Uptake of Water and Minerals during the Day and the Night in Tomato and Cucumber Plants

Abstract

The uptake of water and minerals during the day and the night was investigated or tomato and cucumber plants grown in a nutrient solution containing 8meq/l each of KNO₃ and Ca (NO₃)₂ and 4meq/l each of NH₄H₂PO₄ and MgSO₄, to obtain further information for improving nutrient solution management in NFT water culture.
Water uptake during the night (from 6:00 P.M. to 6:00 A.M.) was about 12% of that in a whole day, while mineral uptakes were 28 to 45% of those in a whole day for tomatoes, and 18 to 46% for cucumbers. Therefore, the uptake ratios for mineral (me)/water (l) were higher during the night. Those values were 52, 25, 25, 20, and 8 for tomatoes, and 38, 27, 25, 23, and 4 for cucumbers, of NO₃-N, P, K, Ca, and Mg, respectively.
When the nutrient solution was increased to double strength, water uptake decreased and mineral uptakes increased. The ratio of night uptake to day uptake of water was unchanged, but that of minerals increased except for P. Electric conductivity (EC) increased slightly during the day, and decreased slightly during the night, irrespective of the strength. The increment of pH was greater during the night than during the day, and greater in the weaker solution than in the strong one.
With tomato culture in NFT system, the EC values and mineral concentrations in the nutrient solution decreased from evening, at 6:00 P.M. to moring, at 6:00 A.M., and increased from morning to evening. Based on these results, nutrient solution managements during the day and the night are discussed in respect of calcium deficiency in tomato fruits.