Restoration of ecosystem function in an abandoned sandpit: plant and soil responses to paper de-inking sludge

Published source details Fierro A., Angers D.A. & Beauchamp C.J. (1999) Restoration of ecosystem function in an abandoned sandpit: plant and soil responses to paper de-inking sludge. Journal of Applied Ecology, 36.
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Summary

In minesoil reclamation, the establishment of a sustainable plant cover often requires improvement of limiting substrate conditions and the re-initiation of carbon (C) and nutrient cycling. This study, an experimental restoration of an abandoned sandpit in Quebec, Canada, was based on organic amendment in an attempt to accelerate the reconstruction of a functional ecosystem.

The interventions consisted of incorporating paper de-inking sludge into the sandy soil, supplemented with nitrogen (N) and phosphorus (P) at a combination of application rates, followed by seeding of tall wheatgrass Agropyron elongatum.

Site description: The experimental restoration was conducted on an abandoned sandpit at Saint-Lambert-de-Lévis, Quebec, Canada (46°34' N, 71°13' W). Agricultural (dairy farming) fields surrounding the sandpit, lie on a Beaurivage sandy loam (12.5 mg C/g, pH 5). In the pit, topsoil had been removed and subjacent layers of sand mined down to about 2 m. The exposed minesoil comprised about 94% medium-textured sand with very little gravel.

Treatments and experimental design: Treatments comprised combinations of: paper de-inking sludge from a local paper mill (0 and 105 dry t/ha); N supplements (3, 6 and 9 g /kg sludge); and P supplements (0.5 and 1 g/kg sludge). Levels of sludge, N and P were selected on the basis of the results of a greenhouse study. An application rate of 105 dry t/ ha corresponded to ≈30% sludge by volume within the incorporation depth.

The experimental design was a split-split-plot with four replications. Sludge treatments were assigned to main plots, N treatments to subplots and P treatments to sub-subplots. Bare-soil corridors of 1 m were left between sludge treatments and 0.5 m corridors between N treatments. Each sub-subplot (experimental unit) was 4 × 4 m, including a 0.5 m buffer along edges.

Nitrogen was applied as urea and P as single superphosphate. In addition, potassium chloride was applied to all plots at 85 kg K/ha. Sludge and fertilizers were mechanically incorporated in the top 0–0.21 m minesoil layer. Tall wheatgrass Agropyron elongatum was drill-seeded (680 live-seeds/m²) – this species had performed well in previous greenhouse trials. Incorporation of sludge, fertilizers and seeding were performed on 25 July 1994 (approximately the middle of the growing season). Plant responses were recorded in the two subsequent growing seasons (1995 and 1996).

Vegetation sampling and analysis: Sampling was underetaken within the central 3 × 3 m of each experimental unit. This was divided into a grid of nine, 1 m² quadrats. At the end of the first and second growing seasons, ground cover was estimated visually in each by three evaluators. The average of the three estimations was used for data analysis.
Two quadrats were randomly selected to record above-ground biomass (hand clipping to ground level, including standing litter). Quadrats sampled in the first year were excluded from sampling in the second year. Biomass dry weight was determined after oven-drying. Agropyron biomass was analysed to determine tissue N and P.

Soil sampling and analysis: Characteristics of the minesoil prior to application of the treatments were determined. Experimental plots were sampled periodically within the nine sampling quadrats of each plot, to a depth of 0.2 m. Analysis of water retention, pH and cation exchange capacity of the amended minesoil were performed on samples collected at 4, 359 and 743 days after sludge incorporation. The last two dates roughly corresponded to the middle of the first and second growing seasons. Soil properties were evaluated for the highest and lowest N rates (3 and 9 g/kg sludge) and for one P rate only (1 g/kg sludge), except for C and N contents for which both P treatments were evaluated.

The following soil properties were thus recorded: soil water retention; electrical conductivity; pH; cation exchange capacity; total C and N; and total P.

Standing plant biomass increased in the presence of sludge after both the first and second full growing seasons. High N application rates further increased biomass yield, especially in the second season. The high P rate improved tall wheatgrass establishment in all cases. Vegetation ground cover increased with time and doubled in the presence of sludge, whereas it declined in the absence of sludge. Phosphorus and N uptake was improved consistently in the presence of sludge.

Conclusions: Application of paper de-inking sludge resulted in improved water retention and cation exchange capacities, and an increase in pH and bulk density of the sandpit minesoil, all of which may have accounted for the significant improvement in plant responses. N and P addition accentuated the positive influence of sludge on revegetation. Levels of soil C and N suggest that the treated area was approaching sustainability.

Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at: http://www.blackwell-synergy.com/doi/full/10.1046/j.1365-2664.1999.00395.x