The experiment was a split-plot design with four replicates initiated in the fall of 2001 (Liang et al., 2007). The dimension of each main plot was 10.4 m 30 m, each main plot was split lengthwise into two 5.2m 30m sub-plots. Three tillage treat- ments applied at the whole plot level in the experiment were no tillage (NT), ridge tillage (RT) and conventional tillage (CT), and rotations of maize and soybean (Glycine max Merr.) were applied at the sub-plot level with both crops present in each year in each whole plot.
Treatments in the CT consisted of fall mouldboard ploughing (20cm) followed by the secondary seedbed preparation in the spring by disking (7.5–10 cm) and harrowing, and ridge-building. In RT, ridges were maintained year-to-year with a cultivator in June, and a modified lister and scrubber were used to form and press the ridge. Under the NT, no soil disturbance was practiced except for the planting using a no-till planter. Maize and soybean was planted with a no-till planter. Planting dates ranged from April 17 to May 17 (Table 1). Planting was done on the same day for all plots each year. The ridge configuration in RT and CT treatments were changed from 16 cm height and 75 cm width in 2002–2009 to 16 cm height and 65 cm width in 2010–2013 to match a different no-till planter width. The crops were harvested in October. After harvest, the maize stalks in NT and RT treatments was cut into about 30 cm pieces leaving 30–35 cm stubble stand, and pieces were then placed on the soil surface. Soybean residues was returned to the soil surface.