Global mapping of volumetric water retention at 100,330 and 15000 cm suction using the WoSIS database

Present global maps of soil water retention(SWR)are mostly derived from pedotransfer functions(PTFs)applied to maps of other basic soil properties.As an alternative,'point-based'mapping of soil water content can improve global soil data availability and quality.We developed point-based global maps with estimated uncertainty of the volumetric SWR at 100,330 and 15000 cm suction using measured SWR data extracted from the WoSIS Soil Profile Database together with data estimated by a random forest PTF(PTF-RF).The point data was combined with around 200 environmental covariates describing vegetation,terrain morphology,climate,geology,and hydrology using DSM.In total,we used 7292,33192 and 42016 SWR point observations at 100,330 and 15000 cm,respectively,and complemented the dataset with 436108 estimated values at each suction.Tenfold cross-validation yielded a Root Mean Square Error(RMSE)of6380,7.112 and 6.48510^(-2)cm^(3)cm^(-3),and a Model Efficiency Coefficient(MEC)of0.430,0386,and 0.471,respectively,for 100,330 and 15000 cm.The results were also compared to three published global maps of SWR to evaluate differences between point-based and map-based mapping approaches.Point-based mapping performed better than the three map-based mapping approaches for 330 and 15000 cm,while for 100 cm results were similar,possibly due to the limited number of SWR observa-tions for 100 cm.Major sources or uncertainty identified included the geographical clustering of the data and the limitation of the covariates to represent the naturally high variation of SWR.

Hydraulic energy indices reveal spatial dependence in a subtropical soil under maize crop in Southern Brazil

Soil physical quality(SPQ)assessment is an important part in the evaluation of soil use,management,and conservation.It can be assessed using several physical properties,hydraulic indices,and functions.Soils from tropical and temperate regions represent different physical behaviors,and the quantification of their physical properties is important to support soil evaluation and modelling.The objective of this study was to evaluate the SPQ in a subtropical field under maize crop cultivation according to its physical properties,hydraulic indices,and functions in an attempt to infer the spatial variability and to determine the behavior of soil physical structure across a spatial domain.Commonly used soil key physical variables,such as texture,bulk density,total porosity,saturated hydraulic conductivity,and organic carbon content,were measured in a regular grid with a soil sampling density of 30 points per hectare,covering an area of0.5 ha.Saturated hydraulic conductivity varied strongly between subsamples and in the field,suggesting the heterogeneity of the soil structure regarding water drainage.The physical variables were combined with other indicators,which were based on the soil water retention curve and the pore size distribution(PSD)function.Correlation analysis was performed to verify the relationship between the measured and calculated variables,and some strong linear correlations were revealed,such as between aeration energy index and microporosity(r=0.608)and water retention energy index with microporosity(r=0.532)and with bulk density(r=0.541).For most sampled locations,the shape and location parameters of PSD showed results outside of the optimum ranges,whereas the hydraulic energy indices and cumulative hydraulic energy functions presented values that were similar to those found for some tropical soils described in the literature.The spatial variability of these indices was described using semivariograms and kriged maps,indicating the variability of the SPQ in this field.