THE EFFECT OF NUTRIENT SOLUTION PH ON PHOSPHORUS AVAILABILITY IN SOILLESS CULTURE OF TOMATO

Abstract

Greenhouse experiments with tomato were conducted in the years 2004-2006. The aim was to study the effect of nutrient solution pH on the availability of phosphorus in soilless culture of tomato. Tomato plants were grown on mats made of shredded rye straw, and on slabs of peat and rockwool. The plants were fertilized with a standard nutrient solution of different pH: 4.5, 5.0, 5.5, 6.0 and 6.5. Such different pH levels of the nutrient solution used in soilless culture modified the pH of the root growth zone. This effect was more evident in rockwool than in the organic media (especially straw). The phosphorus content in the root zone was closely associated with the pH value of the supplied nutrient solution and the kind of growing medium. Considerably lower concentrations of phosphorus were recorded in the organic media (straw, peat) than in rockwool. As the pH level of the nutrient solution increased, so did the pH of the root zone, whereas the amount of available P-PO 4 decreased. The course of these changes was similar in all the substrates. However, the dynamics of the changes was weaker in the organic media. With an increase in the pH of the nutrient solution, the average phosphorus content in tomato leaves decreased. The P-PO4 concentration was higher in the leaves of tomato plants growing in rockwool compared to those in the organic media. A significantly higher marketable yield was obtained from tomato plants cultivated in rockwool than in the organic media. For all the growing media, the highest yield of tomatoes was obtained after feeding the plants with the nutrient solution of pH 5.5.