Good irrigation water on propagation companies to avoid emission of nutrients and crop protection agents

The propagation sector demands a very high quality of irrigation water to avoid negative growth effects and diseases. Discharge of nutrient solution is sometimes used to avoid risks for the crop. The project “Good Irrigation Water” aims to develop sustainable water management and technology for nurseries in greenhouse horti¬culture. The underlying aim is to reduce the emission of nutrients and crop protection agents and to meet the EU Water Framework Directive demands. Within the project quality standards of the irrigation water were drawn up and critical values of these standards were described. Wherever knowledge was lacking, critical limits were established by measuring sets of four levels in bioassays under laboratory conditions. Concerning potentially harmful substances, the tested materials were a disinfectant (sodium hypochlorite), two organic compounds (POW-humic and fulvo acids and coir chips), a growth control agent (Alar) and a surfactant as used in rockwool substrate. Sodium hypochlorite inhibited growth in the bioassays from 45 mg/L on and Alar (daminozide) reduced growth of seedlings from 45 mg/L on. The organic substances with TOC-levels from 0 to 540 mg/L and surfactant with levels from 0 to 100% gave no growth inhibition. A subsequent series of tests showed that advanced oxidation (AOX; the combination of UV light and an oxidizer) is not suitable to destruct sodium hypochlorite or POW humus or the exudate of coir chips when applied in practical UVc/oxidizer doses (up to 250 mJ/cm2 and 1 mmol/L oxidizer). Surfactant with a high dose peroxide (30 mg/L) and 240 mJ/cm2 UVc is broken down for up to 45%. AOX did not readily destruct growth control agents. The concentrations of the oxidant were too low for the entire oxidation of the carbon compounds. With a higher concentration of oxidizer it seems there is still room for an improved breakdown of these retardants.