The magnitude of a soils resistance to detachment depends, in part, on the physical condition of the soil. Thepresence of roots is believed to greatly increase soil strength and enhance its stability. Two laboratory experiments wereconducted to study the influence of living roots on strength, shear detachment, and erodibility of a Plano silt loam soil(finesilty, mixed, mesic, Typic Argiudolls) using a hydraulic flume to simulate concentrated flow. Polyvinyl chloride (PVC)pipes, 102 mm in diameter and 152 mm long, were packed with soil to be used as plant pots. The pots were completelyrandomized; some were planted to ryegrass and some left bare for rooted and fallow treatments, respectively. Erosion testswere run at three different stages (duration) of plant growth. Following each erosion test on rooted soils, living root sampleswere collected and their length determined. Root length density (length of root per unit volume of soil) was related to soilerodibility and detachment rate.Root length density (RLD) increased with growth stage for the duration of the experiments. There were significantdifferences ( = 0.5) in average shear strength between fallow and rooted soils. Withintreatment comparison of shearstrength among stages showed that the difference was more significant for rooted treatments than for fallow treatments. Meansoil detachment rate (Dr) for rooted soils was reduced by as much as 64% of that for fallow treatment. Withintreatmentcomparison of detachment rate among stages showed that detachment rate decreased with time for both fallow and rootedtreatments. Rill erodibility (Kr) for rooted soils was also lower than for fallow soils. There was a decrease in Dr and Kr withincrease in RLD. Both Dr and Kr were exponentially related to RLD. The study showed that there were no significantdifferences in critical shear stress (c) between fallow and rooted treatments and among their respective stages. Critical shearstress appeared to be more closely related to surface condition than to treatment.
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Mamo et al. (2001) studied this question.