Disinfecting the ground while keeping microbes alive

Imagine having invested in a piece of land and the land gets sick, then what? In many cases the answer will be steaming. Because the administration of methyl bromide under plastic, as was done in the past, has now been forbidden for years due to its toxicity and the deposit of all kinds of unwanted chemicals in the soil. However, steaming isn’t everything. It takes a lot of energy, can affect soil structure and composition and it doesn’t guarantee 100% that all plagues will be neutralized. A third way, still relatively new and in development, is the so-called pasteurization.

Together with his son Cas and partner Maarten Koppenol, Marten Barel has years of specialization in the disinfection of growers’ soil. In recent years they have focused on developing and improving the practical applicability of pasteurization. Maarten: "Together with German manufacturer MSD Moeschle Seifert we’ve figured out a couple of tricks that make pasteurization more effective, cheaper and faster. It all comes down to our new steam boilers, which we bring along to growers to disinfect the soil."

Classic steaming - used widely around the world - implies injecting steam of about 130 degrees under a tarp, under high pressure. This has a number of disadvantages. "Generating high pressure takes a lot of energy and isn’t harmless. In addition - and this is even more serious - it doesn’t do what it promises, namely guaranteed cleaning of the soil. This has to do with the fact that steam is used instead of hot air. When water condenses on the soil particles it rapidly cools and forms a barrier for the following steam particles. Because of this you have to steam in the same place much longer, but even after a long time you can’t be sure that the soil has been treated to a sufficient depth. In addition, steaming upsets all sorts of important soil components and kills many microbes beneficial to cultivation. With pasteurization, just as with the pasteurization of milk, soil composition and soil life are not significantly affected."

There’s a notable, growing interest for this technology, particularly from organic growers. According to Maarten this is partly due to the belief that natural soil is to be preferred over an artificial growth medium. "Substrate has undeniable advantages, but do we sufficiently understand the importance of soil life?"

The new technology can amount to significant energy savings, compared to the traditional steaming: from 3 to 0.5 liters of diesel per m2. Feedback from growers shows that pasteurization is also more effective, among other things because the soil can be used almost immediately after disinfection since there are no chemical residues. Furthermore, the success of soil pasteurization goes hand-in-hand with the administration of biological substances leading to rapid multiplication of the desired organisms.

Maarten: "From our partnership Marten and I, each in our own work area, have offered growers an alternative to methyl bromide in recent years. After reintroducing steaming at many companies we are now trying to introduce pasteurization. It may take some time, but while the benefits of pasteurization become more widely known we hope to convince more and more growers."