The quality of water and nutrient solution used in controlled environment agriculture (CEA) production systems, such as greenhouses and vertical farms, is one of the most important factors that affect plant health and yield. Growers monitor water and nutrient solution quality by sending samples for analysis to determine the levels of nutrients and salts. They also use sensors to monitor pH and electrical conductivity (EC) regularly to determine necessary adjustments for the nutrient solution. Growers may also analyze the microbiome, the genetic material of all the bacteria, fungi, and viruses that live in their water and nutrient solution, to evaluate levels of harmful pathogens, such as Pythium and Phytophthora species that cause root rot.
Most greenhouses and vertical farms use recirculated nutrient solution in order to reduce their water use and wastewater. This practice is not only friendly to the environment, but it reduces operating costs as well. Challenges with using recirculated nutrient solution include build-up of salts, pathogens, and biofilm in the circulation system and the root zone of the plants. Without proper management, these conditions can lead to unhealthy plants that are more prone to disease. To reduce salt accumulation in recirculated nutrient solution, its EC and pH need to be monitored and adjusted regularly. Treatments to reduce pathogen and biofilm levels include ozone, ultraviolet (UV) light, pasteurization, or a combination of these systems. However, these treatments kill not only pathogenic microbes but might kill beneficial microbes as well. Some growers prefer not to sterilize their nutrient solutions to promote beneficial microbes, though this may come at a cost of higher levels of pathogens and subsequent disease development.