Oxidation-Reduction Potential (ORP) in Hydroponics

The oxidation-reduction potential (ORP) is an important parameter in hydroponic systems as it influences water quality, nutrient availability, and microbial interactions. ORP quantifies the electrical potential needed to facilitate the transfer of electrons between oxidizing and reducing agents in a solution. It is measured in millivolts (mV). 

The oxidation-reduction potential (ORP) is affected by the levels of reactive chemical substances, such as oxygen, chlorine, and various oxidants, along with reductive agents like organic materials. Elevated ORP readings indicate a more oxidative setting, which aids in controlling pathogens and disinfecting water. In contrast, reduced ORP readings suggest an environment with reductive conditions, which can favor some anaerobic activities and heighten the risk of microbial contamination if not managed properly.

Applications of ORP

Maintaining optimal ORP levels is essential for ensuring clean and safe water. ORP levels between 300–500 mV are generally ideal for most hydroponic systems since they balance microbial control while preserving beneficial microbial communities. Also, research highlights ORP’s efficacy in pathogen suppression. For instance, maintaining ORP above 650 mV effectively controls root rot pathogens like Pythium and Phytophthora, commonly found in hydroponics.

Optimal ORP ensures nutrients remain in their most bioavailable forms to enhance absorption efficiency by plant roots. Studies reveal that ORP levels around 400 mV promote iron and phosphorus availability without compromising root health. Also, hydroponic systems benefit from oxidizing agents like ozone and hydrogen peroxide to maintain water sterility. ORP monitoring ensures these agents are used effectively without causing oxidative stress to plants.

ORP management requires careful consideration of system variables such as pH, temperature, and organic matter content. While high ORP levels enhance disinfection, they may damage beneficial microbes and delicate root systems. Conversely, low ORP levels can harbor pathogens. Advanced ORP sensors and IoT-based control systems offer real-time monitoring that allows growers to adjust parameters for an ideal outcome. Also, integration with IoT and AI-driven platforms enables predictive adjustments that improve system resilience and resource efficiency. However, further studies are needed to determine crop-specific ORP requirements and their interactions with other hydroponic parameters like electrical conductivity (EC), potential hydrogen (pH), and dissolved oxygen.

References:

Yang, X., Khan, Z., Ma, K., Ouyang, Y., Zhang, X., & Shen, H. (2023). Stable buffer couple series for rhizosphere oxidant-reductant potential regulation suitable for rice hydroponic cultivation experiments. Plant and Soil, 493(1–2), 673–696. https://doi.org/10.1007/s11104-023-06243-9

Husson, O. (2012). Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy. Plant and Soil, 362(1–2), 389–417. https://doi.org/10.1007/s11104-012-1429-7

Shimizu, S., & Tojo, M. (2024). Suppressive effects of low-pH solutions on root rot in hydroponically grown Welsh onion. Journal of General Plant Pathology, 90(3), 151–162. https://doi.org/10.1007/s10327-024-01168-2

Kriem, L. S., Pietzka, C., Beckett, M., Gärtling, L., & Wriedt, B. (2023). Electrochemical In Situ Hydrogen Peroxide Production Can Reduce Microbial Load in Bioponic Nutrient Solutions Derived from Organic Waste. Agriculture, 13(11), 2122. https://doi.org/10.3390/agriculture13112122

Mustafa, H., Hayder, G., Abba, S., Algarni, A., Mnzool, M., & Nour, A. (2023). Performance Evaluation of Hydroponic Wastewater Treatment Plant Integrated with Ensemble Learning Techniques: A Feature Selection Approach. Processes, 11(2), 478. https://doi.org/10.3390/pr11020478

Lang, J. M., Rebits, B., Newman, S. E., & Tisserat, N. (2008). Monitoring mortality of pythium zoospores in chlorinated water using oxidation reduction potential. Plant Health Progress, 9(1). https://doi.org/10.1094/php-2008-0922-01-rs