Evidence for Carbon Saturation in a Highly Structured and Organic-Matter-Rich Soil

• Published in: Soil Science Society of America journal Vol. 74; no. 1; pp. 130 - 138
• Main Authors: Chung, Haegeun, Ngo, Kathie J, Plante, Alain, Six, Johan
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.01.2010; Soil Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; Alberta; Biological and medical sciences; Carbon; carbon saturation capacity; carbon sequestration; Chemical, physicochemical, biochemical and biological properties; crop residues; Earth sciences; Earth, ocean, space; ecosystems; Exact sciences and technology; fields; Fossil fuels; Fundamental and applied biological sciences. Psychology; grain crops; Grasslands; mineral soils; nitrogen fertilizers; Organic matter; particle size; particle size distribution; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Retention; Saturation; Soil aggregates; Soil fertility; soil management; soil organic carbon; soil organic matter; Soil science; Soil types; Soils; Surficial geology; temperate soils; Tillage; Alberta; Non metal; saturation; carbon; organic materials; Soil science; Group IVA element; Earth science; soils
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2009.0097

Recent studies suggest that mineral soils of temperate ecosystems have a limit in C sequestration capacity, and we reasoned that C saturation will be most evident in soils that are already rich in soil organic C (SOC) and have been exposed to a broad range of C inputs. Therefore, we determined soil C saturation in an agricultural experiment located in Ellerslie, AB, Canada, where organic-matter-rich soils have been cropped to cereal grain for 25 yr. In this experiment, the soils were subject to a broad range of soil C inputs due to a combination of straw retention, tillage, and N fertilization treatments. We determined if C saturation is occurring in soil size fractions that are functionally different. Soils were highly aggregated, with >85% of the soils consisting of macroaggregates. Straw retention, tillage, and N fertilization had no significant effect on the SOC concentration of most soil fractions. Soil organic C concentration of whole soil and soil aggregates isolated from whole soil did not increase with greater soil C inputs. Most of the soil fractions within the large or small macroaggregates did not sequester additional SOC in response to higher soil C inputs. Conversely, SOC concentration in experimental plot soils was significantly lower than that of adjacent grassland soils, which suggests that the maximum C sequestration level for a specific soil type depends on the management practices used. We conclude that C sequestration is governed by C saturation in this highly structured and high-C soil. Our study suggests that soils of temperate ecosystems that are closer to their C saturation capacity may store additional C less effectively than soils that are further away from their saturation capacity.