Calcium deficiency of glasshouse cucumber as affected by environmental humidity and mineral nutrition

Abstract

SummaryThe effects of interactions between environmental humidity, calcium supply and electrical conductivity (EC) of the growing medium on calcium deficiency in cucumber leaves were investigated in two glasshouse experiments. A low or high humidity during the day was combined with either a low or a high humidity during the night. The 24 h average vapour pressure deficits achieved over the period from planting until calcium deficiency occurred varied from 0.44 to 0.88 kPa. Visible symptoms and the calcium content of the leaves were closely correlated with 24 h average vapour pressure deficit. The effect of humidity on calcium deficiency inceased with increasing EC and decreasing calcium supply. When calcium accounted for more than 47% of all cations in the root environment, the effect of humidity on calcium deficiency was negligible. It was concluded that deficiency symptoms gradually became apparent when the calcium content of the leaf margins fell below 500mmol kg−1 dry matter. At low vapour pressure deficits, the minimum level of calcium required in the root environment is 40% of all cations, which can be reduced to 25% at high vapour pressure deficits. It is recommended that an EC of 2.0 dS m−1 be used to avoid calcium deficiency.