ACCUMULATION OF POTASSIUM, MAGNESIUM, CALCIUM IN FRESH AND COLD STORED LEAVES OF LETTUCE (LACTUCA SATIVA L.) AFTER CaCl2 FOLIAR TREATMENT BEFORE HARVEST

The aim of this study has been to determine the effect of foliar application of CaCl2 before harvest on the accumulation of K, Mg and Ca in fresh and stored lettuce heads. The experimental material comprised cv. Omega lettuce, which was grown in a greenhouse at the Department of Cultivation and Fertilization of Horticultural Plants of the University of Life Sciences in Lublin. CaCl2 solutions of the concentrations of 0.1 M and 0.2 M were sprayed over plants 20 and 10 days before harvest. After harvest, some plants were analysed immediately (fresh plants), while the remaining lettuce heads were cold-stored at 4 degrees C for 7 and 14 days in dark polyethylene bags. The levels of dry matter, K, Mg and Ca were determined in whole leaves and leaf blades (without the midrib) of fresh and stored plants. The accumulation of dry matter, K, Mg and Ca varied depending on the leaf part, CaCl2 treatment and time of storage. The Ca content was lower leaf blades than in whole leaves of fresh plants not treated with CaCl2, but the K and Mg concentrations were on a similar level in both parts of leaves. The results of this study indicated that CaCl2 foliar spray of plants caused higher K and Mg concentrations in whole leaves compared. to the control plants (no CaCl2 treatment) but decreasing Ca and K levels were observed in leaf blades without the midrib from fresh plants treated with 0.2 M CaCl2. During the 14-day cold storage of lettuce, the Ca and Mg levels in decreased whole leaves but increased in leaf blades of the control plants and after the 0.2 M CaCl2 treatment. Changes in the K, Mg and Ca accumulation affected the K:Mg and K:(Ca+Mg) ratios, which rose in whole leaves of stored plants compared to fresh ones.