Evaluation of soil quality

Our ability to assess soil quality is complicated by many physical, chemical, and biological processes and their interactions in time, space, and intensity. It is not usually possible to directly measure the rate of soil processes; instead they can be inferred by measuring specific soil properties that are indicative of these rates. These measurements then can be used in simulation models to predict future changes in process rates and, in turn, soil quality. The properties measured are termed indicators of soil quality. The best soil quality indicators are those that integrate the combined effects of several properties and processes.

A general framework to evaluate soil quality is based on the following sequence: functions, processes, attributes (or properties) indicators, and methodology. Example of a framework (given in part) for evaluating soil quality; characterizing some of the capacities of a soil to perform a specific function (i.e., provide a medium for plant growth) is given in table below.

Process Attribute (or property) Indicators Possible method for determining attribute
Capacity to accept, hold, and release water Infiltration Infiltration rate, sorptivity Tension permeameter
Water-holding capacity Desorption curves Tension table, pressure plate
Permeability Hydraulic conductivity Guelph permeameter
Capacity to accept, hold, and release energy Organic matter Organic C Dry combustion
Labile organic matter Microbial biomass Chloroform fumigation
Carbohydrates Acid hydrolysis
Microorganic matter Dispersion/sieving
Particle size Clay Hydrometer / pipett

(from: Carter et al. 1997)

Research efforts to monitor soil quality need to be balanced with efforts to better define relationships between the status of soil quality indicators and soil functions. In addition, consideration must be given to the simultaneity of diverse and sometimes conflicting nature of soil functions.

Source: NRCS Art by Scott Patton, USDA NRCS http://photogallery.nrcs.usda.gov/

Source: NRCS Art by Scott Patton, USDA NRCS http://photogallery.nrcs.usda.gov/


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