Tile drainage effluent from systems on irrigated land in the San Joaquin Valley of California was analyzed for nitrogen and phosphorus and the quantity of each element found was correlated with the quantity of N and P applied for four different cropping patterns. Large percentages of applied N were found to be lost in tile drainage effluent. Phosphorus losses were not significant.

A four‐year study of drainage effluent obtained from 15 tile drainage systems located in the arid San Joaquin Valley of California showed that the concentration of salts and the various ions discharged in the tile effluent decreased, logarithmically, from the time that the tile systems were installed. Regression equations and correlation coefficients are presented for total salts, boron, sodium, calcium plus magnesium, chloride and sulfate ions, versus time from 0 to 12 years of tile drainage system age. The relationships presented could change with more intensive drainage and more liberal use of irrigation water, providing a more rapid trend toward equilibrium.

Drainage effluent from systems located on irrigated land in the San JoaquinValley of California was analyzed for insecticide residues. Only relatively small quantities of chlorinated hydrocarbon residues were fouad in tile drainage effluent, but higher concentrations were found in effluent from open drains where both surface and subsurface drainage waters were collected. Traces of residue were found in the irrigation water applied to tile drained farms. When the concentration factor is considered, i.e., depth of irrigation water applied/depth of drainage water removed, on a unit basis, the total quantity of insecticide residue in tile drainage effluent does not exceed and is generally less than the total quantity of residue applied in the irrigation water. Tailwater, or surface runoff, contained from 7 to 12 times as much residue as the applied water when DDT was applied to the land and as much as 85 times more residue than the irrigation water when Lindane was applied to the land. Relatively large concentrations of residue were found in the surface soil of the area studied, even wh•re no pesticides had been applied directly to the soil. (Key, words: Drainage; groundwater; insecticides; quality of water) Agricultural efforts are continually directed toward increasing crop production. One practice used to help to obtain improved crop yields is to control or eliminate disease, insect infestation, or any other competitor that may injure, retard, or in any way compete with a growing agricultural crop. A large number of synthetic insecticide, fungicide, and herbicide materials, all pesticides, have been developed to help to control agricultural pests.There has been increasing concern over the fate of the residues from these pesticides, partieularly in the San Joaquin Valley of California, which is an area of concentrated pesticide use. During recent years, about 20% of the agricultural pesticides applied in the United x Joint contribution, Department of Engineering and the Water