Scales of Water Retention Dynamics Observed in Eroded Luvisols from an Arable Postglacial Soil Landscape

Abstract

Soil water retention is frequently described by unique main drying curves measured in the laboratory on intact soil cores. In the field, however, soil pore structure changes as a result of swelling and shrinkage, wetting and drying, or tillage operations. For erosion-affected arable soils characterized by truncated profiles, water retention dynamics could be even more complex. The objective of this study was to separate shorter term hysteretic from longer term seasonal dynamics in field-measured water retention data of eroded Luvisols. Soil water content and matric potential data were from tensiometers and time-domain reflectometry sensors of six lysimeter soil monoliths from two sites. For 2012 through 2014, drying and wetting periods were identified and fitted with the van Genuchten (VG) retention function. The results confirmed that drying water retention curves were steeper than those obtained in the laboratory. Steepness increased and fitted VG parameter values of saturated water content decreased within seasons, indicating that rewetting rates successively declined after each dry-wet cycle. Drying water retention curves returned to a similar level in each spring except for soils of transferred monoliths, where drying water retention tended to increase. Results suggested that water retention dynamics of eroded Luvisols was affected by continual incorporation of subsoil material in the Ap horizon and crop management practices in addition to hysteresis and seasonal dynamics. The disentangling of dry-wet cycles from time series of soil water content and matric potential was found useful for identifying the processes responsible for water retention dynamics and could eventually help improve flow and transport models.

Crop growth and soil water fluxes at erosion‐affected arable sites: Using weighing lysimeter data for model intercomparison

“…Soil texture and soil chemical properties were obtained from disturbed samples. More information on the site and soil properties and the lysimeter setup of SOILCan can be found in Herbrich and Gerke (2017), Herbrich, Gerke, Bens, and Sommer (2017), and Pütz et al. (2016).…”

Soil Variability and Biogeochemical Fluxes: Toward a Better Understanding of Soil Processes at the Land Surface

“…Temporal variability of water retention has been reported, e.g., Jirků et al (2013), that limits the use of retention characteristics obtained from small‐scale core samples or other widely used methods, e.g., pedotransfer functions or inverse modeling. Herbrich and Gerke (2017) compared water retention data obtained from laboratory soil cores and intact soil monoliths of weighing lysimeters representing field conditions. Their results confirmed, first, that the drying retention characteristic is generally steeper for field than laboratory conditions.…”

“…Second, the highly resolved soil moisture and matric potential time series indicated complex and dynamic changes in the field water retention occurring at several time scales. Herbrich and Gerke (2017) identified hysteretic, seasonal, and inter‐annual behavior in soil water retention dynamics in the lysimeter data by disentangling wet–dry cycles. They associated the short‐term dynamics with soil structural and wettability differences in part associated with the presence of vegetation, whereas longer term dynamics reflected soil management and erosion related changes.…”

Studying Unimodal, Bimodal, PDI and Bimodal-PDI Variants of Multiple Soil Water Retention Models: I. Direct Model Fit Using the Extended Evaporation and Dewpoint Methods

“…HYPROP generates high-resolution data typically close to 100 water retention data points in the 0 to 100 kPa soil tension range plus an extra point close to the wilting point by considering the air-entry value as an additional measurement [37]. In recent years, the HYPROP system has been increasingly used and evaluated around the world [4,[38][39][40][41][42][43][44] and promising results have been reported. For instance, Bezerra-Coelho et al [38] evaluated the HYPROP system as applied to the van Genuchten [15] soil hydraulic functions for a wide range of soil textures using the HYDRUS-1D software package [45].…”