Soil compaction and plant root growth

Abstract

Plant roots are subjected to mechanical impedance when soil pore space cannot accommodate the extending root system. The paper examines briefly the theoretical aspects of the combined effects of stress and moisture history in modifying both the pore space available for root growth and soil strength that limits the ability of roots to deform the soil. A root extension model that requires cyclic changes in root apex geometry to overcome pore space confinement is described. Cells in the growth zone of roots are analysed as pressurized thin-walled structures of simple geometrical shape made of a polymeric elastomer reinforced by a network of symmetrical inextensible fibrils. Such structures exhibit somewhat unexpected but unique changes in shape governed by both fibril arrangement and contact stresses acting on the external surfaces. A simplified model of a root apex can be constructed from these structural units and the behaviour of this model lends support to the proposed variable root apex geometry routine evolved by roots to penetrate compact soils. This analysis highlights the crucial role played by physical factors in the growth processes of roots and the disparate models described provide the basis for the development of a comprehensive quantitative model of root proliferation.