What Is Digestate and What Can Farmers Use It For?

How is digestate produced?

Microorganisms consume part of the biodegradable organic material entering the digester and produce biogas. The liquid and solid material remaining is digestate. This means an AD plant shouldn't be considered only as an energy system — it stays closely connected to the farm's wider slurry and nutrient management.

1. 01Slurry or other feedstock
2. 02Anaerobic digester
3. 03Biogas + digestate

Is digestate the same as slurry?

No. Digestate begins with the feedstock entering the digester, but biological digestion changes the material. AFBI notes that the nitrogen in digestate can be more readily available to plants than nitrogen in undigested slurry — agronomically useful, but it also means spreading should be planned carefully, because readily available nitrogen can be lost if applications are poorly timed or managed.

What nutrients are in digestate?

Depending on the original feedstock, digestate may contain nitrogen, phosphorus, potassium, organic matter and other plant nutrients — the exact composition varies. A farmer should avoid treating all digestate as having one universal nutrient analysis; testing the actual material provides a much stronger basis for nutrient planning than generic averages.

Can digestate replace fertiliser?

It may replace some purchased fertiliser, depending on nutrient analysis, crop requirements, soil nutrient status, timing, application method and available land. A Biolectric case study at Rosconnor Dairies, a roughly 680-700 cow farm running a 44kW slurry-fed digester, reports a substantial reduction in the farm's electricity costs after installing its system and returning digestate to the land — a real example, but an individual farm's result rather than a universal saving figure.

Can digestate be spread on farmland?

Yes, subject to the rules applying to the material and land. For England, the Environment Agency states that where the only waste feedstock under the T24 exemption is farmyard manure or slurry, it accepts that the resulting digestate can be spread as fertiliser or soil conditioner without being regulated as waste. Other requirements, including good agricultural practice and rules applying in nitrate vulnerable zones, still apply. Using other feedstocks can change the regulatory position.

Does digestate still need storage?

Yes. AD doesn't remove the requirement to manage material between digestion and land application — digestate volume, storage capacity, seasonal spreading restrictions, rainfall and application windows all still need planning. This is why digestate storage should be considered during the initial AD layout, not after the plant has been installed.