Do carbon farming practices build bioavailable nitrogen pools?

Summary

This field study quantified six nitrogen pools across 20 farms participating in a multi-year carbon sequestration experiment, finding that carbon farming practices produced small but statistically significant increases (3–5%) in total and ISNT-N pools, and a moderate effect (18%) on potentially mineralizable N. Clay content and carbon were the dominant predictors of larger N pool sizes, suggesting that soil texture and organic matter are more explanatory than management practice alone. The study highlights a substantial unidentified nitrogen pool (56–82% of total N) that remains tightly bound or undecomposed, indicating limitations in current extraction methods for assessing soil nitrogen availability.

Regional applicability

The findings are directly applicable to UK farming contexts, as soil nitrogen cycling and carbon sequestration are central to UK sustainable agriculture policy and practice. However, the study was conducted in Finnish conditions; UK soils with different clay mineralogy, climate and management history may show different relationships between soil texture, carbon, and nitrogen availability, requiring local validation.

Key measures

Six soil nitrogen pools: total N, ISNT-N (Illinois Soil Nitrogen Test), ACE protein N (autoclave citrate-extracted), water-soluble organic N, potentially mineralizable N, and inorganic N (nitrate and ammonium); soil clay content, carbon content, and C:Clay ratios

Outcomes reported

The study measured six soil nitrogen pools across 20 farms in a multi-year carbon sequestration experiment, quantifying total nitrogen (7700 ± 1500 kg/ha) down to readily available inorganic N (14 ± 8 kg/ha). It evaluated whether carbon farming practices that build soil carbon pools also enhance bioavailable nitrogen pools.

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