Tomato Fruit Yield, Quality, and Nutrient Status in Response to Potassium: Calcium Balance and Electrical Conductivity in the Nutrient Solution

Abstract

Tomato fruits of high quality and yield are of interest to greenhouse growers. As potassium (K) and calcium (Ca) have been associated with fruit quality, we studied the effect of the balance between such cations and the electrical conductivity (EC) on fruit yield and quality. Plants were fertigated with K (Kext) and Ca (Caext) balances in the nutrient solution varying from 0.54–1.22 and 0.69–1.44 at ECs of 2.3 ± 0.1 dS m−1 and 2.7 ± 0.1 dS m−1, respectively. Optimum balance for fruit yield was 0.82–0.85, and it was associated with high fruit K internal (Kint) concentration (~ 200 mmol kg−1). Higher EC increased firmness when the balance was ≤ 1.00, with the optimum at 0.85; firmness was correlated with Caint when EC was 2.3 dS m−1; however, at 2.7 dS m−1, increasing Kext increased firmness and intensified the effect of Caext. Increasing a* values were associated with high lycopene and uniform maturation when that balance was 0.82 and 1.00 at low and high EC, respectively. Highest a* values were observed when Kint in the fruit was ~ 200 mmol kg−1, while 91 to 130 mmol kg−1 were associated with lower a* values. Fruits contained higher starch (+ 20%), total (+ 12%), and reducing sugars (+ 29%) at high EC. The optimum K and Ca balance, 0.82–0.85, is independent of their concentration and was associated with high yield and firmness, improved fruit color, and increased lycopene and sugar concentrations.