This work aimed to determine chlorophyll concentrations of tomato (Lycopersicon esculentum Mill.) plants cv. Santa Clara fertilized with five nitrogen (N) rates by means of conventional laboratory methodology and by the SPAD-502 portable chlorophyll meter. The relationship between chlorophyll and N values was determined by these two methods. Tomato plants were grown in pots with a clay soil classified as Cambic Red-Yellow Podsol (CRP) and a sand-course soil classified as Quartzic Sand (QS), and received five N rates (25, 125, 225, 325 and 425 mg. dm-3) sidedressed as nutrient solutions. At the onset of 3rd cluster anthesis, chlorophyll concentrations were determined in leaves opposite to this cluster by the portable chlorophyll meter SPAD-502 and at laboratory by Arnon's methodology. NO3-N was determined in petiole sap and in dry matter, while NO3-N, org-N and total-N were determined in leaf blade dry matter. Chlorophyll concentrations increased with N rates irrespective of method of determination, in both soils. Critical levels in soils CRP and QS were, respectively, 77.3 and 83.6 <FONT FACE="Symbol">m</FONT>g. cm-2 by laboratory methodology and 45.5 and 43.8 SPAD units by the portable meter. Correlation coefficients of chlorophyll concentrations with top dry weight and N forms were greater for the SPAD method. Both methods of chlorophyll determination presented greatest correlation with sap NO3-N in soil CRP, and with org-N and total-N in soil QS. The estimative of chlorophyll concentrations (laboratory method) by means of SPAD readings allowed the adjustment of a linear equation (CP = -77.233 + 3.54725** SPAD R2 = 0.766).
tomatoes; Lycopersicon esculentum; chlorophyll; nitrogen; critical level; conventional laboratory methodology and portable meter
