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.