Hydroponic cultivation is a viable alternative, given the water scarcity scenario, since this technique uses water rationally and without waste. However, it is necessary to monitor the salinity of the nutrient solution, especially in leafy vegetables such as lettuce. The aim of this research is to examine the yield of hydroponic lettuce under different salinity levels of the nutrient solution, in greenhouse. The experiment was conducted in a hydroponic system installed in a greenhouse belonging to the Federal University of Campina Grande. The experiment was carried out in a randomized block design, in a 5 x 2 factorial scheme: the first factor is five salinity levels of the nutrient solution (S1 = 1.0, S2 = 1.3, S3 = 1.6; S4 = 1.9 and S5 = 2.2 dS m-1) and the second factor is two lettuce cultivars (Robusta and Bs55), with three replicates. The isolated cultivar factor did not significantly influence any of the analyzed variables of the hydroponic lettuce. The different levels of salinity of the nutrient solution positively influenced the variables analyzed: leaf area, SPAD index, chlorophyll a, b and total, and yield of leaves of hydroponic lettuce. Hydroponic lettuce can be grown up to 2.2 dS m-1 of electrical conductivity of the nutrient solution without any loss in yield.

ABSTRACT:The quantification of chlorophyll in the leaves of the plants is fundamental, since it serves as the basis for estimating the amount of nitrogen present in the leaves. The objective of this study was to evaluate the relationship between SPAD index, total chlorophyll and total soluble solids of the fertirrigated beet, under the effect of different doses of nitrogen. The experiment was in a greenhouse of the Federal University of Campina Grande (UFCG). The treatments consisted of five nitrogen doses (0, 50, 100, 150 and 200 mg.dm-3 of soil), with nine replications, in a randomized block design. The SPAD index, total chlorophyll content and the total soluble solids (° Brix) were determined at 45 and 90 days after transplanting and correlations were made between the variables. The relationships were positive with coefficient of determination above 50%, being less significant at 90 days after transplanting. The leaf nitrogen content (SPAD Index) increased linearly with the increase of ° Brix and total chlorophyll. The study showed that SPAD-502 may be an indication of the need for nitrogen application and as an estimate of total chlorophyll content. KEYWORDS:Intensity of Green, Beta vulgaris L, chlorophyllometer. RELAÇÃO ENTRE ÍNDICE SPAD, SÓLIDOS SOLÚVEIS TOTAIS E