Calcium deficiency provoked by the application of different forms and concentrations of Ca2+ to soil-less cultivated muskmelons

The influences of deficiency concentrations of calcium compounds other than the: calcium nitrate usually used, on the development of Cucumis melo L. cv. Revigal cultivated in rockwool were studied under adverse calcium absorption conditions (low solar radiation, temperature and calcium and high sodium and magnesium levels in the nutrient solution). A standard Ca(NO3)(2) concentration was used for comparison and two different concentrations of Ca-EDTA, CaCl2 and CaSO4 (equivalent to half and to one quarter of the calcium in the control) were used to create calcium deficiencies. The demand for calcium increased substantially during the period of the greatest vegetative growth. Ca-EDTA produced greater Ca deficiency symptoms than CaCl2 and CaSO4, and was not effective in alleviating calcium-associated problems. There were no significant differences in biomass production between the sulphate and chloride treatments with the same calcium levels, although there were great differences in biomass production in the different plant fractions between the two calcium levels applied. The biomass differences were greater half way through the cultivation cycle than at the end. The use of calcium concentrations below 3 mM in the nutrient solution, which represents a net daily calcium uptake of less than 1 mmol per plant throughout the cultivation cycle was insufficient and provoked deficiency symptoms in leaves and fruits in the conditions of this experiment. Calcium levels at the end of the growing cycle were significantly higher in the control than in other treatments in all plant fractions, There were very few differences in calcium content in fractions between the chloride and sulphate treatments, while the Ca-EDTA treatments led to noticeably lower calcium levels in the different fractions. (C) 1999 Elsevier Science B.V. All rights reserved.