USE OF ULTRAVIOLET-DISINFECTED NUTRIENT SOLUTIONS IN GREENHOUSES

Environmental concerns and economics require the recycling of plant nu trient solutions (PNS) used in soilless cultures in greenhouses. To av oid possible outbreaks of plant diseases, disinfection of the recycled PNS might be necessary. This paper describes a case study on the stab ility of Fe3+-chelates, present in PNS and exposed to ultraviolet radi ation (UV 254 nm) for disinfection, and the effect on plant growth. Th ree Fe-chelates, each containing 2 mg Fe3+ 1(-1) in PNS were: i, Fe-ED DHA (Fe-ethylene-diamine-dihydroxyphenyl acetic acid); ii, Fe-Na-EDTA (Fe-ethylene-diamine-tetra-acedic acid); and iii, Fe-DTPA (Fe-diethyle ne-triamine-pentaacetic acid). Seedlings of sorghum, corn and tomatoes were grown hydroponically for four weeks in continuously aerated PNS, which had been exposed previously for 0, 2.5 and 130 s to a UV radiat ion fluence of 80 mW s(-1) cm(-2). The accumulation of plant fresh wei ght (APFW) differed from non-treated controls, depending on chelating agent and on exposure time to UV. The greatest APFW was observed in so rghum (128, 178 and 98%) at 2.5 s UV-exposure for PNS containing i, ii and iii, respectively. For corn and tomato, the respective results we re: 108, 139 and 96%, and 129, 91 and 89% for tomatoes, respectively. The stability of i, ii and iii upon exposure to UV radiation is discus sed.