Agriculture in the Southeast was dominated by cotton in the late 19th century, with Georgia and Alabama as the leading cotton-producing states. In 1896, half of Alabama’s population was employed on the state’s approximately 3 million acres of cotton [36]. Although cotton is a profitable crop, growing it results in a greater risk of soil erosion due to the limited amount of crop residues produced [39]. Soil erosion in the Southern Piedmont major land resource area reduced cotton yields by as much as 4 percent for each centimeter of topsoil lost [9]. Erosion is a natural process by which land surfaces lose top soil gradually through the forces of wind, water and temperature. Crop residues covering the soil surface can significantly reduce or eliminate erosion.
Modern patterns of cultivation and mechanization have increased the rate of soil erosion [28]. Agriculture has historically relied on tillage to prepare the soil for planting and to control weeds. Plowing, or primary tillage, is used to invert the top layer of soil, break up compaction, turn under residues and bury weed seeds. Secondary tillage, including harrowing and/or disking of the soil, results in smooth, clod-free seedbeds. Although these tillage practices can increase cash crop yields, the soil surface is left prone to erosion that degrades cropland due to the loss of carbon and other nutrients. Eventually the soil becomes unproductive [38]. When soil and crop productivity decline, fertilizer and pesticide use increase. In many cases, these increased inputs result in pollution and health problems because they leach or run off into local water bodies [41].
Soil erosion has been recognized as a problem in the United States since the 1700s [4]. Leaving crop residues on the soil surface was one of the first strategies used to protect highly erodible soils planted to cotton. In 1896, J. F. Duggar, in Auburn, Ala., began testing his theory that crop rotations and winter legumes could protect southeastern soils from winter erosion [36].
In 1928, a USDA bulletin written by Hugh Hammond Bennett [5] and William Ridgely Chapline titled Soil Erosion: A National Menace roused national attention and focused the nation’s interest on stopping soil erosion. One of the first federally funded initiatives focused on managing cool-season crop residues in the Southeast. In 1932, the first conservation tillage method, called the “middlebuster,” was developed to manage cool-season crop residues at the Soil Erosion Experiment Station in Tyler, Texas [2]. The middlebuster was a non-inversion tillage method that plowed furrows into winter cover crops. It is similar to in-row subsoiling.
The Dust Bowl began in the early 1930s and resulted in a new era of soil conservation. In 1935, H.B. Hendrickson was transferred to the Southern Piedmont Soil Experiment Station in Watkinsville, Ga., where he further tested the middlebuster. Just north in Hall County, Ga., a farmer, Mr. J. Mack Gowder, developed a stubble-mulch implement [32]. This steel chisel was formed from a worn road grader and tilled the soil while leaving most crop residues on the soil surface. M.L. Nichols and the Peele-Beale team at Clemson, S.C., tested and developed conservation tillage practices under the umbrella of “Stubble-Mulch Tillage.” In 1936, W. Kell and R. McKee published Cover Crops for Soil Conservation, which recommended the use of alternative cover crops as a “green manure,” meaning a supplemental nitrogen source, as well as the use of a soil conservation practice [29].
In the 1930s, the Graham-Hoeme Chisel and the Noble Blade Cultivator were developed by farmers Fred Hoeme and C.S. Noble. Their goal was to reduce wind erosion. Edward Faulkner published Plowman’s Folly in 1943. This controversial treatise generated one of the most significant agricultural debates in the last century [17]. Faulkner recognized the potentially destructive nature of intensive tillage practices and stated that plowing (1) interrupted the movement of water deep in the soil to the topsoil; (2) buried crop residues too deeply, resulting in slow decay using soil moisture that could be used by the growing crop; (3) accelerated the drying out of topsoil; and (4) increased the decomposition of soil organic matter. All of these contribute to decreased crop productivity [38]. Faulkner claimed that “there is nothing wrong with our soil, except our interference” [17]. Faulkner’s work was central to the soil conservation movement, which led to the development of further conservation tillage practices and systems.
In the 1950s, Dudley and Wise [19] worked with John Deere to develop the “Grassland Drill” to plant directly into untilled soil or sod. Competition for soil moisture, soil fertility and sunlight from surviving vegetation plagued conservation tillage efforts and limited farmer adoption. Other major obstacles to adoption included weed pressures, inadequate equipment, soil fertility, insects, disease and economics.
