Effects of Shading in Summer on Yield and Quality of Tomatoes Grown on a Single-truss System

This study was conducted to examine the yield and quality of tomato fruits grown on a single-truss system shaded during the summer. Tomato seeds were sown on the 10th of every month from February to September and the seedlings were grown in NFT. The plants were covered with cheesecloth at the shading level of 0 (control), 30 (light shading), 55 (medium shading), and 83% (heavy shading) from 10 days after the first anthesis. The nutrient solution was cooled to 25°C from July to September. As the shading level increased, total fruit yield decreased with loss of fruit weight. The total fruit yield of each crop was individually correlated linearly with the mean value of daily integrated solar radiation during fruit development. Regression analysis indicated that the decrease of total fruit yield, corresponding to the loss of 1 MJ·m−2 of the daily integrated solar radiation, would increase from 84 to 100 g/plant if the average air temperature increased from 19 to 27°C. Marketable fruit yield in the control plot was highest in the Feb. crop and significantly lower from Apr. crop to Jul. crops, because of the high incidence of cracked fruits. The incidence of cracked fruits was decreased by shading. It was estimated that shading which decreased daily integrated solar radiation to 5–6 MJ·m−2 effectively increased marketable fruit yields when the air temperature exceeded 25°C. Summer harvested fruits had high titratable acidity. Shading was apt to decrease the brix and increase the titratable acidity of fruits.