Fostering soil stewardship through soil quality assessment
Michelle M. Wander
a,∗, Laurie E. Drinkwater
b,1aDepartment of Natural Resources&Environmental Sciences, University of Illinois at Urbana-Champaign,
1102 S. Goodwin Ave., Urbana, IL 61801, USA
bRodale Institute, 611 Siegfriedale Rd., Kutztown, PA 19530, USA
Abstract
Soil quality is not a purchased technology; instead, it is a concept that can be used in making land management decisions. Researchers have generally agreed upon the soil properties that determine soils’ capacity to function and have emphasized that soil quality must be understood in context. Soil quality research has included the following: (1) soil management research, where the effects of management on soil properties and dependent processes are assessed; (2) measurement development for soil quality assessment to be carried out by the farmers themselves, by advisors, or consultants and (3) systems assessments, that consider the physical and cultural contexts that impact soil quality decision-making. Because stewards of the land ultimately determine whether soil quality is improved, maintained, or diminished, many research projects in the US have included the active participation of farmers in efforts to develop the soil quality concept. More effort has been spent on soil management and on the development and testing of farmer oriented measurements than on system assessments. There is growing consensus that the development of soil quality assessments to be used by farmers to solve problems within individual fields will be challenging. Organic matter and organic matter-dependent properties are the most promising indicators for use in a soil quality assessment where the information will be used in management decisions. Unfortunately, the successful development of on-farm measures may not be sufficient to guarantee that soil quality is maintained because there is a mismatch in the temporal and physical scales over which soil quality and farm security are achieved. Educational materials that highlight soil contributions to farm, landscape and global functioning coupled with dialoguing between practitioners, scientists, and policy-makers can communicate the importance of soil quality to sustainability. Successful soil quality efforts will relate soil properties to soil function in a way that fosters stewardship among individuals and builds public support for polices that promote soil management to ensure agriculture, industry, and the natural environment are sustained. Strategies and priorities are expected to vary according to audience, land-use constraints and the intended scale of application. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Soil quality; Minimum data set; On-farm research; Participatory; Indicators; Sustainability; Systems research
1. Introduction
The concept of soil quality has grown out of con-cern about the sustainability of agriculture (Parr et al.,
∗Corresponding author. Tel.:+1-217-333-9471;
fax:+1-217-0244-3219.
E-mail addresses:mwander@uiuc.edu (M.M. Wander), ldrink@rodaleinst.org (L.E. Drinkwater)
1Tel.:+1-610-683-1437; fax:+1-610-683-8548.
1992; Warkentin, 1995; Doran and Zeiss, this issue). A distinguishing characteristic of soil quality research is the use of multidisciplinary approaches to assess-ment. This reflects a major paradigm shift in the field of soil science. Soil quality research has been fueled by the National Research Council’s (NRC) Board on Agriculture recommendation that we ‘conserve and enhance soil quality as a fundamental first step toward environmental improvement’ (NRC, 1993). The NRC further advised that the concept of soil quality be the
principle that guides agricultural policies and prac-tices. Scientists, who find the black and white terms of laws and regulations incompatible with nature’s com-plexity (Moran, 1994), have responded to the NRC call by directing research toward farmer-friendly soil quality assessment strategies.
Soil degradation is a widespread problem having negative consequences on both agricultural productiv-ity and natural ecosystems. The vast majorproductiv-ity of agri-cultural lands in the US already have depleted levels of soil organic matter (SOM) (McGill et al., 1981; Campbell and Zentner, 1993; Lee and Phillips, 1993). Furthermore, nutrient losses through leaching and soil erosion are substantial (Carpenter et al., 1998) and soil loss through erosion often exceeds sustainable rates (Pimentel et al., 1995). Soil degradation in intensive cropping systems may result from (1) carbon additions that are insufficient to maintain SOM; (2) the return of only high carbon, senescent organic residues to the soil; (3) nutrient inputs that exceed harvested exports (Carpenter et al., 1998); (4) excessive tillage or tillage at times that exposes soil to wind and water erosion and (5) rotations that include long fallow periods and temporal monocultures.
