Optimum Plant Density of Greenhouse Tomato Grown in a Soilless System in Golestan Province

Tomato (Solanum lycopersicum L.) is an important commercial food plant. Several factors affect the growth of tomatoes in the greenhouse, and one of them is proper planting density. Investigating and suggesting the best density in hydroponic cultivation can have a significant effect on production efficiency. Therefore, a factorial experiment was conducted in the hydroponic cultivation system based on completely randomized design with three replications and two treatment of cultivar (Dafnis, Izmono and Hirad) and density (at four density levels of 2, 2.5, 3 and 3.5 plants per m2) in the greenhouse of Gorgan Agricultural and Natural Resources Research and Education Center. Characteristics of number of clusters per plant, number of flowers per cluster, percent of blossom drop, number of fruits per cluster, fruit yield per plant and per m2, number of fruits per plant, number of fruits per m2, average fruit weight, fruit diameter, fruit length, pericarp thickness, uniform fruit ripening, distance between clusters, marketable yield, total soluble solids and pH of fruit juice were measured. According to the mean comparisons, the average yield per m2 at high plant density (3.5 plants per m2) in all three cultivars was significantly higher than others. With the increase of density from 3 to 3.5, from 2.5 to 3.5 and from 2 to 3.5 plants per m2, respectively, relative increases in yield per m2 of 2.4%, 28.6% and 43.1% in Hirad, 6.8%, 21.75%, 23.4% in Dafnis and 22.7%, 35% and 51% in Izmono were observed. With the increase of plant density, the percentage of blossom drop of plants decreased significantly. The highest total soluble solids content of one cultivar (Hirad) was observed in the highest density and two other cultivars were not affected. The pH of fruit juice of Dafnis and Izmono at a density of 3.5 plants per m2 was significantly lower than other treatments, but there was no difference for this trait in Hirad cultivar between different densities. The results of this study suggest to increase the density of tomato in hydroponic greenhouse in Golestan province up to 3.5 plants per m2.