[Effects of land use type on soil organic C and total N in a small watershed in loess hilly-gully region].

Based on field survey and laboratory analysis, this paper studied the storage of surface soil (0-20 cm) organic C (SOC) and total N (TSN) in farmland, orchard, woodland and grassland in the Yangou watershed of loess hilly-gully region. The results showed that in the test area, the mean contents of SOC and TSN were 7.56 and 0.71 g . kg(-1), respectively. On an average, farmland had 4.67 g . kg(-1) of SOC and 0.48 g . kg(-1) of TSN, and terrace farmland had lower storage of SOC and TSN than other types of farmland. Compared with farmland, the contents of SOC and TSN in orchard had a slight decrease, being 4. 33 g . kg(-1) and 0.46 g . kg(-1), respectively, while those in grassland were higher. The average contents of SOC and TSN in woodland were 117.7% and 89.4% higher than those in farmland. In this area, the variation coefficients of SOC and TSN contents were 69.7% and 58.4%, respectively, being the highest (62.8% and 54.5%) in woodland, the second in grassland and farmland, and the smallest (18.0% and 22.9%) in orchard. Soil C/N ratio was increased in the order of orchard, farmland, grassland, woodl and. Under these four landuse types, there was a significant positive correlation between SOC and TSN (r = 0.9791). The construction of farmland and orchard didn' t increase the contents of SOC and TSN significantly, while the conversion of farmland into woodland or grassland and the hill-closure forestry promoted the accumulation of SOC and TSN distinctly.