Changes in the chemical composition of the rhizosphere of tomato grown on inert substrates in a prolonged cycle

Abstract

The aim of this study, conducted in 2005-2007, was to determine changes in the chemical composition of extracts from the rhizosphere of tomatoes and of drainage water in tomato culture set up on rockwool, perlite and expanded clay and nourished with one of the two nutrient solutions containing different concentrations of macronutrients (EC I: 2.4 mS cm –1 and EC II: 3.6 mS cm –1 ). Perlite and extended clay were placed in foil sleeves, whose shape and volume corresponded to the weight of rockwool. The tomatoes were grown with a dripping fertilization system and a closed nutrient solution circulation system, without recirculation, for watering. The solution supply frequency, controlled by a soltimer, depended on the intensity of solar radiation. The concentration and proportions of macronutrients in the nutrient solutions were adjusted to the requirements of particular developmental phases of the plants, in accordance with the current recommendations. The plants were grown in a prolonged cycle for 22 clusters (from the beginning of February to mid-October). Extracts from the rhizosphere and drainage water for analyses were sampled at a set time of the day, every four weeks, since the plants were placed on the mats. The analysis of the results revealed significantly more nitrate ions, phosphorus, potassium, calcium, magnesium, sulphates and sodium in extracts from the rhizosphere and in drainage waters sampled from treatments fertilized with the concentrated solution (EC II), compared to the basic solution. In the drainage water from treatments fertilized with a solution of the basic macronutrient composition (EC I), the increase of ion concentrations appeared in the following order: N-NH 4 > P-PO 4 > Ca > S-SO 4 > K > N-NO 3 > Mg, whereas in the drainage water flowing from the treatments fertilized with the solution containing 25% more macronutrients (EC II), the ion concentration range was as follows: N-NH 4 > P-PO 4 > Ca > N-NO 3 > S-SO 4 > K > Mg. In the present study, the sodium content in drainage water was depressed compared to the nutrient solution dosed under plants with either of the two liquid feeds.