The experiments were conducted to clarify the effects of different water-regimes and temperature of irrigation water on the growth of tomato seedlings.
Seeds of “Kurihara” variety were sown in flat. When two or three leaves developed, uniform plants were transplanted to the metal containers on the bench in the greenhouse. The containers were 30×30×10cm in size and were provided with 25 holes on their bottom for drainage. Small gravels were placed 2cm thick on the bottom of each container, and 7.2l of soil was stuffed on it. Ample water was applied to the soils, and after surplus water was completely drained, moisture contents were determined, and they were defined as water capacities (WC). Permanent wilting percentages (PWP) of the soils were determined by BALIR's method using dwarf sunflowers. The soil moisture between WC and PWP was regarded as available water (AW). Compost (volcanic ash soil-1 part : leaf mold-1 part in volume), volcanic ash soil, and sand were used for experiments. Water loss was weighed everyday and, when necessary, a measured volume of water was added to the soil.
1. To set up the plots differing in water-regime, water enough to bring the soil moisture to WC was applied everyday or when 25, 50, 75 or 100% of AW was lost. Growth of the tomato seedlings was markedly affected by the water-regimes in every soil; the most vigorous growth was obtained in the plots in which water was applied everyday, and the drier the soil, the less the growth of seedlings. Growth of the seedlings was closely correlated with the total amounts of water applyed during the experiments. Flower bud developments paralleled to the vegetative growth of the seedlings.
2. Effect of applying limited amount (not enough to bring the soil moisture to WC) of water on the growth of seedlings was tested. Watering the soil to 25 or 50% levels of AW, when 50 or 75% of AW was lost, was compared with the watering to the WC when 25 or 50% of AW was lost. The results obtained, were similar to those of the experiment mentioned above, that is, the growth of seedlings was closly correlated with the amount of water added. This shows that the limited watering which has been prevailing in practical forcing culture of fruit vegetables is unfavorable for the growth of seedlings.
3. Effect of temperature of irrigation water was tested by applying the water differing in temperature (0°, 20° and 40°C) to the tomato seedlings in the plots having narrow and wide water-regimes (100-75, 100-25%). There was no difference due to the water temperature, though significant difference was found due to the water-regime. It is suggested that even if temperature of irrigation water is rather low, it is better for the growth of the tomato seedlings in hot beds to keep, the soil, moist by applying water than to withhold watering.