Effect of different compaction impacts and varying subsequent management practices on soil structure, air regime and microbiological parameters

The impact of structural deformations on soil properties controlling its function as habitat (“soil environment”) as well as the extent and rate of its regeneration are of particular interest for assessing the importance of soil compaction. The functional relationships between compacted soil structures, the resulting soil environments and soil microbial parameters were investigated in a 5-year (2004–2008) model experiment at field scale at Zurich-Reckenholz, Switzerland, using treatments differing in compaction events, soil tillage and irrigation.Soil structure was characterised by laboratory determination of macropore volume and air permeability on undisturbed soil cores. The soil environment was described by repeated field measurements of volumetric soil water content and O2 concentration in soil air. Soil microbial biomass (Cmic) and basal respiration were analysed using mixed soil samples and potential denitrification was determined in undisturbed soil cores. Samplings for both physical and biological analysis were repeated on several occasions.Soil structure analysis confirmed the expected impairment of topsoil properties by the compaction treatments. The results demonstrated clear quantitative and qualitative differences in the structural regeneration of the treatments, e.g. depending on subsequent soil management practices. Regeneration by natural processes clearly produced a different soil structure than alleviation of topsoil compaction by tillage. The effects of soil structure on the soil environment in the treatments strongly depended on the water regime. Compaction reduced air-filled porosity considerably and caused more frequent and pronounced conditions of low O2 concentration in soil air. The air regime in the compacted treatments clearly differed from that in the control treatment during the first 2 years after compaction. Topsoil compaction had a clear impact on subsoil environment and we recommend that this ‘functional subsoil compaction’ be considered in future decision-making on avoiding compaction risks.The clearly adverse effects on soil structure and soil environment resulted in different time courses of microbial parameters. However, repeated soil compaction combined with irrigation was the only treatment that strongly affected most soil microbial parameters. Potential denitrification was enhanced in compacted and irrigated treatments, where anoxic conditions in the field occurred more frequently. Under moist climatic conditions, as simulated in our irrigation experiment, microbial soil properties were not directly affected by the compacted soil structure itself, but by its gas exchange ability, which was strongly determined by the degree of air-filled pore space.

Research highlights▶ Different soil structure after topsoil regeneration by natural processes or tillage. ▶ Effects of soil structure on soil environment strongly depended on the water regime. ▶ Disturbance of air regime in compacted topsoils at least for 2 years. ▶ Topsoil compaction affected subsoil environment too: ‘functional subsoil compaction’. ▶ Microbial properties affected by gas exchange ability of compacted soil structure.