Compaction of sandy soils in Radiata pine forests. I. A penetrometer study

Abstract

The mechanical strength of sandy soils under radiata pine plantations was measured with a penetrometer. Resistance to penetration was largely independent of water content in the range sampled, and was directly related to the bulk density of the soil. Soil strength at constant bulk density increased with depth owing to increase in overburden pressure and to a decrease in soil organic matter. Soil under native scrub was consistently less compact than that from adjacent radiata pine plantations on the same soil type. Soil from pasture was usually more compact in the surface 20 cm of soil than that from pine plantations, but was less compact at depth. Soil from second rotation plantations was more compact than soil on some first rotation sites, but on other sites no differences could be established. Radiata pine roots preferentially penetrated areas of lower soil strength. Root penetration was severely restricted above a critical penetration resistance of about 3000 kPa. Saturated soils were highly compacted even by light loads in a laboratory consolidometer compared to unsaturated soil. In the unsaturated condition compaction was greatest under heavy loads on soils at about 1% organic matter. Causes of the observed compaction in the field are discussed and remedial measures are suggested. Soil compaction reduced porosity but had little effect on water storage capacity. Increased organic matter at constant bulk density also reduced porosity, but greatly increased water storage capacity and unsaturated hydraulic conductivity. The importance of organic matter in maintaining a favourable structure in sandy soils and its relation to maintenance of site productivity is discussed.

Mapping soil deformation around plant roots using in vivo 4D X-ray Computed Tomography and Digital Volume Correlation

“…Soil physical factors that limit root growth rate vary with time and spatial location in the soil domain (Bengough et al, 2006), and roots are known to preferentially follow both paths of low penetration resistance in general (Sands et al, 1979) and macro-pore pathways in particular (Passioura, 1991). At the scale of root tip extension per step (~ 800 μm), the soil matrix was evidently highly heterogenous ( Figure 7).…”

Soil Compaction - Impact of Harvesters' and Forwarders' Passages on Plant Growth

“…It has been determined that a soil resistance of 2.0 MPa or more causes root shortening in most plant species (Atwell, 1993). The critical soil resistance on compacted sands limiting root growth measured for Pinus radiata was 3.0 MPa (Sands et al, 1979). However, roots usually have a lower resistance to soil penetration than the resistance measured by penetrometers, due to the radial expansion and smaller diameter of roots and the ability to curl and minimise friction by means of polysaccharide slime.…”

Potential indicators of soil quality in temperate forest ecosystems: a case study in the Basque Country

“…The values selected for this study were as follows: 0.10 cm 3 cm −3 air-filled porosity (Grable and Siemer, 1968), field capacity at -0.01 MPa matric potential (Haise et al, 1955), wilting point at -1.5 MPa matric potential (Richards and Weaver, 1944), and the soil strength restriction limit at 3.0 MPa (Sands et al, 1979).…”