Root Growth and Function in Relation to Soil Structure, Composition, and Strength

Abstract

Soil is an extremely complex growth medium, with an enormous biodiversity of fauna and flora, widely differing mineral and organic matter composition, and a complex multi-scaled network of three-dimensional pore space. Soil strength and physical conditions can exert a major constraint to root growth. Hard soils with massive structures restrict the accessibility of nutrients and water to plants. In many laboratory and glasshouse experiments, and in much of horticulture, plants are now cultured using agar, nutrient solution, or artificial composts, an environment very different to the natural one. We must understand the most important factors and stresses that limit root growth in soil, so that results gained in vitro can be related to agricultural and natural ecosystems. Laboratory studies should concentrate on the most important, rather than the technically most convenient, problems. These problems must also be considered in appropriate combination — for example, in many soils, water stress will be accompanied by a large increase in soil strength and hence mechanical impedance to root growth. In this chapter the impact of soil structure, composition and strength on root ecology and resource acquisition by plants is considered.