Comparison of Methods to Remediate Compacted Soils for Infiltration and Vegetative Establishment

Abstract

The process of constructing roads and buildings usually involves the removal of topsoil and grading of the subsoil followed by a variety of activities using heavy equipment. This presents multiple challenges in attempts to establish vegetation on these areas: low nutrient soils with little organic matter, high bulk densities, and low infiltration rates. The goals of this preliminary study were to quantify the impacts of soil compaction remediation methods on infiltration, runoff water quality, and vegetation establishment. The objectives were to measure: 1) steady state infiltration rate (IR); 2) quantity and quality of storm water runoff; and 3) ground cover, biomass production, and rooting depth of vegetation during early establishment. We evaluated four treatments: a compacted soil (C), a compacted soil with core aeration (A), a compacted soil with deep (20 - 30 cm) tillage (DT), and a compacted soil with deep tillage and incorporated compost (CT). Sites 1 and 2 received C, A and DT treatments and Site 3 received only DT and CT treatments. At Site 1, runoff from natural rainfall events was collected in plastic tubs at the bottom of each 2 × 1 m plot, and samples were measured for volume and sediment. Infiltration rates were determined using a Cornell Sprinkle Infiltrometer at all three sites. At Site 1, the A treatment had a higher erosion rate during two of four rain events and higher runoff volume during three of four rain events, when compared to C and DT. However, the aerator was only able to penetrate 1 - 2 cm due to the compacted soil. Average event runoff ranged from 0 to 22% (0 - 9.3 mm), 10 to 60% (1.9 - 26.2 mm), and 0 to 3.5% (0 - 1.1 mm) of the total rainfall for C, A, and DT, respectively. There was no difference between C and A for vegetative biomass and IR, but both biomass and IR were greater in the DT plots. Treatment DT had an average IR of 15 cm·hr-1, compared to 0.16 and 0.21 cm·hr-1 for C and A, respectively. Roots were much more abundant at the 20 - 50 cm depths with DT. At Site 2, there were no significant differences in IR, with many values too low to be measured with the infiltrometer. Vegetative cover also did not differ between the three treatments due to poor (16% - 22% cover) grass establishment. Infiltration rates at Site 3 were measured immediately after tillage and were 10× those at Site 2, measured 2 months after tillage, but DT and CT values were not different. The results suggest that deep tillage prior to seeding could maximize long-term vegetation growth and provide areas of high infiltration to minimize post-construction stormwater discharges, as long as vigorous vegetation can be established quickly.