Packaging, storage and application of growing media 

30 JUNE 2021

The fifth and final webinar of the series for certified companies was about packaging, storage and application of growing media. We have already summarised the first four webinars earlier. These were about safety, pH and nutrition, physical aspects and composition of growing media. Now we focus on the last part of the substrate chain.

There are some important physical, chemical and biological focus points to keep in mind when packaging, storing and applying growing media.

Packaging growing media

There are several ways to package growing media. In addition to bulk, for example in bags, big bags, pressed bales and big bales. The problem with packaging is that it mainly serves logistics, not preservation of the quality of the content. The airtightness of a package has consequences for the quality of the growing medium that is packed in it. This is the case with peat-based growing media, but it is even more so with growing media based on other organic raw materials. These can have much more biological activity, creating anaerobic conditions.

Breakdown process
There is always breakdown of organic matter. Micro-organisms need carbon. In order to extract carbon, they affect the organic matter. In this breakdown process, the bacteria also consume nutrients and especially nitrogen. Moisture, temperature and oxygen influence this breakdown process. If there is biological activity, especially the aerobic organisms will consume oxygen. A high temperature can accelerate the breakdown process. But if the raw material is dry, the temperature has much less effect. And if there is no biological activity at all, there also is no deficiency of oxygen and the nutrition and carbon stay alright. The longer the storage time, the stronger breakdown takes place.

Other processes
In addition to breakdown, other processes play a role in the packaging, including the dynamics of components. By liming, pH stabilisation takes place, but CO2 is also formed. This CO2 gas can inflate in the packaging like a balloon. CO2 can also displace oxygen, which accelerates the condition in the packaging to become anaerobic. Mineralisation (ammonification, nitrification) of organic fertiliser has an impact on pH and oxygen. Nutrients from coated fertilisers (CRF) can also be released during storage/transport, if these have been dosed. For each component it is important to consider how it will affect the substrate, to ensure that the growing medium is delivered to the grower as it was intended during production.

Aerobic and anaerobic
Aerobic bacteria also consume nitrogen, which means that at delivery nitrogen in a product can be already immobilised in the bacterial life. Even in well aerated packaging, a lot can happen with a biologically active substrate. Anaerobic conditions are created in the (air tight) packaging due to breakdown and thus oxygen consumption. And when it becomes anaerobic, there can be a loss of NO3 because of denitrification. The nitrogen is released into the air as N2 gas and thus is not plant available anymore. And when that is gone, the bacteria can continue with SO4 (sulfate), resulting in the well-known “rotten egg smell” (H2S gas). After that at severe anaerobic conditions, some bacteria will break down  sugars that are present, resulting in a “manure smell”. Step by step, anaerobicity leads to all kinds of breakdown processes, which can eventually lead to toxicity for plants.

 All this shows that when packaging growing media, much more attention must be paid to maintaining quality. Processes that take place in the packaging must be taken into account.

Storage and transport

The storage time – including the time at the dealer and customer – must be monitored. Temperature is also a point of attention. The higher the temperature, the more breakdown processes can be  aggravated. When storing and transporting a packaged growing medium, attention can be paid to oxygen (perforation packaging, bulk density), moisture (dryer), fertilisation (different, no nitrogen) and the composition of raw materials in the growing medium. A lot of research still needs to be done on this.

Change of properties by adjusting recipe 

When the new growing medium arrives at the grower and is used in the culture, it is important that he knows what will change compared to the previous situation. Then he can anticipate to those changes. It is first of all important to properly map out the various chemical and physical properties of “the current mixture” through analysis. This information is not always available. These properties are the starting point for the adjustment. When the existing and the new mixture show differences, it becomes clear how the grower has to anticipate. It is often advisable to first work with a test mixture in a small section, before implementing adjustments throughout the entire culture. In this way culture problems can be prevented. A grower often has to get used to the new situation.

The grower may need to irrigate differently. The water buffer, water retention, water distribution and water uptake velocity of new growing media are usually very different from what he was used to. It is important that the grower keeps a close eye on what is happening in the culture and anticipates. The water content and the oxygen diffusion have a clear mutual interaction. Where there is water in the root environment, there is no room for oxygen. Irrigation strategies – watering much or little and how often – influence the availability of sufficient oxygen and thus rooting. Water content sensors are a good tool in determining an appropriate irrigation strategy.

It is also possible that the grower has to fertilise differently. Often new growing media will already have high nutrient values at the start and a smaller pH and nutrient buffer, resulting in a less stable pH and less stable levels of cations. This small buffer also has an effect with the mineralisation and nitrification of organic fertilisers. Frequent nutritional analyses (every 4 to 6 weeks) with a focus on strongly deviating values, help to develop the correct fertilisation strategy.

For RHP-certified companies: you can download the hand-outs of the presentations of the webinars at My RHP.

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