Spatial Distribution Features Of Phosphorous In Soil And The Risk Of Phosphorous Loss In A Small Watershed

With the increasing global concern of non-point source pollution, research on the spatial distribution features of soil nutrients and the loss risk of an area, especially a small watershed, has been one of the chief concerns of environmental and agricultural studies.In this paper, a geostatistic method and Geography Information System (GIS) were utilized to characterize the spatial variability of total phosphorous, available phosphorous, and organic matter in topsoil, and to map the spatial distribution of these test variables in the Shixia small watershed, based on the Kriging method. Loss of phosphorous in soil and runoff of the Shixia Experimental Area (located in the watershed of the Miyun reservoir) was studied, along with the data from runoff plots, and used to analyze the effect of different land use on the spatial distribution and the loss risk of phosphorous in soil in the Shixia small watershed. The results are as follows:All the test variables of soil characteristics in the area under study were normally or log normally distributed. Semivariogram analysis showed that organic matter was strongly spatially-dependent, total phosphorous was moderately spatially-dependent, and available phosphorous was weakly spatially-dependent. Kriging analysis maps showed that remarkable spatial distributions with strip and patch features were found for all soil nutrients. The total phosphorous was highest in the southwest and the east of the brim of the small watershed, and the area with 0.873 ~1.990g/kg soil total phosphorous content accounted for 31.7% of the total The spatial distribution of organic matter was a northwest-southeast strip in the small watershed, and the organic matter content of the soil increased from the center of the small watershed to the brim.The loss of soil phosphorous in the Shixia Experimental Area was affected by rainfall, land use, slope, vegetation coverage, soil attributes, etc. The rank of the concentration of dissolved total phosphorous in the runoff is:farmland > orchard > forest > standard area > grassland. The rank of the loss of particulate phosphorous of different land use is:farmland > orchard > forest > grassland.These trends were directly proportional to the soil phosphorous content. Flow and sediment varied among different slopes. The maximal loss of phosphorous in the runoff was found in a range of critical slope degree. When comparing the two modes of phosphorous loss, soil phosphorous is mainly lost in particulate matter, carried by sediment.The Universal Soil Loss Equation (USLE) and Rainfall and Runoff model (made by the Soil Conservation Service of the U.S) was applied to the data of the rainy period of 2006 from the Shixia Experimental Area to calculate the soil phosphorous loss of the small watershed. The results showed that the land type of the highest loss risk of soil phosphorous is farmland with a 0°～22°slope, located in the southwest and the east of the brim of the small watershed.