Background Soil loss tolerances is a fundamental basis for accessing soil loss and ecological conditions, thus analyzing its characteristics plays an important role in practice for providing a guidance to local prevention and control of soil erosion and ecological construction. Current soil loss tolerances are for large regions and they are too general to reflect the detailed variation in soil erosion within projects for soil erosion and water loss control. This study analyzes the characteristics of soil loss tolerance distribution in Beijing, providing data for setting proper soil tolerances and supporting soil and water conservation management in different districts.

Methods Soil loss tolerances of soil genus in Beijing were calculated by the productivity index model and soil thickness. The values of soil subgroups and groups were then obtained by an area weighted method according to those of soil genus and these values were analyzed and compared by nested variance analysis and multiple comparisons. Finally, a distribution map of the soil loss tolerance in Beijing was made by the values for soil subgroups which acted as the mapping unit.

Results In Beijing, the soil loss tolerance of main soil genus were between 50-313 t/(km²·a) with an area weighted mean of 194 t/(km²·a). In most parts of Beijing, these values were < 150 t/(km²·a), 53.4% of the total area were in the range of 100-150 t/(km²·a) and 23.8% were in the range of 50-100 t/(km²·a). These obtained soil loss tolerances of soil subgroups were significantly different while those of soil groups were not significantly different. The soil loss tolerance of skeletal soils (< 100 t/(km²·a)) were lower than others. It indicated that these soils had been severely eroded by washing off fine particles during the formation process, only remaining a thin layer of coarse fragments with low fertility. Mountain soils were suffering severe erosion, and the soil loss tolerance became lower with the increase of erosion intensity. The soil loss tolerance values were < 150 t/(km²·a) in the mountain area in west, north, and northeast of Beijing, while they were >150 t/(km²·a) in the plain area in the southeast.

Conculsions The difference among soil loss tolerance cannot be shown in the soil group level but it is clear in the soil subgroup level. Although the soil loss tolerances in soil genera level are more detailed, it is not easy to use and manage the scattered patches on the map because of their great number. Therefore, it is optimal to select the values in subgroup level as the mapping unit to make soil loss tolerance distribution map in Beijing.