GROWTH INHIBITION, THE USE OF ADVANCED OXIDATION AND THE REDUCTION OF NUTRIENT SOLUTION DISCHARGE IN PRACTICE

Abstract

The EU Water Framework Directive demands a sound ecological and chemical quality for ground and surface waters. The Dutch greenhouse industry is on track towards a sustainable water management with the aim of a zero-emission of nutrients and plant protection products (PPP) in the year 2027. Growth inhibition, especially in rose cultivation, is a major reason for discharge of drain solution in soilless growing systems. Previous research on laboratory scale has shown the benefits of advanced oxidation process (here H2O2 + UV)) as a water treatment method to eliminate growth inhibiting factors. The next step is implementation in practice. Two paths have been explored (i) an endurance test on a cut rose nursery and (ii) monitoring the quantity of water flows in 12 nurseries with gerberas, roses, green peppers, cucumber or tomatoes, which were applying a combination of H2O2 and UV as AOP. In the cut rose experiment, no differences in crop yield were found between the treatments, despite of growth inhibition in the bioassay. The results from this trial led us to make the conclusion that for a period longer than a year, not more than a minimal discharge of drain water is necessary to avoid growth inhibition in a rose crop. Participation of the growers in the monitoring group using AOP led to a greater awareness of their water use and the emission flows on the nurseries, an incentive to learn from each other and willingness to try new things out. The quantities of water flows in the different nurseries have been compared. The average drain water discharge in 2011 has decreased with 45% compared to 2010. The calculated nitrogen emission was 157 and 86 kg N.ha-1, respectively for 2010 and 2011. These discharge figures were compared to model calculations, which calculate nursery-specific discharge based on sodium accumulation only. The model predicted an average discharge of 104 m3 in 2010 and 88 m3 in 2011. Effective doses of AOP for the prevention of growth inhibition are 15-25 mg.l-1 H2O2 and 100-250 mJ.cm-2 UV. With the use of AOP, the growers were more confident in the quality of the irrigation water. At one nursery, AOP was the ultimate solution for the serious growth inhibition problems.