In the US, soil quality research was initially dom-inated by efforts to define terms and develop assess-ment strategies (e.g. Larson and Pierce, 1991; Doran and Parkin, 1994; Seybold et al., 1997). Many defini-tions of soil quality or health emphasized the concept of soil fitness to perform functions (Larson and Pierce, 1991; Warkentin, 1995; Karlen et al., 1997). A widely accepted definition of soil quality is “the ability of soil to function within ecosystem boundaries to sup-port healthy plants and animals, maintain or enhance air and water quality, and support human health and habitation” (Karlen et al., 1997). These functions are impacted by multiple soil attributes. Accordingly, soil scientists also identified a generally agreed upon min-imum data set (MDS; Table 1) of soil parameters that could be used to quantify soil quality (Bouma, 1989; Larson and Pierce, 1991; Arshad and Coen, 1992; Do-ran and Parkin, 1994). The selection of MDS parame-ters has been based upon a wealth of soil management research that relates soil attributes to soil function and ideally relates management practices to soil attributes. Soil quality functions proposed by Larson and Pierce (1991, 1994) and Karlen and Stott (1994) are exam-ples of theoretical frameworks that combine physical,
Table 1
Soil quality minimum data seta
Biological Chemical Physical
Microbial biomass pH Texture Potentially
mineralizable N EC Bulk density Soil respiration N, P, K Depth of rooting
Organic matter Infiltration
Water holding capacity
aDoran and Parkin (1994); Larson and Pierce (1994).
chemical and biological measures to assess soil condi-tion. Even though the soil quality concept is relatively well established and increasingly accepted, it remains difficult to see how the complex and site-specific na-ture of soils will be translated into measurable param-eters that might reflect the state of a soil. Furthermore, it has been unclear exactly how the concept of soil quality will be translated into practices, agricultural policy or regulatory statutes. In this paper we review soil quality research conducted on-farm. Our conclu-sions were based upon our review of the literature and phone interviews with investigators participating in ongoing projects. Our objective is to trace the chrono-logical evolution of soil quality research. We divide soil quality efforts into three categories: (1) soil man-agement research, where the effects of manman-agement on soil properties and dependent processes are assessed; (2) measurement development, where soil quality as-sessment would be carried out by farmers, advisors, or consultants and (3) systems assessments, where the effects of different physical and organizational scales on soil quality and soil dependent phenomena are con-sidered. The assumptions, objectives and accomplish-ments associated with various phases of soil quality research are discussed. Finally, we highlight continu-ing needs of, and promiscontinu-ing strategies for, soil quality research. Soil organic matter management is used as an example to demonstrate how research efforts might overcome barriers of scale and sector to serve the in-terests of a society dependent upon the soil resource.
2. Chronology of soil quality
2.1. Soil management research conducted on-farm
Table 2
Chronology of research approaches
Approacha Assumptions Objectives Outcomes
I. On-farm research On-farm sites provide a unique opportunity to assess effects of management practices because (a) these impacts will be observ-able in sites that have been managed consistently for at least 5 years and (b) soil management will reflect real-world constraints
(a) Compare on-farm sites under contrasting management to deter-mine whether long-term manage-ment practices impact soil quality (b) Determine whether multivari-ate assessment of soils would provide unique and more comp-lete understanding of soil function
(a) Demonstrated that hypotheses could be tested using commercial farms as study sites
(b) Provided examples of suc-cessful experimental approaches to comparative on-farm research
II. Kits and cards: participatory, on-farm research
(a) Farmers’ knowledge of soil characteristics should be used as a first iteration to point- scale evaluation of soil quality (b) Simple approaches to soil quality assessment, including qualitative evaluation, can be used in decision-making
(a) Collaborate with farmers to develop soil quality assessment tools to be used to guide man-agement decisions
(a) Stimulated interest in soil quality and provided a forum for information exchange between farmers, advisors, researchers and other experts
(b) Provide a framework for farmers to assess non-yield based costs and benefits of management choices
III. Indicator screening: participatory, on-farm research
(a) A holistic description of soils and the MDS concept have merit in point scale use
(b) Farmer’s knowledge and opinion should be tapped (c) Soil quality can be optimized under current use while preserv-ing its future potential
(a) Test the hypothesis that biological and physical properties are most affected by management (b) Identify and develop mea-sures for use by farmers to aid them in their soil management decision-making
(a) Farmer perspective and feed-back was invaluable
(b) Farmer contribution to study design was not important (c) Biological and physical prop-erties were most affected by man-agement practices
(d) Calibration of measures is a major problem; this will limit local and national scale use of indicators
IV. Optimizing management
(a) In the near term, consulting will play a more important role than farmer-administered measures
(b) Measures must be directly related to soil performance (c) Organic matter measures have high potential for adaptation to a soil testing/consulting format (d) To ensure sustainability, efforts must promote public support for practices that protect soil quality
(a) Test hypotheses about rela-tionships between management practices, parameters (emphasis is on organic matter fractions) and soil performance determined on-farm and at larger scales (wa-tershed, landscape, globe) (b) Tackle indicator scaling and normalization problems using statistical and empirical models (c) Develop integrative tools and implementation/assessment strategies
(a) Provide examples of how soil scientists can contribute to natu-ral resource management by conducting basic research within a holistic framework to promote sustainability
aThe summary statements that appear in sections II–IV are based upon our review of the literature and telephone interviews with Deborah Allan, Dave Bezdicek, Richard Dick, John Doran, Marianne Sarrantonio, Laura Jackson, Rhonda Janke, and Ray Weil.
