Effect of Nitrogen Deficiency and Toxicity in Two Varieties of Tomatoes

Tomato is one of the most important vegetables cultivated in Mexico. Nitrogen-based fertilizers have greatly contributed to the increase in tomato production; however, the excessive application of this fertilizer may affect yield and fruit quality. A greenhouse experiment was conducted to evaluate the effect of increasing in rates of nitrogen from deficiency to toxic levels. Five N-treat-ments (0, 15, 30, 45 and 60 mM of N) were applied in two tomato varieties, Caballero and Victoria The optimum N doses for leaf growth in both varieties was 30 mM reaching 13.0 and 13.5 cm in Caballero and Victoria respectively. At low toxic levels leaf growth was recovered more easily in Caballero than Victoria. Nitrate concentration for the low toxicity treatment was greater in leaf and stems for Caballero than Victoria; conversely nitrate in fruits was higher in Victoria. Final yield per plant was not statistically different between varieties except at the low toxic treatment where Caballero had a yield of 780 g per plant compared to that of 330 g per plant of Victoria. To-mato quality was also affected by the applied N-doses, where treatment 30 mM reached the max-imum fruit firmness in both varieties while high toxic N-levels decreased significantly this para-meter. Soluble solids and titratable acidity increased with increased N-Doses. Caballero variet