Using plant petiole nitrate testing to reduce nitrogen applications in vegetables

The PI is Dr. Gerald Brust. The duration is 2006 to present. With $5,000 invested per acre of vegetable crop, Chesapeake Bay vegetable growers want to make sure they have enough nitrogen in their soils to produce good yields and high quality produce. Consequently they often apply excessive nitrogen to ensure a good crop. This study examines an in-field nitrate testing procedure to determine at what times and in what amounts nitrogen is needed by the crop.

A series of studies was conducted using a petiole sap testing instrument (Cardy meter) throughout the growing season and harvest period to determine the nitrate content of various vegetable crops, i.e., tomato, watermelon, pepper, and cantaloupe under different fertilizer regimes. This information then is used to determine when and how much nitrogen should be applied to the crop for best yields and quality of produce. Since 90% of all vegetable growers irrigate their crop it is possible to drip-feed (add nutrients through the irrigation lines) nitrogen to most vegetable fields. The goal is to develop thresholds for nitrate sap readings that would indicate nitrogen fertilizer application timing and amounts, similar to IPM strategies where insects must meet a pre-determined threshold before action is taken. Using this new system, nitrogen is applied only when the plant needs it during the growing season.

Two years of field studies demonstrate a 20-50% reduction in nitrogen applications with no reduction in yield or quality of produce. This 20-50% drop in nitrogen application represents 50-125 lbs of nitrogen per acre not being applied to the field where most of it would have resulted in environmental contamination. These findings are for the eastern shore where soils are very sandy and nitrogen is easily lost through leaching.

Impact- The 20-50% reduction in nitrogen applications in this study and the pounds of nitrogen not going into the environment should be readily adaptable anywhere vegetables are grown with drip irrigation. However, more research is needed to verify these findings for the eastern shore and to test the recommendation-system in other soil types in the Chesapeake Bay watershed before BMPs are developed.

For more information, contact Dr. Gerald Brust

Last updated: 02/7/2008