Changes in soil organic carbon and nitrogen as affected by tillage and residue management under wheat-maize cropping system in the North China Plain

The importance of soil organic carbon (SOC) and nitrogen (N) sequestration in agricultural soils as climate-change-mitigating strategy has received robust attention worldwide in relation to soil management. This study was conducted to determine the temporal effects of different tillage systems and residue management on distribution, storage and stratification of SOC and N under wheat (Triticum aestivum L.) - maize (Zea mays L.) cropping systems in the North China Plain (NCP). Four tillage systems for winter wheat established in 2001 were: moldboard plow tillage with maize residues removed (PTO), moldboard plow tillage with maize residues incorporated (PT), rotary tillage with maize residues incorporated (RT), and no-till with maize residues retained on the soil surface (NT). Compared with PTO and PT, significantly higher SOC and N concentrations were observed in the surface layer (0-10 cm depth) under NT and RT. In 2004, the SOC stocks were lower (P < 0.05) under NT and RT than under PT and PTO, however, the opposite trend was observed in 2012. Compared with 2001, the net profile (0-30 cm) SOC sequestration rate was 10.60, 13.95, 13.65, and 14.92 Mg ha(-1) in 2012 under PTO, PT, RT, and NT, respectively. As for SOC stocks in the 0-50 cm profile, no significant differences (P < 0.05) were observed among NT, RT, and PT. The trends in N stocks in profile (0-30, 0-50 cm depth) were NT > RT > PT > PTO in both years. Compared with other treatments, SOC and N stocks were the lowest (P < 0.05) under PTO. Therefore, crop residues play an important role in SOC and N management, and improvement of soil quality. The higher SOC stratification was observed under NT and RT than under PT and PTO, whereas the C:N ratio was higher (P < 0.05) under PT and PTO than under NT and RI systems. Therefore, the notion that NT leads to higher SOC stocks than plowed systems requires cautious scrutiny. Nonetheless, some benefits associated with NT present a greater potential for its adoption in view of the long-term environmental sustainability under wheat-maize double-cropping system in the NCP. (C) 2014 Elsevier B.V. All rights reserved.