YIELD AND WATER USE EFFICIENCY OF SWEET CORN GROWN IN SOLUTION CULTURE AS AFFECTED BY KNO₃ AND SALINITY LEVELS

Two experiments were conducted in autumn and spring of 1989 in an unheated greenhouse, using an aero-hydroponic system. This system consisted of a 130-L covered container for the nutrient solution, a pump for its circulation, and two 30-L boxes in which plants were grown. The roots were continuously sprayed with the nutrient solution. In each experiment, 15 treatments were tested: three KNO₃ levels (2, 7 and 13 mM and 2, 8 and 14 mM in autumn and spring, respectively), and five salinity levels (2, 5, 7, 10 and 12 dS m^-1, at a NaCl:CaCl₂ molar ratio of 4:1).

In both experiments, fresh matter production was decreased by increasing salinity and increased by KNO₃ concentration in the solution. Salt stress above 5 dS m^-1 at any of the KNO₃ levels significantly decreased the fresh weight of the above ground plant organs, dry matter production and yield. Salinity stress increased plant root/shoot ratio, while increasing KNO₃ concentration decreased it, and the interaction between electrical conductivity and KNO₃ was insignificant. The effect of salinity-KNO₃ interaction on dry matter production and ear yield was significant only in spring; its effect on transpiration was significant in both experiments. The positive effect of fertilization on yield vanished under high salt stress. A significant linear relationship between transpiration and dry matter production was found, regardless of the KNO₃ concentration, plant age and growing season; it showed a water use efficiency of 7.2 g dry weight L^-1.

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