Relationship between the Weekly Nutrient Uptake Rate during Fruiting Stages and Fruit Weight of Tomato (Lycopersicon esculentum Mill.) Grown Hydroponically

Tomato 'Ohgata-Fukuju'plants were cultured hydroponically in a greenhouse by using deep flow technique (DFT) and nutrient film technique (NFT) systems. Generally, the rate of uptake of all nutrient components except for PO4 increased from the start of flowering until fruit harvest, and thereafter decreased. Fruit weight of a tomato plant having three trusses and the average rate of nutrient uptake (ARU: me-plant-1·week-1) were measured six times after the onset of flowering. The regression formula of fruit weight to the ARU of PO4 was polynomial, whereas that to the ARU of NO3 or K was linear, with a high correlation coefficient (r) 0.91, 0.91 and 0.97, respectively. The ARU of PO4 and NO3 when maximum fruit weight was recorded, ranged from 15-20 and 50-55 me · plant-1·week-1, respectively. Tomato plants were cultured by using a DFT system under a limited supply of NO3 and PO4; the solution was renewed weekly. Fruit weights in relation to the ARU of PO4, NO3 and K were also examined. Fruit weights relative to the ARU of NO3 and PO4 in these experiments were slightly different from that expected from the regression formula mentioned above. However, the fruit weights under a weekly supply of NO3 and PO4 were not significantly different from the maximum fruit weight of tomato cultured in solution with a constant concentration.