Consequently, localised calcium deficiency can occur in those tissues and organs that do not normally transpire freely. Such deficiencies are the cause of a number of disorders of vegetable crops, including blackheart in celery, tipburn in lettuce and blossom-end rot in tomato.
However, it is not yet possible to predict exactly when calcium deficiencies will occur. The review cited below discusses the causes of these disorders and suggests how they might be controlled.
Genetic make-up obviously has a strong influence on susceptibility to such disorders. Other contributory factors include high salinity around the roots and reduced transpiration by day.
By contrast, high humidity at night can be beneficial, probably because root pressure is increased and this forces calcium into the poorly-transpiring organs.
Any condition that encourages rapid growth is also likely to be a contributory factor because the rate of growth may then outstrip the supply of calcium. In some cases, the disorders can be reduced by applying calcium salts to the affected organs or by passing air over them.
Causes and Control of Calcium Deficiency Disorders in Vegetables: A Review by Olle and Bender (2009). Journal of Horticultural Science & Biotechnology 84 (6): 577-584. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.