Role of Root Development in Conferring Soil Strength.

This project was conducted to increase understanding of the effect of root development on soil stability.  Root development and relevant morphological and mechanical plant attributes were monitored in conjunction with the evolution of soil shear resistance. Avena fatua (wild oats) were grown in pots for one, three, and seven weeks, after which soil cores were collected and two soil strata (depths of 3-8 cm and 11-16 cm) were obtained from each core. Soil strength was assessed for each soil stratum by placing the saturated sections in a modified interface direct shear device and measuring the resistance to shear forces. The root area ratio (RAR) was measured for each soil stratum using the WinRhizo measurement system. Separately, root tensile strength was measured by subjecting clamped root segments (length> 30 X diameter) to progressively larger tensile force until root breaking. Tensile strength was tabulated as a function of segment position --distance from the tip, a measure of developmental stage. We found roots conferred an increase in soil shear strength in the upper soil stratum (3-8 cm), but not until plants were seven-weeks old. RAR in the 3-8 cm stratum increased with age, while RAR in the 11-16 cm stratum increased between one and three weeks, but remained the same between three and seven weeks. Root tensile strength increased with distance from tip for more than 40 cm, equivalent to approximately 400 hours of development (17 days). We conclude that both the increase in root tensile strength and RAR contribute to the observed increase in soil strength. The results call attention to the value of incorporating developmental changes in root mechanical properties into models of soil stability.

Support from Kearney Foundation of Soil Science (#2008.016)