紫色土小流域不同土地利用类型的土壤氮素时空分异特征

以紫色土区12.10 km²的万安小流域为研究区域,于2011年4月(旱季)和8月(雨季)小麦和玉米收获期共采集552个表层土壤(0~15 cm)样品,利用传统统计学和地统计学相结合的方法对流域土壤全氮和硝态氮的时空变异特征进行研究.结果表明,不同土地利用类型土壤全氮含量差异显著,并呈以下顺序:水旱轮作田>林地>旱地;同一土地利用类型旱季、雨季土壤全氮含量不存在显著差异.其中,4月和8月林地、旱地、水旱轮作田土壤全氮含量分别为1.16、0.90、1.21 g·kg^-1和1.13、0.94、1.29 g·kg^-1.但旱季和雨季土壤硝态氮含量差异显著,其中,4月和8月林地、旱地、水旱轮作田硝态氮含量分别为12.08、24.22、31.22 mg·kg^-1和3.98、11.18、2.27 mg·kg^-1,表现出土壤硝态氮旱季累积、雨季流失的特点;受到内部因素和外部因素共同作用,旱地、水旱轮作田土壤全氮空间分布具有中等空间相关性,而林地土壤全氮的强烈空间相关性主要受到内部因素的影响.本研究分析了紫色土区不同土地利用类型条件下的流域土壤氮素的时空变异特征,将会为流域土地资源管理和环境修复提供较好的科学依据.

Spatial and temporal variations of soil nitrogen under different land uses in a small watershed in the purple soil area, China

The spatial and temporal variations of soil nitrogen under different land uses of a small watershed (12.10 km²) in the hilly area of central Sichuan Basin, China, were investigated using conventional statistics, geostatistics and a geographical information system (GIS) to produce nutrient maps and provide information for land management and control of environmental issues. Surface soil samples (0~15 cm) from 276 sites within the watershed were collected in April and August and analyzed for soil total nitrogen (STN) and nitrate nitrogen (NO₃^--N) contents. Characteristics of spatial heterogeneities of STN and NO₃^--N under different land uses and the temporal patterns of soil nitrogen in the dry season and the rainy season were compared by statistical analyses. The results indicated that 1 the contents of STN were significantly influenced by land uses, and the mean STN contents under different land uses were as the following orders: paddy field>forest land>upland field; 2 no significant difference was found for STN under the same land use type between April and August. However, significant decrease in NO₃^--N content was found in August which indicated the nitrate accumulation in the dry season and leaching or diffusing in the rainy season; 3 the geostatistics information of STN in the agricultural land showed moderate spatial dependence while strong spatial dependence in the forest land. This conclusion can be explained by less human disturbance in the forest land. We concluded that the obvious spatial and temporal patterns of nitrogen under different land uses must be considered both in identifying the sites at risk of nitrogen loading and evaluating their potential of generation of diffuse pollution. Land use patterns should be considered for land planning and environmental restoration.