Abstract:

【Objective】 The objective of this study was to explore the spatial distribution of soil available phosphorus, and to provide a firm foundation for scientific formulated fertilizer and identify key regions for controlling agricultural non-point phosphorus pollution. 【Method】 One thousand and fifty eight soil samples were collected from Pinggu County of Beijing and analyzed for contents of available phosphorus in topsoil (0-20 cm) and subsoil (20-40 cm), respectively. The general statistics and geostatistics methods were used to analyze the data. 【Result】 The coefficients of variation of topsoil and subsoil were 1.15 and 1.29, respectively, which belonged to the strong degree of variability. The mean values of available phosphorus in topsoil and subsoil were 32.80 mg?kg-1 and 9.74 mg?kg-1, respectively, and the topsoil content was great than that of subsoil. The ranges of topsoil and subsoil available phosphorus were 14.6 km and 15.8 km, respectively. The spatial distribution of available phosphorus contents was in the order of low mountainous areas ＞plain areas ＞mountainous area, which was mainly affected by the elevation, land use types, and fertilizers application amount. The spatial distribution of subsoil phosphorus was similar with the topsoil, but its content was far lower than that in surface soil. The areas with 70%-90% probability which topsoil available phosphorus content exceeded the critical value (60 mg?kg-1) was 1.9% of the whole areas, where mainly distributed in the north-western low mountainous areas of Pinggu County. The areas with ＜20% probability of topsoil available phosphorus exceeding 60 mg?kg-1 was 70.1% of the whole areas, where widely lied in north-eastern mountainous areas, eastern low mountainous areas and middle, south-western plain areas. 【Conclusion】 Soil phosphorus in the orchard, vegetable and field land has different degrees of accumulations. Organic manure and fertilizer application are main reasons resulting in higher soil available phosphorus contents in Pinggu County. The middle area of Dahuashan and the south-eastern area of Liujiadian town are the key regions for controlling agricultural non-point phosphorus pollution source.

Key words: soil available phosphorus, spatial variability, environmental risk analysis