Pre-Harvest Nitrogen Application Affects Quality and Antioxidant Status of Two Tomato Cultivars

Intensive horticultural crop production usually has to face the problem of excessive application of fertilizer, mainly nitrogen (N). A greenhouse experiment was carried out to understand the effect of an increasing concentration of N on fruit weight and quality of two tomato cultivars (Caballero y Victoria). Nitrogen treatments were applied at concentrations of 0, 15, 30 45 and 60 mM ranging from deficiency to toxicity. After reaching physiological maturity tomato fruits were harvested, and weight, diameter, firmness, acidity, phenols, flavonoids, and antioxidant capacity were measured.  The optimal N concentration, 30mM, had the highest fruit weight, firmness and diameter on both varieties. Increasing the concentration of N to 60mM diminished weight, firmness and fruit diameter in 62, 34 and 35% for Caballero tomatoes, and 74, 43 y 40% for Victoria tomatoes, respectively.  N application influenced the augmentation of acidity and soluble solids with a positive slope of ~0.5°Bx/mM for soluble solids and ~0.007% citric acid/mM for acidity (R²>0.9), on both cultivars. Phenols, flavonoids and antioxidant capacity were also affected by N application; increasing N from 30 to 60mM increased the concentration of phenolics, flavonoids, and antioxidant capacity in 50%, 125%, and 33% on Caballero, and in 60%, 95%, and 24% on Victoria tomatoes, respectively. This work points out how an improper N application affects tomato quality in terms of weight, diameter, firmness, acidity, and soluble solids; and stresses the fruit activating the defence mechanisms, causing an increase in the production of phenolics, flavonoids and antioxidant capacity.