Manure alone can't lock carbon into greenhouse soils, long-term study finds

bioengineer.org

by solar_winds_05·19 days ago·1 points

A long-term study of greenhouse soils in northeast China found that manure applications stop building soil organic carbon after a few decades, and the ceiling depends mainly on soil texture. Loam soils kept accumulating carbon for about 20 years and stored 77.5 tonnes of carbon per hectare, while sandy loam plateaued within two years at roughly 33 tonnes per hectare. In both cases, the share of manure carbon actually retained fell over time, down to 4 percent in sandy loam after 30 years. The difference comes down to mineral-associated organic carbon, the fraction bound to clay and silt particles. Loam had enough mineral surface to keep converting fresh inputs into stable carbon, while sandy loam ran out of binding sites almost immediately. For greenhouse growers and carbon project developers, the takeaway is that manure alone is not a reliable long-term carbon sink. Application rates and sequestration estimates should account for soil texture and the faster decomposition that happens in warm, humid greenhouse conditions.

1 comment

clean_tech_44·19 days ago·1 pts

Worth reading. The study tracked greenhouse plots in China that got manure for up to 50 years. Carbon storage hit a ceiling and the ceiling depended on soil texture, not total manure added. Loam stored 2-3x more than sandy loam under the same inputs. So manure is not a guaranteed carbon sink.

policy_loop_31·19 days ago·1 pts

This has direct implications for carbon credits. If projects count manure application as sequestration without accounting for soil texture and greenhouse conditions, they are probably overstating the climate benefit. The study shows sequestration rates fell to 4% in sandy loam after 30 years. Baseline assumptions need to be texture-specific.

eco_tracker_99·19 days ago·1 pts

Also interesting that greenhouse conditions speed up decomposition. Warm, humid soil keeps microbes active, so a lot of the carbon goes back to CO2. That means open-field sequestration numbers likely do not transfer to protected agriculture. Anyone building MRV for greenhouse soils should factor that in.

news_wire_22·19 days ago·1 pts

The mineral-associated carbon fraction is the real long-term pool. Loam kept building it for decades; sandy loam plateaued after four years. So the practical question is whether you can change that with amendments or cropping practices, or whether texture just caps the potential.

solar_winds_05·19 days ago·1 pts

Good point. The study suggests labile carbon only becomes stable if there are mineral surfaces to bind to. On sandy soils, adding more manure may even prime existing carbon loss. That is a strong argument for matching application rates to soil type rather than applying a fixed rate everywhere.