Chronology of soil quality

62 M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 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 majority 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 set a 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 a Doran 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 management 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 promising 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 In the 1980s, before the concept of soil quality had come into widespread usage, several efforts to M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 63 Table 2 Chronology of research approaches Approach a 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 testingconsulting 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 implementationassessment 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 a The 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 improvement Warburton et al., 1938. This strategy continues to be a significant component of technology transfer programs today. In the 1980s, research was done on-farm in order to test basic hypotheses about the influence of management practices on farming sys- 64 M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 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. Research explicitly addressing the soil quality concept began in earnest in the early 1990s as inves- tigators sought to validate holistic approaches to soil assessment and test the efficacy of the MDS. On-farm soil quality research has included a continuum of ap- proaches Table 2: Approaches I–III, ranging from farmer-oriented, applied projects, to those that use state-of-the-art methodologies to test some of the hy- potheses inherent in the soil quality concept. Related research has often employed farmer-participatory strategies for philosophical and practical reasons Table 2: Approaches II and III, including the as- sumption that soil quality measures developed and refined within a farming context would be more suc- cessful Walter et al., 1997. Liebig et al. 1996 em- phasized farmers’ knowledge of soil characteristics should be used as a first iteration to point-scale eval- uation of soil quality farm, field or location within a field. Even when farmers were not directly involved in the research, use of commercial farms as study sites has fostered informal interactions that have educated academic researchers about the farm context. M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 65 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 qualityhealth 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. The low cost and relative ease of qualitative assess- ment tools makes them attractive for use by land man- agers in decision-making. Although no quantitative evaluation of soil quality assessment cards has been published, farmers and extension personnel have been consistently able to distinguish between soils of diver- gent management histories using only sensory evalu- ation Weil and Drinkwater, unpublished data. While sensory evaluation of soils with different long-term management histories can be informative, use of qual- itative assessment over time to detect changes in soil properties in response to management is more chal- lenging. McCallister and Nowak 1998 have pointed out that farmer knowledge, even if consistent, might include misconceptions that should be rectified rather than reinforced. Field-based soil assessment tools will have their greatest impact where cause and effect re- lationships between practices, observable traits and process outcomes are well understood. For example, highly accurate measures of soil erosion are surely not needed to convince managers that soil left bare is highly susceptible to erosive forces. Similar general- izations about other indices can be difficult to make. It is not clear that an absence of earthworms or low soil respiration rates observed on an individual day indi- cates soil has limited biological activity or low nutri- ent supply potential. Accordingly, scientists have been hesitant to endorse proscriptive or subjective mea- sures perceived to have out-paced research. In some 66 M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 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. There has been notable similarity in the approaches to, and outcomes from, these indicator-screening ef- forts. A 1993 project, funded by Northwest Area Foundation, quantified the effects of the conserva- tion reserve program CRP on soil quality indi- cators Karlen et al., 1999. Researchers in Iowa, North Dakota, Washington, and Minnesota conducted on-farm multi-paired site studies and compared both their procedures and results. The analytical proce- dures used were generally similar but not always identical except for aggregation indices, which were tailored according to soil type and susceptibility to wind or water erosion. Although trends for all measures were not consistent across all sites, soil M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 67 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 altered 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 difficulties 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. Even without quantitative integrative tools, the im- mediate utility of soil quality information can be im- proved by relating promising indices to soil function 68 M.M. Wander, L.E. Drinkwater Applied Soil Ecology 15 2000 61–73 Table 3 Hands-on soil quality activities and demonstrations a 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 Managementsoil 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 Managementorganic 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 Biolog plates inoculated with extracts from soils with different management histories reveal substrate utilization patterns a Activites are grouped into three broad areas: soil composition, impacts of SOM and soil biology. The same set of contrasting soils can be used for all activities. Marianne Sarrantonio and Ray Weil contributed to this list. 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