Effect of different management methods on yield, yield components and water use efficiency of tomato in hydroponic culture

Deficit irrigation is the strategy used to produce a crop with maximum income and profits. This method has attracted attentions due to the intensification of the water crisis and population growth. Basinger and Hellman (2006) suggested that deficit irrigation increases the water use efficiency by 72%, but it has little effect on reducing the amount of the product. Negaz et al. (2013) experimented the efficiency of optimum water use of lettuce, in different irrigation regimes (30, 60 and 100% of plant water requirement), in Tunisia. The results showed that the highest water use efficiency was related to 30% water requirement and the lowest was 100% water requirement with 34.3 and 14 kg/m3, respectively. Haghighi (2008) compared the PRD (Partial root zone drying) irrigation method and conventional irrigation on greenhouse tomato growth and concluded that PRD treatment increased the water use efficiency of the plant and increased the total soluble solids. While, no significant difference was observed between the two treatments in the number of fruit, color and fresh and dry weight of root. On the contrary, PRD reduced the dry weight of the shoot and the weight of the fruit. Also, the rate of handling and distribution of red fruit was higher in PRD treatment. This study were investigated the effect of regulated deficit irrigation (RDI) and PRD on tomato, under hydroponic culture conditions. The treatments of experiment consisted of five treatments: RDI irrigation at 85 and 70% of plant water requirement and PRD irrigation at 85 and 70% of the plant water requirement, and control treatment. The experiments were carried out in a completely randomized design with four replications. The water requirement of the plant was determined by the evaporation rate from class A evaporation pan (located in the greenhouse) and multiplying it at the plant shadow level. To feed the plants, Resh nutrient solution (2005), which contains macro and micro nutrients for plant growth, was used. For preparing of solution, urban drinking water was used with EC=1.8 mS/cm. The leaf area was measured every two weeks by a ruler. After applying the treatments, the greenhouse tomato product was manually harvested in 5 times. The number of harvested fruits only consisted of fruits that were fully grown and ready to be harvested. According, every 2 weeks, the fruits were counted, harvested and weighted. After the end of the growth period, the fresh and dry weight of root, fresh and dry weight of leaf, leaf water content, leaf area, fresh and dry weight of stem and biomass and dry weight of plant were measured. Also, leaf area index (LAI), special leaf area (SLA), leaf area ratio (LAR), harvest index, water use efficiency and efficiency of biomass water use were calculated. The results showed that different methods and levels of deficit irrigation had significant effects on fresh and dry weight of root, fresh and dry weight of stem, plant dry weight, fruit weight and water use efficiency. But, the levels of applied water did not significantly affect fresh and dry weight of leaf, leaf water content, leaf area, leaf area index, special leaf area, leaf area ratio, biomass weight and harvest index. The results showed that the plant with irrigation application of 85% of plant water requirement showed different results in fruit weight index and water use efficiency, in comparison with the control treatment. Deficit irrigation of PRD treatment in the weight of fruit increased by 3.5% and water use efficiency increased to 22 percent, compared with control treatment (2572.5 g and 16.07 kg/m3, respectively). But, RDI treatment in fruit weight decreases by 20% and reduces water use efficiency by 5.5% compared with control treatment (1997.8 g and 12.48 kg/m3, respectively).With reducing applied water to 70% of plant water requirement, the behavior of the plant was different, and RDI treatment showed a lower reduction for the fruit weight index and water use efficiency than PRD treatment. Accordingly, the RDI treatment in fruit weight decreased by 35% and water use efficiency decreased by 7% (1614.2 g and 12.24 Kg/m3, respectively). While, PRD reduced 52% in fruit weight and decreased 31% of water use efficiency (1189.5 g and 9.02 Kg/m3, respectively). Eventually, PRD treatment with 85% of plant water requirement was selected as the best method for hydroponic culture of tomato in greenhouse.