A rapid screening method for good root-penetration ability:: Comparison of species with very different root morphology

The restoration of the physical structure of soil by plant roots depends on the ability of roots to penetrate strong soil. The sensitivity of root growth to mechanical impedance can be considered as a possible screen for species suitable as 'biological subsoilers'. The ability of roots to penetrate hard wax layers in sand cores has recently been identified as a useful tool for identifying rice varieties that are good at penetrating strong soil, and this method provides the possibility of a rapid laboratory screen which can be used to identify other species with the same characteristic. However, comparing plants with very different root anatomy may be more difficult than comparing the performance of root systems that are essentially similar, except for the number and length of roots, as is the case with rice. In this paper, we compare the penetration of roots of barley, chicory, lupin, red clover and lucerne through soft and hard wax layers installed at 50 mm depth in sand columns. Barley had the lowest fraction of roots that penetrated the hard wax layer, although it had a higher absolute number of roots penetrating the hard wax than the other species. The numbers of chicory, lupin, red clover and lucerne roots penetrating the hard wax layer were similar, although lucerne had the highest number. The proportion of roots penetrating the hard layer as a proportion of those penetrating the soft layer was highest for lucerne. Comparison with previous data for barley and lucerne supports the use of the wax layer screen for identifying species with good root penetration.