Mountain region citrus production systems occupy large parts of the landscape prone to soil erosion in the Three-Gorges Area of China. Several soil conservation measures, such as terracing hedgerows, are widely implemented in citrus orchards to control soil erosion. However, little is known about the effect of those measures on soil properties. The objective of this work was to analyse the changes of soil properties in citrus orchards subjected to different conservation measures. Experiments were conducted in four plots: control plot (SC, sloping orchard without conservation measures), sloping orchard with contour hedgerows (SCH), terraced orchard (TC) and terraced orchard with grass cover (TCG). Samples of soil surface from 0 to 15 cm were collected to analyse texture, bulk density (BD), aggregate stability, saturated hydraulic conductivity, soil organic matter (SOM) and soil nutrients. The spatial variability of those properties was also evaluated at slope and field scales. The results showed that the three conservation measures significantly increased saturated hydraulic conductivity, aggregate stability, SOM and available N, P, K, but decreased BD. The terracing with grass cover measures were the most effective in improving soil fertility among the three measures. The average SOM, available P, N, K in TCG were 0Á27, 0Á50, 1Á74 and 1Á72 and these rates are larger than for the in SC. Compared to SC, silt content was increased the SCH, while clay content was increased with TC and TCG. There was a downslope increase in clay content and total N but a decrease in gravels in the SC plot. However, that trend did not exist in the other plots. At the field scale, the soil aggregate stability and total nitrogen were significantly higher near the hedgerow under SCH, and the available N was significantly higher in the middle position under TC; the other soil properties had no significant trends based on the distance to hedgerow or stone bunds. Results of this study will contribute to a further understanding of the environmental influence of soil conservation measures.

Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N 2 O and CO 2 under wheat-maize (WM) and/or faba beanmaize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N 2 O and CO 2 as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization were recorded during 2006 maize crop cultivation. Soil N 2 O and CO 2 fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N 2 O emissions from soils with maize were considerably greater after faba bean (345 g N 2 O-N ha -1 ) than after wheat (289 g N 2 O-N ha -1 ). However, the cumulated N 2 O emissions did not differ significantly between WM and FM. The difference in N 2 O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more N 2 O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N 2 O fluxes represented 534 g N 2 O-N ha -1 (AWM) and 512 g N 2 O-N ha -1 (AFM) under A. fruticosa species, 403 g N 2 O-N ha -1 (VWM) and 423 g N 2 O-N ha -1 (VFM) under Vetiver grass. We observed significantly higher CO 2 emission in AFM (5,335 kg CO 2 -C ha -1 ) from June to October, whereas no significant difference was observed among WM (3,480 kg CO 2 -C ha -1 ), FM (3,302 kg CO 2 -C ha -1 ), AWM (3,877 kg CO 2 -C ha -1 ), VWM (3,124 kg CO 2 -C ha -1 ) and VFM (3,309 kg CO 2 -C ha -1 ), indicating the importance of A. fruticosa along with faba bean residue on CO 2 fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N 2 O and CO 2 emissions in the present environmental conditions.