Yields of Greenhouse Tomatoes Managed to Maintain Specific Petiole Sap Nitrate Levels

Abstract

Abstract ‘Caruso’ tomatoes (Lycopersicon esculentum Mill.) were grown in peat-perlite-vermiculite in a greenhouse with five nitrate-nitrogen (NO3-N) fertilization concentrations in irrigation waters managed to maintain 200, 400, 600, 900, or 1200 µg NO3-N/ml in petiole sap as determined by weekly NO3-N quick tests. Nitrate-N fertilization concentrations immediately were increased 50% when petiole sap NO3-N levels first fell below these target levels; thereafter, NO3-N fertilization concentrations were increased only after petiole sap levels fell below target levels for 2 consecutive weeks. The critical target level of sap NO3-N was defined as the lowest petiole sap NO3-N target level producing maximum marketable fruit yields. Total fruit yields increased with increasing petiole sap NO3-N target levels through 1200 µg·ml–1. Marketable fruit yields were maximized at 3.2 kg/plant, with an estimated critical sap NO3-N target level of 1105 µg·ml–1. Application of the sap NO3-N management rules used in this experiment resulted in five adjustments in N fertilization concentrations over the 27-week crop cycle, with an average of 4.5 weeks between adjustments. This approach to the management of N fertilization based on the sap NO3-N level of the crop has potential to provide significant benefits in improved N use and crop productivity at a modest cost.