In the mid-1980s, growers in the region realized the need to adopt conservation practices on highly erodible cropland. However, techniques such as high-residue management, in-row subsoiling and strip tillage, which work well on the sandier Coastal Plain soils of southern Alabama and southern Georgia, did not do as well as conventional tillage with cotton in the “red lands” of the Tennessee Valley. Strict no-till as used in the loessial soils of western Tennessee and Kentucky did not do as well as conventional tillage with cotton on the red lands. Conservation tillage worked much better on the sandier soils of the Sandstone Plateau/Sand Mountain region. The silt loams and clay loams of the valleys apparently did not respond to in-row subsoiling because they rarely develop traffic pans as do the sandier Coastal Plain soils . A traffic pan is a 2- to 4-inch thick layer of compacted soil that results from the downward pressure of tillage equipment . Deep spring tillage on red-land soils often brings up wet, clayey soil that can result in severe clodding when it dries. This limits deep tillage on these soils to the late fall and winter months when winter freezes can break up the soil. High residue tends to keep valley soils cooler and wetter in the spring, and this is not desirable for cotton production because growing degree days are limited in the region.
Conservation tillage in the Tennessee Valley proceeded in small steps before a complete system could be developed. Cotton farmers in the Tennessee Valley who tried no-till in the late 1980s and early 1990s reported 8–15 percent yield reductions compared with conventional tillage [2, 3, 8]. Most farmers were planting cotton into old cotton stubble using no-till techniques and reporting reduced cotton stalk growth after a few years. Research at the time supported either a lack of cotton-yield response to no-till or a yield reduction when no-till practices followed conventional tillage on these highly eroded soils low in organic matter [9, 11]. While in-row subsoiling showed positive corn and cotton yield responses in the Coastal Plain soils of South Alabama, in-row subsoiling on a Decatur silt loam in the Tennessee Valley actually reduced cotton yields . Valley cotton farmers began using small-grain cover crops more intensely in the mid-1990s. Research showed that a surface compaction layer was limiting cotton growth and yields. Planting wheat or rye after cotton harvest breaks up the compacted layer and improves growth and yields [3, 7].
The recommended conservation tillage system finally developed for the valleys consisted of non-inversion deep tillage such as paratilling under the row in the fall coupled with a high-residue rye cover crop . Fall tillage allows these heavier soils to “mellow” over the winter, which reduces the number of clods and surface roughness. A fall cover crop with fall tillage helps control erosion and provides a surface cover to conserve soil moisture. Research over a seven-year period showed that cotton, no-till planted into wheat cover crop residue, out yielded conventional-tillage cotton by over 16 percent . On the sandstone plateaus, soybean and grain producers can be successful with no-till, strip till and high-residue management systems that are common on the sandy Coastal Plain soils.
Traditionally, cover crops were never popular on the large fields of the Tennessee Valley. They kept soils cooler and wetter in the spring when early cotton planting is critical. However, gradually declining soil organic matter with conventional tillage, continued soil erosion and stagnant yields led many growers to reconsider the use of cover crops. Cover crops, typically wheat or rye, with no deep tillage can produce yields similar to deep tillage on these silty and clayey textured soils [5, 8]. Irrigation coupled with cover crops has been shown to improve cotton yields and fiber characteristics . Wheat and cereal rye are by far the most popular winter cover crops for this region. They are easier to kill with glyphosate in the early spring than winter legumes, and they produce dry matter earlier than most legumes.