EFFECT OF REPEATED PHOSPHATE FERTILIZATION ON THE HEAVY-METAL ACCUMULATION IN SOIL AND PLANTS UNDER PROTECTED CULTIVATION

In order to study the effects of repeated phosphate fertilization unde r protected cultivation, tomato (Lycopersicon esculentum Mill.), radis h (Raphanus sativus L.), celery (Apium graveolens L.), and lettuce (La ctuca sativa L.) plants were grown in subsequent cycles on the same su bstrate and fertilized with increasing amounts of superphosphate conta ining varying amounts of heavy metals. The accumulation of metals in t he soil and the consequent increased uptake of metals by plants did no t result in any reduction in the marketable production. The reduced pl ant yield observed in lettuce and in radish with the increase in the a ddition of superphosphate was most likely due to the increased salinit y of the growth substrate, which affected the metabolic processes of t he plants. The high concentration of salts as a result of the addition of high amounts of phosphorus fertilizer made it unadvisable to reuse the substrate under the experimental conditions adopted.