Soil biology promoters: Promising but unproven?

Improving soils by adding soil biology promoters to reap greater profits sounds ideal. But does it work?

It’s messy to make, and your standard sprayer may need modifying to apply it, but compost tea is the best way to improve soil condition, says Joel Williams of Laverstoke Park Farm, an organic 1060ha commercial and research unit in Hampshire.

Compost tea is basically a soil drench containing a blend of bacteria and fungi which used to occur naturally in soils but have become depleted in intensive systems. It’s relatively low cost to produce on the farm, and you need very little, so it’s great value. “

You may already use manure or sewage sludge, but the former is high in nitrogen so it encourages mostly bacteria while the latter has a fairly low microbial content. Fungi are lacking in most arable systems, warns Mr Williams.

“We offer a soil analysis service called the Soil Foodweb, which is like a food chain as opposed to NPK analysis. From research and data modelling, we know roughly how many species of the four main groups of micro-organisms – bacteria, fungi, nematodes and protozoa – we need to find in soils to get a balanced soil environment, so we know when something is lacking. Many UK soils are low in beneficial species.”

Why do we need them? A rich soil biology can allow reductions in nitrogen fertiliser inputs while maintaining yields, increase water retention and store carbon. It may even aid stubble digestion and disease control, he suggests.

There are many products on the market claiming to enhance the natural soil environment and thus boost crop production in some way or another. Some stimulate chlorophyll and root production, others mobilise relatively insoluble nutrients. Mr Williams believes they may have a place but fears some are too specific and could actually create an imbalance.

“Buying in a product doesn’t guarantee you a result because it could contain less than 20 species. That could be effective if there is just one problem to put right, but you’ve a better chance using compost tea that typically contains more than 1000 species,” he says.

If you’re not into making your own, you can buy a ready-made microbial blend and just mix it with water in the spray tank. Laverstoke produces up to 30,000t a year of formulated Mycolife, for farm use and sale.

Research

Lack of consistency is precisely the reason Colin Lloyd isn’t prepared to recommend soil biology promoters yet.

Masstock‘s research development manager, Throws Farm, supports the drive to create a sustainable soil environment and believes that one day he may well be advising growers to apply compost tea or “friendly bugs”. But what works on one farm or in one part of the world may not work elsewhere, he warns.

“We’ve tested nitrogen-fixing bacteria that are used in Brazilian sugar cane to great effect, but failed over five seasons to get statistically significant data here. We need randomised, replicated trials results to confirm that whatever a product claims to do is applicable to the UK, and indeed cost-effective here.”

Masstock is involved in the RHIBAC project, a European initiative to show whether potentially huge savings in N fertiliser could be realised using strains of Bacillus subtilis sourced from Chile and Turkey. In the first year of trials at Throws Farm, a 7-8% increase in yield was achieved using 50-100kg/ha less ammonium nitrate with the addition of the rhizobacteria.

Mr Lloyd is hopeful that the second years’ results mirror the first. He is happy to hear that individual farmers find success with specific products, and is enthusiastic about finding new approaches to help growers comply with the water framework directive.

“I expect we’ll soon reach a level of understanding that will see me saying have a go with this or that bug. But not before research organisations have proved a product could feasibly be characterised, put in a bottle, and still offer a consistent, cost-effective response.”

Impractical

Mark Middleton’s fascination with “biological agriculture” took him to Australia to learn about this new approach to soil management.

“It’s basically a US term for organic farming, though it’s more like integrated crop production with a few bells on. We spent a week learning how to enrich soils with natural biological promoters and compost tea.”

A conventional arable grower, Mr Middleton was starting to question his total reliance on pesticides and synthetic fertilisers at White Lodge Farm. The course gave him the confidence to experiment with two products he’d never tried before on the 560ha heavy land farm in Northamptonshire.

He set up a trial in an 8ha field of early March-sown Xi19, and in late May applied TwinN, a freeze-dried alternative to traditional nitrogen fertiliser containing N-fixing microbes, and Biomex SA, a liquid containing rhizobacteria to enhance rooting and protect plants from disease attack.

“The latter was messy to mix, but the products went into the sprayer together in non-chlorinated water. They may not have had the best start since the TwinN label states it requires moisture to work effectively, and that was sadly lacking. Still, we had omitted 60 kg/ha of nitrogen fertiliser on the back of it.”

In a strip left untreated, the crop didn’t look any different to the rest. But the whole field was amazingly free from disease. Was that just a result of this relatively dry season? Will there be a yield benefit? The crop wasn’t ready to harvest at the usual time so he couldn’t say.

With hindsight, Mr Middleton regrets being so ambitious with his trial. “We tried too much all at once, so we won’t be able to distinguish the effects of each action. We’d never before sown Xi19 that late, nor omitted Atlantis and fungicides, nor cut back so hard on nitrogen fertiliser.”

Next season, he will omit Atlantis again, and cut back on fungicides but keep up N inputs. He will consider dabbling in soil biology promoters like TwinN again if independent UK trials can show a consistent benefit.

“Products such as TwinN and Microlife compost tea have a place in organic systems where growers need all the help they can get, but I’m not convinced yet that they can help the conventional grower.”

For further information on Mr Middleton’s trial read his blog at biologicalfarmuk.blogspot.com/