Emerging Measurement Methods for Soil Hydrological Studies

Abstract

Monitoring and protecting the natural resources of soil and water, and their ecosystems, is intended to ensure the long-term conservation of their functions. To understand the reasons for resource degradation or ecosystem alterations and interactions, knowledge is required of processes and parameters on different scales of landscapes. Soil hydrological studies are an essential part of ecosystem and landscape research. The aim of our study was to develop new research methods and technical equipment to understand and monitor soil hydrological processes. The investigations were carried out on different scales, starting with laboratory and lysimeter measurements, followed by investigations in the field. To measure soil hydrological properties, we developed the Extended Evaporation Method (EEM) and the HYPROP device. In this chapter we report on some innovations in this field. Using new cavitation tensiometers and applying the air-entry pressure of the tensiometer’s porous ceramic cup as the final tension value allowed us to quantify both hydraulic functions close to the wilting point. Additionally, both soil shrinkage dynamics and soil water hysteresis can now be quantified easily and reliably. The experimental setup followed the HYPROP system, which is a commercial device with vertically aligned tensiometers that is optimized to perform evaporation measurements. Depending on the soil and the evaporation rate, the measurement time varied between 2 and at most 10 days. The simultaneous measurement of multiple soil samples was possible with only one balance. Pedotransfer functions (PDFs) were created on the basis of various measured soil water retention and hydraulic conductivity functions. In the next step, a method for quantifying deep seepage and solute leaching under field conditions was developed, tested and applied at more than 40 soil hydrological field plots in Germany. The method is based on tension and soil water content measurements down to a depth of 3 m at arable and grassland sites and a depth of 5 m at forest sites. These data were used to construct a field water retention curve. This pF curve was fitted, the relative hydraulic conductivity function K(θ) was derived and relative deep seepage rates were calculated based on DARCY’s law. To obtain reliable discharge rates, the K function was matched to the water balance. Lysimeter experiments confirmed the validity and reliability of this soil hydrological field method. It works like a virtual lysimeter on sandy to loamy soils which have a deep water table and a zero flux plane above the measurement depth The EEM and the soil hydrological field method have the potential to improve soil hydrological studies, and water and solute transport monitoring systems could be installed in Eurasia.