Limiting Water Range: A Case Study for Compacted Subsoils

Abstract

There is a need for improved knowledge of the limits to the available water range for root growth in the subsoil. The objective of this study was to recalculate the upper and lower limits of the least limiting water range (LLWR) concept by using respectively the air‐filled porosity (εa) at which 0.005 of the relative gas diffusivity (Ds/Do) is reached and readily available water (RAW). The refined upper limit estimates the variation in εa related to pore connectivity and the refined lower limit expresses the boundary at which plants suffer physiological water stress. This study was based on soil sampled in compaction trials on two sandy loam soils. Soil samples were taken from plots with no compaction (Control), and compaction with 78 kN (M8) and 58 kN (M6) wheel loads with multiple wheel passes. The soil cores were analyzed for εa, Ds/Do, bulk density (ρb) and penetration resistance (PR). Heavy farm machinery impact of M8 and M6 led to subsoil compaction up to depth of 0.5 to 0.7 m for the soils under study. The subsoil structure was affected by compaction across depths with the decrease in εa (∼33–46%) and Ds/Do (∼37–61%) and increase in ρb (∼4–8%) and PR (∼40–50%, at −100 hPa at 30‐cm depth). The refined LLWR showed a wider water range compared to the original approach. We anticipate that the refined LLWR well reflects the limiting soil physical conditions for root growth for the studied soils, but validation by combined soil physical and plant growth measurements is needed. Core Ideas Heavy traffic‐induced compaction narrows LLWR in the subsoil. Air permeability at critical limit of gas diffusivity take in pore organization. Using readily available water as the lower limit represents a drought stress boundary.

Limiting water range: Crop responses related to in‐season soil water dynamics, weather conditions, and subsoil compaction

“…(1994) than the Pulido and Munkholm (2019) LLWR approach at any combination of treatment and depth ( p < .05) (Supplemental Figures S1 and S2). We used the Pulido‐Moncada and Munkholm (2019) LLWR approach for further analysis of the in‐season water dynamics because the da Silva et al. (1994) approach suggested that at mean ρ b there was zero or very small LLWR for root development and growth (Figures 4 and 5).…”

“…(1994) approach integrates the volumetric water content variation with soil bulk density at −100 hPa (i.e., field capacity, θ FC ), at 10% of air‐filled porosity (θε a,10% ), at −15,000 hPa (i.e., wilting point, θ WP ) and at 2 MPa of penetration resistance (θ PR ). (b) The refined approach proposed by Pulido‐Moncada and Munkholm (2019) considers the air‐filled porosity at which relative gas diffusivity reaches 0.005 (θε a,0.005 ) as the upper limit and the critical moisture level based on the definition of readily available water (θ RAW ) as the lower limit. (c) The resulting least limiting water range (LLWR) in the light of the two approaches for Taastrup site at 0.3 m depth.…”

“…When the refined approach by Pulido‐Moncada and Munkholm (2019) was calculated, the LLWR between θε a , 0.005 and θ RAW was also drastically reduced by compaction. However, the refined limits provided a broader range compared with the da Silva et al.…”

“…When sampling, in spring 2017, the subsoil (0.3 m depth) of the compacted plots was characterized by a significantly higher soil bulk density (1.77 Mg m −3 ) and lower air‐filled porosity (0.06 m 3 m −3 ) and gas diffusivity (0.0034) compared with the control treatment (1.62 Mg m −3 , 0.10 m 3 m −3 , and 0.0084, respectively) (Pulido‐Moncada, Schjønning, Labouriau, & Munkholm, 2020). Further details on the experimental field, treatments, and results of soil physical parameters during the compaction experimental years and after completion of the compaction experimental period have been reported in previous studies (Pulido‐Moncada & Munkholm, 2019; Pulido‐Moncada et al., 2020; Schjønning, Lamandé, Crétin, & Nielsen, 2017; Schjønning, Lamandé, Munkholm, Lyngvig, & Nielsen, 2016).…”

“…The LLWR was determined using two approaches: da Silva et al. (1994) and Pulido‐Moncada and Munkholm (2019). To determine the LLWR as described in da Silva et al.…”