Beyond T: Guiding Sustainable Soil Management
Soil and Water Conservation Society, 2008
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Why Beyond T?
Getting Beyond T
Scientists, conservation advisors, and producers recognize the need for a more comprehensive and integrated approach to soil management that (1) considers the multiple production and ecological functions soil provides, (2) evaluates multiple factors of soil degradation, (3) provides standards or thresholds for managing soil to sustain its multiple production and ecological functions, and (4) results in more comprehensive recommendations for soil management and conservation. The Soil and Water Conservation Society (SWCS) undertook a project, funded by the Wallace Genetic Foundation, to help accelerate the development of more comprehensive soil assessment, management, and planning tools. This report summarizes the results of an expert consultation held May 22–24, 2007, at the LiedConferenceCenter of the Arbor Day Foundation in Nebraska City, Nebraska, to recommend actions to move toward more comprehensive soil assessment, management, and planning tools.
This report has been developed in collaboration with those participating in the expert consultation. The participants were not, however, asked to formally sign on to or endorse the report. They participated as individuals and experts, not as official representatives of their agencies or organizations. The content of this report is solely the responsibility of SWCS.
More Comprehensive System Needed
Participants agreed that soil conservation standards and tools that enable a more comprehensive assessment of management and conservation systems on multiple production and environmental endpoints are needed to meet the conservation challenges we face today.
The most widely used soil conservation standard in the United States is the Soil Loss Tolerance Standard (T). The most widely used soil conservation planning tools in the United States are the Revised Universal Soil Loss Equation version 2 (RUSLE2) and the Wind Erosion Equation (WEQ). Taken together, T, RUSLE2, and WEQ have made possible dramatic improvements in soil conservation and erosion control since they were developed, but they do not address the full range of ecosystem services provided by soils. Specifically these tools only (1) account for one type of soil degradation, erosion, but do not address salinization, compaction, organic matter depletion, and other important threats to soil resources, (2) account for the effect of soil erosion on soil depth and productivity, and (3) evaluate soil management according to what is thought to be an acceptable rate of soil loss; they do not estimate the full extent to which soil resources are being improved through management.
Current Tools Get Us Part of the Way to the System We Need
Participants in the consultation discussed the capabilities of an ideal system of soil conservation standards and planning tools. The capabilities clustered into three categories: (1) soil assessment and monitoring, (2) soil management and conservation planning, and (3) conservation program management. Participants also agreed an ideal system must be capable of assessing and managing the off-site environmental effects of soil management as well as on-site effects on productivity. Participants evaluated the strengths and weaknesses of the Soil Conditioning Index (SCI) and the Soil Management Assessment Framework (SMAF) and recommended improvements to both tools to enhance their capabilities to contribute to an ideal system.
Improving the Soil Conditioning Index
The SCI is a tool used to predict the effect of soil management on the trend in soil organic carbon. The SCI is a predictive tool that allows the user to compare the performance of alternative management and conservation systems based on their predicted effects on soil organic carbon. SCI can and does contribute to more comprehensive conservation planning, and SCI values can be and are used to augment T when evaluating the performance of conservation systems. SCI appears to work well on pasture and in cropping systems with simpler rotations of more traditional crops in rain-fed areas, land uses that represent much of the agricultural landscape in the United States. Finally, SCI can and has been used in national or regional level assessments of trends in soil quality.
SCI, however, evaluates only one indicator of soil quality—soil organic carbon. In addition, SCI has not been subjected to significant peer review in the scientific community, and the applicability and performance of SCI has not been widely tested, at least in some important agricultural regions of the United States. There is particular uncertainty about the performance of SCI when applied to irrigated systems and to cropping systems with diverse rotations and inputs of carbon and nitrogen, especially when such systems involve multiple field operations or organic amendments.
Participants recommended the following steps be taken to improve SCI:
1. Develop and publish in the scientific peer-reviewed literature documentation of the development and evolution of SCI.
2. Use carefully selected studies already in the scientific literature to regionalize SCI inputs and processes to reflect differing crop varieties, different soils, and other regional characteristics and to assess the performance of SCI in irrigated systems and in diverse and nontraditional cropping systems.
3. Use the Conservation Innovation Grants program and other grant programs as vehicles to encourage additional testing, validation, and improvement of SCI.
4. Facilitate the collection of literature into a common, public database that supports SCI inputs and coefficients.
Improving the Soil Management Assessment Framework
SMAF is a tool for assessing and monitoring soil quality following three basic steps: (1) indicator selection, (2) indicator interpretation, and (3) integration into an overall soil quality index value. SMAF was designed as and is best used as a soil assessment tool. It provides a comprehensive snapshot of current soil conditions that can be used to suggest opportunities for improving soil quality. The interpretations of multiple indicators in SMAF are accessible to nonscientists, are tied directly to the goals specified by the user, and enable the integration of productivity and environmental concerns. SMAF can be used to monitor changes in soil quality if repeated measurement and interpretation of the same selected indicators are made at the same location.
SMAF does not enable the user to predict the effect of changing management and conservation systems on soil quality, which limits its application to conservation planning. The most important factor, however, limiting its application is the requirement to measure and sample indicator values at the site to be assessed. In addition, a limited number of scoring functions have been developed to date and a limited but growing number of validation studies have been conducted to test the framework under various management systems and locations.
