Reuse of Leached Nutrient Solution in Tomato Soilless Culture

The advantage of closed soilless systems is protection of surface and ground water from pollution with nutrients and pesticides. Beside that, savings of water and nutrients can be made. The aim of the research was to determine amounts of added and leached nutrient solution during the tomato growing period, their composition and possibility of reusing leached nutrient solution for fertigation after filtration and UV-sterilization. Tomato plants were planted on 11 February. During the harvest period from 12 May till 27 October, 39.1 kg m(-2) of marketable fruits were harvested. Number and duration of fertigation rates depended on the plant development stage and weather conditions. Amounts of leached nutrient solution were measured with installed percolate collectors. Leached nutrient solution was collected, filtered and UV-sterilized. After sterilization it was mixed with a new nutrient solution in a 1:3 ratio. Composition of nutrient solution was determined periodically (every two weeks) at the laboratory, while pH- and EC-values were measured with a portable pH- and EC-meter once a week. During the growing period 919 L m(-2) nutrient solution was added and 371 L m(-2) was leached. The ratio between added and leached nutrient solution ranged from 18.7 to 55.4%. For all macro-elements, with the exception of phosphate, higher concentrations (from 43% for K+ to 101% for Mg2+) were recorded in leached than in added nutrient solution. Phosphate concentration was 58% lower in leached than in added nutrient solution. Reuse of leached and sterilized nutrient solution is feasible but requires constant control of the composition and pH- and EC-values of nutrient solution to avoid higher deviations, which might have a negative effect on tomato yield. The closed soilless system is ecologically acceptable because excess nutrient solution is adequately disposed of and reused in the production cycle.