Effect of fertilizer levels on tissue nitrogen concentration of greenhouse tomato plants grown in substrate culture

It was determined the effect of three nitrogen fertilizer levels on dry matter accumulation and tissue nitrogen concentration of indeterminate and determinate greenhouse tomato plants, hybrids Monte Carlo and Saladette, respectively. Plants were grown in bags filled with four litres of a commercial organic substrate. The control (T(2)) was supplied by means of a formulation currently used in Southern Brazil to grow commercial tomato crops in bags with organic substrates, with de following quantities of fertilizers, in g/plant: KNO(3), 4.6; Ca(NO(3))(2), 7.3; superphosphate (20% P(2)O(5)), 1.7; MgSO(4), 3.5. Iron chelate and micronutrients were supplied separately by commercial mixtures. Quantities of these fertilizers, in a per plant basis, were dissolved in one (1) litre water volume and supplied once a week to each plant by fertigation. Only water was delivered to plants during the six days between two consecutive fertigations. To reduce loss of nutrients, irrigation was stopped at first signs of drainage at the bottom of bags. In treatments T(1) and T(3), quantities of fertilizers were multiplied by 0.5 and 2.25, respectively. Dry matter and tissue nitrogen concentration of shoot organs was determined periodically, from anthesis of the first truss to ripening of first fruits. Results showed nitrogen concentration in shoot tissues was higher at anthesis of first truss, decreasing thereafter until ripening of first fruits. The data obtained in each experiment fitted well to the power model described in the literature to explain the nitrogen dilution curves of C(3) species.