Zero discharge of nutrients and pesticides to the environment in hydroponic production

Abstract

Presently, agriculture uses about 70% of the available freshwater resources, and the environmental impact of agricultural waste (water polluted with fertilizers and pesticides) is significant. Greenhouse horticulture, and especially soilless cultivation, is pre-eminently capable of improving both crop yield and water-use-efficiency. Emission of drain water from the greenhouse into the environment can compromise surface and groundwater quality. Stricter legislation forces Dutch growers to decrease discharge of water with nitrogen and phosphate to almost zero in 2027 and of plant protection products by 95% in 2018. Environmental measurements illustrated growers with so-called closed growing systems still discharged 5-10% of the supplied nutrient solution to surface water or sewage system. The aim of this research is to show that cultivation without any discharge is feasible without loss of production and quality, and with currently available cultivation techniques. In 2014, an autumn cucumber (Cucumis sativus) crop and in 2015 a year-round sweet pepper (Capsicum annuum) crop were grown to compare zero discharge cultivation on stonewool with traditional discharge cultivation. In 2016, sweet peppers were grown on stone wool and in coir substrate. Coir is not inert and requires a different irrigation and fertilization strategy and it contains large amounts of sodium. The main technical adaptations for zero discharge, compared to traditional cultivation were the introduction of a circular drip irrigation network, non-rinsing filters, weekly analysis of the nutrient composition including crop uptake calculations, completely recirculating the nutrient solution, and a special strategy to finish the cultivation by exhausting nitrogen and water content in substrate. In all three years the production and quality of the produce was optimal in zero discharge cultivation. In two years there was zero discharge, in one year a minor discharge was required due to a calamity. From the results we concluded that full recycling of all drainwater does not affect sweet pepper production negatively. Complete recycling was realized with available technology, in combination with an adapted irrigation strategy.