Effects of calcium and magnesium on growth, fruit yield and quality in a fall greenhouse tomato crop grown on rockwool

Tomato (Lycopersicon esculentum Mill.) 'Trust' was grown on rockwool with two concentrations of calcium (150 and 300 mg L-1) in combination with four concentrations of magnesium (20, 50, 80 and 110 mg L-1) in fall, 1999, to investigate their effects on plant growth, leaf photosynthesis, and fruit yield and quality (fruit firmness, dry matter, soluble solids and russeting). High Ca (300 mg L-1) concentration increased fruit yield and reduced the incidence of blossom-end rot (BER) and fruit russeting, compared with the low Ca concentration (150 mg L-1). High Ca concentration reduced fruit firmness but did not affect fruit size and leaf photosynthesis. Plants grown at 20 mg L-1 Mg started to show leaf chlorosis on both the middle and bottom leaves 8 wk after planting. Leaves with moderate chlorosis lost about 50% of their photosynthetic capacity. Fruit yield in the late growth stage decreased at 20 ing L-I Mg. Blossom-end rot incidence increased linearly with increasing Mg concentration in the early growth stage at low Ca, but BER incidence at high Ca was not affected by Mg concentration. Fruit firmness increased with increasing Mg concentration at low Ca. At high Ca, Mg concentration affected fruit firmness only late in the season; fruit firmness at 80 ing L-1 Mg was higher than at 50 mg L-I Mg concentration. Fruit russeting in mid-season was affected by nutrient treatments, being the least at 300/50 mg L-1 Ca/Mg. Therefore, for a fall greenhouse tomato crop, the optimum Ca/Mg concentration for tomato production is estimated to be 300/50-80 mg L-1. The Mg concentration may be started at 50 mg L-1 and gradually increased to 80 mg L-1 towards the end of the season, to improve plant growth and fruit firmness.