characterize soils within a multidisciplinary frame-work were initiated in on-farm settings (Table 2: Approach I). This research marked a departure from traditional on-farm research that began in the US dur-ing the 1930s as a strategy for extension efforts in soil
sys-tems. This emergence of on-farm, multidisciplinary research probably reflects ideas from several fields, including: (1) agroecology, which advocated that farm lands be studied as ecosystems (Odum, 1984); (2) systems research, which emphasized the impor-tance of complex interrelationships among system components (Csáki, 1985) and (3) farming systems research (FSR) methodologies, which promoted use of multidisciplinary assessments in solving produc-tion problems on small farms in developing countries (Zandstra et al., 1981; Shaner et al., 1982). Farms were expected to provide a more realistic setting for agricultural systems research than experiment sta-tions, where both management and resource-use in-tensity are greater (Thompson and Thompson, 1990). Work conducted on-farm could capture field scale variation in soil and microclimate while experimen-tal plots minimized important differences in soil and landscape features (Stevenson and van Kessel, 1997). Moreover, use of actual farms as study-sites permit-ted assessment of producer practices (Ikerd, 1993) and the socioeconomic and cultural contexts of the systems being compared (Shennan et al., 1991). An additional strength of on-farm research, from a soil quality perspective, is that it allowed the cumulative effects of farming practices on slowly changing soil properties, which are vital to soil function, to be quantified. Of course those soil properties could be studied in long-term experimental trials, but the cost of long-term trials is greater and the range of practices represented therein is necessarily restricted.
Studies that had the greatest influence on soil qual-ity research were not only conducted on-farm; they also emphasized the ecology and complexity of soils. A work by Reganold et al. (1993) is noteworthy because it considered the physical, biological and chemical properties of soils on 16 adjacent biody-namic and conventional farms in relationship to farm economy. This study has been criticized because of the statistical analyses used and because the individ-ual influences of amendments and cultivation on soil attributes cannot be discerned (Wardle, 1994). The objective of the study was to compare complete man-agement systems rather than to identify the impact of specific or individual practices. Drinkwater et al. (1995) also investigated a wide array of soil prop-erties in a comparison of organic and conventional tomato production systems. They assumed alterations
in soil processes would affect net productivity through plant–pathogen and plant–herbivore interactions as well as nutrient availability. The influence of organic and conventional practices on soil processes was de-tected across a range of soil types despite notable variability in the farming practices of individual pro-ducers. Franco-Vizicano (1997) compared soil prop-erties of nine pairs of farm fields in central Michigan to determine the influence of residue diversity on soil quality and found that residue diversity, which would influence quantity, quality, timing and placement of resources, and P availability, influenced soil proper-ties. By treating soils as complex, multivariate sys-tems, researchers have gained insight into the system being considered. Multivariate analysis can elucidate ecological ramifications not revealed by univariate statistics (Lechowicz and Shaver, 1982). The studies described above made three major contributions to fu-ture soil quality research. First, they demonstrated that hypotheses could indeed be tested using commercial farms as study sites. Secondly, they provided examples of successful experimental approaches to comparative on-farm research. Thirdly, they demonstrated that a full understanding of management impacts on soils required that, in addition to chemical properties, soil biological and physical attributes must be assessed.
2.2. Kits and cards
The perception that farmer participation in research was critical led many investigators to focus their ef-forts on assessment tools to be used by growers. Both simple quantitative measures and qualitative assess-ment strategies have been explored in collaborative projects involving farmers (Table 2: Approach II; Romig et al., 1995; Sarrantonio et al., 1996; Janke, personal communication, 1998). These works were an extension of traditional on-farm research in that they were oriented towards meeting the needs of farmers. Implicit in this approach was the assumption that on-farm soil quality assessment could provide meaningful information that could be readily inter-preted and used by producers to aid their decision-making.
