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United States Department of Agriculture

Agricultural Research Service

Title: Soil Organic Matter Stratification As An Indicator of Soil Quality in Cropland

Author
item Franzluebbers, Alan

Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 3, 2000
Publication Date: July 3, 2000

Interpretive Summary: Simple indicators of how soil responds positively or negatively to land management are needed for assessing soil quality. Stratification of soil organic matter with depth is common in most undisturbed systems (i.e., natural ecosystems of grasslands and forests and managed ecosystems of undisturbed grazinglands and turfgrasses), as well as when degraded land is restored with conservation tillage. This report describes how soil organic matter stratification (i.e., the concentration of a soil property in the top 2 inches compared with the concentration of this same property at a depth of 6-8 inches) could be used to express an improvement in soil quality, irrespective of the climatic environment in which a producer is located. Often, landowners in cooler climates have inherited much more soil organic matter than in warmer climates. Disturbance of soil with tillage causes a uniform mixing of soil organic matter that often leads to poor water infiltration, potentially high erosion, and loss of inherent soil fertility. Conservation tillage systems, on the other hand, minimize soil disturbance and return the soil condition to one mimicking a more natural condition, i.e., stratified in soil organic matter.

Technical Abstract: It is hypothesized that the degree of stratification can be used as an indicator of soil quality, because surface organic matter is essential to erosion control, water infiltration, and conservation of nutrients. 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 between CT and NT was inversely proportional to the standing stock of soil organic C (SOC) to a depth of 15-20 cm. Greater stratification of soil C and N pools with the adoption of conservation tillage under inherently low SOC conditions (i.e., warmer climatic regime or coarse-textured soil) suggests that standing stock of SOC alone is a poor indication of soil quality. Stratification of biologically active soil C and N pools (i.e., soil microbial biomass and activity) tended to be greater than that of SOC under NT, but more similar to that of SOC under CT. High stratification ratios of soil C and N pools could be good indicators of soil quality, independent of soil type and climatic regime, because ratios >2 would be uncommon under degraded conditions.

Last Modified: 7/30/2014
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