Fertilizer Substitutions in Hydroponically Grown Greenhouse Tomatoes

Abstract

Experiments were carried out to evaluate two salts, K2SO4 and NaCl, as materials to supplement the electrical conductivity (EC) of the basic nutrient solution in nutrient film technique (NFT). The effects of these materials on the growth, yield and fruit quality of greenhouse tomato (Lycopersicon esculentum Mill.) grown by NFT were quantified. These effects were tested by increasing the recirculating solution EC from a base value of 1500 μS·cm-1 to that suitable for the crop growth stage with normal feed (macronutrients), 0.38 m (0.53 lb/gal) K2SO4 or 1.14 m (0.55 lb/gal) NaCl, at a common pH of 6.2. In 1995 and 1996, there were no significant effects of the treatments on crop growth. In 1995, the early marketable yield was significantly lower when K2SO4 was used but the yield at the end of the season did not differ among the treatments. Furthermore, with K2SO4, the proportion of grade #1 fruit in early total yield was lower than in the control, while, fruit biomass content was higher than in the NaCl treatment. In 1996, the cumulative marketable fruit weight was unaffected by the treatments. A trend toward high number of large grade fruit occurred with the NaCl treatment. The pH and EC of the fruit homogenate were favorably affected by the NaCl treatment. Adding K2SO4 or NaCl in partial substitution of macronutrients in the recirculating solution may have a role in NFT systems in not only reducing environmental pollution (from nitrates and phosphates) and fertilizer costs, but also in improving fruit quality and, therefore, profit margins.