Steam sterilisation - more trouble than it's worth?

Would I use steam sterilisation again?

Around ten years ago, Wight Salads on the Isle of Wight (recently re-owned by a wonderful family business (the Pearson’s) and re-named APS Produce Ltd) attempted steam sterilisation of the soil in one 0.2 ha glasshouse. The aim was primarily to eradicate an outbreak of the fungus Pyrenochaeta, which was severely affecting crops. Dr Phil Morley tells us about his experience with this costly process.

A range of other issues arose

Following steaming, we found that a range of other issues arose. The previously light and airy biological soil became compacted and lifeless. Even though we tried to re-inoculate it with our own-made compost, it took around four years to recover its texture. Steaming did seem to reduce Pyrenochaeta outbreaks, but soil drainage proved difficult to manage after steaming, resulting in many other problems including inevitable nutritional issues.

In retrospect, I think a biological approach would have been the best solution, even though it may have taken time to bio-remediate the soils and at that time the technology and equipment to measure was not really in existence. Anyway, the Soil Association’s Head of Horticulture, Ben Raskin, suggested we try biochar, so we have been trialling Carbon Gold activate (with biology of course) to help maintain a positive biome in the soil. This seems to have worked well, though we have not yet measured improvements in the biome, simply observed the impacts on yield and quality. Both of which have improved. Still, there is a long way to go and we are continuing to try to understand exactly what ‘better soil health’ is in reality.

There’s still a lot to learn

We have been considering the biology of our soils since inception of organic production in 1999, and tried to gather the best knowledge from around the world (including, historically, remember the Soil Food Web principles taught by US researcher Prof Elaine Ingham). Still relevant and interesting. Nowadays, we have some very practical and applied research groups, including AHDB’s GREATSoils initiative, and the Innovative Farmers field labs. These are well worth looking into when considering how best to prepare, maintain and improve your soils.

As we have already said, there is still a lot to learn, and the development of tools to understand the complex, dynamic life of soils is something many people are progressing and is generating a lot of scientific interest (consider the current revolution in human health and the gut microbiome as a parallel area of research) . Did you know that we (humans) are only 10% by cell count and in terms of total genes only 1% ‘human’. So how complex are we and how complex is the soil and indeed plant biomics? I am sure a more biological approach is the future of horticultural and agricultural production, whether organic or conventional  as well as the whole future consideration of human health regarding biomes.

We need to think about the soil as a biome

Overall, though our soil steaming trials were by no means scientific, my advice would be not to steam, too much like a soil ‘antibiotic’  instead incorporate the best biological compost you can find (which might take time to produce or source, compost production is a whole science of course), and think about the soil as a biome rather than a physical entity. Of course, there are other fairly well established non-steam techniques for re-balancing soils, such as the use of a crop of caliente mustard incorporated into the soils to help remediate the biome. We have not tried this, though some report fair successes in soils with microbe problems.

You may be aware of a wealth of work going on trying to understand the human gut biome. My own interest in this fascinating new area of research has much in common with soil biomes. Perhaps a whole line of argument and discussion for future articles. I think the important thing is to know how healthy your soils are now, rather than steaming them and effectively creating a blank canvas. After our experiences we would not consider soil steaming again in the future, as it caused as many problems (if not more costly ones) as it may have helped solve.