LAUSR

Desalinated water has become a legitimate alternative water resource for the irrigation of intensive crops in semiarid regions. The concentrations of calcium (Ca) and magnesium (Mg) in water (C Ca and C Mg , respectively) supplied from desalinated plants are much lower than the values typically found in irrigation water resources in semiarid regions. blossom-end rot (BER), a physiological disorder at the blossom-end part of the fruit resulting in tissue disintegration and dehydration, is considered a Ca-related disorder and therefore the optimization of C Ca has to consider not only total fruit production but also the occurrence of BER. There is a lack of information regarding the optimal C Ca and C Mg and Ca/Mg ratio in low-salinity water under Mediterranean conditions for high-quality yield of tomato fruits.The main objective of the research was to optimize C Ca and C Mg for the production of high tomato fruit yield with minimal occurrence of BER. A secondary objective was to determine critical levels of Ca, Mg and Ca/Mg ratio in leaves in relation to yield and the occurrence of BER.Tomato plants were grown in an inert media and fed with a wide range of C Ca and C Mg . Fruit yield was shown to decrease significantly when C Ca was at or below 0.40 mmol l –1 . In moderate C Mg (1.4 mmol l –1 ) treatment, BER was negatively correlated to Ca level up to and including 1.4 mmol l –1 and was not manifested above that level under the prevailing conditions. Elevating C Mg above 0.25 mmol l –1 enhanced BER occurrence. Concentrations of Ca and Mg in tomato organs increased with the respective mineral concentration in irrigation solution, whereas each element was reduced in organs as a function of the increased solution concentration of the other. The Ca concentration in diagnostic leaves (the diagnostic leaf is the fully developed youngest leaf) for optimal fruit yield with minimum BER was found to be 1.6%. The optimum C Ca for high fruit yield with minimal BER occurrence was found to be in the range of 1.5–2.5 mmol l –1 combined with C Mg at 0.25 mmol l –1 .