The Soil Management Assessment Framework : A Quantitative Soil Quality Evaluation Method

bold et al., 1998). Because improper management can lead to deleterious changes in soil function, a need for Erosion rates and annual soil loss tolerance (T) values in evaluatools and methods to assess and monitor SQ was recogtions of soil management practices have served as focal points for soil quality (SQ) research and assessment programs for decades. Our obnized (e.g., Doran and Jones, 1996). jective is to enhance and extend current soil assessment efforts by Although some misconceptions exist, the recent empresenting a framework for assessing the impact of soil management phasis on soil function (and dynamic soil quality) is not practices on soil function. The tool consists of three steps: indicator seintended to detract from the importance of soil taxonlection, indicator interpretation, and integration into an index. The omy, where inherent soil properties, resulting from the tool’s framework design allows researchers to continually update and five soil forming factors (Jenny, 1941), and land use suitrefine the interpretations for many soils, climates, and land use pracability are emphasized. Soil quality uses taxonomy as a tices. The tool was demonstrated using data from case studies in Georfoundation (Karlen et al., 2003). The specific definition gia, Iowa, California, and the Pacific Northwest (WA, ID, OR). Using of soil quality for a particular soil is dependent on its an expert system of decision rules as an indicator selection step sucinherent capabilities, the intended land use, and the mancessfully identified indicators for the minimum data set (MDS) in the case study data sets. In the indicator interpretation step, observed inagement goals. For instance, optimum levels of organic dicator data were transformed into unitless scores based on site-spematter (and other soil properties) will differ depending cific algorithmic relationships to soil function. The scored data resulted on the condition under which the soils formed, leading in scientifically defensible and statistically different treatment means to variation in potential functioning. The use-dependence in the four case studies. The efficacy of the indicator interpretation step of the SQ concept can be illustrated simply: the funcwas evaluated with stepwise regressions using scored and observed intions, properties, and processes necessary to hold up a dicators as independent variables and endpoint data as iterative dephysical structure are not the same as those needed to pendent variables. Scored indicators usually had coefficients of detergrow a crop. More subtly, the soil qualities (functions or mination (R2) that were similar or greater than those of the observed properties) critical for environmentally benign land apindicator values. In some cases, the R2 values for indicators and endplication of animal waste are not identical to those for point regressions were higher when examined for individual treatments rather than the entire data set. This study demonstrates signifimaximized production—even within the same field or cant progress toward development of a SQ assessment framework for under the same crop. adaptive soil resource management or monitoring that is transferable As with defining SQ, assessing SQ also requires conto a variety of climates, soil types, and soil management systems. sideration of taxonomy, land use and management goals. Appropriate SQ assessment measures a soil’s changes in function in response to management, within the conH rates of soil erosion, losses of organic matter, text of what the soil is being asked to do, its inherent propreductions in fertility and productivity, chemical erties, and environmental influences, such a temperature and heavy metal contamination, and degradation of air and precipitation. The target or optimum soil quality is and water quality have sparked interest in the concept of not one standard for the USA or the world; instead, it soil quality (SQ) and its assessment (Larson and Pierce, is a series of thresholds defined by limiting factors and 1991; National Research Council, 1993; Doran and Paruser needs. kin, 1994; Karlen et al., 2001). Although it has a variety Indicators of SQ can be defined loosely as those soil of (sometimes conflicting) definitions in the current litproperties and processes that have greatest sensitivity erature, SQ is most often defined as “the capacity of the to changes in soil function. Doran and Parkin (1996) soil to function” (Karlen et al., 1997). Some important emphasized that SQ indicators should correlate well with soil functions (or ecosystem services) include: water flow ecosystem processes, integrate soil properties and proand retention, solute transport and retention, physical cesses, be accessible to many users, sensitive to managestability and support; retention and cycling of nutrients; ment and climate, and, whenever possible, be components buffering and filtering of potentially toxic materials; and of existing databases. Indicator groups or MDSs, used maintenance of biodiversity and habitat (Daily et al., to indirectly measure soil function, must be sufficiently 1997). The term dynamic SQ refers to the effects of hudiverse to represent the chemical, biological, and physiman use and management on these soil functions (Seycal properties and processes of complex systems (Gregorich et al., 1994; Doran and Parkin, 1996; Snakin et al., S.S. Andrews, USDA-NRCS, Soil Quality Institute, 2150 Pammel Dr., Ames, IA 50011-4420; D.L. Karlen and C.A. Cambardella, USDAAbbreviations: AGG, water-stable aggregates; AWC, plant-available ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011water-holding capacity; Db, bulk density; EC, electrical conductivity; 4420. Received 20 Nov. 2003. *Corresponding author (andrews@nstl. MBC, microbial biomass C; MDS, minimum data set; NRI, Natural gov). Resources Inventory; PMN, potentially mineralizable N; R2, coefficient of determination; SMAF, Soil Management Assessment FramePublished in Soil Sci. Soc. Am. J. 68:1945–1962 (2004).  Soil Science Society of America work; SOM, soil organic matter; SQ, soil quality; T, soil loss tolerance; SAR, sodium adsorption ratio; TOC, total organic C; WS, watershed. 677 S. Segoe Rd., Madison, WI 53711 USA