Measuring and Modelling Soil Depth Functions

Abstract

Hans Jenny stated that the anisotropy of soil with depth means that the soil has a unique profile. Therefore, naturally every soil property has its specific depth function. The changes of soil particle size distribution in a soil profile can be used as an indicator of soil formation and processes and has been used as a proxy for soil age or degree of development. Uniform, gradational and rapidly changing (duplex) soil textures are examples of soil profile forms used for soil classification in Australia. Various parametric and nonparametric depth functions have been used to describe the variation of soil properties with depth. We have identified 7 typologies of depth functions: uniform, gradational, exponential, wetting front, abrupt, peak and minima–maxima. These depth functions are related to soil-forming processes. To test these functions, a proximal soil sensor was used to perform in situ digital morphometrics by which soil properties are measured along a soil profile wall at small depth increments. We explore the possibility of horizon boundary detection based on the changes in elemental concentrations. It was concluded that digital morphometrics enables soil scientists to measure the soil’s depth functions and weathering history quantitatively directly in the soil pit and assists in more objective delineation of soil horizons.