Modelling pea (Pisum sativum) root growth in drying soil. A comparison between observations and model predictions

Abstract

SUMMARYPeas were grown in the glasshouse for 29 d in duplicate 1 m tall containers packed with soil at field capacity (a matric potential of –0·005 MPa) to a bulk density of 1·30 Mg m−3 and with an initial penetration resistance (PR) of 0·35 MPa. Counts of new root contacts on the sides of the containers and matric potential (Ψm) measurements at 0·1 m depth increments were made every two days. Although the plants were not watered, matric potential was never less than –0·041 MPa and was unlikely to have directly limited root growth, but it was used as a predictor of PR and hence of the effect of PR on root growth rate. The effect of PR on root growth was predicted using experimentally determined relationships between root growth rate and PR, and PR and Ψm. These results were used with the ROOTMAP root growth model to give two different model scenarios: (1) variable resistance (VR), allowing mechanical impedance to vary with time and depth in line with the observed values of Ψm and (2) constant resistance (CR), maintaining mechanical impedance at its value at the start of the experiment. CR predictions gave a gross overestimate of the rate at which new root contacts were made on the container walls, whereas VR predictions agreed with experimental observations to within the limits of accuracy of the model and the observations. The comparison between CR and VR predictions gives a clear demonstration of bow the increase in soil strength caused by roots drying the profile can result in a reduction in the size and extent of the whole root system.