Use of ultraviolet-disinfected nutrient solutions in greenhouses

Environmental concerns and economics require the recycling of plant nutrient solutions (PNS) used in soilless cultures in greenhouses. To avoid possible outbreaks of plant diseases, disinfection of the recycled PNS might be necessary. This paper describes a case study on the stability of Fe3+-chelates, present in PNS and exposed to ultraviolet radiation (UV 254 nm) for disinfection, and the effect on plant growth. Three Fe-chelates, each containing 2 mg Fe3+ 1(-1) in PNS were: i, Fe-EDDHA (Fe-ethylene-diamine-dihydroxyphenyl acetic acid); ii, Fe-Na-EDTA (Fe-ethylene-diamine-tetra-acedic acid); and iii, Fe-DTPA (Fe-diethylene-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 radiation fluence of 80 mW s(-1) cm(-2). The accumulation of plant fresh weight (APFW) differed from non-treated controls, depending on chelating agent and on exposure time to UV. The greatest APFW was observed in sorghum (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 were: 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 discussed.