Modelling the effect of variable soil impedance on pea root growth
Experiments were conducted: (i) to investigate varietal differences in pea (Pisum sativum L.) root response to mechanical impedance, (ii) to study the effect of mechanical impedance on root growth and morphology and (iii) to predict root growth in soils whose mechanical impedance varied temporally and spatially by adapting the Diggle (1988), ROOTMAP, model. Pea varieties whose root growth rates did not differ under unimpeded conditions had their root growth rates reduced by significantly different proportions in response to mechanical impedance. Highly significant correlations between first order lateral elongation rate and diameter were observed for pea roots grown in moist vermiculite. There was also evidence that regular stimulation of the root tip is required to trigger lateral emergence. An experimental procedure for obtaining ROOTMAP input parameters was devised and the growth and distribution of pea roots grown for 29 days in soil whose mechanical impedance varied with time and depth as a result of soil drying out, was successfully predicted. These findings highlight the potential that exists for selecting and breeding varieties based on root characters that confer insensitivity of response to mechanical impedance and for using ROOTMAP to investigate the growth response of different crop varieties in realistic soil scenarios.