Background The Loess Plateau is one of the typical ecologically fragile areas of China, due to the lacking of research on the temporal stability of soil moisture, unreasonable vegetation selection and planting density in the long-term afforestation process have caused the problem of soil drying, here we try to clarify the characteristics of soil moisture in the slope of watershed of the gully land consolidation watershed in the Loess Plateau, and to further guide the implementation of the gully land consolidation project and vegetation restoration in this area,

Methods This study selected a typical slope facing southwest with a gentle gradient of a watershed of the Loess Plateau as the research object. The soil moistures of different slope positions (up-slope, mid-slope and lower slope) were monitored by TRIME-PICO TDR, with 4 monitoring points per slope position. The monitoring time was from May to September 2017 of a total of 4 times. The soil moisture was analyzed with multiple statistical methods, and its temporal stability was analyzed using Spearman rank correlation coefficient, relative deviation, temporal stability index, mean absolute deviation and root mean square error.

Results 1) The average soil moisture of different slope positions increased with the increase of soil depth, and the variability of soil moisture content decreased with the increase of depth at the up-slope and mid-slope, and decreased first and then increaseed at the lower slope. 2) On different slope positions, the distribution characteristics of soil moisture content were as follows: up-slope < mid-slope < lower slope position. 3)The differences in soil moisture content between the up-slope and lower slope, mid-slope and lower slope were significant (P < 0.05). 4)The temporal stability analysis of the soil moisture content showed that a high stability between August and September of the soil moisture content of the 0-50 cm soil layer, and the correlation of two month data was extremely significant (P < 0.01), while the soil moisture content of the soil layer in the 50-100 cm range had a significant correlation between May and June. 5) The time stability of soil moisture in the mid-slope position was the highest, followed by the up-slope position, and the temporal stability of the soil moisture in the lower slope position was the lowest. 6) The best time stability point in the study area was the M3 point of the mid-slope position, as the representative point of optimal time stability of 0-100 cm soil layer on slope.

Conculsions The temporal stability of the moisture on the mid-slopes of the Loess Plateau is stronger. The results are expected to provide a reference for the selection of vegetation structure and evaluation of soil moisture content in soil and water conservation and ecological restoration of the watershed of Loess Plateau.