Nutrient recirculating soilless culture system as a predictable and stable way of microbial risk management

Abstract

Concern about the microbial risk due to nutrients and water reuse is one of the most significant barriers to the global transition of the soilless culture to the sustainable closed-loop system. Although sterilization technologies are available in the field, the reuse system’s microbial risk is still recognized as higher than that of open-loop systems. However, the consequences of closed-loop microbial transport properties on the microbial management performance in a nutrient recirculating system have been largely overlooked. Open- and closed-loop soilless culture systems have different water and nutrient management scheme. The combined effect of an irrigation system and microbial transport may reveal intrinsic characteristics of microbial population dynamics in both systems. This study was designed to test this hypothesis by examining the different microbial dynamics according to irrigation management system aspects. An integrated model for UV sterilization and soilless culture system was constructed for stochastic analysis of the microbial dynamics in the open and closed-loop water management system. Subsequently, the greenhouse experiment was conducted to test the theoretical predictions from the simulation analysis. Through simulation analysis, it was found that the microbial population in the open-loop soilless culture showed irrigation dependency; the level of the microbial fluctuations and plateau were determined by the irrigation frequency. In the closed-loop soilless culture with an UV disinfection device, it was found that the number of microbial populations increased over time and remained at an average steady-state after a certain period of time. In addition, the plateau level of microbial concentration was mostly determined by the combined effect of the UV germicidal power and irrigation frequency. Colony-forming unit investigation in field greenhouse cultivation confirmed these theoretical predictions. The close agreement between the theoretical predictions and cultivation experiment demonstrates a more predictable system response of the closed-loop system with UV flow-through disinfection than the open-loop system. These findings suggest a modified concept of the conventional microbial management risk in the closed-loop soilless culture and are expected to provide a useful theoretical and experimental framework for replacing the open-loop soilless culture with the sustainable closed-loop system.