Influência da temperatura e vazão da solução nutritiva sobre o crescimento, acúmulo de pigmentos e nitrato na alface.

Abstract

This study aimed to evaluate the influence of temperature and flow rate of the nutrient solution in a crop of lettuce (Lactuca sativa L.) kind Vera, hydroponically, on growth, photosynthetic pigment content, nitrate content and flow behavior thermal on the plant. There were four nutrient solution flow rates: 0.5, 1.0, 1.5, and 2.0 L.min"1 and three temperatures: 15°C, 25°C and room temperature. We used a completely randomized design in a factorial design (4x3) with 10 repetitions. Each plot consisted of a channel containing ten plants cultivation. To determine the leveis of nitrate, was used colorimetric method described by Cataldo et al. (1975), from the nitration of salicylic acid and spectrophotometric reading at 410 nm. For the determination o f chlorophyll in lettuce leaves two methods were used, a nondestructive, the chlorophyll index Falker, and other destructive method described by Lichtentaler and Welburn (1983). During the experiment were five readings of chlorophyll content and nitrate content (at 28, 35, 42, 49 and 56 days after the sowing). The growth parameters were obtained by measuring stem diameter, leaf number and height of the plant. These parameters were measured at 21, 28, 35, 42, 49 and 56 days after the sowing. At the end of culture were performed readings of total fresh weight, root fresh weight, fresh weight of leaves, stem fresh weight, shoot fresh weight, measuring stem length, total dry weight, root dry weight, mass dried leaf, stem dry weight and shoot dry mass, leaf area , specific leaf area, leaf weight ratio and leaf area ratio. The thermal images were obtained using a Testo imager brand model 881. The results show that the nitrate content and photosynthetic pigments were only influenced by the temperature of the nutrient solution. The amount of nitrate in lettuce leaf is within the standards recommended by the World Health Organization and the European Community. The chlorophyll estimated with good accuracy the content of photosynthetic pigment on lettuce leaf. The flow influenced the absolute growth rate of stem diameter, plant height and number of leaves of lettuce Vera when higher flow rate, the greater the absolute growth rate. The absolute growth rate of stem diameter, plant height and number of leaves of lettuce Vera tended to increase with the development of the plant cycle. The flow rate influenced the absolute and relative growth of stem diameter, plant height and number of leaves of lettuce Vera, when higher the flow, the greater the absolute growth rate. The highest yield of fresh mass of shoots was 286.19 grams, and the lowest was 145.07 grams. The fresh mass of shoots was influenced by the temperature and flow of the nutrient solution when higher flow rate and temperature of the nutrient solution, the higher the dry matter production. The highest total dry matter production was 35.72 grams, and the lowest was, 13.19 grams. The total dry matter production was influenced by the temperature and flow of the nutrient solution when higher flow rate and temperature of the nutrient solution, the higher the dry matter production. The thermal behavior of lettuce plants irrigated with nutrient solutions at different temperatures there is a tendency of the temperature of the plant come into equilibrium with the temperature of the médium.