Tillage system and crop rotation effects on dryland crop yields and soil carbon in the central Great Plains

Winter wheat (Triticum aestivum L.)-fallow (WF) using conventional stubble mulch tillage (CT) is the predominant production practice in the central Great Plains and has resulted in high erosion potential and decreased soil organic C (SOC) contents. This study, conducted from 1990 through 1994 on a Weld silt loam (Aridic Argiustoll) near Akron, CO, evaluated the effect of WF tillage system with varying degrees of soil disturbance [no-till (NT), reduced till (RT), CT, and bare fallow (BF)] and crop rotation [WF, NT wheat-corn (Zea mays L.)-fallow (WCF), and NT continuous corn (CC)] on winter wheat and corn yields, aboveground residue additions to the soil at harvest, surface residue amounts at planting, and SOC. Neither tillage nor crop rotation affected winter wheat yields, which averaged 2930 kg ha(-1). Corn grain yields for the CC (NT) and WCF (NT) rotations averaged 1980 and 3520 kg ha(-1), respectively. The WCF (NT) rotation returned 8870 kg ha(-1) residue to the soil in each 3-yr cycle, which is 2960 kg ha(-1) on an annualized basis. Annualized residue return in WF averaged 2520 kg ha(-1), which was 15% less than WCF (NT). Annualized corn residue returned to the soil was 3190 kg ha(-1) for the CC (NT) rotation. At wheat planting, surface crop residues varied with year, tillage, and rotation, averaging WCF (NT) (5120 kg ha(-1)) > WF (NT) (3380 kg ha-1) > WF (RT) (2140 kg ha(-1)) > WF (CT) (1420 kg ha(-1)) > WF (BF) (50 kg ha(-1)). Soil erosion potential was lessened with WCF (NT), CC (NT), and WF (NT) systems because of the large amounts of residue cover. Levels of SOC in descending order in 1994 were CC (NT) WCF (NT) WF (NT) = WF (RT) = WF (CT) > WF (BF). Although not statistically significant, the CC (NT) treatment appeared to be accumulating more SOC than any of the rotations that included a fallow period, even more rapidly than WCF (NT), which had a similar amount of annualized C addition. Reduced tillage and intensified cropping increased SOC and reduced soil erosion potential.