Improved no-till management techniques have allowed greater cropping intensity in the central Great Plains. Organic carbon (OC) contents in the soil have increased because of greater plant biomass production and less carbon loss from oxidation. Increased OC in the soil leads to improved soil physical properties and better crop production. The plots were located at the Central Great Plains Research Station at Akron, Colorado on a Weld loam. Samples were collected at depth increments of 20-95 mm, 115-180 mm, 200-275 mm, and 295-370 mm. We measured OC from plots in a winter wheat–fallow rotation (WF), a winter wheat, corn, millet rotation (WCM), and a permanent grass treatment in 2005, after 15 years in the respective system. The permanent grass plots had greater OC, greater water stable soil aggregates > 0.25 mm (WSMA), and greater saturated hydraulic conductivity compared with cropped plots. Plots with the WCM rotation had greater OC and WSMA than plots with the WF rotation. There were no cropping system effects on bulk density or pore size distribution. The greatest OC for all plots was in the surface Ap horizon. The greatest WSMA was in the Bt2 horizon at the 200-275 mm depth. There was poor correlation between OC and WSMA but a good correlation between WSMA and other soil properties. Increasing soil OC may improve soil properties over time but many years may be needed for measurable improvements to be noted. Investigation is needed in the constituents of soil OC provided by continuous grass species to identify the greater effects these species have on improving soil properties compared with crop species.