Detachment Rate, Soil Erodibility, and Soil Strength as Influenced by Living Plant Roots Part Ii: Field Study

Living plant roots have long been known to increase soil shear strength and enhance aggregate stability. A fieldexperiment was conducted to study the influence of living roots of corn (Zea mays L.) and soybean (Glycine max L.) onstrength, detachment rate, and erodibility of a Plano silt loam soil (finesilty, mixed, mesic, Typic Argiudolls) using preformedrills to simulate concentrated flow. The experimental site was conventionally tilled, cleared of all plant material, divided into15 plots, and completely randomized by stage. Each plot was further divided into four soil conditions, and rill plots, 2 m wideand 5.5 m long, were prepared for freshly tilled, fallow, soybean, and corn treatments. With the exception of freshly tilled plots,erosion experiments were conducted at three stages of plant growth. Following each erosion measurement, root samples werecollected and their length determined. This root parameter was later related to soil detachment rate and erodibility.Differences in soil strength indices, detachment rate, and rill erodibility between rooted and fallow soils were significant(P < 0.05). Shear strength for corn and soybean plots was in excess of 20% greater than for fallow plots. Mean soil detachmentrate (Dr) values for corn and soybean were reduced to one half that for fallow soils, and rill erodibility (Kr) for corn andsoybean was less than one half that for fallow plots. There were exponential relationships of the form Y = aebx between rootlength density, root length per unit volume of soil, and both Dr and Kr. Root length density (RLD) for corn was much higherthan for soybean, but there was no significant difference (P > 0.05) in soil strength, detachment rate, and rill erodibilitybetween the crops. Comparison of average Dr and Kr values among physiological stages of development for crops and timesince tillage for fallow soils within each treatment showed that there were significant differences (P < 0.05) in Dr and Kramong stages for fallow soils. For cropped soils, while the general trend was for Dr to decrease with increase in stage, nosignificant difference (P > 0.05) was observed between stages II and III for soybean and among all three stages for corn.