Cover crop residue effects on machine-induced soil compaction

Crop production systems which utilize the biomass produced by rye (Secale cereale ) to suppress weed growth and conserve soil moisture have been developed at Virginia Tech. The success of alternative, reduced-input crop production systems has encouraged research into the potential for breaking the traffic-tillage cycle associated with conventional tillage crop production systems.

The fragile residues encountered in agricultural crop production, whether incorporated into the soil or distributed on the soil surface, provide minimal protection against compaction by wheeled vehicles. The potential of an intact cover crop to reduce machine-induced effects on soil properties that affect primary crop growth was the subject of this study.

A randomized complete block experiment was conducted at the Whitethorne Farm in Montgomery County, Virginia. One set of plots was arranged on a terrace adjacent to the New River in a fine, mixed, mesic, Aquic Argiudolls. Another set of plots was arranged on an upland site, a river terrace tread, in a fine-loamy, mixed, mesic, Typic Hapludults.

Three rye cover crop treatments were examined. In one, a live cover crop was completely undisturbed prior to tracking by a wheel-type tractor. In another, the cover crop was chemically desiccated, and in the third treatment, all above-ground biomass was removed from plots prior to machine traffic. The treatments permitted investigation of the effects of crop condition on machine-induced soil compaction and the contribution of root reinforcement to the alteration of soil response to machine traffic. A fall-tilled fallow treatment served as an experimental control.

Three levels of traffic were investigated: one pass, three passes, and five passes. Undisturbed soil core samples were analyzed to determine machine-induced effects on dry bulk density, pore size distribution, and saturated hydraulic conductivity.

The treatments affected soil response to machine traffic. The cover crop treatments altered the soil-plant microenvironment, affecting soil parameters that influence compactibility. Soil compaction was attenuated by the reinforcing effect of a network of undisturbed roots within the soil. There was no convincing evidence that above-ground biomass contributed directly to the reduction of machine-induced compaction effects. Soil response to machine traffic was limited to the uppermost 15 cm of the soil profile.