Where There’s Muck There’s Grass

Viable end use from cost-effective soil amelioration

By Robin Truslove, senior forestry consultant with Lockhart Garratt Ltd (LGL)

Bunny Landfill site sits on the northern side of a ridge running west-east across south Nottinghamshire. From the 1940s to the late 1970s the hillside was worked for brick-making clay. Gypsum underlies the hills and this secondary product was historically stockpiled for transfer to the neighbouring commercial mine. Shanks acquired the site in the late 1990s and continued operations as a materials recycling facility (MRF) using residue material to complete the voids in May 2005.

Landscape fit of the final design was the priority, as opposed to the visual screening required during operational phases. A matrix of broadleaf woodland and grassland (for sheep and horse grazing) with linking native hedgerows was agreed with Nottinghamshire County Council to reflect that present across the local landscape.

Seven hectares of agricultural grassland, using a high proportion of rye grass for good production, were suitable over the membrane-sealed (more active) western area of the site. Four hectares of oak-ash-field maple woodland were possible in the absence of the membrane (no issues with membrane puncture or restricted rooting) on the northern boundary comprising the clay wall of the cell and on the southern inert fill area.

Diligent preparation of the ground following soil placement has been key to the success of the above features. First, prior to topsoil placement, laboratory analysis was commissioned to determine the available nutrient, organic matter and contaminant levels in the recycled soil being produced on site. This revealed a clayey silt loam, which was friable if slightly alkaline, and recommended the addition of organic matter to improve drainage and structure.

The project was accelerated when Lockhart Garratt Ltd’s chairman, John Lockhart, introduced Envar to the site. As a contracting body of the former government agricultural advisory service ADAS, they had links with suppliers (water boards, paper factories etc) of a variety of organic matter as a by-product of industry. It was agreed that sewage sludge cake would be an ideal medium to ameliorate the available soils and provide early nutrient, but the real advantage was that Envar could supply, spread and incorporate this on a cost-neutral basis given the agreements they share with the material providers. Envar also secured Environment Agency permission.

Following the placement of a plastic membrane, up to 1.2m of subsoil and 300mm of topsoil, the land was ripped using a winged-tine subsoiler to 500mm depth to relieve compaction and, in particular, encourage root development in the woodland planting. A network of V-ditches (1,700m length) was also cut on the boundaries of the cells for long-term land drainage. Seven hundred tonnes (dry solids weight) of sludge cake were applied in October 2006 over 7ha of land using rear-discharge muck-spreaders within a two-week period to minimize nuisance smells. This was incorporated immediately behind the spreaders by plough and power-harrow prior to seeding by quad-broadcaster over the subsequent two days. Given the late-season timing of operations, some rutting was inevitable on wet areas despite the use of low-ground-pressure tyres, but this has been easily rectified by heavy rolling in 2007–08.

The results have been very encouraging. In 2007 the sward was bailed and removed to open up the placed soils for settlement and drying. This was contracted at –£150 per hectare given the early weed burden of hemlock. In 2008, however, following diligent selective herbicide application, a return of +£75 per hectare per cut (two per annum should be possible) is now being achieved for use as animal fodder.

The woodland planting has thrived with ash at 1.8m height in their third growing season and 98% stocking achieved. This will develop into a viable habitat to extend the ancient semi-natural ash woodland crowning the ridge. Some 0.25ha of wildflower meadow were sown on an area of nutrient-poor stoney clay soil, which was excluded from treatment to encourage a more biodiverse sward.

Other issues, including vermin control by ferreting, will be tackled next, to ensure the trees have continuity of browsing protection once their individual tree shelters are removed in years 5 to 10.

The local planning authority and the Environment Agency have been involved from the outset of restoration, and feedback has been excellent, with the site being placed into aftercare in December 2007.

In summary, it was early innovative thinking that allowed the investment in site preparation at Bunny, and partnership with the right providers is delivering a viable end use for a visually prominent site in this rural location.

For further information, contact the author on tel: (01536) 408840; or email: [email protected]