Departamento de Fitotecnia, Universidade Federal, 36570-000, Vi?osa-MG. Brazil
Journal of Applied Horticulture, 2006, volume 8, issue 1, pages 8-11.
Abstract: This study evaluated the feasibility of using SPAD-502 chlorophyll meter and plant visual aspect for N management in drip fertirrigated tomato plants (Lycopersicon esculentum Mill.) under unheated greenhouse. Two separate experiments were carried out at Universidade Federal de Vi?osa - MG ? Brazil in leached and non-leached soils under greenhouse. Six treatments were evaluated in a randomised complete-block design with four replicates. In treatment 1, N was applied at the time SPAD reading in leaf dropped below a critical value previously established for the specific plant physiological stage (SPAD-1). In treatments 2 and 3, SPAD critical values were increased 20 % (SPAD-2) and decreased 10% (SPAD-3), respectively. In treatment 4, the visual aspect of tomato plant (PVA) was utilized as a criterion of N management. In treatments 5 and 6 (check), N rates were 280 and 0 kg N ha-1, respectively. Total applied N rates ranged from 0 to 594 kg N ha-1. In both the experiments, total and marketable fruit yields were highest in SPAD-1 treatment which only differed from the check plot. All five criteria allowed high total tomato fruit yields but, as experiments average, N use efficiency was highest with the PVA treatment. The highest net income was obtained with SPAD-1 treatment and was associated with the highest yield. The results indicate that a SPAD meter can provide a quantitative measure of the N requirement of the tomato plants as long as appropriate SPAD critical values are established. Visual ratings of plant canopy needs to be more evaluated and improved.