Soil organic matter stratification ratio as an indicator of soil quality

• Published in: Soil & tillage research 2002-07, Vol.66 (2), p.95-106
• Main Author: Franzluebbers, A.J
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Conservation tillage; Cropping intensity; Fundamental and applied biological sciences. Psychology; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Potential nitrogen mineralization; Soil microbial biomass; Soil organic carbon; Soil quality; Soil science
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/S0167-1987(02)00018-1

Soil quality is a concept based on the premise that management can deteriorate, stabilize, or improve soil ecosystem functions. It is hypothesized that the degree of stratification of soil organic C and N pools with soil depth, expressed as a ratio, could indicate soil quality or soil ecosystem functioning, because surface organic matter is essential to erosion control, water infiltration, and conservation of nutrients. Stratification ratios allow a wide diversity of soils to be compared on the same assessment scale because of an internal normalization procedure that accounts for inherent soil differences. Stratification ratios of soil organic C were 1.1, 1.2 and 1.9 under conventional tillage (CT) and 3.4, 2.0 and 2.1 under no tillage (NT) in Georgia, Texas, and Alberta/British Columbia, respectively. The difference in stratification ratio between conventional and NT within an environment was inversely proportional to the standing stock of soil organic C to a depth of 15–20 cm across environments. Greater stratification of soil C and N pools with the adoption of conservation tillage under inherently low soil organic matter conditions (i.e., warmer climatic regime or coarse-textured soil) suggests that standing stock of soil organic matter alone is a poor indication of soil quality. Stratification of biologically active soil C and N pools (i.e., soil microbial biomass and potential activity) were equally or more sensitive to tillage, cropping intensity, and soil textural variables than stratification of total C and N. High stratification ratios of soil C and N pools could be good indicators of dynamic soil quality, independent of soil type and climatic regime, because ratios >2 would be uncommon under degraded conditions.