Dynamics Of Soil Organic Carbon, Fertility And Water In Different Land Uses From The Semi-arid Loess Plateau, China

Three land uses: seeded alfalfa (Medicago sativa L.) with different growth years, abandoned fields after cropland with series succession proceeding and Caragana korshinskii shrubs with different growth years, from Loess Plateau of China, were used to evaluate the effect of land uses on soil organic carbon (SOC), light fraction of organic C (LFOC), soil biomass microbial C (MBC) and N (MBN), soil P and N elements, aboveground biomass and soil water content, for a purpose of providing insights into the development of sustainable agriculture systems and vegetation restoration and construction on the Loess Plateau. The results as shown follows:In the different growing years of artifical alfalfa (Medicago sativa L.) grasslands (2-, 3-, 7-, 13-, 19-, 23-year alfalfa grassland), 23-year alfalfa grassland is a sloping field on a hillside, and the other treatments are all flat fields in a valley. In these six grasslands, the 2-year alfalfa was growing in a mixture with pea in the seeding year and pea was in the rotation the year before seeding, and was pure alfalfa grassland since the second year; the other treatments were all monocropped with wheat in rotation before seeding, except the 23-year alfalfa was native grassland before seeding. All the grasslands were unfertilized and mowed twice one year. The soil water content, soil water potential decreased and the desiccated layers grew with the number of growing years of alfalfa. Correlationship between forage yield and increasing years was curvilinear (y =-38.186x~2+841.86x +1154.7, R~2 = 0.4188**, P＜0.01), therefore the highest forage yield was achieved when alfalfa has been growing for 11 year. Soil LFOC, MBC and MBN all increased with the number of growing years. When alfalfa has been growing for more than 13 years, the soil MBC increased slowly, suggesting that MBC value is likely to reach a constant level. SOC, soil total P (STP), available P (AvaiP) and the ratio of SOC to soil total N (C/N) all tended to decrease monotonically with the growing years of alfalfa up to 13 year, and then increased. SOC was significantly positive correlated with STP, AvaiP, soil total C (STC, including SOC and inorganic carbon SIC), soil total N (STN) (R = 0.627**, 0.691**, 0.497*, 0.546*, respectively). MBC and LFOC was significantly positive correlated with the number of...