Two experiments were carried out in a plastic greenhouse in autumn and spring 2001. Sowing dates were February 17th and July 3rd, respectively. At 41 (1st experiment) and 36 days (2nd experiment) after sowing, plantlets were transplanted to 5.5 dm³ bags placed inside gullies, using a commercial substrate, in a plant density of 3.3 plants m-2. Treatments consisted of three nutrient solutions. In T1 treatment, fertilizer concentrations were, in mol. L-1: KNO3, 0.04: Ca(NO3)2, 0.027; MgSO4, 0.012. Phosphorus (P) was added by 1.5 g L-1 of superphosphate (20% P2O5), and micronutrients by a commercial mixture. For T1 plants, 1 L of the above nutrient solution was supplied once a week, containing 14.9 g L-1 of macronutrients. For T2 and T3 treatments the amounts of nutrients from T1 were applied in duplicate and triplicate, resulting in a total of macronutrient of 29.8 and 44.7 g L-1, respectively, supplied once a week. Drained volumes from each irrigation were collected and re-used in the next fertigations, after correcting nutrient concentrations in order to reach the original threshold level previously fixed for each treatment. Average electrical conductivity (EC) values of drained nutrient solution were 3.7; 6.8 and 8,9 dS m-1 at the first and 3.3; 5.2 and 7.4 dS m-1 at the second experiment, respectively for T1, T2 and T3. From 40 to 82 days after planting date (DAP) in autumn and 37 to 79 DAP in spring. Plants were periodically harvested to determine growth and development. In spring, ripe fruits on remaining plants were harvested and weighed to determine fruit yield. No significant differences were found for the number of fruits among treatments. In autumn, total and vegetative dry mass were lower on T3 plants, whereas fruit dry mass was higher. In spring, means of total and vegetative dry mass were lower on T3 plants, but fruit dry mass did not differs among treatments. Fruit yield decreased by effect of increasing values of EC. Based upon these results we concluded that it is possible to re-use drained nutrient solutions, when growing the tomato crop in substrates, and negative effects of salinity on fruit yield are observed only for EC values up to 4.9 dS m-1.
Lycopersicon esculentum; fertigation; soilless culture; nutrient solution
