Effects of rotational tillage practices on soil structure, organic carbon concentration and crop yields in semi-arid areas of northwest China

Continuous conventional tillage can cause serious soil degradation in rain-fed agriculture, which reduces crop productivity. Adopting suitable tillage practices is very important for improving the soil and increasing crop productivity. Between 2007 and 2010, a 3-year field study was conducted in semi-arid areas of southern Ningxia, China, to determine the effects of rotational tillage practices on bulk density, soil aggregate, organic carbon concentration and crop yields. Three tillage treatments were tested: no-tillage the first and third year and subsoiling the second year (NT/ST/NT); subsoiling the first and third year and no-tillage the second year (ST/NT/ST); and conventional tillage each year (CT). A conventional tillage treatment was used as the control. Under the rotational tillage treatments, the mean soil bulk density at a depth of 060 cm was significantly (P < 0.05) decreased by 4.9% compared with CT, and with the best effect under ST/NT/ST. The soil organic carbon (SOC) concentration and aggregate size fractions and stability at 040 cm depth were significantly (P < 0.05) increased in rotational tillage treatments when compared with the conventional tillage, and the ST/NT/ST treatment produced the highest increases. Significant differences were detected in the SOC concentration in 2 to 0.25mm size fractions at 030 cm depth between rotational tillage treatments and conventional tillage. Biomass and grain yield with the rotational tillage practices were significantly positively influenced over 3 years, and ST/NT/ST produced the highest average crop yields among the three treatments. Therefore, it was concluded that the application of rotational tillage with subsoiling every 2 years and no-tillage every other year (ST/NT/ST) should be of benefit in promoting the development of dryland farming in semi-arid areas of northwest China.