Simulation model of soil compaction and root growth

Abstract

Soil compaction is understood to reduce root growth by increasing soil resistance to root elongation and by decreasing O2 transport to root surfaces. Although mathematical models have been proposed for each of these processes, there remains a need for a more comprehensive model of root growth if the effects of soil compaction on carbon and nutrient cycling are to be represented in larger ecosystem simulation models. In the model presented here, root growth simulated in each horizontal layer of the soil profile is taken to be the lesser of that enabled by soil strength and that by carbon respiration. Soil strength is calculated from the bulk modulus of soil elasticity, estimated from bulk density, water content and organic matter content, and carbon respiration is estimated from the availability of O2, nutrients and reduced carbon in the roots. This model represents an attempt to integrate the effects on root growth of soil physical characteristics, such as water content and bulk density, with those of soil chemical characteristics, such as nutrient and O2 concentrations, and those of plant biological activity, such as the production of reduced carbon. The mathematical equations on which the model is based are presented, and the behaviour of the model is discussed. Further knowledge of how root branching is controlled will be needed for further model development. In the accompanying article, this model of root growth is tested against experimental data recorded in soil columns at different soil bulk densities.