Calcium Deficiency in Cucurbits
· Cucumber · Pumpkin · Zucchini · Melon
The symptoms of calcium deficiency 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 a stunted growth. With a severe deficiency, flowers can abort, and the growing point of new leaves take have a burnt aspect or simply die. Fruits are smaller and unsavory, and may develop a rot at the blossom end.
Calcium-deficiency disorders are generally related to unfavorable growing conditions for the plant. This nutrient is transported to the tissues via the water that is absorbed by the roots and later evaporated at the leaves, a phenomenon called transpiration. Tissues with high transpiration rates are thus less predisposed to suffer from deficiencies. By contrast, new leaves, which grow faster and transpire less than the older foliage, are the first to show the symptoms. Drought and sandy soils, which are prone to drought and leaching of nutrients, favor the appearance of deficiencies. High salinity, and the excess of potassium or ammonium could also be problematic for the uptake of calcium by the plant. Finally, high air humidity, flooding of soils, or root diseases can also slow down the transport of water to tissues, and therefore hinder the absorption of calcium.
For small farmers or gardeners, crushed eggshells ground very finely and mixed with a weak acid (vinegar)can be used. Organic matter can be added to the soil in order to improve its moisture-retaining capacity. Compost or manure can also be sprayed to improve soil calcium content.
Calcium can be supplied using lime (calcium carbonate), gypsum (calcium sulphate) or liquid fertilizers. Dolomitic or high-calcium limestone can be used to supply calcium to the plant and correct soil pH. Liming can be performed two to four months before planting. An adequate soil moisture is also necessary for a good calcium absorption. If the pH is already correct, gypsum is recommended. Existing calcium deficiency can be reduced by regular foliar sprays of fully soluble calcium nitrate. However, foliar applications are only partly effective because of the poor transport of calcium within plant tissues. Spraying calcium should not be a substitute for proper irrigation and fertility management.