The soil health test kit was developed by the Agricultural Research Service in collaboration with individuals at the Rodale Institute (Sarrantonio et al., 1996). According to John Doran (personal commu-nication, 1999), the kit was inspired by the efforts of the Practical Farmers of Iowa (PFI), a producer group organized to conduct applied research. The PFI wanted to adapt the spring soil nitrate tests for use by individual farmers in their fields. For the soil health test kit, soil measurements were simplified and tailored for in-field use by individuals not trained as soil scientists. According to Doran, on-farm measures allowed farmers to develop and refine their theories about cause and effect relationships and then try to adapt their practices accordingly. Doran noted the soil health kit’s ability to revitalize the exchange between farmers and scientists, or other experts, willing to ap-ply those measures in an on-farm context. Liebig et al. (1996) conducted a study on soils from grassland and cropland on two farms in North Dakota to evaluate the accuracy and precision of indicator measurements us-ing the field soil quality test kit. The most notable dif-ferences were between the grassland and agricultural soils of both farms. Some tests were able to distinguish between the conventional and organic systems used on those farms and these differences agreed with those reported in more rigorous studies. Field measurement of electrical conductivity, soil pH, soil nitrate, and gravimetric water content values compared well with values determined by standard laboratory procedures. The Natural Resource Conservation Service (NRCS)
has developed a technical guide for the use of a com-mercially available version of the kit (USDA, 1999a). An alternative to the kit is the use of qualitative sen-sory evaluation of soils. Farmers worldwide already used this approach to soil evaluation to varying degrees (Chambers et al., 1989). Several soil quality assess-ment cards have been developed to capture farmers’ perceptions in a systematic format (Romig et al., 1995; Seiter et al., 1997). The hallmark of these cards, which provide evaluation criteria for farmers to apply to their fields, is the involvement of farmers in identifying and prioritizing the characteristics that define a healthy soil. For instance, the Wisconsin soil quality/health card was developed in response to farmer interest in gaining information about soil biological quality. The NRCS has promoted the use of farmer-based, quali-tative assessment by producing a handbook that de-scribes how to develop and adapt score cards for use around the country (USDA, 1999b).
instances, the mechanisms that underlie soil quality must be addressed through relatively basic research before indices or recommendations are put forward. In other cases, careful control of the context (timing, location, and intensity) of observations can vastly im-prove their interpretability and hence utility.
Even though many on-farm measures may fail to produce information that scientists would accept as re-liable, or allow extrapolation beyond their intended or accepted use, the importance of on-farm or in-context resource assessment must be recognized. According to Hilborn and Ludwig (1993), politicians, resource managers, and community stake-holders should not and cannot look to scientists as the sole guide for their resource-use decisions. Communities knowingly or unknowingly make decisions about the allocation of their natural resources before scientific consensus is reached or clear environmental policy has been formed (Hilborn and Ludwig, 1993). Soil quality kits and cards might function as stewardship-accounting tools used by proactive managers. According to indi-viduals working in the soil quality arena, information exchanged informally with farmers during the de-velopment and testing of farmer-oriented assessment tools (both kits and cards) revealed more about the causes of soil degradation than the tools themselves (Allan, Dick, Drinkwater, Wander, and Weil, personal communication, 1998). Participatory approaches capture information about non-technical aspects of resource allocation patterns that impact farming prac-tices (Rhoades and Booth, 1982). Farmer participation in soil quality assessment will help identify press-ing problems and palatable solutions that need to be addressed by programs that reward soil stewardship (McCallister and Nowak, 1998). Qualitative assess-ments can reinforce a systematic approach to soil management, where producers adapt practices and monitor their influence on soils, to have lasting effects on stewardship (Weil and Dick, personal communi-cation, 1998). If successful, such efforts may prevent the need for regulatory action addressing soil quality.
