Blevins et al. 1983; Elliot and Papendick, 1986). This was spurred by the 1970s energy crisis, and although a portion of the crop residue remaining after grain harvest had traditionally been harvested and used for animal feed or bedding, off‐site transport of the crop residues was the critical issue being questioned (Karlen et al., 1984). On‐farm use resulted in recycling of nutrients and organic matter via manure disposal, but off‐site transport would likely prevent closing field‐specific carbon cycles.
Soil Quality Assessment
Following the 1970s oil crisis, new questions regarding the potential use of crop residues for bioenergy began to emerge as a conservation issue directly linking urban and rural communities. Field research designed to quantify the impact of crop residue harvest on SOM and subsequent productivity resulted in the evolution of a soil health assessment framework. An experiment in southwestern Wisconsin that quantified soil and corn yield response to removing, doubling, or retaining crop residue for 10 years (Karlen et al., 1994a) with moldboard‐, chisel‐, or no‐tillage practices (Karlen et al., 1994b). To more effectively interpret the combined biological, chemical, and physical responses to those treatments, a soil quality/health assessment framework that later becomes known as the Soil Management Assessment Framework (SMAF) (Andrews et al., 2004) was developed. Simultaneously, other assessment tools including an expanded Soil Conditioning Index (SCI), AgroEcosystem Performance Assessment Tool (AEPAT), and Cornell Soil Health Test (now known as the Comprehensive Assessment of Soil Health or CASH) also began to evolve.
The soil tilth review (Karlen et al., 1990) prompted advancement of soil quality/soil health concepts through a Rodale Foundation workshop (Rodale Institute, 1991) that was described by Haberern (1992) as coming “full circle” in reference to J. I. Rodale’s 1942 vision of a “soil‐care revolution.” Rodale had stated that greater awareness to soil health was needed to create “a healthy society, a country of prosperous farms, and healthy, vigorous people.” An important outcome of the Rodale workshop was consensus regarding the need for soil assessments that went beyond productivity and included environmental quality, human and animal health. There was also a realization that assessing and monitoring soil health was complicated by the need to consider multiple soil functions and integrate physical, chemical and biological attributes (Papendick and Parr, 1992; Parr et al., 1992; Warkentin, 1995). Discussions regarding subtle differences between inherent and dynamic soil quality indicators were another important outcome of the Rodale workshop.
Soil quality activities around the world expanded rapidly during the early 1990s, driven in part by increasing recognition of the role soils had in buffering and mitigating factors affecting environmental quality (Warkentin, 1992). However, the true global driver and inspiration for the advancement of soil health or quality was Dr. John W. Doran, to whom this book series is dedicated. His perspective stating that “soil health, or quality, can be broadly defined as the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health” (Doran, 2002) is to us, the ultimate goal for soil health. He also emphasized that soil health will change over time due to natural events or human impacts.
In Australia, Powell and Pratley (1991) developed a “Sustainability Kit” that provided guidelines for measuring soil structure, acidity (pH), salinity, and soil/water temperature. This kit also served as a precursor to John Doran’s field‐based soil health kit developed in collaboration with scientists at the Rodale Research Center and tested throughout the country (Liebig et al., 1996). Marketed with a USDA Soil Management Manual, the “Soil Health Kit” described simplified tests for soil respiration (Liebig 1996; Doran 1997), infiltration (Ogden et al., 1997), bulk density (Doran 1984), electrical conductivity (EC), pH, and nitrate‐nitrogen (NO3‐N) concentrations (Smith and Doran, 1996); a soil structure index and penetration test (Bradford and Grossman 1982); soil slaking and aggregate stability tests (Herrick et al. 2001); and an earthworm assessment protocol (Linden 1994). Since that time, the power and potential for on‐farm testing of soil health indicators has been greatly magnified by development of the internet, smartphones, and applications such as the Land‐Potential Knowledge System (LandPKS; Herrick et al., 2013).
Other developments included a symposium sponsored by the North Central Region Committee No. 59 that focused on SOM at the Soil Science Society of America (SSSA) meetings. That event led to the SSSA publishing two books that became known as the “blue” (Doran et al., 1994) and “green” (Doran and Jones, 1996) soil quality guides that are the precursors for this two‐volume series. Doran (2002) also provided important insight stating that although soils have an inherent quality associated with their physical, chemical, and biological properties, their sensitivity to climate and management practices means that land manager decisions ultimately determine soil health. He continued stating a pivotal role for scientists is translating scientific information regarding soil functions into practical tools that land managers can use to evaluate the sustainability of their management practices. Soil health indicators thus became the tools for making the assessments, but there is no single indicator or technology that will always be appropriate.
Soil health assessment has also been advanced by the NRCS, through databases at the Kellogg Soil Survey Laboratory (KSSL), National Soil Survey Center in Lincoln, NE that currently have analytical data for more than 20,000 U.S. pedons and at least 1,100 more from other countries (Brevik et al., 2017). Collectively, morphological descriptions are available for about 15,000 pedons (https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/research/?cid=nrcs142p2_053543#:~:text=Summary,1%2C100%20pedons%20from%20other%20countries) (verified 6‐12‐2020).
The NRCS also has extensive data on basic soil properties, landscape characteristics, and interpretations for use and management. Those databases, describing inherent soil properties, provide a resource to match various land uses with inherent ability of individual soils to perform critical functions (Karlen et al., 2003a). Building upon those resources, the NRCS created several cross‐cutting teams during the 1990s, including the Soil Quality Institute (SQI) whose scientists developed many of the first‐generation soil quality/soil health scorecards, assessment tools, and information packets. The SQI compiled soil quality information for NRCS staff to help them integrate soil quality concepts into conservation planning and resource inventory activities for their stakeholders (SQI, 1996). The SQI also provided leadership and collaboration for research studies designed to evaluate soil quality indicators at several scales, including Natural Resources Inventory (NRI) sites within four Major Land Resource Areas (Brejda et al., 2000a, 2000b, 2000c).
Linkages between soil and environmental quality were significantly strengthened by the National Academy of Sciences Soil and Water Quality: An Agenda for Agriculture publication (NRC, 1993). It prompted Dr. L.P. Wilding, 1994 president of the SSSA, to appoint a 14‐person committee (S‐581) with representatives from all SSSA Divisions. Appointees were asked to define the concept of soil quality, examine its rationale, determine if pursuing its development should be a core SSSA activity, and identify soil and plant attributes that would be useful for describing and evaluating soil quality (Karlen et al., 1997).
One of the first comprehensive soil quality/health assessments was used to quantify benefits of the CRP. Following passage of the 1985 Food Security Act, that program took 14.7 million hectares (36.4 million acres) in 36 states out of production (Skold, 1989). Recognized as environmentally sensitive or highly erodible land (HEL), the primary goal was to reduce soil erosion. Secondary CRP goals included: protecting the nation's ability to produce food and fiber, improving air and water quality, carbon sequestration, reducing sedimentation, fostering wildlife habitat, curbing production of surplus commodities, and providing income support for farmers (Allen and Vandever, 2012; FAPRI, 2007; Follett et al., 2001; Li et al., 2017). In exchange for retiring HEL for 10 years, USDA paid CRP participants (farm owners or operators) an annual per‐acre rent and half of the cost of establishing a permanent land cover (Young and Osborn, 1990).
Soil