Participants recommended the following steps be taken to improve SMAF:
1. Place highest priority on exploring options to use modeled values—rather than measured values—as inputs to SMAF and on options to simplify or reduce the number of measured indicators that are required to complete the assessment.
2. Increase the number and accuracy of scoring curves available to interpret measured indicators by building a common, public database to help develop and calibrate scoring curves.
3. Work with commercial soil testing laboratories to incorporate soil quality interpretations into their programs and to collect and measure data that would enable interpretation of additional indicators.
4. Enrich the interpretive text that accompanies each indicator report.
Current and Potential Roles for SCI and SMAF
SCI and SMAF are complementary tools with different strengths and weaknesses. Both tools, either individually or in combination, fall short of the ideal system outlined by participants in the expert consultation. SCI and SMAF can take us closer to the ideal system immediately given their current strengths. If improved as recommended above, the two tools can make an even more important contribution to building the ideal system.
SCI and SMAF in Soil Assessment and Monitoring. SCI is already being used in conjunction with the USDA Natural Resources Conservation Service (NRCS) National Resources Inventory to conduct national and regional assessments of trends in soil carbon as part of the USDA Conservation Effects Assessment Project (CEAP). SCI in national and regional assessments can and should be used now to report the proportion and location of acres on which management is likely degrading, sustaining, or building soil carbon. The indicator interpretation step of SMAF was successfully modified to interpret modeled data for carbon in the National Nutrient Loss and Soil Carbon Database Report for CEAP. SMAF is currently being tested as a soil quality monitoring tool in CEAP watershed studies. The results of those tests should be carefully considered in developing plans for wider use of SMAF in assessing and monitoring change in soil resources at regional and national scales.
SCI and SMAF in Soil Management and Conservation Planning. Both SCI and SMAF can and should be used now to enable producers and their advisors to consider factors in addition to soil erosion that should be part of a more comprehensive conservation plan.
SCI is a predictive tool and therefore already is and should continue to be used to evaluate the relative performance of alternative conservation practices and systems available to producers. SCI values already are and should continue to be used to augment T when evaluating whether current management is adequate to protect and enhance soil resources. SCI, if linked through a common interface with other tools such as phosphorus indices, would expand the number of endpoints affected by soil management that could be evaluated as part of the planning process.
SMAF has not been developed as a predictive tool to date, which will limit its use in conservation planning. Participants concluded the feasibility and desirability of trying to turn SMAF into a predictive tool remains an open question. Participants did agree, however, that SMAF has the potential to serve as a soil benchmarking tool that could inform soil conservation planning by identifying other important factors that should be considered during the planning process.
SCI and SMAF in Conservation Program Management. Participants urged caution when attempting to use SCI or SMAF to set quantitative standards for eligibility to participate in conservation programs or to scale payments based on estimated or measured changes in dynamic soil properties. Unless SCI or SMAF results are adjusted to common baseline conditions, soil types, and climates, payments based on an increment of change in a SCI or SMAF score will result in payments flowing to those producers whose baseline conditions, soil types, and climates make it easy to produce large changes in SCI and SMAF scores. Such payments may have little relation to the cost the producer incurs in sustaining soils that are already in good condition or in producing the improvement in soil resources, which will raise questions about the fairness and credibility of the resulting payment schedule. Participants recommended using SCI and/or SMAF to identify conservation practices and systems that will most improve soil resources at the lowest cost and give those practices and systems priority within the appropriate conservation programs. Actual payments should be related to the cost of applying the selected practices and systems. Participants were encouraged to learn that NRCS was developing the Soil and Water Eligibility Tool (SWET) as a more appropriate tool for determining eligibility and payment rates for conservation programs.
SCI will likely continue to be the tool used to help manage and direct conservation programs given its operational advantages. Therefore, it is imperative that USDA improve SCI as recommended above. NRCS must strengthen its support for SCI if any of the opportunities outlined above are to be seized. Currently, there is not a secure institutional home for SCI within NRCS, and one staff person is solely responsible for updating and maintaining the RUSLE2 databases on which SCI depends.
Coordinated Strategy Needed
As outlined above, using SCI and SMAF as currently developed can bring us closer to the comprehensive soil assessment and management system we need. We are, however, still falling short of the ideal system outlined by participants in the expert consultation.
USDA must develop a coordinated a plan in collaboration with current and potential partners in academia, federal, state, and local agencies, as well as nonprofit and for-profit entities to improve both SCI and SMAF in a coordinated fashion that plays to unique strengths of each tool. Such a coordinated plan should focus on those investments in improving SCI or SMAF that will have the most immediate impact on our ability to assess and plan for conservation of soil resources. Such a plan must look for opportunities to reduce the cost of data collection and to link SCI and/or SMAF with other tools that can contribute to a comprehensive approach to conservation planning and soil management. A suite of existing or developing tools, each with its own unique strengths, linked through a common interface with geographic information system capability may well be the most efficient approach to building an ideal system. A coordinated plan will make the best use of people and money to advance toward the capabilities of an ideal system.
Framework for Sustainable Soil Management
Beyond T Expert Consultation
Soil and Water Conservation Society. 2008. Beyond T: Guiding Sustainable Soil Management. Ankeny, IA: Soil and Water Conservation Society.