M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 69
in a way that is meaningful to producers. Several of the previously discussed on-farm projects have indi-
cated that SOM and SOM-dependent properties may be attractive indicators of sustainability because they
are responsive to management practices. Soil organic matter and several associated physical and biologi-
cal properties are equated with soil quality because of their positive influence on soil performance Gregorich
et al., 1994; Karlen and Cambardella, 1996; Herrick and Wander, 1997. Additionally, the positive or neg-
ative effects of management practices on SOM levels are relatively well understood; this makes it possible
for producers to identify practices that will improve or degrade soil quality over time. Many on-going soil
quality efforts emphasize SOM and its relationship to management. There have been efforts to develop
educational materials about organic matter fractions and SOM-dependent properties. Table 3 lists a number
of activities and demonstrations that have been used successfully in workshops for farmers and extension
agents. These types of activities, some of which origi- nated as a component of soil health kits, bring obscure
mechanisms such as aggregate stability to life.
Materials or demonstrations that emphasize the composition of soil and SOM as understood by scien-
tists have little utility unless they provide practical in- formation. Accordingly, information targeting farmers
has tended to emphasize SOM contributions to crop productivity and yield stability Table 2: Approach
IV. Many researchers have responded to producer in- terest by developing educational materials that relate
management practices to consequences for SOM. Ide- ally, materials should emphasize components that can
be managed within a reasonable timeframe. Both the biologically-active and slowly-cycling organic matter
pools, which are predicted to have half lives ranging from days or weeks active to decades slow, are
significant to scientists and farmers interested in soil quality. Active fractions influence nutrient cycling,
biological activity and biologically mediated soil physical properties while passive or slowly-cycling
fractions contribute to soil physical condition and habitat quality. Particulate organic matter is a com-
ponent of SOM that has been identified as a partic- ularly promising index of organic matter status and
its contributions to soil andor organic matter quality Gregorich et al., 1994; Wander et al., 1994; Sikora
et al., 1996. This measure is attractive because it’s half-life, which is a decade or so, equals the amount
of time that an individual would farm a parcel of land. Additionally, POM, which can be obtained by
a variety of techniques including some easily per- formed in a demonstration setting Table 3, can be
positively correlated with biologically-active fractions and aggregation. Accordingly, POM is an index of
stewardship, recording the cost or contributions of management to soil quality.
In order to convince producers that SOM manage- ment is truly a worthwhile endeavor, SOM and its con-
tributions to productivity and environmental function must be demystified. Procedures to compare soils with
different SOM levels or with different management histories Table 3 have been devised to demonstrate
the impacts of SOM on aggregate stability, soil water relations, and plant growth. Many demonstrations em-
phasize impacts on soil biota that are assumed but not always known to be positively and consistently corre-
lated with soil functions. Research establishing defini- tive relationships between management, SOM and, for
example, microbial metabolism is badly needed and in demand by producers.
3. Needs and challenges
Soil quality efforts have thus far been focused largely on the development and assessment of tools for
use on-farm or to be delivered in a soil-testing format. By emphasizing the production of data or technical
tools to be used on-farm, researchers developing soil quality information have worked in a context where
short-term considerations are most pressing. Tools that will be adopted by farmers must produce data
relevant to producer’s priorities, which necessarily reflect current economic pressures and therefore re-
volve around yields and short-term profitability. But, if taken too far, this approach to information develop-
ment and delivery will reduce soil quality to a mere synonym of soil productivity. By focusing on the au-
thority individual farmers have over soil management decisions, soil quality efforts imply farmers are solely
responsible for maintaining soil condition. Farmers are in effect being asked to subsidize sustainability.
Few farmers believe they can afford to include the value of soil as a resource or long-term sustainability
as immediate goals of their farming practices. This
70 M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73
Table 4 Minimum data set reflecting scale of information application
a
Biological Chemical
Physical Field, farm, watershed indicators
Crop yield, appearance, NPP Soil organic matter
Soil thickness, morphology Weed pressure
pH Infiltration
Crop nutrient deficiency Nutrient availability
Runoff Earthworms
Conductivity Sediment fans
Canopy Losses
Ease of tillage Soil structure
Regional or national indicators Productivity, yield stability
Organic matter trends Desertification
Diversity and food web relations Acidification
Cover Biomass density and abundance
Salinization Erosion
Water quality Siltation of rivers and lakes
Air quality
a
Karlen et al. 1997.
is an example of what Lee 1993 refers to as a mis- match in the scale of human responsibility. Unless
producers and the public, who both benefit from the environmental services performed by soils, pay the
full cost of soil exploitation, economic exhaustion of the resource will result. This problem is well known.
An USDA special publication, Soils and Men, pub- lished in 1938 acknowledged, “there are both private
and public purposes in the use of soil. It is widely ac- knowledged today that public purposes are not being
achieved satisfactorily” USDA, 1938.
Unfortunately, the public has little appreciation for the additive benefits of soil building practices that are
derived through their indirect contributions to ecosys- tem services. Connections between management prac-
tices and the productivity of a farm field, the quality of water in a lake, and the amount of carbon sequestered
by an ecosystem are frequently made. Because the physical or temporal scale of these linkages vary, the
cause and effect relationships between management practices and these soil-dependent phenomena are
typically considered separately. Even when the pub- lic is aware, the diffuse rewards of stewardship may
not be pressing enough for those rewards to motivate policy. Agricultural policy decisions tend to be made
in relation to perceived political problems rather than as the result of efforts to maximize social welfare
Bates, 1998. There is a soil risk-based assessment of soil quality based on soil erosion and salinization in
the agricultural and environmental policy framework developed by the Organization for Economic Coop-
eration and Development OECD and its 29 member countries Parris, 1999. That framework will use
indicators to translate environmental problems into policy. That policy may be able to reduce soil degra-
dation but will have little capacity to enhance soil quality or the environmental and productive efficiency
associated with its optimization.
Our ability to derive the benefits from appropriate field-, watershed- or municipal-scale soil building
practices will depend upon the approaches to research, education, and policy we employ. The techniques
used will logically vary depending upon the scale of interest Halvorson et al., 1997. Recognizing this,
Karlen et al. 1997 specified MDS components for use at different physical and decision-making scales
Table 4. Efforts reviewed in this document include positive examples of methods that might be combined
to formalize a process for research and education that could promote soil quality as a means to achieve sus-
tainable farming systems. Bouma 1997 advocated the establishment of ‘research chains’ where inter-
disciplinary analysis would identify basic research needs. The results of appropriately targeted basic
work would then be communicated to, and analyzed by, a diverse team that would integrate the information
into practice. That strategy would be compatible with an US extension tradition that has emphasized the
diffusion of useful and practical information. It may not, however, adequately educate or prepare those
M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 71
involved in agriculture to problem solve in a com- plex and rapidly changing environment. According to
Ikerd 1988, the challenges of the 21st century will force cooperative extension to switch its emphasis
from the use of practical information to the education of those involved in agriculture. Participatory aspects
of some of the projects cited here could be developed to facilitate relationships between scientists, farmers
and members of public and private organizations. The education derived from these interactions will
help farmers, community members, political repre- sentatives and scientists determine when and how to
effectively promote and reward soil stewardship.
4. Summary
