WINTER-WHEAT RESPONSES TO SURFACE AND DEEP TILLAGE ON THE SOUTHEASTERN COASTAL-PLAIN

Conservation tillage practices have seldom been used to produce winter wheat (Triticum aestivum L.) on the U.S. southeastern Coastal Plain, primarily because of inadequate planting equipment and the need for de ep tillage. Despite improved equipment, little is known about the effe cts of surface and deep tillage (ST and DT) systems on winter wheat de velopment and grain yield on the Coastal Plain. Objectives of this 2-y r study were to a) determine whether ST affects the grain yield respon se of winter wheat to DT and (ii) examine the effects of ST and DT on winter wheat development. The soil was a Goldsboro loamy sand (fine-lo amy, siliceous, thermic Aquic Kandiudult). Treatments were ST (disked twice or no surface tillage) and DT (deep tilled using a ParaTill or n o deep tillage). Averaged over years and levels of DT, the number of e merged seedlings was 16% less with no ST than with disking. With DT, t he number of heads per square meter was similar for the two levels of ST treatment, indicating that wheat grown with no ST produced more hea ds per plant than with disking. Soil water contents were usually lower in 1995 than in 1994 for all treatments (<2 g kg(-1) prior to inflore scence emergence in 1995). Aboveground dry weights near inflorescence emergence, kernel no. m(-2), and grain yields averaged 39, 26, and 22% less, respectively, in 1995 than in 1994. Deep tillage increased abov eground dry weight, kernel no. m(-2), and grain yield more for wheat i n no-surface-tillage plots than in disked plots. When deep tilled, ST had no effect on grain yield in 1994, but yields were 25% greater for wheat grown with no ST in the drier year of 1995. There may be no need to disk the soil if DT is performed and proper planting equipment is used to produce winter wheat on the southeastern Coastal Plain. Yield increases due to DT in this region should be greater with no ST than w ith disking.