Co-compost Nitrate Capture
Citation: Kammann CI, Schmidt H-P, Messerschmidt N, Linsel S, Steffens D, Müller C, Koyro H-W, Conte P, Joseph S (2015). Plant growth improvement mediated by nitrate capture in co-composted biochar. Scientific Reports 5: 11080. https://doi.org/10.1038/srep11080 (open access)
What it is: A greenhouse pot study with quinoa that compares untreated biochar with the same biochar after co-composting. It’s the vault’s clearest controlled contrast between “hungry” raw char and charged char.
Key figures
| Figure | Value | Where | Check |
|---|---|---|---|
| Design | Full-factorial pot study, Chenopodium quinoa, sandy nutrient-poor soil; biochar at 2% (w/w) | Abstract and methods | ✓ full text |
| Co-composted biochar | Biomass 139–305% of the control, depending on nutrient supply; the relative gain was largest at the lowest supply | Results, fig. 2 | ✓ full text |
| Untreated biochar | Biomass cut to 60% of the control (significant at the low-N level, not at the high-N level) | Abstract; results | ✓ full text |
| Total N in biochar particles | 1.04% co-composted vs 0.43% untreated (+6.2 g N kg⁻¹) | Results | ✓ full text |
| Nitrate held in co-composted particles | ~2.1–2.2 g NO₃⁻-N kg⁻¹ by electro-ultrafiltration; 5.2 g kg⁻¹ by sequential washing (electro-ultrafiltration found only ~40% of the total) | Results, figs. 3–4 | ✓ full text |
| Mature compost, for comparison | 0.98 g nitrate-N kg⁻¹ | Discussion | ✓ full text |
| Other nutrients | K loading 1.6-fold; Ca +63% (3,735 → 6,077 mg kg⁻¹); Mg low and slightly reduced | Results | ✓ full text |
| Fate of captured nitrate | Largely protected from leaching, partly plant-available, didn’t stimulate N₂O | Abstract | ✓ full text |
Use with care
- Correction to earlier vault notes: “+305%” overstates the result. Co-composted biochar biomass reached up to 305% of the control, about 3× (roughly +205%). Untreated biochar reached 60% of the control.
- The vault’s “~3–5 g NO₃⁻-N kg⁻¹” range isn’t this paper’s number. It reports ~2.1–2.2 g kg⁻¹ by the standard method and ~5.2 g kg⁻¹ by exhaustive washing.
- A pot study in one soil at 2% w/w: a demonstration of mechanism, not a field yield estimate.
Related: Biochar Inoculation for Fertilizer · Biochar Nutrients and Fertilizer Chemistry · reviews co-composted biochar soil effects · Key Sources