Fig. 1
Three tillage practices were selected for analysis, no-tillage (NT), ridge tillage (RT, including RT with minimal soil disturbance), and subsoiling tillage (ST, including in rotation tillage with NT). Under NT, the soil was not disturbed except for planting using a no-till planter. RT was characterized by ridge building with a cultivator and no-till planter was also used for seeding. ST required deep loosing operation to ~30 cm and it was often conducted as a one off operation in NT and RT system. Conventional tillage (CT) was chosen as a control for calculating the effects of the three practices on crop yield and/or SOC concentration. Other site characteristics such as mean annual temperature (MAT), mean annual precipitation (MAP), crop planting pattern, experiment duration, and other soil physical and chemical indicators were also collected.
Mean annual temperature (MAT) of these studies ranged from 0.5 to 10.4 ℃, mean annual precipitation (MAP) from 407.7 to 714.0 mm, and experimental duration from 1 to 32 yrs. According to the quantity and distribution of data, studies were divided into categorical groupings, as listed in Table 1.