Reusing drain water to lower the emission of nutrients in the cultivation of Phalaenopsis

Phalaenopsis is the top-selling ornamental pot plant in the Netherlands, and the area under its production was 242 ha in 2014. Previously, production systems of Phalaenopsis (open or free to drain systems) resulted in high emission of nutrients to the ground and surface water, approximately 1500 kg N ha^-1 year^-1, in the Netherlands. Little is known of the response of Phalaenopsis to water reuse systems, as orchids have been exempt from recirculation obligations owing to their salt sensitivity. Regulations aimed to reduce nitrogen (N) emissions to a maximum of 150 kg ha^-1 year^-1 in 2018, with the ultimate goal being 0 kg ha^-1 year^-1, in 2027. Wageningen University and the Research Business Unit Greenhouse Horticulture were commissioned by the government as well as the Phalaenopsis grower association of the Netherlands to develop a system that could achieve the current goal of a maximum of 150 kg N ha-1 year^-1. A recirculation system with UV disinfection and the reuse of drain water was utilized at the experimental site in Bleiswijk. Two recirculation treatments were tested with the aim to maintain the current production and quality levels while also lowering the emissions to the standard of 2018, with the possibility of further improvements to achieve the desired standards for 2027. The aim of the first reuse treatment was to discard small amounts of drain water to keep sodium at a maximum of 1.2 mmol L^-1. In the second treatment, as much drain water was reused as possible. Emissions of N were reduced to 182 and 60 kg ha^-1 year^-1, respectively. Plant growth parameters including leaf number, total leaf area, and number of spikes and flowers, showed no significant differences. In this experiment reuse of drain water reduced emissions considerably without any adverse effects on plant growth or disease incidence.