Diurnal uptake of nitrate and potassium during the vegetative growth of tomato plants

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Abstract
Tomato plants (Lycopersicon esculentum Mill.) of the F1 hybrid variety Turbo were grown in a NFT system for 22 days. On days 16 and 20–22 inclusive of the experiment, the diurnal variation in nitrate (NO3), potassium (K), and water uptake rates were measured. Nitrate and K uptake rates were subject to large diurnal variation with maximum uptake rates occurring during the day period. Two peaks of diurnal uptake rates were identified, one large peak during the day period and a second much smaller one during the first 2–4 hours of the night. Under the conditions of the experiment, night nutrition made up 35 to 40% of the total daily uptake of K and NO3. Water uptake rates followed a diurnal oscillation with a single peak pattern. Highest rates occurred at the middle of the photoperiod and lowest rates were measured at night. Over the entire day and night cycle there was no correlation between the rates of water and nutrient uptake. This may be of importance in the fertilization of hydroponically grown plants since in horticultural practice nutrients and water are supplied together in quantities large enough to meet plant water demand but not nutrient requirements.