| CO2 and N2O has been paid great attention due to their substantial contribution to global warming and ozone depletion. It has suggested that agricultural soil is an important source of CO2 and N2O. Nowadays, many researchers have focused on demonstrating the soil CO2 and N2O fluxes of forests, grassland and farmland ecosystems, few report was found on trace CO2 and N2O fluxes from contour hedgerow intercropping system, one of the agroforestry patterns. We examined the effects of hedge prunings returning to field on the fluxes of soil N2O and CO2 under wheat-maize rotation in Amorpha fruticosa and Vetiveria zizanioides intercropping systems on a loamy clay soil, at Xianning, Hubei province, China. Soil CO2 and N2O fluxes were determined using the closed chamber-gas chromatography method. Some potential factors such as soil temperature, soil water, soil carbon, soil nitrogen, soil microbial biomass and plant growth were also measured during winter wheat-summer maize growth period in 2008-2009. The main results were as follows:(1) Soil CO2 and N2O fluxes from different plots had obvious seasonal variation, with the highest in summer, higher in spring and autumn, and the lowest in winter. With the annual flux from 3417.59 to 6435.91 kg C hm-2 a-1, soil CO2 flux under different systems ranged from 3.77 to 213.88 mg m-2h-1. Soil N2O flux under different systems ranged from-3.84 to 92.11μg m-2 h-1, with the annual flux from 0.49 to 1.33 kg N hm-2 a-1.(2) As expected, hedge prunings returning to field enhanced the release of soil CO2 and N2O. Significant difference in soil CO2 flux was observed among different hedge species prunings management practice, following the order of Incorporated-pruning> Surface-applied pruning> Removal of pruning, and the effect of A.fruticosa system was more obvious. The soil N2O flux of Incorporated-pruning was higher than Surface-applied pruning in winter wheat growing season, whereas the opposite trend was found during summer maize growth period. Furthermore, conversion from cropland to A.fruticosa forestland and/or Vetiver grassland might increase the release of soil CO2 and N2O to what extent.(3) The influence of soil temperature and moisture on soil CO2 and N2O fluxes is significantly different with seasonal variation. During winter wheat growth period, soil CO2 and N2O fluxes were strongly exponentially correlated with soil temperature among all treatments, and the influence of soil moisture was of minor status. However, soil CO2 and N2O fluxes were significantly affected by soil moisture in summer maize growing season. (4) Correlation analysis indicated that the average of CO2 flux was significantly positively correlated with soil organic carbon, average microbial biomass carbon and total nitrogen, but the relationship between soil microbial biomass carbon and soil CO2 flux under different growth stages was lower. Under hedgerow intercropping systems, the total nitrogen and soil NO3--N were significantly positive correlative with production of soil N2O flux, the opposite trend was observed for soil NH4+-N. However, no clear relationship existed between soil inorganic nitrogen and N2O flux in A.fruticosa forestland and/or Vetiver grassland. No significant dependence of N2O flux on the soil organic carbon, soil C/N ratio and soil microbial biomass nitrogen was observed among treatments.(5) Correlation analysis showed that soil CO2 flux was mainly affected by wheat growth during winter wheat growth period. However, it was commonly influenced by the growth of maize and hedges in summer maize season. Soil N2O flux was well correlated with wheat biomass and maize biomass. It indicated that crop growth was one of the important factors influencing soil CO2 and N2O fluxes. In addition, different hedge species also remarkably influenced soil N2O flux.(6) In A.fruticosa and/or Vetiver intercropping system, monoculture crop and monoculture hedge systems, there were significant linear relationships between soil CO2 flux and soil N2O flux.(7) Analysis of carbon budget showed that the intensity of carbon sequestration or source ranged from-493.28 to 2380.23 kg C hm-2 in different systems. The ratio of NPP/Rs for winter wheat and summer maize growing season ranged from 0.70 to 2.40 and from 0.85 to 2.83, respectively. Hedger intervening farmland system changed its feature of carbon sink and source. Vetiver intercropping system acted as carbon source of the atmosphere CO2 over winter wheat growing season, whereas the opposite trend during summer maize growth stage. A.fruticosa intercropping system, which carbon sink strength was bigger than Vetiver intercropping system, was a carbon pool of the atmosphere CO2 throughout the year. Furthermore, the land use conversion from cropland to A.fruticosa forestland and/or Vetiver grassland might increase the carbon sequestration to a great extent, and the carbon pool was greater in Vetiver grassland than that in A.fruticosa forestland.
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