Abstract
Abstract. Although soil compaction is widely recognized as a soil threat to soil resources, reliable estimates of the acreage of overcompacted soil and of the level of soil compaction parameters are not available. In the Netherlands data on subsoil compaction were collected at 128 locations selected by stratified random sampling. A map showing the risk of subsoil compaction in five classes was used for stratification. Measurements of bulk density, porosity, clay content and organic matter content were used to compute the relative bulk density and relative porosity, both expressed as a fraction of a threshold value. A subsoil was classified as overcompacted if either the relative bulk density exceeded 1 or the relative porosity was below 1. The sample data were used to estimate the means of the two subsoil compaction parameters and the overcompacted areal fraction. The estimated global means of relative bulk density and relative porosity were 0.946 and 1.090, respectively. The estimated areal fraction of the Netherlands with overcompacted subsoils was 43 %. The estimates per risk map unit showed two groups of map units: a “low-risk ” group (units 1 and 2, covering only 4.6 % of the total area) and a “high-risk” group (units 3, 4 and 5). The estimated areal fraction of overcompacted subsoil was 0 % in the low-risk unit and 47 % in the high-risk unit. The map contains no information about where overcompacted subsoils occur. This was caused by the poor association of the risk map units 3, 4 and 5 with the subsoil compaction parameters and subsoil overcompaction. This can be explained by the lack of time for recuperation.
Highlights
Soil compaction is recognized as one of the major soil threats
Note that the box plots for risk map unit 1 and 2 are based on 4 and 5 measurements only. For both subsoil compaction parameters, the risk map units can be aggregated into two distinct groups: a group with relatively low subsoil compaction consisting of map units 1 and 2 and a group of relatively high subsoil compaction consisting of map units 3, 4 and 5
Differences between risk map units within the same group were small compared to differences between groups
Summary
Soil compaction is recognized as one of the major soil threats. Van Camp et al (2004) recognized soil compaction as one of the eight soil threats requiring further attention. In 2006 the Thematic Strategy for Soil Protection was launched by the European Commission (European Commission, 2006). Subsoil compaction is of more concern than topsoil compaction because of its persistency (Alakukku, 2000; Berisso et al, 2012, 2013). Subsoil compaction is defined as compaction of the soil below the cultivated layer. This compacted layer is referred to as the pan layer, hardpan or plow pan. The pan layer is often the bottleneck for the functioning of the subsoil because it is denser and less permeable for roots, water and oxygen than the subsoil below this layer
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