Produce Your Own Slurry Additive: What Lactic Acid Bacteria Achieve in Slurry Storage

In autumn, our brewing system is in continuous operation: 500 liters of compost tea for the neighboring farm, the next batch for our green manures the following week. And when the fields are resting, the machine still doesn’t stop working. In winter, we use it to produce EM ferments – as an additive for slurry.

Why Slurry Benefits from an Additive

Slurry is the farm fertilizer you already have. Nevertheless, you lose a portion of it before it even reaches the field: nitrogen escapes into the air or migrates into the groundwater.

In my opinion, we are starting at the wrong end when it comes to fertilization. We discuss purchased units and watch nitrogen disappear from storage. Anyone who has experienced the price fluctuations of recent years knows how expensive this dependency is.

Ferment or Compost Tea: The Difference Lies in Oxygen

Compost tea is aerated. The oxygen content must remain in the aerobic range throughout the entire brewing process – above 6 mg/l of dissolved oxygen. This is precisely what makes it a foliar stimulant.

A ferment works in reverse: it operates under anaerobic conditions. Lactic acid bacteria and their companions multiply anaerobically and acidify the batch.

This is crucial for slurry. A slurry storage is an anaerobic environment. Aerobic microorganisms from compost tea have no place there. Anaerobic ferments, on the other hand, are at home in this environment.

What Lactic Acid Bacteria Do in Slurry

Four things happen, and they are interconnected.

First, they consume the sugar. Slurry contains carbohydrate residues from feed. Lactic acid bacteria break them down into lactic acid. This deprives putrefactive bacteria of their food source – preventing them from thriving.

Second, the pH drops. The lactic acid acidifies the storage. This is not an end in itself, but the lever for everything else.

Third, nitrogen remains where it is. The ammonium nitrogen in slurry is in equilibrium with gaseous ammonia. How this equilibrium stands is determined by the pH value.

At pH 7.5 – typical for untreated cattle slurry – just under one percent of ammonium nitrogen is present as volatile ammonia. At pH 6.5, it is only one-tenth of that. Each pH level down means ten times less of the nitrogen that escapes from your storage. And pH 6.5 is precisely the range we achieve in practice with an EM ferment.

Fourth, the bacteria incorporate nitrogen into themselves. What is contained within a bacterial cell cannot off-gas. The nitrogen is biologically bound and is only released back into the soil – where you want it.

You will see the result in storage before you measure it. The slurry becomes more fluid, fewer crusts and floating layers form, and the putrefactive odor decreases. In the field, it is more plant and soil compatible because it contains fewer corrosive substances: it infiltrates faster and sticks less to the leaves.

Who Gives Up in an Acidic Environment

A slurry storage is also an intermediate storage for pathogens. Streptococci and Klebsiella come from the barn into the slurry as mastitis pathogens, Clostridia and Enterococci via feces and bedding – and return to the cow via feed and soil.

Look at where these germs have their optimum: at pH 7 and above. That’s exactly where untreated slurry is. So, we store it under conditions that suit them perfectly.

With an EM ferment, we reach approximately pH 6.5 in practice. This does not kill anyone. But it removes the optimal range for each of these germs – while the lactic acid bacteria are still fully active there because their optimum is lower.

In addition, there is a second lever that is often underestimated: the lactic acid bacteria consume the sugars that the others would live on. The pH is what is visible, nutrient competition is what is effective.

Herbs from Your Own Flower Strip

Our perennial flower strip is not just an insect habitat. Various herbs grow there, which we use as a base for our herb ferments.

The process is simple: cut herbs, put them in the net bag, dip the bag into the batch. The plant substances transfer into the water, and the microorganisms multiply on them.

The advantage over a purchased product is obvious. You know what’s in it, you pay almost nothing for it, and the composition suits your location. No canister, no logistics, no waiting time.

Reto Diener from Früchtehof Morgestärn does the same on his farm: he propagates lactic acid bacteria directly on the farm, with his own herbs – in the same EdaLife V500 that he uses to brew compost tea for his cherries.

One Machine, Three Processes

Aerobically propagate or anaerobically ferment – the EdaLife can do both. The same system we use to produce compost tea in summer and compost extract in autumn makes the ferments in winter.

One point is important here: ferments need warmth. For EM, room temperature in a cold barn is not enough. That’s why the brewing systems come with integrated heating, control, and insulation – this equipment is necessary for ferment production, but not for compost tea in summer.

This makes the machine profitable for significantly more months. Compost tea in spring and summer, compost extract in autumn, ferments in winter.

Make Success Visible – and Quantify It

A vitalized slurry storage is not a matter of faith. You can measure whether the environment has actually shifted.

We offer two things for this: a slurry environment analysis and microbial analyses of slurry quality. This shows you the state of your storage and whether the additive is achieving what it should. We work with various laboratories and select the analysis that suits your question.

Then there’s the plant side. We use a leaf sap analysis two to three weeks after slurry application to check if nitrogen incorporation is working – and which trace elements are needed at your location for the plant to efficiently incorporate nitrogen into proteins and achieve high photosynthetic performance.

This is more interconnected than many think. A high nitrate content in feed means a lot of non-protein nitrogen, which ends up as urea in milk. Even worse: nitrate can be converted into nitrite in the cow, which binds oxygen in the blood – leading to abortions. Less nitrate means healthier animals, better milk, and better slurry biology, because the initial quality of the slurry is decided in the feed.

The cycle thus closes: feed, animal, slurry, soil, plant. The slurry additive is one link in this chain – not the entire chain.