FIELD-EVALUATION OF LABORATORY TECHNIQUES FOR PREDICTING THE ABILITY OF ROOTS TO PENETRATE STRONG SOIL AND OF THE INFLUENCE OF ROOTS ON WATER SORPTIVITY

The ability of two laboratory screening techniques to predict the abil ities of roots of eight crop species to penetrate a compacted soil wer e evaluated and compared in a field experiment. A soil tilled to remov e the effects of mechanical resistance was planted with the same speci es to serve as a control. Depth of root penetration, root density and the influence of the roots on the sorptivity of water were measured. R oots of all species penetrated deeper in the deep tilled than compacte d soils. There were differences in the ability of roots of the species to penetrate the compacted soil. Generally dicotyledonous species had more roots penetrating to depth in both the compact and deep tilled s oils. Within the main species classifications, lupin and safflower (di cotyledons) and oats and barley (monocotyledons) had the highest penet ration into the compacted soil. Water sorptivities in the deep tilled soils were higher than those of the compact soil. Soil from planted tr eatments had higher sorptivities than soil which had not been planted. This is attributed to biopores left by the roots. Sorptivities of soi ls which had dicotyledonous species were generally higher than those o f monocotyledons. The soil planted with safflower produced the highest sorptivity in the compacted layer (0.1-0.3 m). A comparison of the ac curacy of the two laboratory screening methods in predicting the field penetration of roots suggest that the method involving mechanical str ess was better than that involving osmotic stress. Relative root diame ter was found to be a better indicator of the penetration ability of r oots than relative root elongation.