304 Effects of Calcium and Magnesium on Growth, Fruit Yield, and Quality of Greenhouse Tomato Grown in Rockwool

Abstract

Tomato (Lycopersicon esculentum Mill.) cv. Trust was grown in rockwool in summer and fall 1999 and 8 calcium/magnesium nutrient treatments, formed by two levels of calcium (Ca: 150 and 300 ppm) and four levels of magnesium (Mg: 20, 50, 80, and 110 ppm), were applied to investigate the effects on growth, fruit yield and quality. High calcium (300 ppm) increased overall fruit yield and size, reduced incidence of blossom-end rot and fruit cracking. However, high calcium also reduced the dry-matter content, soluble solid content and firmness of tomato fruit, and increased fruit russetting. Magnesium did not affect early growth or fruit production. However, 2 months after applying the treatments, the plants grown under 20 ppm Mg started to show Mg-deficient symptoms (leaf chlorosis), and Mg-deficient leaves lost more than 50% of their photosynthetic capability. The Mg concentration required for achieving high yield of firm fruit with high soluble solids and dry-matter content increased as the plant aged; i.e, 50 ppm in early stage of fruit production and 80 ppm in later stage of fruit production. At the end of experiment, the plants grown with 80 ppm of Mg also had the best root systems. Therefore, for both better yield and quality, a concentration of 300/50-80 ppm Ca/Mg may be recommended. Mg concentration may be started at 50 ppm and gradually be increased to 80 ppm in the later stage of fruit production.