2.3. Indicator screening
Growing recognition of the need to quantify man-agement effects on the soil ecosystem in situ has promoted on-farm hypothesis testing. Soil quality research that followed in this vein has targeted
indi-cator screening and development (Table 2: Approach III). The main distinction between these projects and the work started in the 1980s is their explicit goal of soil quality assessment and their use of a more specific array of measures (variants of the MDS). Several of these projects included farmer input as a critical element of the research process. By enlisting the participation of farmers in the process, investiga-tors attempted to make the research more responsive to farmers needs (Walter et al., 1997). The nature of farmer participation has varied tremendously among these projects. In Oregon, cooperating farmers were asked to manage researcher-defined treatments in veg-etable productions systems (Richard Dick, personal communication, 1998). In this case, only changes in rapidly changing properties would be readily ob-served. In other studies, producers influenced exper-imental design (which management practices were studied) without requiring that new treatments be physically established. In Illinois, farmers requested that a non-disturbed benchmark be included in the study (Wander and Bollero, 1999) and in Minnesota producers asked researcher to collect information about rotational grazing (Deborah Allan, personal communication, 1998). In Maryland, farmers were asked to select locations for sampling within their fields where soil was in relatively good or poor con-dition (Ray Weil, personal communication, 1998). In all three cases, the relationship between management practices or inherent soil characteristics and slowly changing soil properties would have been revealed. In some cases (MN, OR, IL) efforts were made to formally assess and record farmer perceptions during the course of the project.
biological properties were generally enhanced by CRP and were more sensitive to CRP management than were chemical or physical properties. Staben et al. (1997) published a detailed account of the Washing-ton State CRP-cropland comparison and found that biotic factors and parameters associated with micro-bial and organic matter dynamics were significantly enhanced by CRP after 4–7 years. Staben et al. (1997) clearly identified the need for soil scientists to find parameters and linkages that reveal the direction and impact of change in soil quality in the smallest time scale possible. Wander and Bollero (1999) conducted a study on 37 farm fields as a first step toward identi-fying how the concept of soil quality could be mean-ingfully applied in Illinois. Their objectives were to determine whether recent adoption of no-till practices in the region had generally altered soil quality and to screen potential soil quality indices by assessing the effects of region and of tillage practices on MDS properties. No-till practices improved the biological and physical conditions of soil (0–15 cm) despite in-creased consolidation. The biological and physical aspects of soils that are influenced by organic mat-ter were the properties most almat-tered by agronomic practices. Particulate organic matter (POM) was a highly promising soil quality measure. In Oregon, a long-term study has been initiated to identify proper-ties that respond quickly to management change and to identify time-efficient indexing procedures (Buller and Dick, 1998). All of these indicator-screening efforts simultaneously tested hypotheses and re-fined the MDS. All determined that biological and physical properties associated with organic matter were more subject to change than inorganic chemi-cal parameters. Most projects identified measures of active organic matter fractions as potentially sensitive indices.
2.4. Optimizing management
Although many scientists started with the as-sumption that farmer-oriented evaluation tools would provide the critical mechanism needed to involve prac-titioners in soil quality, they have increasing doubts about the potential impact of these tools. Farmer re-sponse to on-farm measures contributed to this opin-ion. For example, focus groups of farmers participat-ing in Illinois indicated that while they were interested
in obtaining information about soil quality, they did not want to collect the information themselves (Wal-ter et al., 1997). Only producers committed to more environmentally benign or sustainable practices are expected to use soil quality rhetoric and demand quan-titative assessment strategies (Weil, personal commu-nication, 1998). Components of the testing kits are more likely to persist if consultants or testing agencies support them. The results of on-farm projects are as likely to support the development soil-testing tools as measures for use on-farm. For example, Gruver and Weil (1998) are working to adapt macro-aggregation measures for soil testing purposes using soils col-lected as part of an on-farm soil quality project.
Soil quality efforts include examples of the three components of scientific analysis (problem perception, mechanistic understanding, and strategic assessment) that Ehrlich and Daily (1993) deemed necessary for natural resource management. Still, there are some barriers to implementation of soil quality information. Many researchers involved in indicator screening stud-ies encountered difficultstud-ies associated with measure calibration and standardization across sites that may limit the applicability of soil quality measurements on individual farms (Allan, Dick, Wander, Weil, personal communication, 1998). Before measures can actually be used in soil quality assessment, reproducible and interpretable values must be produced and standards against which they can be compared must be devel-oped. The relevant contributions to this end made by component-style research are too numerous to review here. Most researchers we spoke with speculated that several ‘MDS’ properties would come into wider use when combined in ratios or used in statistically or the-oretically weighted variables, or as inputs to simple models. The results from on-farm assessments, which can reveal the extent of positive or negative change associated with practices, are retrospective and do not help us anticipate where we are going in terms of soil quality unless they are combined with forward-looking tools (Wagenet and Hutson, 1997). According to these workers, scientists might use simulation modeling, ex-isting databases, and new data produced by supple-mental soil quality measures to foster sustainability through decision trees or other integrative tools.
