Available water capacity (AWC) is one of the important soil properties influencing soil functions and threats to the soils as it is directly related to a number of soil and hydrological properties and processes. So, a thorough knowledge of its spatial variability across a landscape is crucial for a better soil and crop management plan including forestry, and also for several environmental policy and research studies. We investigated the spatial variability of topsoil AWC (0 to 20 cm soil depth) in a rather heterogeneous landscape across Central Jutland in Denmark covering an area of about 7,100 km² and mapped its distribution for the entire study area at a regular grid of 30.4 m. Soil texture components and organic matter content of about 6,950 point observations through out the study area were extracted from the Danish Soil Classification Database and AWC (cm³ cm^-3) in these locations were derived using pedotransfer functions specifically developed for the Danish soils. A regression-rules based digital soil mapping technique was applied to build a prediction model in which eighteen environmental variables including elevation, slope, wetness index, land use, soil map etc. were used as predictors. A fraction of 80% of the total observations were selected randomly for model building and the rest were kept aside for validation. Spatial autocorrelation of AWC was studied using a variogram. The model performance was assessed with RMSE, R² and residual prediction deviation (RPD) indices using 20% hold-back samples. The results showed an R² of 0.52, RMSE of 2.1, and an RPD higher than 2, all suggesting a stable and an effective prediciton model. AWC was found to be highly variable in our study area with lower values in the south-west part which consists of sandy soils compared to the central-east which are rich in clay content. The mean value and CV of predicted AWC in the study area were 18.8 cm³ cm^-3, and 23.5%, respectively. The range of spatial dependence of AWC distribution was about 8 km. 

Keywords: Available water capacity, Regression-rules, Variogram, Digital soil mapping, Denmark