Water Retention and Preferential States of Soil Moisture in a Cultivated Vertisol

Abstract

Core Ideas Water retention data from saturation to oven dryness were collected for a Vertisol. New water retention and differential water capacity models were developed. Draining of intra‐aggregate pore space triggers the dry field soil moisture state. Mode of the textural pore space controls shift to wet field soil moisture state. Vertisols are well suited for rainfed agriculture in water‐limited environments as a result of their unique water transfer and retention characteristics. Despite their importance, the agro‐hydrological behavior of these soils under seasonally dry climates is not yet fully understood. We collected water retention data for a Vertisol, measured from saturation to oven dryness on 27 undisturbed topsoil (0–0.05 m) samples from an experimental field in south‐central Spain and related this information to the occurrence of field‐observed preferential soil moisture states. A continuous function was fitted to the mean gravimetric water retention data, Θ, consisting of the sum of a double exponential model and the Groenevelt and Grant model. An inflection point at pressure head |h| = 1.1 × 105 cm, Θ = 0.12 kg kg−1, and an equivalent pore radius, δ = 14 nm, was interpreted as the boundary between the clay inter‐ and intra‐aggregate pore spaces, corresponding with the transition from the intermediate to the dry field soil moisture state. The mode of the textural pore space (|h| = 7.3 × 103 cm, Θ = 0.21 kg kg−1, and δ = 200 nm) matched the transition from the wet to the intermediate field soil moisture state. We related these characteristics of the soil water retention curve with the spatiotemporal soil moisture dynamics and patterns observed in the field, characterized by fast transitions between preferential soil moisture states. The proposed framework is suitable for comparing the effects of different soil management strategies on the agro‐hydrological performance of Vertisols.

Water Related Properties to Assess Soil Quality in Two Olive Orchards of South Spain under Different Management Strategies

“…The data of this figure were estimated with the Kosugi water retention curve, whose results were similar to those computed with the van Genuchten equation, except for some soil samples of the Pedrera farm, whose retention curve did not show a clear air entry state. This property, also found in the SWRC of swelling soils of the zone [37], posed some problems to other authors [38]; Pierson and Mulla [13] suggested the addition of a second-degree polynomial to the van Genuchten water retention equation.…”

Comparison of the performance of 22 models describing soil water retention curves from saturation to oven dryness

“…0 = log 10 (ϕ 0 ), ad = log 10 (ϕ ad ), and [-] is a smoothing parameter. Vanderlinden et al (2017) combined the double exponential model (Dexter, Czy, Richard, & Reszkowska, 2008) with the Groenevelt and Grant (2004) model to describe the full range of the water retention curve (EG model):…”

Water retention and field soil water states in a vertisol under Long‐Term direct drill and conventional tillage

“…This is particularly true in seasonally dry climates, where water‐limiting conditions persist during long periods and soil water content becomes the single most important control for numerous ecohydrological and biogeochemical processes that take place at or near the soil surface (Wang, Manzoni, Ravi, Riveros‐Iregui, & Caylor, 2015). Under such environmental conditions and in the light of climate change, clay soils become of prime importance for dryland agriculture as a result of their capacity to retain large amounts of water and supply it to crops under conditions of large atmospheric water demand (Vanderlinden et al, 2017).…”

“…Vanderlinden et al (2017) modelled a multimodal SWRC and the equivalent pore‐size distribution of a Vertisol, and related characteristic points of the SWRC with field‐measured preferential soil moisture state data. Jensen, Schjønning, Watts, Christensen, and Munkholm (2019) confirmed the need for such an approach by showing that unimodal pore‐size distributions cannot capture soil management effects.…”

“…Jensen, Schjønning, Watts, Christensen, and Munkholm (2019) confirmed the need for such an approach by showing that unimodal pore‐size distributions cannot capture soil management effects. Here we build further on the framework of Vanderlinden et al (2017) to compare the hydrological performance of this soil under conventional tillage (CT) and direct drill (DD), which are contrasting soil management systems that are commonly implemented on these soils by local farmers.…”