Root growth and phosphorus uptake in relation to the size and strength of soil aggregates. II. Prediction by a stochastic model

Abstract

Root growth of several plant species was simulated in beds of aggregates of varying sizes and strengths. This was achieved by combining a simulation model of an aggregate bed with a model based on the probability of root penetration of any single aggregate in the bed. The probability of root penetration is dependent on the angle of incidence of the root axis, the size of the preceding void, the size and strength of the aggregate, and the pressures exerted by the roots. Relative phosphorus uptake was predicted by assuming unit uptake where the root axis grows through an aggregate, and zero uptake where it grows in a void. The trends in phosphorus uptake in relation to the size and strength of the aggregates were compared with phosphorus uptake determined experimentally. The proportion of the total length of roots penetrating the aggregates decreased with increased size and strength of aggregates. Consequently, relative phosphorus uptake was lower from large and strong aggregates than from small and weak aggregates. The results are discussed in relation to the structures produced by various tillage implements and the intensity of tillage operations.