Influence of cultivation on organic carbon in three typical soils of China Loess Plateau and Canada Prairies

The dynamics of organic carbon in 3 soils of China Loess Plateau and Canada Prairies was significantly different: in China, the Huangmian soil (Calcaric Cambisols, FAO) lost 77% of total organic carbon (0-20 cm) within 5 years of cultivation, with a decrease rate of 2.11 tons C.hm-2.yr-1, which was mainly caused by water erosion and tillage erosion; and the Huihe soil (haplic greyxems, FAO) lost 70% of total organic carbon (0-20 cm layer) at the rate of 0.961.06 tons C.hm-2.yr-1, because of water erosion and decomposition over 42 years. However, the orthic brown chernozem in Canada lost 11% and 44% of the total soil organic carbon (0-20 cm layer) after 40 and 80 years of cultivation, respectively, with a corresponding rate of 0.17 tons C hm-2.yr-1 and 0.45 tons C hm-2.yr-1. The improvement in tillage and rotation system, which prevented soil from wind erosion and increased current residues into soil, was responsible for the decrease of the loss rate. The dynamics of soil light fraction organic carbon (LFOC) was similar to that of total organic carbon: Huangmian and Heilu soil lost 73% and 90% of LFOC, while orthic brown chernozem lost 74% and 70% of LFOC after breaked in 1920 and 1960, respectively. Among the test soils, Huangmian and Huihe soil had the fast SOC depletion due to the difference in the allocation of organic carbon between LFOC and HFOC.