Managing a Substrate-Based Production System

Monday, April 25, 2022

The shift from soil to substrate is more involved than simply switching the grow medium and hoping for the best. Every base growing material is going to have different physical and chemical properties that impact the way it behaves in production. As a result, management is going to vary across soilless substrates. Despite the differences across alternative grow media, there are a handful of things, however, which do hold true when switching out of soil-based crop production

Irrigation Management is Crucial. 

Managing the water demands of a crop that is restricted to its container is very different than that same crop being grown in 'infinite' soil. The biggest differences you will see is the rate at which it dries out - a 4L pot has a significantly decreased ability to hold moisture compared to a soil-based farm. On that same note, the ability to drain water is also different when producing in a restricted volume of growing media. The potential for over-saturation of the growing media, as well as the heightened risk of salt accumulation, are also important characteristics to be aware of. 

Growing in a container is going to result in a smaller root volume on a plant, which is going to impact the ability to uptake water. For containerized crops we see that water needs to be more readily available for uptake compared to a soil based system. This metric is referred to as 'moisture tension'. Moisture tension can be measured a handful of ways (tensiometers, squeeze tests, capacitance probes), and it is important to recognize that the target moisture tension values are going to be different than a soil-based system. The ideal moisture tension for peat-based tomatoes runs from 1 to -5kPa, which is higher than what a field producer would aim for. By maintaining the moisture tension in this range, the plant roots have consistent access to water that is readily available for uptake. Values higher than this indicate a substrate that is too wet, which will limit air pockets in the media and increase the risk of disease in the roots. Values lower than this mean that your substrate is running too dry for your crop. The miniaturized root system is unable to extract water from the pore spaces in the media, and plant growth will be immediately impacted. 

Fertilizer Management Regime

Soilless substrate inherently contains very little, if not zero, baseline nutrition for your crop. While soil systems rely on pre-treatment of the soil and scattered nutrient applications through the season, a substrate-grown crop should be fertigated multiple times per day. By combining your irrigation and soluble fertilizer applications, you can be sure that the crop is getting the right amount of nutrients to sustain healthy and productive plant growth. 

What happens if I only fertigate once a day, and the remainder of the crop receives straight water? Any fertilizer that has been applied will be significantly diluted, if not completely run out of your substrate by selectively applying fertilizer through the day. Consistency bodes well for containerized crops in producing a healthy and productive root system, so save yourselves the trouble and plan accordingly for your daily watering regime. 

The soluble fertilizers that are being introduced into your system should be monitored on a regular basis. Daily checks of the EC and pH of the water that is being fed to your crop will ensure that your dosing system is working properly and that your fertilizer mix was diluted accordingly. These systems can see change on a daily basis, so it is important to stay on top of it to maintain healthy plant growth.
Speaking of pH....the target values for a soilless substrate are going to be lower than what you are aiming for in a soil-based system. While this depends on what the base material of your growing media is, you can anticipate that the pH of the fertigation solution should be somewhere in the 5.4-5.8 range.

If you are interested in learning more about managing a substrate-based production system, click here to check out our new factsheet. If you have any questions that were not addressed here, don't hesitate to reach out and we will be happy to talk to you about your production setup.

Posted by: Talia Plaskett