During the 1960s, farmers were encouraged to adopt other conservation practices including crop rotations, contouring, strip cropping, terraces, conversion to grassland, and in extreme cases, conversion to woodlands. The southeastern landscape today reflects this conversion as we often see grass or trees rather than cropland. Eroded cropland was converted to grasslands, and if the land was highly eroded, it was converted to forestland. Major obstacles to conservation tillage began to be addressed by farmers and researchers in Virginia, Ohio, Texas, Kentucky and Illinois [16, 32, 50]. The emphasis was “non-inversion,” with corn planted into a cool-season sod.
Also in the 1960s, herbicides were developed that diminished or controlled competition from weeds. The herbicides paraquat and atrazine were critical in the sustained development of conservation and no-till practices for corn [32, 50]. Development of 2,4-D, dicamba and glyphosate provided grass and broadleaf-weed control. Equipment innovations were taking place as well. Triplett et al. [49] modified a John Deere Grassland Drill by adding rolling coulters ahead of disc openers to cut surface residue and to allow proper seed placement into untilled soil. Jerrell Harden, an innovative farmer near Banks, Ala., developed an in-row chisel subsoil implement in the early 1970s. This implement is the forerunner of the in-row subsoiling implements used today.
Nationwide, conservation tillage increased from 2.3 percent of cropland in 1965 to just above 10 percent in 1979. Early conservation tillage research focused on small grains, corn and soybeans. For these crops, the time-saving and moisture-saving benefits of conservation tillage were especially advantageous [13]. Early adoption of conservation tillage in states along the Appalachian Mountains was encouraged because the soil, despite being insulated by crop residue, warmed early enough for timely spring planting of corn and wheat. Southeast states with farmland in the Appalachian Mountains include Alabama, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee and Virginia. By 1972, Appalachian state adoption rates were the highest in the nation. In contrast, adoption rates in the Mississippi Delta and Southeast regions lagged due to persistent weed problems in cotton, soybeans and tobacco [13]. New challenges began to arise with the increasing adoption of conservation tillage during the late 1970s into the 1990s. These challenges included shifts in the types of weeds, diseases and pests, as well as fertility problems. This fueled a new era of conservation research.
The Food Security Act of 1985 provided a boost to conservation tillage adoption; it aimed to reduce production on highly erodible lands and to increase the use of soil conservation practices by including them as a qualification for crop subsidy programs. Conservation tillage was one of the eligible conservation practices and had to be initiated by 1990. As a result, there was a sharp increase in the rate of adoption between 1989 and 1991 [53]. In 1996, the farm bill included a mandate for the Environmental Quality Incentives Program (EQIP), a voluntary conservation program. Approximately 30 percent of EQIP funds were used to combat soil erosion by giving farmers incentive payments to adopt conservation tillage and cover crops [11]. According to Claassen et al. [11], these programs have resulted in a significant reduction in soil erosion across the United States.
In the mid-1990s, the availability of glyphosate-resistant crops increased adoption of conservation tillage by effectively replacing tillage with herbicides for weed control. This greatly simplified weed management and dramatically reduced herbicide costs. The cost of glyphosate-based herbicides declined $40–$45 per gallon ($10.60–$11.90 per liter) in 1990 to $12–$16 per gallon ($3.20–$4.20 per liter) in 2005 [25]. Givens et al. [26] found that 33 percent of growers in the Southeast converted to no-till after adopting glyphosate-resistant crops. Most growers shifted to either continuous glyphosate-resistant cotton or continuous glyphosate-resistant soybeans. Culpepper [15] estimated that between 1997 and 2003 the number of acres planted in glyphosate-resistant cotton increased from 23 percent to 90 percent of total cotton planted. They reported similar patterns in soybeans but not for corn. The continued use of herbicide-resistant varieties has given rise to a new problem: weed species that are more tolerant or resistant to glyphosate [15].
As of 2004, over 50 percent of all corn and soybean acres in the Southeast were planted using conservation tillage practices, with cotton just surpassing the 40 percent mark. The use of conservation tillage in peanuts lagged because of harvesting methods [12]. Bergtold et al. [7] reported that 69 percent of crop producers in Alabama use conservation tillage and 66 percent use cover crops for soil protection, winter annual grazing or forage. While adoption rates continue to increase, increased weed resistance has resulted in some farmers reverting to intensive tillage to control weeds.
Conservation tillage has become more than just a tillage practice. Conservation tillage systems have evolved to include the use of cover crops that produce a considerable amount of residue, referred to as high-residue systems. These systems also emphasize the use of crop rotations to maintain the productivity of cash crops and to break pest cycles. New agricultural research has investigated production systems that dynamically integrate multiple crops, livestock and other agricultural enterprises.