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Organic farming not a clear winner in the soil microbial biodiversity stakes

Studies of the communities of microbes living in agricultural soil show that the difference between organically and conventionally managed soils is negligible, when compared with the impact of other factors.

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Maintaining stable carbon, nitrogen and pH, can protect the vital soil microbiome structure

Studies of the communities of microbes living in agricultural soil show that the difference between organically and conventionally managed soils is negligible, when compared with the impact of other factors. This is good news, confirming that, by sticking to recommended practices, farmers can maintain a healthy soil microbiome to support productive crops, in either organic or conventional systems.

The research is due to be published in the Society for Applied Microbiology’s Journal of Applied Microbiology.

Researcher Dr Caroline Orr is a molecular ecologist with an interest in greenhouse gas emissions from agriculture. Her work began with looking at how nitrogen is cycled between the atmosphere and the soil.

Dr Orr said “Nitrogen cycling involves quite a few different species of soil bacteria, so we were interested to see whether different agricultural management techniques affect microbial community structure.”

As well as comparing different soils on highly controlled research plots that are used to study specific aspects of organic and conventional farm management, under varied crops, Dr Orr and her colleagues tracked the changes in the make-up of the microbes in the soil over several years.

“We found that any changes in carbon, nitrogen, or pH – how acidic the soil is – had a really significant impact on the make-up of the soil microbe communities, regardless of whether the plot was organic or not. This means that where the management type – organic or conventional – does not affect carbon, nitrogen, or pH, little difference will be observed in the soil microbiome.

“The most dramatic difference in the soil microbiome showed up when we compared samples from different years,” Dr Orr explained.

So, what was different from one year to the next? The answer is potentially weather related, particularly with regard to rainfall.

“The thing about rain is that it can actually change the chemistry of the soil, especially if there is a lot of it. We think this could possibly lead to differences in conditions within the soil, leading to differences in the types of bacteria in the soil, year on year,” Dr Orr concluded.

This research confirms that recommended agricultural management processes, which successfully maintain stable carbon, nitrogen and pH, can protect the vital soil microbiome structure. It also suggests that the comparison of organic and conventional arable soils really needs to take into account more variables than has been done previously.

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