Response Of Soil Organic Carbon Fractions To Different Growth Years Of Alfalfa Field And Rotation Systems On The Western Loess Plateau

The effects of soil organic carbon fractions under lucerne(Medicago sativa L.) field with different cultivating ages and lucerne-crop rotation of rainfed agricultural area on Western Loess Plateau was studied by long-term positioning experiments in Lijiabu, Dingxi City, Gansu Province.The different cultivating ages of lucerne respectively are 3 years, 8 years and 12 years. Different Lucerne-crop rotation system including Lucerne-Lucerne(L-L), Lucerne-Fallow(L-F), Lucerne-Wheat(L-W), Lucerne-Corn(L-C), Lucerne-Potato(L-P), and Lcerne-Millet(L-M). The different characteristics of soil organic carbon and its fractions under different cultivating ages and lucerne-crops rotation systern was discussed. In order to reveal the rule of forage crop rotation system, and provide to scientific basis for lucerne management for sustainable and stable yield of dryland crops on the loess plateau arid. The results showed that:(1) It has significant difference between soil organic carbon and its fractions Under different fixed number of year of the planting lucerne, with the increase of the ages of years, the specific performance was 8a>12a>3a.(2) Compared with Lucerne-Lucerne, lucerne field rotation and other food crops after 0~200 cm total organic carbon(TOC) are declining, shown as: L-F(Lucerne- Fallow)>L-L(Lucerne-Luce-rne)>L-M(Lucerne-Millet)>L-C(Lucerne-Corn)>L-W(Lucerne-Wheat)>L-P(Lucerne-Potato).With the deepening of the soil, TOC was gradually decreased in 0~200 cm soil profile, Higher levels was showed in 0~50 cm, then it showed the decreased trend under 50 cm soil layer.(3) Compared with Lucerne-Lucerne, readily oxidizable organic carbon(ROC) by lucerne field rotation and other food crops of 0~200 cm was showed:L-L(Lucerne-Lucerne)> L-F(Lucerne-Fallo-w)>L-C(Lucerne-Corn)>L-M(Lucerne-Millet)>L-W(Lucerne-Wheat) >L-P(Lucerne-Potato). ROC in 0~200 cm soil profile from the surface to the lower level gradually reduce trends, with higher levels of 0~30 cm, 30 ~110 cm soil layer smaller volatility rises, 110~200 cm ROC content is gradually diminishing.(4) Compared with Lucerne-Lucerne, lucerne field rotation and other food crops after 0~200 cm humus organic carbon(HOC) are declining, shown as: L-L(Lucerne-Lucerne)>L-M(Lucerne-Mill-et)>L-C(Lucerne-Corn)>L-F(Lucerne-Fallow)>L-W(Lucerne-Wheat)>L-P(Lucerne-Potato).HOC presents in the 0~200 cm soil layer with the deepening of the soil movements decline trend, and between different processing HOC content difference is small, with higher levels of 0 ~10 cm, to 10 cm below the soil content of HOC appeared a downward trend.(5) Compared with Lucerne-Lucerne, lucerne field rotation and other food crops after 0~200 cm soil layer of hot-water extraction carbon(HWC) are declining, shown as: L- L(Lucerne-Lucerne) > L-C(Lucerne-Corn) >L-F(Lucerne- Fallow) >L-W(Lucerne-Wheat) > L-M(Lucerne-Millet) > L-P(Lucerne-Potato).HWC in 0~200 cm soil layer presents a decreasing trend with the deepening of the soil fluctuations, 0~50 cm soil layer HWC content is higher, each process in the 50~170 cm soil HWC content difference is bigger.(6) Compared with Lucerne-Lucerne, lucerne field rotation and other food crops after 0~200 cm Light Fraction Organic Carbon(LFOC) light group were on the rise, shown as:L-M(Lucerne-Millet) >L-F(Lucerne- Fallow) L-P(Lucerne-Potato) >L-W(Lucerne-Wheat) > L-C(Lucerne-Corn)> L-L(Lucerne-Lucerne).LFOC in 0~200 cm soil profile from the surface to the lower level gradually reduce trends, among them with a scale of 0~80 cm soil LFOC content is higher, below 80 cm soil layer LFOC content gradually decreased;Compared with Lucerne-Lucerne, lucerne field rotation and other food crops after 0~200 cm soil organic carbon content(HFOC) heavy group weredeclining,assumed:L-F(Lucerne-Fallow)>L-L(Lucerne-Lucerne) >L-C(Lucerne-Corn)>L-M(Lucerne-Millet)>L-W(Lucerne-Wheat)>L-P(Lucerne-Potato).HFOC presents in the 0~200 cm soil layer with the deepening of the soil movements degressive trend, including 0~30 cm soil layer HFOC content is higher, 30 cm below the soil and surface HFOC content difference is smaller.(7) In lucerne rotation system continuous cropping was beneficial to the improvement of the index of soil carbon library management, library of carbon management index of lucerne is obviously better than the continuous cropping lucerne- crop rotation mode.