Spatial distribution of soil total phosphorus in Yingwugou watershed of the Dan River, China

• We researched the distribution of soil total phosphorus (STP) in a small watershed.
• We revealed the spatial heterogeneity of STP in the source area of the middle Dan River.
• We assessed the impact of land use, elevation, slope and aspect on STP.
• We estimated the STP mass and the vertical variability of STP in the watershed.

P is an essential and commonly limiting element for plants. P losses from agricultural production systems are known to contribute to accelerated eutrophication of natural waters. In this study, soil total phosphorus (STP) concentration and STP mass were estimated from a soil survey of a small watershed of the Dan River, China, after which the spatial heterogeneity of STP distribution and impacts of land-use types, elevation, slope and aspect on STP were assessed. A total of 190 sites were sampled, and 539 soil samples from a soil profile of 40 cm were collected by field sampling in a 100 m × 100 m grid. The results indicated that classical kriging could successfully interpolate STP concentration in the watershed. The STP concentration showed a downward trend with increasing soil depth. The STP variability in the three soil layers was moderate, and there were significant differences among soil layers (p < 0.01). Statistical analysis by ANOVA indicated that land use had a great impact on STP concentration, and the spatial variation of STP concentrations among the land use types was significant (p < 0.05). The STP mass of different land-use types followed the order of forestland > cropland > grassland. On average, the mean STP masses of forestland, cropland and grassland at a depth of 0–40 cm were 0.39, 0.35 and 0.28 kg/m2, respectively. The topographic factors of altitude and aspect exerted the greatest influence on STP concentration, and the STP concentration increased with decreasing altitude; however, STP concentration and slope showed no significant correlation. The soil bulk density also played a very important role in the assessment of STP mass. In conclusion, the soils in the source area of the middle Dan River would increase STP with conversions from cropland to forest.