relationship 

 between the two factors. Here the heaviest nitrogen ferti- 

 lization occurred and the greatest amount of nitrogen was 

 discharged. However, rather heavy applications of fertilizer 

 were also made in the Tulare Lake and Byron-Westley areas for 

 at least ten years with no appreciable effect on the nitrogen 

 concentrations observed in the drainage. Also, fertilizer 

 application for certain individual tiled fields was much 

 higher than the average fertilization rates indicate; however, 

 nitrogen concentrations still remained about 10 mg/l . The 



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