Table 3
Hands-on soil quality activities and demonstrationsa
Demo Title Concepts illustrated Description
Soil composition
Soil particle size distribution Soil particle sizes: gravel, sand, silt, clay Sieve series shows differences in soil particle sizes (rocks to clay), participants can sieve different soils
Soil pie Proportion of air, water, organic matter, and particles in soil; emphasizes presence of significant air and water, soils of different textures can be constructed to convey importance of soil texture
A literal pie chart constructed from the real material in a cake pan shows the percentage composition of soil components
Macro-organic matter floatation Ecosystem and management effects on macro-organic matter; great for contrasting natural and agricultural systems
Mason jars with soil and water that have been shaken and allowed to settle; can be done in field, long-lived after setup Particulate organic matter fractions Composition of the major pool of active
organic matter, progressive nature of stages of decomposition and humification, manage-ment effects on POM
Vials or bowls of wet-sieved POM fractions from soils with different management histo-ries
Impacts of SOM
Water holding capacity: compost vs. soil
Differences in bulk density and water holding capacity between compost (humus proxy) and the mineral soil components
Two graduated cylinders containing equal weights of soil and compost with the addi-tion of equal amounts of water; suitable for large group demonstrations
Management and soil infiltration rate
Management effects on soil structure, specif-ically soil infiltration rate, an integrative measurement
Test kit infiltration rate using a ring of irri-gation pipe, sarhan wrap and a timer; field activity; great activity for group participation Aggregate stability with
use of coffee filters
Management/soil organic matter differences and aggregate stability, erosion potential
Water is poured through coffee filters that contain dry soil aggregates. Top soil and subsoil can be compared for dramatic differ-ences in color, organic matter and aggregate stability
Aggregate stability with use of fish bowls
Management/organic matter differences and aggregate stability, slaking, soil porosity and aeration
Dry soil clods are gently dropped into beakers or fish bowls of water. Because air bubbles escape when clods are submerged soil structure effects on aeration are also evident
Soil quality and plant growth.
Soil quality impacts growth of both roots and shoots
Seedlings are grown in clear containers so soil effects on shoots and roots are visible
Soil biology
Observation of soil fauna Complex food web in soil, lively, interesting critters are an important part of the soil ecosystem, can be done semi-quantitatively to illustrate differences in soil communities between soils
Dissecting scopes with extracted soil fauna in petri dishes. Nematodes, myccorhizal spores, oligocheates, mites and collembola are usually prevalent
Observation of roots, root hairs and nodules
Role and complexity of roots and root hairs Viewing of plant roots, root hairs and nod-ules under dissecting scopes
Paper decomposition Decomposition process, identity of primary decomposers, management can effect de-composition rate
Graph paper incubated on soil in petri dish; suitable for viewing fungal hyphae with dis-secting scope
Biolog plates Management practices affect microbial com-munity function (either through changes in composition or metabolic status)
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 and/or 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
Table 4
Minimum data set reflecting scale of information applicationa
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
aKarlen 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.
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
The concept of soil quality has undergone an evo-lutionary process that began with a definition and the identification of parameters that could be used to as-sess soils in a holistic fashion and relate soil proper-ties to processes and management practices. The need to assess farming system impacts on soil condition and to capture aspects of soils that change slowly over time made on-farm studies attractive if not manda-tory. Participatory formats emphasized on-farm as-sessments and proved that hypotheses could be tested in commercial farm settings. Soil quality researchers have generally shared the assumption that measures are being developed for producers’ use. However, we should also recognize soil quality data must be used to advance our understanding and to influence the ac-tions of society at large. Interaction with producers, and possibly other community members, is vital dur-ing the phases of problem perception and strategic assessment. Scientists do not expect that soil quality will be achieved principally as the result of farmers collecting either subjective or quantitative measures. Economic pressures felt on-farm force producers to focus on soil productivity rather than on soil contri-butions to environmental function. Educational tools may make soil stewardship a higher priority by in-creasing both producers’ and society’s understanding of the relationship between soil properties, soil func-tion and management choices. Organic matter man-agement has emerged as a practical approach to soil quality. Selected organic matter fractions have poten-tial as stewardship indices because their
characteris-tics reveal the effects of management accrued over 5–20 years. On-going work strives to definitively link soil quality measures to ecosystem services and to make the value of those services known to the pub-lic. Soil quality and agricultural sustainability will ul-timately be determined by the public, who will or will not decide to compensate producers for steward-ship.
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