The application of appropriate amounts of water and the usage of associated techniques improve the yield and quality of tomato fruits, assuring better profits to the farmer. We studied the effect of different water depth applications and carbon dioxide (CO2) injection in the irrigation system of a tomato crop, cv. Débora-Plus. An experiment was conducted in Piracicaba, São Paulo State (Brazil), under two greenhouses, using 40; 60; 80; 100; 120 and 140% of the water depth needed by the crop and C0 = 0 g of CO2.L-1 of water and C1 = 7.73 g.L-1 of CO2 concentrations were applied through irrigation water during 1999. The experiment was conducted in completely randomized blocks, with four replications. The CO2 treatments were applied in separate greenhouses. The irrigation was accomplished by using a drip irrigation system, based on reduced evaporimeters and tensiometers. The gas application was accomplished using a commercial cylinder and a Venturi type injector during the period necessary to reach the minimum water level. The application of CO2 through irrigation water increased the yield by 8.2%, raised the weight of small size fruits by 13% and the dry matter content of fruits by 8.5%. However, CO2 injection was ineffective in increasing the number and weight of medium sized fruits. The soil solution analysis indicated that CO2 possibly contributes to the improvement of the nutritional conditions of the tomato crop. The gas injection was economically feasible. The water depth did not have any significant effect on the yield, on total number of fruits, medium fruit weight and dry matter content of fruits. The maximum yields, adjusting data to quadratic functions, were 78.82 t.ha-1 and 86.36 t.ha-1, corresponding to application of 335.2 mm and 333.6 mm of water for the greenhouses without and with CO2 application, respectively. For a variation range of the marginal physical product, from 0 to 1, the economically optimal water depth varied from 335.2 mm to 322.4 mm without CO2, and 333.6 mm to 323.8 mm with gas injection through irrigation water.
Lycopersicon esculentum Mill.; drip irrigation; water stress; protected ambient; yield; crop production functions; income net
