Biofertiliser: A Substance, Often Containing Living Micro-organisms, Claimed To Increase Plant Growth If Added To Plants, Seeds, Soil, Roots Etc. They Are Claimed to Colonise The Rhizosphere & Increase Plant Nutrients & Benefit Plants. But Do They?

There is a UK  biofertiliser certification scheme so it would be easy to assume these products work. But the scheme is very specific and certifies the digestate that comes out of anaerobic digesters and is focused mainly on farmers. But gardeners tend to use the term biofertiliser much wider, to mean any sort of product, with or without living organisms in it, that is claimed to be beneficial to plants. Often the fact they are organic, as opposed to containing living organisms, sways people to use them.

Whilst I’m convinced about the value of organic matter in the garden, I am not yet convinced by all biofertilsers.

What Is a Biofertiliser?

As I say above it’s a product or substance, that often contains living organisms, that will be beneficial to plants. It’s a bit like a probiotic for plants. And when it comes to probiotics some people swear by them and others have reservations. And because they aren’t medicines probiotics aren’t tested as vigorously as medicines.

The same applies to biofertilisers. Testing and verifiable research isn’t common and all sorts of clams are made.

In recent years we’ve come to recognise the value of soil fungi and bacteria. There is no doubt in my mind that they are essential to plants growing in normal soil conditions.

Based on the recognition of the role of soil fungi and bacteria in the rhizosphere we’ve seen several biofertiliser products come onto the market. Products such as RootGrow which is licensed by the RHS.

Do Biofertilisers Work?

If only it were the easy.

21 Fungi Facts that amaze people.
21 Fungi Facts that amaze people.

We know that soil fungi and bacteria are essential to most plants. So their presence will be a huge boost to plant life. What we don’t know is if soils are normally depleted and, if so, whether adding them in the products currently on sale would help.

According to the RHS, who licence Rootgrow, phosphorus “is often in very short supply in natural soils” and that phosphorus can disrupt the establishment of soil fungi and bacteria. They say “Phosphorus-rich fertilisers are widely used in cultivated ground and not only reduce the need for this activity but are thought to actually suppress the mycorrhizas.”

My interpretation of this is that garden soil, that have had fertilisers applied to them, are possibly going to act as a fungal suppressant. If this is true then adding the products is not going to be beneficial.

However, I don’t believe that most soils are naturally phosphorus deficient. They have plenty of phosphorus, BUT it isn’t always in a form that is available to the plant. So whereas there might be a deficiency in terms of plant requirements, there is plenty in the soil, but it is unavailable to plants. Is it unavailable to fungi?

Certainly when I grew commercial crops I never added P. My crops didn’t suffer any P deficiencies, we had above average yields.

This however isn’t the issue. The issue is whether there is enough P in the soil to prevent soil fungi and bacteria establishing. There is no point adding them if they cannot survive. And most gardens have had a lot of phosphorus added over the years, in manures and artificial fertilisers.

So I believe the jury is out on this one. I’ve seen organisations that sell fungal additives say they are needed and that plants grow better when it is used. But to misquote Mandy Rice-Davies, they would say that wouldn’t they.

I’d like to see independent verifiable research before I spend money on these products. It could be that a spade full of soil from another site might be just as effective as the additives. It will contain billions of bacteria and fungi. What’s the difference?

Aren’t Soil Fungi and Bacteria Already Present In The Soil?

The soil is very complex and brimming with a mix of billions of microscopic lifeforms. Many fungal spores are airborne, spread far and wide, and can enter the soil. So may the case not be that if we plant our crops then suitable soil fungi will quickly colonise and increase on numbers? Assuming of course that the phosphorus levels aren’t too high?

And might it be that even if P levels are high that the soil microbes will still increase? Remember the RHS only advise not using the product they license because P levels affect its efficacy. What they say is that it “is thought to actually suppress mycorrhizas.” The word thought seems to be little uncertain. They don’t say it actually does.

It seems to me that there is little firm evidence for, or against, the use of biofertiliser use.

What we do know is that soil fungi and bacteria are beneficial to plants. So adding them as biofertilisers isn’t likely to do any harm. They might even do some good!

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Tag: Biofertiliser & Mycorrhizal Fungi Additives For Gardening & Agriculture

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