STUDY the Fenland soil map and its all grade 1 land worth as much as £10,000/ha (£4,000/acre).
Take a spade to that soil and its a rather different story; the value could be less than half that sum.
For the land grading map, designed not for farming use but for planners to ensure that the most productive farmland would not disappear under concrete, is no longer the Bible it once was.
Loss of peat by oxidisation combined with a great change in farming and cropping techniques means that a good proportion of those black soils are no longer worth what they once were.
Indeed, as they demand an intimate knowledge of their management, buying demand is frequently greater for the grade 2 and 3 soils on the higher land beside them.
Jim Major of Brown & Co based at Wisbech with peat to the left, peat to the right, peat behind and peat before him is ideally placed to assess just what has happened to these extensive areas of grade 1.
"Many a soil map has been hanging on the office wall for decades; the colours have faded and more often than not there is little to differentiate the grade 1 from 2 and 3. That is perhaps indicative.
"The crucial factor then is what lies underneath. If its clay, thats not so bad; if its loam over chalk, rather worse, but you can live with it.
"If its gravel, sand – or worst all black sand – then youre in trouble because it heats up so much and is so much less likely to withstand drought."
Taking a 250ha (100 acres) block he says that if it is good peat, with irrigation you are looking at £3,000 to £4,000 an acre depending on demand. Without irrigation it will be less, towards the bottom end of that.
The same area with outcrops of clay but still with a peat mix will be around the £3,000 mark.
But with sand or gravel it will fall to around £2,500 to £2,750 an acre and without water it could go to as little as £2,000. If it has been worked hard and has an eelworm problem – which a lot of fen has – it will be even lower than that.
This too, is land that needs knowing – and managing. Demand will always determine values and the Fen country does not beckon outsiders. The amenity element is not high and houses tend to be rather ordinary.
Mr Major says he could guarantee that if you gave most arable growers the option of buying black grade 1 or "what we laughingly call high land" chalky/loam classified grade 2/3 theyd take the latter. "Easier to farm, better understood and more flexible if you are restricted on water."
All this comes as no surprise to Rodney Burton who specialises in peat soils at the Soil Survey and Land Research Centre at Cranfield University. Called in to do a soil profile on one farm, he reassessed all of the so-called grade 1 land as grade 3.
"No change was made to the map and it was later sold as grade 1 though the owner certainly knew that it was far from that.
"What is more it has sold again since – again as grade 1. It is easy for unsuspecting buyers to be duped."
He has recently carried out a survey for a project which aims to return some of this land to the wetland it once was.
He explains that it is not merely the loss of peat as a growing medium which is so serious. With it goes the all important water-holding property making the ability to irrigate absolutely vital. This at a time when demand for irrigation is soaring.
Then, in addition, around 30% of peat soils have a very acid subsoil which it is not possible to lime. Once roots reach it they are killed off.
• For existing owners and those intending to buy, the Soil Survey carries out rapid assessments using soil profiling. Details from the survey call tel. 01525 863000.
What is peatland really worth? Sally Smith investigates.