In the latest part of our Farming on the Edge series. Abby Kellett visits Blagdon Estate to see how the farm manages to stay productive while working round an active open cast mine, stripping away soil and restoring it years later.
For every farmer, soil management is a fundamental part of what they do, but never more so then on the Blagdon Estate, Northumberland.
With 586 hectares (1,448 acres) set aside for surface coal mining, restoring land, particularly back to arable production, is a huge challenge.
But it is something farm manager Andrew Crewdson and Banks Mining landscape manager Richard Hutchinson work hard to get right on the Shotton and Brenkley sites which encroach onto Blagdon Estate.
According to Richard, the future productivity of land post-restoration can be influenced as early as when the first soils are removed.
“Firstly, top soil is stripped off and we do this in summer to minimise soil damage,” he says.
“We usually remove about 30cm which is stored in mounds around the periphery of the site. This is covered in a grass-based mix which helps look after soil while it is in storage and provides greenery for those looking onto the site.”
Sub-soil is then stored in separate mounds, which is also seeded.
Soil storage mounds are designed to preserve soil biology throughout the duration of mining operations.
“The size of individual soil mounds are limited in order to ensure soil organisms, such as worms and fungi, are not destroyed,” says Richard.
When it comes to reinstatement, firstly the overburden, including the rock and other materials which are removed from the void, are put back and consolidated to form an initial layer.
“We aim to put a 900mm layer of subsoil back across the whole site and 300mm of topsoil on top. It is important we get the falls and depths right as drains will need to be installed further into the restoration so it is crucial there is enough soil coverage.
Although millions of tonnes of coal is extracted from the site, no extra material is needed to fill the void, which exceeds 100 metres (328ft) in depth in parts of the site.
“We actually end up with a higher land form than we had previously as the underlying rock between the coal seams bulks up,” says Richard.
Both the subsoil and topsoil are stone picked to remove any stones which may damage machinery. It is then subsoiled and cultivated before a temporary grass ley is established.
The replacement of topsoil marks the start of the five-year ‘aftercare’ programme, whereby Banks Mining are responsible for restoring the land to a standard which is appropriate for its end use and was previously agreed at the planning stage.
Throughout this five year period, standard practice is to maintain land as a grass ley. Firstly, a short-term rye-grass and red clover mixture is established until the under-drainage is installed, followed by a longer term grass mixture.
Andrew says: “The rye-grass and red clover mix is prolific and contains some hybrid species which have long tap roots which penetrate down through the subsoil. This improves the soil structure and natural drainage throughout the early aftercare period prior to installation of the under-drainage.
“The red clover fixes nitrogen, which is released into soil to assist the establishment and productivity of the following crop.”
In terms of management, grass is usually made into silage, with cattle grazing land towards the end of summer.
But, prior to under-drainage being installed, Andrew has to be particularly cautious when it comes to travelling on land with heavy machinery.
“We make sure we do not go on the land when it is wet, which tends to be standard practice anyway.
“So, following initial silage cuts, if we cannot harvest the regrowth later in the season, we mulch it instead,” he says.
In years one and two of the aftercare period, the site is fenced and hedges and trees are planted. If the land is destined for arable or grassland production, underdrainage is installed. This is usually done about 18 months after the soils are replaced.
The restoration team look to balance soil pH and apply fertilisers, working towards phosphorus and potassium indexes of two.
Richard says: “If, on commencement of the aftercare period, soils are low in P and K, this can be hard to achieve as there are limitations to the amount of P and K which can be applied at any one time, partly due to potential animal health implications.”
When Andrew regains control of the land, soil nutrient levels can be variable and so he conducts regular soil analysis and applies nutrients and lime variably across the field in an attempt to balance the soil.
He says: “The huge variation in P and K lends itself to variable application because on most farms you don’t usually see that level of difference.”
However the most recent change on Blagdon Estate is the movement from a cropping rotation consisting winter wheat, spring barley, oilseed rape and spring beans to 50 per cent wheat and 50 per cent cover crops – a decision based on economics but also a need to boost soil organic matter levels, according to Andy.
“Before, the yields we were getting from other crops were just too variable and margins were too tight and we made the decision wheat offered the best return. Obviously we will need to keep our eye on this to ensure this continues to be the best policy.
Most cover crop mixes are sown in spring and then desiccated, flailed and incorporated in late summer, ahead of winter wheat establishment.
“Most of the soil at Blagdon is heavy clay loam. A lot of it is ex open cast and not easily worked so we hoped by increasing organic matter levels through the use of cover crops, we will improve the soils organic matter and structure.
Although the new rotation has only seen one cycle, Andrew is already considering further options to increase his organic matter status.
He says: “This is a livestock area so straw is in high demand but if there is an opportunity to incorporate straw and potentially increase yields it is something worth considering.
“We currently spread a lot of muck and bought-in compost, but we have not done this on the open cast sites yet, but it is something we will be looking to do in the future.”
In order to find out whether it was possible to reduce the length of the after-care period, one field on the Brenkley site was reinstated to arable production three years earlier than standard practice, after being under drained in 2013/14.
It was sown with winter wheat in year two, as opposed to remaining in grass for the full five-year aftercare period.
Defying the odds, the 17ha (42 acre) field of Reflection yielded 9.14t/ha (3.7t/acre) on average, a commendable yield, ex open cast or not.
“Nobody could believe how well the field did. More than 50 per cent of the field averaged more than 9t/ha (3.6t/acre),” says Andrew. “We didn’t treat this crop any different to our other wheat crops, other than we prioritised it for early drilling to give it the best possible start.
“Because I manage 2,500 acres when this field was too wet to spray or spread fertiliser we could start somewhere else on the estate, allowing the field to dry up, so it did get special treatment in this respect.”
However, Andrew says it was the attention to detail during restoration which allowed a wheat yield nearing 12t/ha (4.9t/acre) in some parts of the field.
“Everybody who was involved in the restoration, from the guys on the bulldozers, the engineers who put the soils down to the contractors who did the stone picking and drainage, it was the whole package which made this work.”
As a result of this success, Andrew says he would consider establishing a crop in year two again.
He says: “One of the challenges here is it is such a bitty site. At some point there will be a large area to be restored at the same time, so there is a lot of grass which will need managing.
“If we can get at least some back to arable production earlier, it would relieve a lot of pressure and reduce the need for more livestock.”
Richard adds: “Introducing arable crops earlier is also improving diversity from an ecological perspective and could potentially provide a greater return, depending on commodity prices.”
Looking to the future, Andrew believes maintaining the high standards which have been set will be his biggest challenge.
“Short-term it looks good but I just hope this carries on year on year. I am going to get an increasing amount land back from restoration and with this will come less flexibility.
“I also have to remember restored land is still in recovery, although the yields, worm numbers and large root mass suggest otherwise, so we mustn’t get complacent and think our job is done.”