根における水および元素の吸収速度の動的評価

抄録

Dynamic and simultaneous evaluation of the rates of uptake of water and mineral nutrients by roots of the plant population was enabled in the NFT (Nutrient Film Technique) system. The system is composed of a circulation unit (an NFT bed, a reservoir tank, etc.) and a water supply unit (a water supply tank, a solenoid valve, etc.) for controlling the nutrient solution. A water level sensor is installed in the circulation unit to detect the decrease in the volume of nutrient solution caused by the uptake of water by plants. The circulation unit is automatically replenished with fresh nutrient solution from the supply unit by the on-off action of the solenoid valve which is manipulated according to a feedback signal from the water level sensor. Therefore, the rate of water uptake by roots can be evaluated from the supply volume per on-off action of the solenoid valve and the frequency of the on-off action. The rate of uptake of mineral nutrients by roots can be evaluated based on the quantity of mineral nutrients introduced with the supplied fresh nutrient solution and the change in the concentration of mineral nutrients in the circulation unit. High accuracy in dynamic and static characteristics of the evaluation system was demonstrated by the performance test in which the rates of uptake of water and a mineral nutrient were changed in stepwise every hour. The system is applicable to short and long-term measurement of uptake rates affected by fluctuating solar radiation and salt stress in the greenhouse.