Influence of potassium and calcium on acid content of tomato fruits in sand culture

The effects of two levels each of potassium and calcium in factorial combination on acidity of tomato fruits and leaves were studied, using Fukuju No. 2 variety in sand culture. In the next, a study was made to investigate whether acidity of fruits was affected by the restraining of potassium supply for the different stages of growth period.1. High level of potassium in the solution induced the increase of the titratable, total and combined acidities, and potassium content in the water extract of whole fruits. On the other hand, high level of calcium decreased the titratable, total and combined acidities, and potassium content, only when combined with high level of potassium. The effect of calcium was less than that of potassium. The titratable acidity made up about 60% of total acidity, regardless of potassium or calcium treatments. In case the fruits were separated into gelatinous pulp and outer wall, acidities and potassium content in both tissues were affected similarly to those in whole fruits by these treatments.2. Period between the flowering stage of the first truss and the coloring stage of the sixth truss was divided into two parts, at the flowering stage of the sixth truss. When potassium level in the solution was lowered during the period between the flowering stage of the first truss and that of the sixth truss, reduction of the titratable, total and combined acidities was induced in the fruits on the second to the sixth trusses. In case that potassium supply was withheld after the flowering stage of the sixth truss, the acidities of fruits on the third to the sixth trusses were significantly decreased. Accordingly, the acidities of fruits were affected by the potassium level in the solution for almost all their developmental stages, except for the fruits on the first truss which had higher acidities and showed no differences of acidities by the treatments.Moreover, decreased acidities were accompanied by the lower contents of potassium in fruits. Titratable and total acidities in fruits were very closely correlated with the potassium content, with correlation coefficients +0.91 and +0.96, respectively. They were also correlated with combined acidity, correlation coefficients being +0.92 and +0.97, respectively.3. In tomato leaves, content of malic acid was 2-3 times as high as that of citric acid, contrary to fruits in which citric acid was a major organic acid. High level of potassium in the solution increased the titratable, total and combined acidities in the young leaves, while it decreased these acidities in the old leaves. High level of calcium tended to decrease the titratable, total and combined acidities in leaves of both ages, but much more in the old leaves. The changes of malic and citric acid contents induced by potassium or calcium treatments were similar to that of the total acidity. The titratable acidity made up about 16% of total acidity in the young leaves, and about 10% in the old, irrespective of the treatments.