Pedotransfer function

Abstract: Digital cameras are becoming increasingly popular in environmental sciences and proximal soil sensing as low cost, but high quality and high-resolution sensors. The high spatial resolution of the images shows a great potential for mapping predicted soil properties at small scales, from soil profiles to the microscale. To explore the potential of digital cameras for the morphometric analysis at a fine scale, we took 50 samples plus 3 microplate scale excavations from a profile wall of a Luvisol and analyzed samples for soil organic carbon (SOC) and Fe content for model calibration. Images of sieved and ground soil samples were taken under standardized laboratory conditions. After image correction, RGB colors were obtained for each sample and transformed into different color space models. Based on the obtained soil colors, different regression models were built to predict SOC and Fe content. Simple regression produced predictions with R2adj values of 0.90 for SOC (using HSV V) and 0.70 for Fe (using CIE a*) for ground soil samples. For sieved samples, R2adj values were lower with 0.69 for SOC using HSV V and 0.61 for Fe using CIE a*. Multiple linear regression models with interaction terms could improve those predictions for sieved samples to R2adj values of 0.94 for SOC and 0.89 for Fe, using the complete HSV and CIELab color tristimulus, respectively. Based on the best pedotransfer functions, we predicted SOC and Fe contents for the excavated microplates at a 1 × 1 mm resolution. With this method we were able to map the microscale variability of SOC and Fe content with great accuracy. This study showed, that accurately calibrated digital images can be a cost-effective method to map the distribution of SOC and Fe and potentially other soil physical and chemical parameters at a very fine scale.

Abstract: The field capacity concept of Veihmeyer & Hendrickson was studied verifying the existing definitions of the phenomenon. The field experimental was carried out on a Red Yellow Latosol, medium texture, in a 6 x 4 m plot on which twenty tensiometers were installed along the natural slope of 0.025 m m -1 , in order to measure soil water potential at depths of 0.15 and 0.25 m from soil surface. Due to the slope of the area, the wetting of the soil profile was non-uniform, and soil drying was followed by measurements of soil water potential and soil water content, both in depth and over time; soil water content was measured through auger sampling. Results exhibited great variability of the drainage process within the experimental plot, in terms of soil water content, soil water potential, and soil water storage. This indicates that the values of these parameters are a consequence of the field wetting-drying process that occur in the soil, in determining field capacity.

Abstract: A French data set was used to evaluate how well two widely used analytical functions describe measured soil water characteristic (SWC) data. Both the van Genuchten (sigmoidal) and Campbell (power-law) equations gave good descriptions of the data (mean R 2 of 98.1 and 97.1% respectively). Methods of predicting SWC data were also evaluated. When a power-law equation was parameterised using just two measured SWC points and bulk density (the 'two-point' method), a very good SWC prediction was obtained for the French data (mean R 2 of 94.8%). An empirical equation for prediction of the SWC was also assessed using the French data set. This method was developed using multiple regression analysis from Australian soil data and requires soil texture and bulk density as input. The predictions (mean R 2 of 85.2%) lacked accuracy and precision in comparison with the two-point method but the empirical approach uses more readily available input data. The accuracy of prediction from both methods was similar to that observed previously for Australian data sets. The empirical approach developed from Australian soil data has reasonable applicability to French soils. The approach of assuming a power-law model and empirically predicting slope and air entry potential is shown to have merit. A strategy for achieving adequate coverage of soil hydraulic property data for France is suggested incorporating hydraulic prediction methods such as those evaluated here.