What’s happening in the root zone?

In this article we’ll investigate what chemical processes are taking place around the plant roots, influencing the well-being of your crops. To answer this question we first need to take a look at the different processes that are taking place within natural growing media in general. Once we have a clear understanding of these processes, we will be able to understand what is happening in the root zone.

Chemical processes in different types of substrate

Let’s start by differentiating between growing media composed of natural materials and inert growing media.

Organic growing media

Chemical processes are continuously taking place within substrates composed of organic materials. There’s a constant interchange of nutrients and other chemical elements between the plant roots and the surface of particles within the mixture. The natural components within the substrate mix make the interchange smooth and stable. Organic media components are acting as an airbag/cushions in molecule interchange, helping with the reduction of big fluctuations and ultimately reducing stress.

Inert growing media

Chemical processes take place differently in inert growing media. Rockwool, plastic-based media, or mineral components like perlite are all considered inert soilless media. The chemical interaction between the substrate and the plant roots is at a lower level. Inert growing media solutions are almost solely focused on physical support, not on other important aspects. This means that nutrient management and pH are done entirely through fertigation and the cushioning effect of growing media is not there. Adjusting the water quality, pH, anion/cation balance, and composition of your fertilizers can result in immediate changes within the root environment.

Now we’ve got that covered, we’ll zoom into the processes taking place within organic growing media.

Buffering capacities of natural growing media

Substrates composed of natural raw materials like peat or sphagnum allow valuable nutrients to be stored. It also provides a buffer of pH which is a balancing factor for optimal and constant nutrient uptake.

To really understand the processes taking place within the root zones, we need to take a closer look. We can identify so-called “ion exchange sites” within the substrate. These exchange sites are like “parking places” to which ions are connected.

The particles within the natural substrate are mainly negatively charged and carry H⁺ molecules. These molecules have a big influence on the pH level of the substrate, which in its turn directly influences the nutrient absorption by the plant.

When any of the essential nutrient molecules are needed for the plant’s metabolism, the root system creates a sink for it and drives that molecule by diffusion. If the exchange site on the substrate particle already has some of these nutrients stored, it will exchange the nutrients for H⁺ with the plant roots.

For this reason, the surface area of the root system is very important for the chemical processes as it increases the interchange of molecules between plants, nutrient solution (through water-filled pores), and substrate particles (through exchange sites).

In BVB Substrates growing media, this characteristic can be tailored to perfectly fit the crop’s needs.

What is substrate acidity?

An important thing to understand is that the pH of a substrate is actually the pH of the moisture within the substrate. The pH (potential Hydrogenii) is determined by the concentration of hydrogen ions (H⁺) in the moisture within the substrate.

By adding dolomitic limestone (calcium magnesium carbonate) the pH level of the substrate can be adjusted. By doing so, the pH level rises. This is caused by the way that Ca²⁺ and Mg₂⁺ bind to exchange sites. This means the acidic H⁺ elements are neutralised and the moisture within the substrate becomes less acidic.

Water Alkalinity?

Water quality and hardness have a broad effect on the pH.

The capacity of moisture to resist changes within the pH with the addition of acid is called alkalinity. This is determined by the number of carbonates (CO₃^2-), bicarbonate (HCO₃^–), and hydroxide ions (OH^–) within the solution.

pH buffering capacity

Different organic raw materials offer different pH buffers. A pH buffer means that the raw materials reduce the changes in pH, allowing for more stable nutrient absorption. The pH buffer within the substrate is determined by the quantity of H⁺ that is absorbed when the pH increases and the amount released when the pH decreases. More simply put: if the pH increases (meaning that H⁺ that was present in the moisture is being bound or absorbed), the substrate buffer would release H⁺ to compensate for the decrease, thus reducing fluctuation and cushioning the pH level.

Cation Exchange Capacity

The Cation Exchange Capacity, or CEC, resembles the substrate’s ability to supply and regulate cations toward the plant. A cation is a positively charged element. It’s important to understand that all these chemical processes and the interchange of cations and elements are constantly ongoing. These processes help maintain an equilibrium between the nutrients present in the irrigation water applied, the substrate, and the plants.

Within natural growing media the CEC can also be tailored to fit the plant’s needs.

So, about that root zone

So, let’s get back to the title of this article and see what’s happening in the root zone! Your plants absorb the nutrients they need through their root system. This influences the entire root zone environment.

Through the uptake of elements the pH of the root zone environment is influenced as well. If the plants absorb cations (positively charged elements), H⁺ will be released in return. As we’ve seen in the paragraphs above, this in turn will increase the acidity of the substrate and thus lower the pH level.

If a plant in its turn absorbs negatively charged elements (anions), OH^– is released. This lowers the acidity and increases the pH level.

If the substrate offers a good nutrient and pH buffer, it will cushion these effects, allowing for a more stable pH level.

As you may understand, this is important to keep in mind when composing your nutritional program. Different growing phases of your crop call for adjustments in the nutrition, due to varying plant needs. However, a good balance between anions and cations is important to keep the pH stable.

Keep an eye on the main steerable elements

When composing your nutritional program, make sure to keep a good balance between nitrate (NO₃^– ) and ammonium (NH₄⁺). As well as a balance between potassium and magnesium.

Potassium and ammonium are preferred nutrients by plants and if there are no ‘counterpart’ ions, excessive absorption can cause chlorosis. This is very often the case with an oversupply of potassium. When magnesium chlorosis appears it also affects the nitrogen cycle.

Potassium is given in higher amounts during the generative stages (flowering and fruiting). When plants absorb potassium, it can cause the pH to drop.

In inert growing media or hydroponic growing with a small pH buffer, the uptake of nutrients by the plants can cause much more volatile changes in pH levels.

How to achieve ultimate control

This all means that plants take up nutrients in proportion to availability. Plants have no way of knowing if it’s Saturday or if it is the Holiday season. They react to the current conditions and the available environment which is provided to them. Balancing nutrients, energy, and water uptake correctly and keeping a buffer zone, offers your crop an environment to thrive. This can be achieved by using needed inputs just in time when the plants need them for their metabolism.

Choosing organic growing media can give your crop a buffer, but choosing tailored growing media can give you a tool to use in addition to your environmental conditions. This all works in favor of your crops when you match them together in an ideal way.

Please don’t hesitate to contact our experts if you need advice or if you’re interested to hear more about tailored options for your business.

Learn more about plant health by reading these related articles:

• Physical performance of substrates
• Best soilless substrate performance for leafy greens in hydroponic systems
• Beneficial micro life in substrates