Hydrion-Line, Towards a Closed System for Water and Nutrients: Feedback Control of Water and Nutrients in the Drain

Abstract

The development and market introduction of affordable ion specific sensors, like the ISFET sensor, has paved the way for completely new systems for application of fertilisers to crops in greenhouses. This paper describes the use of information feedback from flow sensors and ion specific sensors to regulate the supply of water and nutrients to a model gully. When a controller keeps the drain flow and the concentrations of the individual ions in the drain at a sufficiently high fixed value, the uptake of the plants is intrinsically compensated, i.e. the demand of the plants is exactly satisfied. Time series measurements of flow and concentration in supply and drain are used to design the controller for applying nutrients to a tomato crop in a near-practice greenhouse. Data are shown of fertiliser concentrations and flow in supply and drain during the design phase and test phase of the controller.

Ion-Specific Nutrient Management in Closed Systems: The Necessity for Ion-Selective Sensors in Terrestrial and Space-Based Agriculture and Water Management Systems

“…The aforementioned needs for ion-selective sensing are in addition to the benefits that ion-selective nutrient solution management would provide to growers in terms of increased shelf life [30], taste manipulation [30] and improved food safety [33,42,87]. …”

“…There has been great interest in their specific relevance in soil and nutrient solution monitoring for plant growth [5,6,36,135–138]. And there have been several explicit tests of ISEs for hydroponic nutrient solution monitoring [5,14,41,42,44,139,140]. Concluding remarks included; “The ion selective electrodes used here proved to be temperamental devices with a number of inherent problems.” [139], “In light of the potential limitations of ISE technology in individual ion based control systems, other advanced sensor types are being explored.” [14], “Yet, a number of practical difficulties still need to be resolved, in particular the stability and robustness of the measuring system, and the life expectation of the sensors.” [42], “No sensors of acceptable quality have been offered on the market yet.” [44].…”

“…And there have been several explicit tests of ISEs for hydroponic nutrient solution monitoring [5,14,41,42,44,139,140]. Concluding remarks included; “The ion selective electrodes used here proved to be temperamental devices with a number of inherent problems.” [139], “In light of the potential limitations of ISE technology in individual ion based control systems, other advanced sensor types are being explored.” [14], “Yet, a number of practical difficulties still need to be resolved, in particular the stability and robustness of the measuring system, and the life expectation of the sensors.” [42], “No sensors of acceptable quality have been offered on the market yet.” [44]. The literature raises the following specific limitations with ISEs, drift/stability [5,14,44,140–143], electrical interference [144–148], temperature sensitivity [14,140,142], lifetime [42,44] and the requirement of a reference electrode [144].…”

“…Several other references include discussion of both ISE and ISFET sensor types with relevance to plant growth systems [42,44,141,156,157]. Compared to ISEs, ISFETs allow for further miniaturization, reduced response times and reduced susceptibility to external electromagnetic fields [154].…”

Extension and evaluation of a model for automatic drainage solution management in tomato crops grown in semi-closed hydroponic systems

“…However, automation of this process requires either online measurement or model-based prediction of the salt concentrations in the DS (van Os et al, 2008;Kim et al, 2013). On-line monitoring of individual ion concentrations in hydroponic nutrient solutions is an interesting approach but the currently available equipment is expensive and not reliable in the long term (Gieling et al, 2005;Massa et al, 2011). The development of reliable and inexpensive ion-selective electrodes is currently at an experimental level (Kim et al, 2013;Rius-Ruiz et al, 2014).…”