Residual effects of compaction on the subsoil pore system—A functional perspective

Abstract

Subsoil compaction caused by heavy traffic affects the soil pore system, resulting in long‐term damage to soil functions. The study contrasted two treatments from compaction experiments conducted at three different sites in Denmark: non‐trafficked control soil and soil subjected to four annual traffic events (2010–2013) with a wheel load of 58 to 78 kN. A cover crop of fodder radish (Raphanus sativus L.) was grown in half of the initial experimental plots after completion of the compaction treatments (2013 and onwards). In the spring of 2017, undisturbed soil cores were sampled at 0.3 and 0.5 m depth. The air‐filled porosity (εa), air permeability (ka) and gas diffusivity (Ds/Do) were quantified for samples equilibrated to –100 hPa matric potential. Soil pore structural indicators were estimated from the combination of εa, ka, and Ds/Do. The ratio of non‐Darcian to Darcian ka (R) was also used as a pore morphology indicator. For all sites and depths, compaction reduced εa, Ds/Do, ka‐Darcy, PO1 (ka‐Darcy/εa) and the effective radius ([(8ka‐Darcy)/Ds/Do]0.5) compared to control soil (p < 0.05). The Buckingham‐X variable relating Ds/Do and εa tended to be smaller for compacted soil, significantly for one of the sites. Compacted soils were also characterised by a significantly smaller R‐ratio at high levels of ka‐Darcy (> 32 μm2), but also by having a tendency for the R‐ratio to decrease rapidly with increasing pore air velocity compared to the control. The results reflect a compaction‐induced reduction in the number of marginal pores connected to large arterial pores, promoting a simple pore system formed by continuous vertical pores. The compaction effect was not affected by the cover crop. Neither natural recovery nor fodder radish‐induced mitigation of soil compaction was evident for the studied soils.

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

“…This is in agreement with the results found in the same experiment by Pulido‐Moncada et al. (2020), which indicated that compaction significantly increased ρ b and decreased gas transport for depths of 0.3 and 0.5 m.…”

“…It was assumed that the water content variation with ρ b at 0.3 m depth was applicable at 0.6 m depth because of a similar ρ b distribution in the deeper subsoil layer. The mean ρ b of the 0.5‐m soil layer from samples taken in 2017 (Pulido‐Moncada et al., 2020) was assumed to represent the conditions at 0.6 m, based on the LLWR results from 0.5 and 0.7 m depth at the same experiment assessed by Pulido‐Moncada and Munkholm (2019).…”

“…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).…”

Anisotropy of subsoil pore characteristics and hydraulic conductivity as affected by compaction and cover crop treatments

“…This interpretation is discussed below. In previous studies from the same experiment, smaller vertically oriented samples (100 cm 3 ) showed increasing deviation between the two estimates of air permeability with increasing levels of permeability (Pulido‐Moncada et al., 2020b; Schjønning et al., 2019). In those studies, the measured range of air permeability was larger (0.01–1000 μm 2 ) than those obtained in the present study (0.01–100 μm 2 ), which may be related to the sample scale.…”

“…Pulido‐Moncada et al. (2020b) also reported a compaction effect on k a from 100‐cm 3 samples taken in the vertical direction at Aarslev and Flakkebjerg in the same year of evaluation. Reductions in k a have been shown to reflect a disruption of connected porosity and a decrease in the volume of macropores (Mossadeghi‐Björklund et al., 2016).…”