In June 2024, Slygen Animal Health Director, Romney Jackson featured alongside Terrafarmer‘s soil health specialist, Tom Tolputt, in an article in Cow Management. You can read the article below, or head to Cow Management and request a free copy.
How to get more from slurry and why reducing plants’ ‘reliance’ on bought-in fertiliser offers more than just cost saving benefits.
Optimising slurry applications – to meet soil, crop and environmental requirements – is complex, but it’s well worth the time and effort. So says Terrafarmer’s soil health specialist Tom Tolputt.
“Slurry presents producers with opportunities to better utilise nutrients and to increase grassland performance. The challenge is that, because success is dependent on management, effective use of slurry requires time and effort, and carefully testing both soil and slurry nutrients levels is also required.”
Sylgen Animal Health’s Romney Jackson adds that soil-borne microbes are also key. “Maximising the value of slurry is about capturing the nutrients as soon as possible and holding them in a microbial form,” he explains. “Not only does this retain nutrients, but also ensures their longer and slower release in a bioavailable form and reduces emissions of harmful gases while minimising many of variable costs associated with managing slurry.”
Soil assessments, slurry analysis and accurate measurements of outputs are important so producers know what their limiting factors are, and whether they’re making optimal management decisions.
Mr Tolputt explains that slurry should analysis start with pH, and nitrogen (N), phosphorus (P) and potassium (K). “These drive grass dry matter yields, and using this pH and nutrient data, alongside detailed soil analysis, allows producers to target applications.
Where, for example, there are good soil indices of organic matter (OM), P and K, more liquid slurries can be used. But where soil OM and key nutrients are low, more solid slurries and farmyard manure (FYM) can be applied. “Having the two – soil and slurry analyses – in tandem, producers can use apply slurry nutrients more efficiently and effectively, and reduce their bought-in fertiliser costs.”
As well as considering the chemical and physical composition of soils, Mr Tolputt says producers should also take their biological make up into account. “Where soils have a good fungal content, there’s an opportunity to use slurries and fertiliser, but where soils are dominated by bacteria, it’s important to add more carbon sources through organic matter, such as FYM.”
In his experience, decision-making on the back of detailed analysis often leads to reductions in bought-in fertiliser use of between 10% and 20%, though savings of 40% are possible.
As well as cost savings, reducing the use of synthetic fertiliser also reduces carbon emissions and improves the long-term health of soils, according to Mr Jackson.
“One challenges associated with using synthetic or bought-in fertiliser is that plants become reliant on it,” he explains. “By providing a source of readily available nutrients, plants no longer need to ‘invest’ in their relationships with soil microbes that would ordinarily scavenge nutrients from the soil in exchange for carbon-rich exudates from plant roots.
“These microbes play a number of other important functions – like transporting water, releasing plant growth hormones and triggering plants’ resistance to pests and pathogens. Plants lose out on these when they rely on bought-in fertiliser as their primary source of nutrients. And, as a result, grass is less resilient to many biotic and abiotic stresses.”
Slurry also poses some challenges for the soil biome. Cow slurry has a biological oxygen demand (BOD) of 10,000 to 20,000mg O2/litre – it consumes a lot of oxygen in its decomposition. “In comparison raw domestic sewage has a BOD of 300-400 mg O2/litre. Heavy slurry applications can effectively suffocate the soil and its biology,” says Mr Tolputt.
Mr Jackson agrees: “If left untreated, anaerobic microbes will dominate and the slurry will kill the natural surface biome. Many of the nutrients are lost and its application in too high a concentration will be detrimental to grassland productivity.”
He adds that this is why the slurry inoculant SlurryForSoil contains ‘facultative anaerobes’. These are bacteria and fungi that are naturally aerobic, but when conditions force them to, can survive anaerobic conditions.”
While Mr Jackson acknowledges that it not always possible due to the weather, a biologically- improved slurry that’s applied at a lower rate, more regularly, feeds the soil bacterial and fungi much more ‘sympathetically’. “And is more likely to result in better nutrient utilisation by plants,” he says.
“Producers avoid giving their cows a massive nutrient load all in one feed because nutrients will either be excreted, or make them sick. It’s exactly the same principle for the soil’s inhabitants. The soil is an advanced biological environment.”
“Similarly, producers avoid meeting cows’ protein requirements by using just one source. A diverse range of sources, found in forage and concentrates, is fed. Yet often with soils all the nitrogen is supplied in one format, like urea or ammonium nitrate. Slurries and manures can be a much more balanced way of delivering these nutrients.”
“I urge producers to visualise their soil as another ruminant on the unit and part of the livestock enterprise. This can really help them to understand how to better manage it,” adds Mr Tolputt.
Minimising costs
When it comes to slurry storage and spreading, new technology is often more efficient. But it’s also a significant investment. Mr Jackson says that producers should take a close look into the grants that are available. “Slurry storage is just one small part of the jigsaw when it comes to effective management, but the Slurry Infrastructure grant could help producers in England who are looking to improve or expand slurry capacity to six months,” he says.
“For other fixed costs, such as existing machinery and infrastructure, it’s important to keep up with maintenance to prevent costly leaks, spills, or equipment failures.”
He adds that variable costs associated with slurry are largely unaccounted for, yet quickly begin to add up.
“This is where slurry inoculants can help. By breaking down slurry-store crusts, they reduce the amount of stirring needed, saving labour and fuel. A more homogenised slurry will also flow through newer application technology more easily, and with fewer blockages, more time and diesel is saved.”
