High Energy Moisture Characteristics: Linking Between Soil Physical Processes and Structure Stability.

Water storage and flow in soils is usually complicated by the intricate nature of and changes in soil pore size distribution (PSD) due to modifications in soil structure following changes in agricultural management. The paper presents the Soil High Energy Moisture Characteristic (Soil-HEMC) method for studying soil PSD at near saturation, and the Soil-HEMC model (version 1.0). A modified Van Genuchten equation with 6-8 parameters yields soil structure parameters (e.g., wet aggregate stability) by quantifying differences in moisture characteristic curves, thus providing better understanding and quantification of possible interactions among soil physical processes and management practices. The model utilizes the R language (software), where the input data are matric potential and moisture content.  The model output results include initial and predicted moisture content, specific water capacity, volume of drainable pores and most frequent pore size range (modal suction). Results from > 200 soil samples from humid and arid zones showed that effects of management practices on soil PSD for macro pore dynamics and soil structure stability indices strongly depend on soil type, clay mineralogy, organic matter content, texture, and conditions prevailing in the soils. The ratio of volume of drainable pores to modal suction for humid zone soils with a predominantly kaolinitic clay was less sensitive to management, soil texture and wetting conditions and was greater than that observed for arid zone soils with a predominantly smectitic clay type. In the latter soils the ratio was higher for minimum tilled soils and increased with increases in either the clay content or organic matter. Detailed analyses of the contribution of temporally and spatially varying soil inherent properties and extrinsic conditions to inter- and intra-aggregate porosity and to the model parameters near saturation may enhance our understanding of soil hydraulic conductivity, solution transport and runoff generation processes.