The effects of different temperature regimes of irrigation water on the growth rate of Spinacia oleracea L. were determined in the greenhouse for 8 weeks. Thespinach seedlings were irrigated with water heated to various temperatures (24, 26 and 28°C) via pumps connected to 4 sets of water tanks each maintained at the experimental temperatures using Dolphin aquarium heaters. Unheated water from the tap supplied from the fourth tank served as control. All the plants were supplied with a mixture of Ocean HYDROGRO and Ocean HORTICAL nutrient solutions containing all essential elements. After 8 weeks of growth, results showed that leaf length (mm), leaf number and total fresh and dry weights (g per plant) was higher in plants grown at elevated temperatures compared with the control plants with optimum growth being recorded at 28°C. These results suggest that controlled production of spinach during winter seasons is possible by irrigation with heated water in a greenhouse.
Key words: Growth rate, root weights, shoot weights, leaf length, leaf number.
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