Image source: https://www.loftygreens.ca/index.php/hydroponic-systems/
When we think of hydroponics, we probably think of water, but are we considering how that water may be affecting the safety and quality of the plants growing in it? How we choose to irrigate crops in a Controlled Environment Agriculture (CEA) setting can have a big impact on the food safety of the crops produced.
How do we know what those food safety impacts might be? In general, when we think about food safety risks typically associated with irrigation systems, we are concerned about things like:
How likely is the water going to touch the harvestable (edible) portion of the crop during the growing process?
How likely is that water to be contaminated? (In most CEA cases, water is mixed with a nutrient solution and is often recirculated within the system, so the water is probably not very “clean”)
During handling and harvesting, what is the likelihood of cross-contamination from the water on to the harvestable part of the plants?
What is the quality of the water to begin with? (In this article, we are going to assume that each system is using a clean water source, free from detectable generic E. coli.)
With those questions in mind, let’s look into some of the most common irrigation systems used in Controlled Environment Agriculture.
Drip irrigation is generally considered to be a low-risk irrigation system for fresh produce. In drip irrigation, water is emitted very slowly directly on the crop’s substrate or growing medium.
Nutrient Film Technique
In Nutrient Film Technique (NFT), a water and nutrient solution fills a shallow container, or channel. Plant roots fit in holes in the top of the channel to reach the water and nutrient solution inside the channel, which is typically aerated with an air pump and recirculated. Cross-contamination with the recirculating water and nutrient solution is a potential food safety risk, especially in crops that tend to have droopy leaves.
Aeroponics is an irrigation technique that involves water spraying up from beneath the exposed plant roots within an enclosed chamber. While this is a very efficient technique and suitable for most plant types, it requires higher set up and maintenance costs than other techniques. It is also prone to leaking water, which poses a food safety risk.
Deep Water Culture
A very common and popular hydroponic irrigation system, Deep Water Culture (DWC) features plants growing on floating “rafts” or trays, with plant roots free to float in the water. The water is typically mixed with a nutrient solution and oxygenated with an air pump. Plants in DWC have a high exposure to recirculated water and there is a high risk of cross-contamination during handling and harvest.
The riskiest irrigation system for food safety, overhead sprinklers distribute high-pressure water directly onto the plants. This type of irrigation has the highest risk for contamination because the water distributed through the overhead sprinklers directly touches the edible portion of the crop.
Want to learn more?
Michigan Produce Safety Technicians are ready to help you meet your on-farm produce safety goals. We will work with you to identify, manage, and minimize risks to food safety on your farm, and help you create a comprehensive food safety plan to prepare you for a MI Produce Safety Risk Assessment Certificate. Working with Produce Safety Technicians is always free and confidential, and there is no cost to apply for the certificate. Click here to get started.
Article by Landen Tetil, Produce Safety Technician