Effects of NaCl or nutrient-induced salinity on growth, yield, and composition of eggplants grown in rockwool

The effects of increasing the salt concentration of a basic nutrient solution from 2.1 up to 4.7 dS m(-1) by providing either additional amounts of nutrients or 25 mmol l(-1) NaCl on growth, yield, fruit quality and mineral composition of eggplants were investigated. The extra nutrients used to raise the electrical conductivity were added either at the same ionic concentration ratio as in the basic nutrient solution or at an increased ratio of K to total cation concentration. The vegetative growth and the number of Rowers per plant were not influenced by any of the salinity treatments. In contrast, the fresh fruit yield of eggplant was significantly reduced to the same extent in all salinity treatments. The yield depression was a result of a decline in mean fruit weight, whereas the number of fruits per plant was not affected. However, recalculation of the data on dry weight basis revealed no significant differences between the treatments. The percentage of eggplant fruits graded Class 1 was significantly reduced at 4.7 dS m(-1), whilst the kind of salts used to induce salinity had no significant effect on fruit quality. The increase of electrical conductivity up to 4.7 dS m(-1) by the addition of extra nutrients did not result in a higher nutrient uptake, with the exception of P in roots, and P and organic N in the petioles of older leaves. In contrast, the concentrations of Mg and NO3-N were reduced in some plant parts when salinity was increased by the addition of extra nutrients, regardless of the proportions of cations in the nutrient solution. All salinity treatments reduced the concentration of Mg in the leaves to the same degree, thus indicating that this salt effect is not ion specific. (C) 2000 Elsevier Science B.V. All rights reserved.