Soil erosion from cropland in the United States has been recognized as an important problem for over sixty years. Concern initially was centered on the loss of fertile topsoil and the fear that agricultural productivity would decline. Recently, however, there has been a growing understanding of the off-farm impacts of sediment and chemical transport (U.S. Environmental Protection Agency, 1995). Therefore, both private (on-farm) and public (off-farm) benefits can be gained from reducing erosion from the nationās agricultural lands.
Conservation tillage is one of many conservation practices developed to reduce soil erosion. In its broadest sense, conservation tillage is defined as a tillage system that leaves enough crop residue on the field after harvest to protect the soil from erosion. In general, tillage that leaves a residue cover of at least 30 percent after planting is deemed conservation tillage; residue cover will vary, however, according to soil type, slope, crop rotation, winter crop cover, and other factors.
Additional benefits are associated with the use of conservation tillage beyond keeping the soil on the field. After several years under the practice, the soilās organic matter and structure may improve, thus increasing the quality of the agricultural soil. The change in organic content and the lack of soil disturbance also serve to sequester carbon, which may have long-term environmental benefits. Cropland on which conservation tillage is used also can serve as important habitat for wildlife. The residue left on the field offers food for some species and shelter for others.
Conservation tillage is not used on most U.S. cropland. The decision to change production technologies is based on many factors. Farmers will adopt conservation tillage if they perceive a gain in net benefits from switching technologies. These benefits can represent more than just the direct monetary factors reflected on a business balance sheet. Farmers also include nonmonetary adjustment costs, such as having to learn new skills or deal with new suppliers, when they assess whether to change production practices. What is not typically included in farmersā private decisions are the benefits or costs to society associated with the use of a new practice.
The purpose of this book is to identify and quantify, as much as possible, the likely benefits and costs associated with the use of conservation tillage that would accrue to farmers and to the public.
The current status of conservation tillage adoption is described in Chapter 2. The use of the technology varies widely by crop and by region, and factors affecting the adoption decision are discussed.
In Chapter 3, the on-farm and off-farm benefits and costs of conservation tillage adoption are identified. Conservation tillage and conventional tillage are compared with respect to yields and costs of production. Differences in input use are also described. As with many resource-conserving technologies, the relative advantage of conservation tillage depends on farm and regional characteristics (Caswell, Zilberman, and Casterline, 1993). The off-site or off-farm impacts of soil erosion, particularly with respect to water quality, are identified, and the benefits of tillage adoption on wildlife habitat and the reduction of carbon emissions are discussed.
An analysis is conducted to estimate the reduction of soil erosion that would result from the adoption of conservation tillage on lands for which the technology is considered suitable. Using figures developed by Ribaudo (1989) and Huzsar and Piper (1986), estimates are made of the public benefits that would be realized from the adoption-induced reductions in off-site erosion impacts. The results of this analysis are presented in Chapter 3.
If the off-site and on-site benefits of increasing the use of conservation tillage are greater than the costs to farmers of adopting the technology, several public policies can help influence farmers to adopt conservation tillage. A lexicon of these policy options is provided in Chapter 4. The U.S. government, primarily through the U.S. Department of Agriculture (USDA), has developed a suite of policies to promote the use of preferred agricultural practices. These policies and their effect on the adoption of conservation tillage are also described.
Before the discussion of current conditions and policies, let us first consider a brief history of conservation tillage in the United States.
CONSERVATION TILLAGE IN HISTORICAL CONTEXT
The use of crop residue in the United States to sustain soil productivity dates to the early eighteenth century. Colonists from Europe, observing the more severe storms in the New World than in the Old, realized the need to use cover crops and crop residue to mitigate soil erosion (Moldenhauer, Kemper, and Langdale, 1994). Throughout the nineteenth century, farmers experimented with alternative production practices to produce food and fiber without degrading the soil resources in the process. It was only in the 1920s, however, that field experiments were initiated to assess objectively the effects of sheet and rill erosion1 and wind erosion on soil productivity. These early efforts were disparate and tended to focus on issues of concern to a specific geographic area, for example, corn in Illinois (Odell et al., 1984). Unfortunately, no objective measures are available that describe how these efforts affected farmer behavior and net farm income (private benefits) or the extent to which soil erosion was reduced (public benefits) and soil productivity enhanced.
With the establishment of the Soil Conservation Service in 1935, a more organized and comprehensive assessment of conservation tillage began. A large number of conservation tillage practices, such as mulch tillage, were evaluated at land grant university experiment stations throughout the United States (Moldenhauer, Kemper, and Langdale, 1994). It was quickly realized that due to spatial variation in soil characteristics and weather patterns, farming with conservation tillage required a different approach to soil preparation, fertilizer application, and weed and insect control, as well as an awareness of the topography of the land farmed in relation to water sources. Therefore, conservation tillage technology was difficult to transfer unilaterally across major soil resource areas. Thus, conservation tillage diversity would be the norm, meaning that conservation tillage practices would have to be tailored to the specific crops grown and to the climatic conditions in a geographic region. A characteristic that all such practices would possess, however, was a need for the farmer to understand and use appropriate management practices.
Following World War II, plow planting methods were refined by the U.S. Department of Agriculture and land grant university researchers. It was shown that the best soil conservation contribution of these methods was surface roughness to control runoff. Although cool season crop residues were managed near the soil surface, some secondary cultivation was required for weed control, even though selective herbicides were available.
Many other forms of conservation tillage emerged during the 1960s and 1970s, including ridge tillage for cold wet soils of the Corn Belt and strip till for restrictive horizon Ultisols of the Southeast. It was during this time period that the use of conservation tillage became widespread.
The following chapters will place in perspective the role that conservation tillage can play in sustaining agricultural productivity and improving the environment.