Does Following the Recommended Potato Nitrogen Fertility Guideline Contribute to Groundwater Contamination?.

The Tulare Lake Basin in the Southern San Joaquin Valley has high measureable nitrate levels in the groundwater.  A State Water Resources Control Board commissioned report has indicated that crop land agriculture is the main source of nitrates in the groundwater. The area has also had a significant dairy presence for many years.  Annual rainfall is less than 20 cm, thus irrigation is necessary for a high productivity vegetable crop endeavor. A project was undertaken to evaluate current cropping practices in potato production and its contribution, or lack thereof, to nitrate movement and potential nitrate contamination of groundwater.  Eight potato fields were monitored for plant uptake and potential nitrate leaching. Pre-plant and post-harvest soil samples were collected to a depth of 2 meters.  Plant, root and tuber samples were collected and analyzed for nitrogen content. Soil moisture and irrigation amounts were monitored.  Irrigation water did not penetrate deeper than one meter through excellent irrigation scheduling.  Nitrate not taken up by potato remained in the root zone for subsequent crops.