Soil Health Analysis, Set. Группа авторов

studies such as those by Van Doren and Klingebiel (1952) and Klingebiel and O’Neal (1952) provided data that would now be regarded as critical soil health information. They reported that under virgin conditions, surface soil structure in most Corn Belt loam and silt loam soils was granular or crumb‐like. The soils were also highly aggregated and generally had low bulk density. However, as tillage intensity increased and crop rotation diversity decreased, the granular soil structure deteriorated to a fine, fragmented or massive condition. Annual moldboard plowing, coupled with multiple near‐surface tillage operations to prepare appropriate seedbeds and enhance oxidation of plant roots and other residues, was recommended, it ultimately resulted in decreased SOM levels, increased raindrop compaction, decreased infiltration, increased runoff, and greater soil erosion. Declining SOM also decreased plant available N, but post‐World War II advances in chemical N fixation and availability of new fertilizer materials resulted in a gradual substitution of capital for labor and SOM. This transition was described by Melsted (1954) as “replacing the art of farming with the science of farming” (Karlen et al., 1990).

Without question, the “Father of Soil Conservation” Hugh Hammond Bennett focused public attention on the critical need for and merits of soil conservation. In his overview of our American land, he clearly articulated the perils of soil erosion and how it has resulted in humankind “wasting the gifts of nature.” Continuing, Bennett clearly described the importance of productive land; emphasized that soil conservation is simply proper use and care of the land; outlined problems that soil conservation could help prevent; presented stratigies for conserving soil resources; and introduced Soil Conservation Districts (SCD) which began to be organized near his home in Anson County, NC, in 1937. It was through SCDs that farmers and land owners were introduced to detailed farm plans and new soil management practices (e.g. building of terraces, contour cultivation, soil testing, drainage, strip cropping, cover crops, increased perennialization, restoring woodlands and pasture, stubble mulching, and planting windbreaks). Differences in on‐farm soil resources, fundamentally linked to inherent soil properties and processes, were articulated through land capability maps and the identification of Class I to Class VIII soils based on their potential and sustainability requirements. Farmers and soil conservationists were encouraged to work together to determine the best possible use for every part and parcel of each individual farm. Is this not what every soil health initiative is advocating?

      Furthermore, since humankind had already ignored warnings from Plato, Aristotle, Columella, Fitzherbert, Fream, as well as an untold number of indigenous leaders regarding the care and management of our soil resources, ravages of the American Dust Bowl could likely have been predicted. However, a steadily increasing population, growing demand for food, feed, and fiber, advances in technology regarding how to till vast areas of the Great Plains, and well‐intentioned, but inappropriate federal land use policies, coupled with farm economics due to the Great Depression, changes in regional weather patterns and other cultural factors contributed to the disaster (History.com Editors, 2020). Fortunately, due to science‐based leadership by Yoder, Lowdermilk, Bennett and others, the U.S. Congress passed Public Law 74‐46, which recognized "the wastage of soil and moisture resources on farm, grazing, and forest lands is a menace to the national welfare." The act created the USDA Soil Conservation Service (SCS), now known as the Natural Resources Conservation Service (NRCS), and helped promote many of the practices outlined by Bennett (1950), including sound land use, adherence to carrying capacity, and development of farm conservation plans.

      With arrival of another prolonged drought in the 1950s, Congress passed the Great Plains Conservation Program which focused financial assistance for conservation in the Plains states. SCS provided financial and technical assistance to meet multiple objectives of conservation and economic stability. This included providing technical assistance for the Soil Bank Program (SBP), precursor to current Conservation Reserve Programs (CRP). The SBP paid to retire degraded cropland and provided financial incentives to farmers for planting protective cover crops (NRCS, 2018).

      Conservation was given another boost under the Kennedy and Johnson administrations in the 1960s when SCS’ role was expanded to address both rural and urban land use. Through an emphasis on rural development, SCS began to work with landowners in areas larger than small watersheds or conservation districts. The late 1960s can also be characterized as a time of broad popular concern regarding the environment, health, and welfare of people throughout the United States and around the world (e.g., Norman Borlaug and the Green Revolution). The first Earth Day in 1970 increased environmental awareness, and ultimately a national framework of environmental policies was created that changed the way the SCS put conservation on the ground. Soon, federal agencies were required to evaluate and report on the environmental impacts of their activities.

Water quality and non‐point source pollution became important areas of concern. Protection of wetlands emerged as critical issue with SCS participation in the Water Bank program and provided incentives to landowners to protect wetland habitat (NRCS, 2018). During the 1970s, SCS also gained greater authority to monitor and assess the nation’s natural resource base through the National Resources Inventory (NRI) – a focal point for future soil quality assessment studies. Finally, in response to these expanded authorities, the Congress changed SCS’s name to the Natural Resources Conservation Service (NRCS) in 1994 (NRCS, 2018).

      For brevity, this chapter references only a few significant soil research studies, laws and policies. For example, one federal program that did lead efforts to include soil health in the research portfolio for was the Sustainable Agricultue Research and Education (SARE)] program, but until recent private sector efforts (Chapter 1) steadily increasing farm size and purchased inputs minimized the impact of that program across the broader agricultural community. This chapter has also likely failed to appropriately recognize many of the pillars in soil management research and extension (Karlen et al., 2014a) that contributed substantially to the soil conservation foundation upon which soil health has evolved. Some of those outstanding contributions include studies by Balfour, Bidwell, Hole, Hyams, Jenny, Leopold, Rodale, Whitney, Yaalon, and many others. Without question, all contributed significant knowledge and understanding the soil functions providing the science‐based foundation for current soil health endeavors.

From 1970 to 2000 – Soil Quality Emerges

      Concept Development

As noted previously, soil physical and chemical aspects of soil management dominated post‐World War II activities for most soil and crop scientists. We suggest this reflected our limited understanding of soil biological properties and processes as well as the lack of instrumentation and analytical tools that are now available. None‐the‐less several well recognized soil microbiologists such as Allison (1968, 1973), James P. Martin (1939, 1940, 1971), Eldor Paul (Mathur and Paul, 1967; Paul and Voroney, 1980; Paul, 2014), and Martin Alexander (Alexander, 1961, 1980; Acea et al., 1988) contributed insights that expanded the foundation upon which soil health has evolved. There was also an increasing awareness that decreased use of crop rotations, increased size and weight of farm tractors and implements, as well as increased use of conservation tillage practices, were having measurable soil tilth effects in the northern Corn Belt (Voorhees, 1979). Soil compaction, caused by those factors, was recognized as being important for several reasons, including its effect on annual freezing and thawing processes (Voorhees et al., 1978; Voorhees, 1983; Voorhees and Lindstrom, 1984). Coupled with increasing concern regarding soil degradation, Pierce et al. (1983, 1984) conducted several erosion – productivity studies and Dormaar et al. (1988) intentionally eroded a Dark Brown Chernozemic soil (Mollisol) to demonstrate that applying commercial fertilizer or manure could restore soil productivity. However, during a subsequent drought, only the sites that received manure maintained yields and furthermore, after five years those treatments showed increased SOM content and improved water‐stable aggregation.

      Warkentin and Fletcher (1977) introduced the concept of soil quality, which in many ways became the foundation for current soil health activities. The transition to soil quality emphasized the multiple ecosystem services (i.e., food and fiber production, recreation, and recycling or assimilation of wastes or other by‐products) that soils must provide (Carter et al., 1997). A focus on soil quality required recognition that: (1) soil resources are constantly being