Variations in Diurnal Uptake of Water and Nutrients by Tomato Plants Grown Hydroponically

Abstract

Water and nutrient uptake by tomato (Lycopersicon esculentum MILL cv. Ohgata-Fukuju) plants during the day (7:00 to 19:00) and night (19:00 to 7:00) was estimated for 4 consecutive days during 4 seasons of the year. Percentage of uptake rate during the night to that of the 24-hr day is expressed as URN. URNs of phosphate ions ranging from 40 to 50% were always the highest among the nutrients examined. URN of water tended to be high during the cool seasons. Changes in URN of nutrients, except for Ca, did not always correspond to the URN of water.
The balance between the cations and anions absorbed was calculated. More cations than anions were absorbed during the day but the situation was reversed at night. Electrical imbalance of either cations or anions was negligible when calculated for the entire day.
These observations indicate that phosphate ions and other nutrients are taken up actively against the concentration gradient (culture solution) at night and that URNs of nutrients are influenced little by the rate of water uptake. Diurnal variations in phosphate ions uptake are small.