The value of pulverized refuse fines (PRF) as a substitute for topsoil in land reclamation. 1. Field studies

Published source details Chu L.M. & Bradshaw A.D. (1996) The value of pulverized refuse fines (PRF) as a substitute for topsoil in land reclamation. 1. Field studies. Journal of Applied Ecology, 33, 851-857.
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Summary

On urban clearance sites deficiencies in organic matter and nutrients may hamper revegetation. The suitability of pulverized refuse fines (PRF) as a topsoil substitute to improve growing conditions in the reclamation of an urban clearance area in northwest England was studied in the field for 26 months.

Study site: Urban clearance area in Liverpool (National Grid ref: SJ 345925) Prior to the experiment the surface was scraped off by excavator in dry weather to remove weathered substrates and weeds. There was a thin layer of decomposed brick rubble and subsoil overlying decomposed brick waste and concrete slabs.

Treatments: Small plots (1 x 1 m) separated by 50 cm gaps were established in fenced areas and one of the following treatments applied (five replicates, randomized block design):

i) untreated (control);

ii) NPK fertilizer added (rate equivalent to 50 kg/ha nitrogen) and 5 t/ha limestone;

iii) 10 cm of topsoil

iv) 20 cm of topsoil

v) 10 cm of PRF

vi) 20 cm of PRF

In April 1985, each plot was sown with perennial ryegrass Lolium perenne (rate equivalent to 100 kg/ha). Plots were hand-weeded regularly. The grass was harvested four times in October 1985, June and October 1986, and June 1987 by cutting at 5 cm above soil level. Samples were cleaned and oven dried to determine dry weight.

October 1985 and 1986 samples were analysed for nitrogen content. Soil pH, organic matter content, total available nitrogen (N), phosphorus, potassium, calcium and magnesium were also determined. PRF samples from 20 cm plots (at 10 cm depth) were analysed after 3, 6, 12, 18 and 26 months to investigate mineral and mineralizable N content, and initial and final N content assessed.

Substrate analysis: The PRF and topsoil had a neutral to slightly alkaline pH. The PRF was high in total available N (193 µg/g) compared to the topsoil (19.9), and the brick waste itself (9.6).
The waste was alkaline (pH 8.5) had abundant available calcium, but was very low in organic matter, nitrogen and phosphorus.

Grass establishment: Growth of perennial ryegrass Lolium perenne was very poor on untreated substrates. Fertilized or top soiled substrates produced better yields. However, the highest yields were clearly obtained from substrates spread with 20 cm of PRF at all sample times.

Nutrients The concentration and uptake of nitrogen in the ryegrass was highest in the PRF plots. Despite the relatively high C:N ratio (38) of PRF, mineralization of nitrogen occurred readily and supplied sufficient N for plant uptake within the study period, suggesting the organic nitrogen in PRF is in an easily decomposable form.
The potential of PRF to supply available nitrogen was about 6-12 times that of the topsoil used.

Conclusions: Application of PRF appeared to overcome structural and nutrient stresses and provide a nutrient store within its organic matter which are slowly released and become available to plants. The use of PRF has the added advantage of the need for landfill disposal. However, in some cases it may not meet requirements for toxic elements, dependent on the type of refuse input to make the material.

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