Subsoil compaction of a clay soil in South-East Norway and its amelioration after 5 years

Abstract

The main objective was to evaluate to what extent subsoil compaction on an arable clay soil (Stagnosol (Drainic)) may be alleviated after 5 years under the climate conditions in South-East Norway. Therefore, field plots which had been ploughed and under minimum tillage were compacted through wheel impact (10x) with a 6.6 Mg wheel load. Samples were taken from the ‘compacted’ and ‘non-compacted reference’ treatments at depths of 40 and 60 cm both before and directly after compaction and again 5 years later. The soil physical parameters revealed that pre-compression stress, bulk density, air capacity, air conductivity and saturated hydraulic conductivity at depths of 40 and 60 cm were impaired by compaction, especially under ploughed. After 5 years, bulk density and pre-compression stress remained almost unchanged, while air capacity, air conductivity and saturated hydraulic conductivity had increased at both the 40 and 60 cm depth on both plots as compared to the compacted state and to R for the most part, indicating the recovery of the soil structure in the subsoil. The compaction status evaluated by the ‘compaction verification tool’ indicates the relative reduction of ‘harmful soil compaction’ (after wheel impact) with a change towards ‘slightly harmful compaction’ for the most part with an as yet limited saturated hydraulic conductivity at both depths after 5 years.