SOIL COMPACTION AROUND A SMALL PENETRATING CYLINDRICAL BODY AND ITS CONSEQUENCES

Penetrometerprobes as well as roots and earthworms push soil particles (grains or small aggregates) radially during penetration and/or thick ening due to growth. By this, the adjacent soil within a concentric la yer is compacted. The degree of compaction depends on soil texture and soil physical properties that are influenced by soil moisture status. In the present study an estimate of the mean but constant increase of the initial bulk density and of the outer radius of this concentrical ly compacted zone, which are interdependent, is given. For instance, a n increase from 1.2 g/cm3 to 1.6g/cm-yields a compacted zone of radius 0.5 mm when a body of radius 0.25 mm penetrates into a soil. This est imation is less laborious, but also less exact than that of Dexter ( 1 987: Comparison of soil around roots. Plant Soil, 97: 401-406). This s tudy shows that the distance between adjacent penetrations, when measu ring resistance to penetration, should be greater-than-or-equal-to 10 times the probe radius. It is moreover supposed that the compaction pr oduced by roots and earthworms makes it easier for them to anchor with in (loose) soil. However, it possibly diminishes infiltration and exch ange of soil solution.