Biochar Boosts Soil Carbon Near the Surface, But Lessens It Deeper Down

Jun 08, 2026

Biochar has been widely praised as a great tool for improving soil health and trapping greenhouse gases in farmland. However, a 12-year field study published in the journal Biochar shows that its effects are more complicated than scientists previously thought.

The research reveals that while biochar does an excellent job of locking away stable carbon in the surface layer of fields, it actually has the opposite effect deeper underground. This means that future farming strategies must look closely at soil depth to truly understand biochar’s environmental benefits.

The secret to stable soil carbon: Dead microbes

To understand how biochar works, it helps to look at microbial necromass carbon—which is simply the remains of dead bacteria and fungi. While it might sound unappealing, this dead material is actually one of nature’s best building blocks for trapping carbon in the ground for long periods.

As microscopic organisms grow and die, their leftovers become trapped and protected in the dirt. Because this material resists breaking down, scientists use it as a key indicator to measure how much carbon a piece of land is successfully storing long-term.

Topsoil vs. subsoil

The researchers tested a single application of wheat-straw biochar across two different types of cropland in China. When they returned to test the dirt 12 years later, they found two completely different stories depending on how deep they dug:

The topsoil (0 to 20 cm deep):
- Near the surface, biochar worked wonders. It increased the amount of stable carbon from dead microbes by 23% in naturally rich soil, and by a massive 39% in nutrient-poor soil. The change was mostly driven by fungi. The biochar made the topsoil healthier, giving the microbes better nutrients so they could thrive, multiply, and leave behind plenty of carbon when they died.
The subsoil (20 to 40 cm deep):
- Deeper down, the amount of stable carbon dropped by roughly 18% to 30%. Because the biochar stayed near the surface, the deeper soil suffered from a lack of nitrogen. This stressed the underground microbes, forcing them to survive by eating and breaking down the existing carbon stores rather than building up new ones.

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Video: Dicamba Returns for Georgia Farmers: What the New EPA Ruling Means for Cotton Growers

After being unavailable in 2024 due to registration issues, dicamba products are returning for Georgia farmers this growing season — but under strict new conditions.

In this report from Tifton, Extension Weed Specialist Stanley Culpepper explains the updated EPA ruling, including new application limits, mandatory training requirements, and the need for a restricted use pesticide license. Among the key changes: a cap of two ½-pound applications per year and the required use of an approved volatility reduction agent with every application.

For Georgia cotton producers, the ruling is significant. According to Taylor Sills with the Georgia Cotton Commission, the vast majority of cotton planted in the state carries the dicamba-tolerant trait — meaning farmers had been paying for technology they couldn’t use.

While environmental groups have expressed concerns over spray drift, Georgia growers have reduced off-target pesticide movement by more than 91% over the past decade. Still, this two-year registration period will come with increased scrutiny, making stewardship and compliance more important than ever.