Nitrate concentrations in the unsaturated zone beneath some selected row-crop fields

Today's nitrogen fertilization practices for row-crop production (especially vegetables) in the Santa Ana Drainage Basin leave various amounts of NO3-N in drainage water. In nine sites selected for this study, the average NO3-N concentrations in the drainage water in the unsaturated zone (that portion of the soil profile from the root systems to the 50-ft depth or water table) were all above the 10 ppm NO3-N public standard for drinking water. Six sites had average NO3-N concentrations more than five times greater than this standard, whereas, two sites had NO3-N concentrations more than 10 times greater. The amount of NO3-N in drainage water was affected by N inputs, removal of N when crops are harvested, drainage volume, and gains and losses of NO3.