The dynamic changes of soil air‐filled porosity associated with soil shrinkage in a Vertisol

Abstract

Soil aeration is critical for crop growth, which is generally assessed by air-filled porosity (AFP). In non-rigid soils with high shrinkage and swelling, the AFP is not only related to the total porosity and soil moisture, but also to the soil shrinkage behaviour. However, the relationship between AFP and soil shrinkage has not been clarified. The objectives of this study were to (1) establish a mathematical equation to describe the behaviours of AFP associated with soil shrinkage (AFP sh ); and (2) to evaluate the influence of tillage practice on the AFP sh . Undisturbed soil core samples were collected from the 0-10 cm to 10-20 cm layers in a Vertisol under four tillage treatments (No tillage, NT; Rotary tillage, RT; Subsoiling, SS; Deep ploughing, DP) to measure the changes in the volumes of soil core, soil water and air at different soil matric potentials. Our results showed that an equation of AFP sh as a function of moisture ratio (ϑ) was well established based on the developed soil shrinkage model (R 2 > 0.990, RMSE <0.012). Compared with the AFP under a constant pore assumption (AFP c ), the AFP sh was significantly decreased by 10.6% to 60.3% as soil water matric potentials were at <À33 kPa in the 0-10 cm layer or at <À10 kPa in the 10-20 cm layer (p < 0.05). According to the AFP sh curve of the Vertisol, soil moisture content (θ) was approximately 68%-80% of the field capacity when AFP sh reached non-limiting status (0.10 cm 3 cm À3 ), where the soil matric potential was close to the wilting point (À1500 kPa). Deep tillage treatment (SS and DP) increased AFP sh , showing good performance in decreasing the risk of soil aeration deficit relative to the NT and RT treatment. Our results demonstrate that neglecting the porosity variations during shrinkage may lead to a high bias in the AFP prediction. Highlights• An equation of AFP associated with soil shrinkage was established.• AFP was significantly decreased when soil shrinkage was considered for a Vertisol.

Soil physics matters for the land–water–food–climate nexus and sustainability

“…They further established new shear strength equations for root-soil complexes of D. linearis based on the modified Wu-Waldron model and Coulomb's formula. Based on experimental measurements, Wang, Zhang, et al (2022) established a mathematical equation capable of describing the kinetics of changing air-filled porosity (AFP) along soil shrinkage process. They further demonstrated that porosity variations during soil shrinkage are often significant and would largely bias the AFP prediction, and thereby are indeed not negligible.…”