The road to sustainable water and nutrient management in soil-less culture in dutch greenhouse horticulture

Since the expansion of soil-less culture in the Netherlands in the mid-eighties of the previous century, emission of nutrients and plant protection products (PPP’s) used in the root environment was considered as a huge problem. Eventually, the government and growers organisations reached an agreement which aimed at reducing the N, P and PPP emissions. For soil-less culture, reuse of drain water or closed growing systems became obligatory. Recently, the regulation changed by shifting the focus on reaching emission targets for N rather reaching 100 % closure of the systems. Yet, recirculation is still the key issue for reaching the goal of zero emission by 2027. These closed systems will potentially lead to substantial reduction of mineral leaching to the environment, however, they require adequate water quality and nutrient management. Moreover, satisfactory disinfection to control root diseases and removal of organic components is needed. In practice, substantial loss of water and minerals still occurs occasionally, when growers decide to flush the system and drainage water is partially discharged to the surface water or sewage system, causing emission of nutrients and PPP’s. There are several reasons for growers to discharge e.g. accumulation of Na, mismanagement in EC or pH or nutrient supply, and serious problems with soil borne diseases or growth inhibition. This paper will give an overview of the state of the art of systems for nutrient solution recycling, and the requirements for water treatment, water quality and nutrient supply and strategies to obtain the highest efficiencies for nutrient and water use.