Researchers at Duchy College found that SlurryForSoil™ – a complex blend of microorganisms and enzymes – not only reduces the need for synthetic fertilisers, lowers emissions and increases grass yields, but suggest it benefits soil health and can contribute to reducing carbon emissions too.
The in-depth study, commissioned by Europe’s leading mozzarella manufacturer, Glanbia Cheese, explored the nutrient value of treated and untreated slurries, as well as the yield and nutritional value of resulting silage.
Duchy College trial – enhanced nutritional value of slurry and silage
Duchy College conducted the research on its Future Farm, a facility that was created through the Agri-tech Cornwall Project with the support of the European Regional Development Fund, UK Government, Cornwall Council, the Council for the Isles of Scilly and the Centre for Innovation Excellence in Livestock.
“With facilities that enable the splitting of our dairy herd into groups and the separation of their slurries, we’re perhaps uniquely placed to do this type of research,” explains Paul.
“In this trial, we had 67 cows in each group. Keeping everything else equal – housing, feed etc – we applied the slurry inoculant, SlurryFroSoil, to one group’s dedicated slurry lagoon, leaving the other untreated. We sent samples to NRM labs for nutrient analysis after the first and second dose. We then applied the treated and untreated slurries to a temporary grass ley, and had the nutritional quality of the resulting silage analysed.”
Results showed an increase in the retention of key nutrients (Table 1) as well as magnesium, copper, zinc and calcium.
Table 1 – The difference (%) in retained nutrients between treated and untreated slurry
|Total Phosphorus (P)
|Total Potassium (K)
|Total Sulphur (S)
Analysis of the resulting forage, showed yield increased by an average of 17.8% across all four cuts with the application of the treated slurry, with some cuts seeing more than a 30% yield increase.
“Quality measures levels were also higher in the silage which had received the treated slurry,” observes Paul. “Across all four cuts, the mean increase in protein was 5.78% and plant nitrogen levels are on average 39% higher in treated silages than untreated.
“These results were consistent with the on-farm trials which showed an average increase in protein levels of 27% in first cut silage,” he notes.
According to Paul, these increases far outweigh the potential benefits of the nitrogen retained in the slurry and potentially shows the microbes are playing a broader role both within the soil and the plants.
“Metabolisable Energy (ME) and sugars were also higher, although harvest timings were shown to have a substantial impact.”
Neutral Detergent Fibre (NDF) across almost all cuts was also substantially down and the same trend was seen in further analyses on the trial farms, a finding with potentially important implications according to Paul: “This suggests a less fibrous and stem-heavy forage and instead a less fibrous leafy silage. This combination should provide a boost to yields whilst lowering methane emissions although further testing would be needed for verification.”
Table 2 – The mean difference (%) in key silage factors between silages fertilised with treated slurries and untreated slurries across 4 silage cuts
|Key factors (Dry Weights)
|Mean difference (% change)
|Dry Matter (g/kg)
|Crude Protein (g/kg)
|Nitrate Nitrogen %
|Buffering Capacity meq/kg
|Fresh wt. Yield (T/Ha)
|DM Yield (T/Ha)
Different roles of fungi and bacteria
The benefits seen both in the Duchy College trial are a result of the different microorganisms and enzymes in the slurry inoculant.
“It’s in this second generation produce, we’ve really focused on fungi and bacteria which have soil and plant health benefits,” explains Romney Jackson, Director of Sylgen Animal Health
“Initially, slurry isn’t an ideal medium for feeding the bacteria and fungi. It needs breaking down and we include enzymes to kick start that process. However, once the microbes start metabolising the slurry, they produce their own enzymes. The fungi are particularly useful in producing lignases to break down the more fibrous material, for example.”
“Traditionally, slurry additives contain just a couple of different species, often it’s just one – Bacillus subtilis – which is a really useful bacteria but alone, is limited in its range of beneficial effects.”
SlurryForSoil™ contains 18 species of bacteria and fungi, as well as four enzymes.
“They are all either plant growth promoting rhizobacteria or fungi,” he continues.
“They’ve all been scientifically proven to mobilise nutrients and micronutrients – though they have their specialities. Many have also been found to control pathogens and diseases, predominantly through the stimulation of the plant hosts’ own defence mechanisms, and some control pests like nematodes, molluscs and insects. The fungi, in particular, break down certain pesticides and organophosphates which can indirectly hamper grass growth.”
Environmental benefits for farmers and the supply-chain
“Historically, we were focused on the immediate on-farm benefits of slurry additives – the easier handling of slurry, for example – but they’ve potential to make a far larger contribution to meeting our environmental objectives,” says Romney.
“These initial trials indicate that they are improving soil health. Just from the retention of nitrogen and the offsetting of synthetic fertiliser use in these trials, we estimate that the adoption of technology like SlurryForSoil™ could reduce carbon emissions by nearly 19,000 tonnes across Glanbia’s supply chain.”
It’s this potential for wider environmental benefits that caught Glanbia Cheese’s attention.
“While there was a product that goes into the tank, what really intrigued me was that it is really about helping farmers feed their soils,” says the company’s Sustainability Manager, Ben Williams. “I’m very comfortable with the idea that a slurry additive retains nitrogen – it was proven years ago, but my real interest was in its value in regenerative practices.”
Manufacturing 90% of the commercial grade mozzarella in Europe, Glanbia Cheese buys a significant proportion of the milk produced in Northern Ireland and Wales.
“We’ve a moral and commercial obligation to our customers and suppliers,” he explains. “Increasingly, customers have their own environmental targets to meet, and it’s essential we protect both ours, and our farmers’, right to supply. Part of that is demonstrating we’re making a concerted effort to protect the broader environment – not just lowering emissions but enriching the biodiversity within soils, building organic matter, sequestering carbon and offsetting the use of synthetic fertilisers.”
Ben also likes the approach taken by Sylgen Animal Health: “They wanted robust quantitative data on the downstream impacts on nutrient availability, soil health and grass yield – that was the point of the Duchy research and it has helped build trust in the formulation. The other part, and perhaps more importantly, was the qualitative data. How did it work on farm? What did the farmers feel about using the product? Would they want to use it? So far, the answers to those questions, has been ‘yes’.”
Find out what Carmarthenshire dairy producer, Anthony Gibby thought about his on-farm trial, click here.