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METHODS TO IMPROVE POLLUTION CONTROL
POTENTIAL OF WOODCHIP CORRALS
AJA Vinten 1 , D Merrilees 2 , G Sym 2 , J Parker 2 and C Crawford 2
1
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK,
E-mail: a.vinten@macaulay.ac.uk; 2 SAC, West Mains Road, Edinburgh, EH9 3JG,
UK
SUMMARY
This project investigated the efficacy of different potential sublayers for removal of
some key residual pollutants after passing slurry through woodchip corrals. Pollutants
studied were: ammonium, nitrate, Escherichia coli, mineral phosphate and organic
carbon (TOC). The sublayers investigated were loamy sand subsoil, sandy loam
topsoil, iron ochre granules (to remove P by adsorption) and straw (to remove N by
immobilisation). Good pollutant removal was obtained by all sublayer treatments,
with the exception of the straw treatment. This suffered from problems with packing
the straw between woodchips and subsoil, leading to uneven flow conditions.
Nitrate concentrations in leachate rose to > 40 mg/L but results suggest significant
denitrification was occurring. The value of the iron ochre and straw was demonstrated
in a laboratory column experiment, in which removal of nutrients equivalent to 188 kg
N/ha and 92 kg P/ha was achieved by straw and ochre layers.
INTRODUCTION
In Scotland, woodchip corrals are being widely used as a means of overwintering
beef cattle. The leachate from corrals still has a considerable pollution potential
(Vinten et al., 2006), some of which can be mitigated if it has the chance to pass
through suitable sublayers before release to ground or surface waters. The idea of
this project was to investigate the efficacy of different sublayers for removal of the key
pollutants: ammonium, nitrate, E. coli, suspended solids, phosphate and dissolved
organic carbon (DOC). The sublayers investigated were sandy subsoil, sandy loam
topsoil, iron ochre granules (to remove P by adsorption) and straw (to remove N by
immobilisation).
MATERIALS AND METHODS
Eight lysimeters (1.1 x 0.9 x 1 m) were set up at SAC Auchincruive (Figure 1). There
were four sublayer treatments (each in duplicate): control (40 cm of sandy subsoil
of Dreghorn series from the site area), topsoil (40 cm of sandy loam topsoil of
Dreghorn series, from the site area), iron ochre (10 cm of dried granular iron ochre
from waste lagoons at Polkemmet open cast coal mine, underlain by sandy subsoil)
and straw (20 cm of barley straw coarsely chopped, underlain by sandy subsoil).
Overlying these sublayers were 20-cm depth of medium-size woodchips (approx.
15 x 5 x 5 cm chips) and 20 cm of large woodchips (20 x 10 x 10cm). Weekly inputs
of slurry (14 mm equivalent depth) containing 1800 mg/L NH 4
-N, 33,000 mg/L
total organic C (TOC), 3.4 x 107 colony forming units (cfu) E. coli/100 mL and with
electrical conductivity of 14 mS, along with natural rainfall were applied from January
to September 2004. Weekly accumulated samples of leachate were analysed for
ammonium, nitrate, phosphate, dissolved organic (DOC), and electrical conductivity
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