TILLAGE AND CROPPING SYSTEMS Tillage System and Crop Rotation Effects on Dryland Crop Yields and Soil Carbon in the Central Great Plains

CT crop–fallow system in the central Great Plains (Shanahan et al., 1988; Halvorson, 1990; Peterson et al., Winter wheat (Triticum aestivum L.)–fallow (WF) using conven1993; Halvorson and Reule, 1994; Farahani et al., 1998). tional stubble mulch tillage (CT) is the predominant production practice in the central Great Plains and has resulted in high erosion potential Winter wheat yields in a WCF rotation, even with 3 to and decreased soil organic C (SOC) contents. This study, conducted 4 mo less fallow time, are usually equal to those in WF from 1990 through 1994 on a Weld silt loam (Aridic Argiustoll) near and may be potentially greater than in the monoculture Akron, CO, evaluated the effect of WF tillage system with varying degrees WF system, thus making the RT and NT systems more of soil disturbance [no-till (NT), reduced till (RT), CT, and bare fallow profitable (Halvorson et al., 1994b; Dhuyvetter et al., (BF)] and crop rotation [WF, NT wheat–corn (Zea mays L.)–fallow 1996). (WCF), and NT continuous corn (CC)] on winter wheat and corn Reducing tillage with herbicidal weed control and yields, aboveground residue additions to the soil at harvest, surface intensifying the cropping system also has the potential residue amounts at planting, and SOC. Neither tillage nor crop rotato increase SOC (Campbell and Zentner, 1997; Halvortion affected winter wheat yields, which averaged 2930 kg ha 1. Corn son et al., 2002; Havlin et al., 1990; Havlin and Kissel, grain yields for the CC (NT) and WCF (NT) rotations averaged 198