ORP Meter and Measurement in Agriculture Applications
- Seb
- 6 days ago
- 4 min read
What is ORP and When ORP Meter Is Used?
Oxidation-Reduction Potential (ORP) which is also referred as “potential redox” is an important water quality parameter to monitor in water treatment application to control the efficiency of the disinfection.
An ORP meter measures a solution's oxidizing or reducing potential, indicating the water's ability to either gain or lose electrons.
The ORP value of a solution indicates how well it can break down organic waste and contaminants. This ability relies on the oxygen available in the solution.
The ORP is therefore related to water oxygenation and biological activity of a solution.
The ORP value is given as mV (millivolts) with a usual range from -2000 mV to +2000mV.
In agricultural applications, ORP is used to manage the pH level and oxidizing (disinfection) agents used in irrigation.
Measuring the ORP level in agricultural irrigation ensures that water treatment is effective, preventing damaging risks to the soil and nearby environment.
Understanding ORP Values
Low or negative ORP values of a solution might indicate a presence of organic matter and biological activities.
High ORP values are considered to have high capability of killing bacteria and pathogens, which in turn reflects a sterile environment.
ORP should be kept above 600mV to eliminate harmful fungal spores and bacteria.
Drinking Water ORP Recommendation: around 600-700mV, oxidants can be added to water to prevent development of pathogens.
Testing ORP in Hydroponics
Measuring ORP helps hydroponic growers with monitoring the quality of their hydroponic solutions that they use to grow crops.
This is particularly important for growers using water recirculation systems (RDWC).
Prolonged exposure to water with a high ORP value (500 mV and above) can negatively impact plant development by damaging the roots that are in contact with the water.
On the flip side, low ORP values (below 250 mV) can make crops more susceptible to infections and may reduce nutrient absorption in plants.
The recommended ORP range in hydroponic water is between 300 to 450 mV.
This range helps stopping the growth of microorganisms without harming the roots.
A reductive solution with an ORP value under 100mV is likely to contain microorganisms like fungi, bacteria, and viruses, or it might have organic molecules. These microorganisms will consume the dissolved oxygen, lowering the amount of oxygen available for the roots.
Ozone, hypochlorous acid or hydrogen peroxide may be added to the hydroponic solution to adjust the ORP value and boost the disinfection ability of the solution.
ORP in Soil Management
Evaluating the soil's redox potential will give you insight into the oxygen content, microbial activity, and overall soil condition, which are important for understanding nutrient availability, root respiration, and microbial activity.
Monitor ORP in Fruit and Vegetable Disinfection Bath
In the fruit and vegetable industry, postharvest treatments are required to ensure successful conservation during supply chain and an extended shelf life for retail.
Microbial spoilage can lead to substantial losses due to contamination by disease.
The most common method to avoid and reduce losses is to use a disinfection water bath to wash the fruits and vegetables.
This bath helps to remove soil, small particles and microorganisms such as fungi, bacteria, and other contaminants.
Chemicals such as chlorine and hydrogen peroxide may be added to the water bath. This disinfection bath water is also often recirculated.
ORP monitoring of chlorinated water bath helps to ensure sanitation efficiency of the solution. ORP values help growers with adjusting the dosage of the disinfection chemicals.
The ORP value of wash water is related to the required contact time between the solution and the fruit to effectively eliminate harmful bacteria. For example:
· Wash water with ORP value of 665 mV or above will destroy E. coli and Salmonella bacteria in less than 20 seconds.
· Wash water with ORP value of ORP of 550 mV requires 60 seconds of contact time for the same level of disinfection.
How to measure ORP with a Pocket Tester
ORP meters use a platinum electrode and have a range from -1000 mV to +1000 mV.
The meter should be immersed in the sample solution and it will display a value within seconds.
We recommend Horiba LAQUAtwin ORP-11 meters that offer an accuracy of +/- 2mV.
It is waterproof for a safe field use and has a temperature compensation function.
The meter should be checked with the standard solution at 225 mV.
This meter can also display Eh value (voltage reading vs. the Standard Hydrogen Electrode) also referred as SHE.
Conclusion
An ORP measurement offers an oxidation-reduction perspective on the chemical characteristics of a sample that basic pH and EC analysis cannot provide.
With this information it is easier to determine the following:
Whether your solution lacks sufficient oxygen,
Whether your hydroponic solution might be harmful for your plants' roots
Sterilization potential of your cleaning bath.
P.S. If you are a hydroponic grower, check out complete testing kits for precision agriculture that hundreds of growers across Americas use to monitor their nutrient levels.
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