| This study was carried out in Sunjia Watershed in Yujiang County, Jiangxi Province, subtropical China. The watershed is a 46.9-ha agricultural area with 70.3% of upland and 28.5% of paddy field. The dominant soil type on upland is highly-leached acidic red soil (Agri-Udic Ferrosol). Our objectives were: 1) To assess the impacts of different land use patterns (peanut field, orange field, peanut-orange intercropping field and Chinese chestnut field) and vegetation successions on soil quality, especially on soil biological properties; 2) To investigate the dynamics of nutrients loss and deposit caused by erosion processes and its relationship with land use patterns.It was found that the physical, chemical and biological properties of red soil were altered by land use patterns. Peanut field and peanut-orange field showed lower soil bulk density compared with orange field and Chinese chestnut field (p<0.05). Total organic carbon (TOC) contents in surface (0-10 cm) soil layer were in the order of Chinese chestnut > orange > peanut-orange > peanut and similar tendency was observed for total nitrogen (TN) and available nitrogen (AN) contents. However, total phosphorous (TP) and available phosphorous (AP) contents of peanut field and peanut-orange field were higher than Chinese chestnut field. Soil microbial biomass C (SMBC) in surface soil of Chinese chestnut field and orange field were also higher than peanut-orange field and peanut field, while soil microbial biomass N (SMBN) of Chinese chestnut field and peanut field were the highest. Soil chemical and biological properties varied with slope sites. TOC, TN, AN, TP, AP, SMBC, SMBN and soil enzyme activity increased from upper slope to lower slope, which may be explained by the translocation of fertile surface soil caused by erosion along upland slope.Monitoring data obtained from peanut field, orange field, peanut-orange field, Chinese chestnut field and paddy field showed that AN and AP were more liable to loss than TOC, TN and TP during raining. Soluble N and P and particulate N and P in runoff in initial stage were higher than the later stages. Soil particulate in runoff showed significant nutrient enrichment in all land use patterns and the enrichment ratios of different forms of nutrients were different: TN was 1.11 - 1.47, AN was 1.05-1.36, TP was 1.02-1.26 and AP was 1.12-1.59, respectively. The enrichment ratios of N and P in soil particulate in runoff from Chinesechestnut field and orange field were higher than those of other fields. There were positive correlations between the nutrient contents in runoff particulate and the nutrient contents in original surface soil.Land use patterns on upper fields also affected the chemical and biological properties of sediments in water bodies. The sources of sediments in four ponds were different. The sediments in A, B, C and D pond mainly came from Chinese chestnut field runoff, paddy field runoff, peanut field runoff and village runoff, respectively. Nutrient contents in the sediments of D and A ponds were higher than B and C ponds. TOC, AN, TN and TP contents in the sediments were much higher than upper field soil, but AP contents of the sediments in any ponds were extremely low. No significant difference of sediment pH was observed for all ponds (pH=7.32-7.59). The variations of invertase, urease and acid phosphatase activity in sediments with land use patterns and pond types were similar to nutrients. Both nutrient contents and enzyme activity in sediments declined with depth.The effects of plant succession on soil quality were studied in five soil-plant ecosystems (bare land, lichen, moss, grass and forest). Results showed that vegetation was very important for the restoration of heavily eroded red soils. Bryophyte and lichen played significant role for improving soil quality of shallow surface layer. AN content in 0-2cm soil under lichens was approximately 1.9 times higher than bare land and TP and TN contents were also significantly higher. The contents of TOC, AN, TN, AP, and TP in 0-2cm soil u...
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