Although most conservation tillage systems include cover crops, cover crops can present unique challenges with the clayey prairie soils. Winter annual legumes such as crimson clover, hairy vetch and lupine do poorly, while Balansa clover (Trifolium michelianum subsp. Balansae (Boiss) “Paradana”) has looked promising as a reseeding winter-legume cover crop in Mississippi tests [3]. Small-grain cover crops do well, but the residue that is valuable on sandier soils creates problems with timely planting and early-season crop growth. These problems can reduce yields, especially in wet years [23]. Surface residues increase soil moisture and contribute to anaerobic soil conditions that can cause nitrogen loss through denitrification [21]. The soil surface in conventional tillage dries more quickly without a cover crop. This reduced soil moisture at planting results in improved seed placement and seed-soil contact, as well as better stands and higher yields. However, tillage has to be balanced with the benefits of supplying a mulch to reduce surface crusting in the non-cracking soils of the region.
There has been limited research concerning the use of wheat as a cover crop planted in the furrow during the bed-forming operation as a one-pass tillage system. Using an air seeder that blows the wheat seed underneath the bedder sweep during the fall bedding operation resulted in a successful stand of wheat in the bed furrow [4]. However, corn yield was 13 percent lower than conventional tillage and no-till corn without cover crops. The lower corn yield may have been associated with the higher incidence of Pythium spp. and chinch bugs (Blissus leucopterus) when a wheat cover crop was used. Further research is needed to determine if the bed surface can be exposed to drying conditions when the soil is wet while the wheat protects the furrow from erosion. There are some farmers in the Blackland who use wheat or rye broadcast as a winter cover crop for corn or double-cropped with soybeans. They have experienced wet soil conditions that delayed herbicide application and corn planting in some years.
Double-cropping is effective for soil erosion control in this region. Double-cropped winter wheat and soybeans had the lowest runoff and lowest erosion rate when compared to monocrop tillage systems [13]. But historically, it often has not been the most profitable rotation due to low commodity prices and wet soil conditions that often delayed wheat harvest and soybean planting. Dry soil conditions at wheat harvest also result in delays in planting soybeans or seed germination since there is not sufficient soil moisture for germination. This can result in unprofitable yields.