2 November 2026
Digestate has long been valued as a replacement for bagged fertiliser. It’s packed with nutrients, it recycles what would otherwise be waste, and it helps cut input costs.
But new research suggests it’s doing a lot more beneath the surface than simply feeding the crop.
What did the study look at?
Researchers in Shanxi Province, China, ran a field trial on dryland maize between 2021 and 2023. Their findings were published in the journal Carbon Research in October 2026.
They compared six approaches. One plot received no top-up fertiliser at all, one received standard chemical fertiliser, and four replaced 25%, 50%, 75% or 100% of the chemical nitrogen with liquid digestate, applied through drip irrigation.
The team then tracked something called dissolved organic carbon. This is the most active, mobile part of the carbon in soil. It feeds soil microbes, moves through the soil profile and plays a big part in whether carbon is used up or locked away.
What did they find?
The results show that digestate changes how carbon behaves in the soil, and that timing really matters.
- An early carbon boost. Around tasselling, soils treated with digestate held almost 17% more dissolved organic carbon than those given chemical fertiliser. The more digestate used, the bigger the increase.
- Then it gets used. By the time the crop reached the milk stage, that picture had flipped, with around 20% less dissolved carbon than the chemical plots. The researchers believe roots and soil microbes were busy using that fresh carbon during the crop’s hungriest growth period.
- A shift towards more stable carbon. The carbon left behind under digestate showed signs of being more humified and chemically stable, the kind of carbon that’s more likely to stay in the soil.
- Carbon moves down the profile. Later in the season, digestate appeared to help move carbon from the surface into deeper soil layers.
Interestingly, the biggest factors shaping soil carbon were soil depth and crop growth stage, followed by the fertiliser treatment itself. In other words, digestate works with the soil and the crop, not in isolation.
Why does this matter for farmers?
The key message is that digestate isn’t just a nitrogen substitute. It’s also a tool for managing how carbon cycles through your soil.
That means it’s worth thinking about:
- When you apply it, so the boost in soil carbon lines up with when the crop and soil life need it most
- How much you replace, as higher digestate ratios produced bigger changes
- Your soil profile, because different layers hold and move carbon in different ways
With fertiliser prices still high and growing pressure to improve soil health, that’s a valuable extra benefit from a resource many farms already have on hand.
A note on the research
This trial was carried out on dryland maize in northern China, so conditions are very different from most UK farms. The authors are also clear that more long-term work is needed to confirm exactly how the carbon is being transformed.
Even so, it adds to a growing body of evidence that digestate has a real role to play in building healthier, more resilient soils.
Want to know more?
If you’d like to find out how digestate could work on your land, or how anaerobic digestion could fit into your farm business, get in touch with the Adapt Biogas team. We’re always happy to talk it through.
Sources
Liang, X. et al. (2026). Effects of biogas slurry topdressing on soil dissolved organic carbon: a field experiment. Carbon Research, 5, Article 49. doi.org/10.1007/s44246-026-00295-z
News summary: Biogas slurry reshapes soil carbon dynamics in dryland maize fields, Bioengineer.org, 29 October 2026
