The symptoms are primarily visible in the rapidly growing tissues like new shoots and leaves. Young shoots are poorly developed and over time their number is reduced. Initially, the new or intermediary leaves may show randomly scattered chlorotic stains in the limb. If not amended, they start to curl downward or upward and their edges take gradually a necrotic and scorched aspect. Mature and older leaves are generally unaffected. The root system develops poorly and plants have a tendency to wilt and show stunted growth. With a severe deficiency, flowers can abort, and the growing point of new leaves appear burnt or simply die. Fruits are smaller and unsavory, and in the case of cucumber, pepper and tomato may develop rot at the blossom end. Seeds have a lower germination rate.
Symptoms are generally related to the availability of this nutrient to the plant rather than to low soil supply. Calcium is not mobile in the plant and its absorption is tightly linked to the uptake and transport of water in the plant. That explains why new leaves are first to show deficiency symptoms. Heavy soils and irrigated soils are good at dissolving calcium and bringing it to the plant. However, sandy soils, with a poor water retention capacity, are prone to drought and can limit its uptake. Allowing the soil to dry out too much between watering can also cause the symptoms. Soils with low pH, high salinity or soils rich in ammonium can also be problematic. High air humidity or flooding of soils can slow down the transport of water to tissues, and therefore less calcium is absorbed.
For small farmers or gardeners, crushed eggshells ground very finely and mixed with a weak acid (vinegar) can be used. Alternatively, apply calcium-rich substances such as algal limestone, basalt flour, burnt lime, dolomite, gypsum, and slag lime. Organic matter in the form of manure or compost can be added to the soil in order to improve its moisture-retaining capacity.
- Use soil fertilizers containing calcium (Ca). - Examples: Calcium nitrate, lime, gypsum. - Consult your agricultural advisor to know the best product and dosage for your soil and crop. Further recommendations: - It is recommended to do a soil test before the start of the cropping season to optimize your crop production. - Soluble calcium nitrate is a foliar spray for existing deficiency. - When using calcium chloride, do not spray if the temperature is over 30°C. - During field preparation, use lime if the soil pH is acidic and use gypsum if the soil pH is alkaline. - Liming can be performed two to four months before planting.