Efeito de diferentes lâminas de irrigação sobre os componentes de produção e rentabilidade da cultura da alface cultivada em ambiente protegido

In Brazil, lettuce cultivation has great relevance in the socioeconomic scenario and in the diet, constituting an excellent source of minerals and vitamins. The cultivation in protected environment is extremely important for lettuce cultivation, being more and more widespread and used by the producers of this vegetable. One of the main difficulties of lettuce cultivation in this environment, especially in the Bambuí / MG region, is due to the lack of information about the appropriate moment of irrigation and the correct amount of water to be applied, as well as the scarcity of data related to the costs of production and profitability of the crop. The objective of this work was to make a technical and economic evaluation of the effect of different irrigation slides on the growth and productivity of lettuce cultivated under protected environment, under the edaphoclimatic conditions of the Bambuí region. The experiment was conducted in a greenhouse at the experimental area of the Olericultura sector of the Federal Institute of Minas Gerais - IFMG Campus Bambuí, using the Vanda lettuce cultivar at 25 cm x 30 cm spacing. The experimental design was a randomized block with 4 replicates and 5 treatments, totaling 20 experimental units. The treatments were characterized by irrigation slides, named T1, T2, T3, T4, T5, corresponding to 25%, 50%, 75%, 100% and 125% of crop evapotranspiration (ETc), respectively. In order to meet the proposed objectives, the following variables were evaluated: commercial head diameter, fresh shoot mass, leaf numbers, shoot dry matter, shoot height, productivity, water use efficiency and costs of production. The data of the variables were submitted to analysis of variance with the F test and the regression analysis to the level of significance of 5% of probability, using the computer program "Sisvar". In the edaphoclimatic conditions in which the experiment was conducted, it can be seen that the irrigation depth of 125% of ETc was higher than the others in all evaluated agronomic characteristics, except for water use efficiency and number of leaves per plant. Regarding the cost of production, the treatment 5 (125% of ETc) was the one that obtained the highest costs, nevertheless it presented the best profitability for the producer. In conclusion, treatment 4 (100% of ETc) presented satisfactory results, very close to those found for treatment 5, with the advantage of using a smaller amount of water, which is interesting considering the growing concern about the scarcity of this resource and also for the shortest time of use of the irrigation system and motor pump, causing less wear of the same over the years.