An improved model of root growth in structured soil

Abstract

The growth of roots of maize, sorghum and soybean is modelled through beds of spherical aggregates. Effects of aggregate size and strength, and effects of the spread or distribution of aggregate strengths are investigated. This is achieved by a combination of a statistical model for soil structure with a statistical model for the penetration behaviour of a root at a void/aggregate interface. It is shown that the behaviour of a root at such an interfac is dependent on the previous history of the root in its passage through the soil. It is concluded that the smaller the aggregate size, the greater is the nutrient availability per unit length of root. The influence of aggregate size decreases with increasing soil strength. An increase in aggregate strength reduces the availability of nutrients per unit length of root. However, the rate of nutrient uptake per root axis goes through a minimum at a strength (for maize) of around 80 per cent of the maximum limiting aggregate strength for root penetration. An increase in the spread of aggregate strengths usually results in a proportional increase in nutrient availability. This effect is more pronounced with smaller aggregate sizes.