Short-term effects of compaction on soil mechanical properties and pore functions of an Andisol

Several studies on soil physical quality have related soil structural properties to bulk density, proposing values for critical limits in relation to the soil compaction status. However, these values are not applicable to Andosols due to their very low bulk density (< 0.9 Mg m-3). This work aimed to evaluate the short-term effects of soil compaction on the soil physical quality of an Andosol. The experiment was established in May 2019. Soil cores were collected from the soil surface and field measurements (penetration resistance, volumetric water content and air conductivity) were conducted to monitor changes in the soil physical quality after compaction events. The soil was compacted using rollers (weighing between 1.20 and 1.37 Mg) to reach three bulk densities (T0: 0.65, T1: 0.75 and T2: 0.85 Mg m-3) by controlling the number of roller passes. Soil compaction induced an increase in the soil bulk density that resulted in an increase in the mechanical strength (e.g. maps of penetration resistance revealed values from (T0) 500 kPa to (T2) 1500 kPa) and caused a decrease in the volume of macropores (e.g. air capacity in T0 and T2 was 22% and 11%, respectively) responsible for water infiltration and flow. The latter provoked an increase in the volumetric water content in the upper 10 cm of the soil, which decreased the field air conductivity due to the reduced pore space and its continuity. Bulk density also increased due to wetting and drying cycles, showing the effect of the natural rearrangement of soil particles, which was more intense in the soil with the lowest bulk density. When the bulk density of the tilled soil increased to values over 0.80 Mg m- 3, soil pore functions related to soil aeration reached critical values (air capacity < 10% and air permeability < 1 mu m2) concerning soil compaction, while the soil precompression stress (around 60 kPa) and plant available water (> 20%) remained within an optimal range.