Spatial interpolation of red bed soil moisture in Nanxiong basin, South China

Soil moisture is an important indicator for monitoring land degradation and plays an important role in soil biogeochemistry. Mapping the spatial distribution of soil moisture provides fundamental information for soil management and agricultural production. In this study, 225 sampling points in the study area, Nanxiong basin, were investigated to map the spatial distribution of soil moisture in the typical ecological degradation red beds area. Four interpolation methods including inverse distance weighting (IDW), ordinary kriging (OK), radial basis function (RBF) and empirical bayesian kriging (EBF) were used to estimate the continuous soil moisture distribution. The results showed that the soil moisture of the study area ranged from 8.12% to 32.82% with an average of 18.42% and a median of 18.20%. The annual average temperature and soil bulk density had significantly negative correlations with soil moisture, of-0.53 and - 0.31, respectively. The regional soil moisture had a moderate variation with the variation coefficient of 21.66% and strong spatial dependence with the nugget-to-sill ratios of 32.23%. The IDW method obtained a more accurate estimation on the spatial variability of soil moisture in the Nanxiong basin. The spatial distribution of soil moisture in the study area was drawn by different interpolation methods. The results show that the red bed degradation in the eastern part of the Nanxiong basin is more severe than in other areas, in which the geomorphic characteristics of red bed desert have appeared with the lowest soil moisture in this study. In addition, the spatial heterogeneity of soil moisture is also pertinent to human disturbance and land use. The results of spatial soil moisture distribution are of great significance for monitoring land degradation and agricultural drought in the red bed area.