培養液濃度がトマトの収量と品質および養液成分の濃度変化に及ぼす影響

Abstract

Tomato plants, Lycopersicon esculentum Mill., cv. ‘TVR-2’ were grown in a deepwater culture system. After pinching above the 5th truss, plants were treated with different strengths of the standard nutrient solution, and yield and quality of fruits as well as changes of mineral concentration in the nutrient solution were determined during the culturing period from the middle of April to the end of July. The standard nutrient solution contained NO3-N, P, K, Ca and Mg at the concentrations of 16, 4, 8, 8 and 4 meq/l, respectively.1. Both electric conductivity (EC) and concentrations of NO3-N, P, K in a half-strength solution decreased from planting to pinching, while concentrations of Ca and Mg remained as in the initial concentration. After the nutrient solution was replaced at the time of pinching, the EC value and concentrations of NO3-N, Ca and Mg tended to increase, but K concentration showed little change. Phosphorus was occasionally consumed before adding fresh water and minarals. In the standard strength solution, all the mineral concentrations were increased except P. This tendency was pronounced in a three-halves strength solution which showed a higher fluctuation range of mineral concentrations.2. Relationships between plant age and changes of mineral concentrations in a half-strength solution were examined. Concentrations of NO3-N and Ca in the solution cultures for 70-, 105- and 125-day-old plants were decreased, unchanged and increased, respectively, after 9 days culture. Concentrations of P and K were decreased irrespective of ages. Magnesium concentration was not changed in the solution culture for 70-day-old plants and increased in the solution for 105- and 125-day-old plants.The values of minerals absorbed (n') of NO3N, Ca and Mg per unit volume of water absorbed (w') were decreased as plants aged. The n'/w' values of P and K were nearly constant irrespective of ages, and were higher than those in the initial nutrient solution.3. The three-halves strength solution resulted in significantly higher soluble solids content and higher titratable acidity in tomato fruits juice. On the other hand, fruit yield was slightly decreased, and the percentage of cracked fruits and blossom-end rot fruits was also decreased.Therefore, increasing the strength of nutrient solution after pinching would improve fruit quality with only slight decrease in fruit yield.