TALKING POINT
TALKING POINT
When is an acre not
an acre?When its
viewed from a
"spy-in-the-sky"
satellite, says
Charlie Flindt
What size is your farm? Lets be more specific: Choose a field, and ask yourself how big it is. Take, for instance, the first field that visitors to Flindt Towers see through the July downpours as they draw back the magnificent velvet curtains in the guest wing. Its not the prettiest sight at the moment, yellow set-aside with green patches indicating that, once again, the glyphosate hasnt done a 100% job.
And the brown mess shows weve just lobbed this years muck on it. You wont see it in next years Beautiful Hampshire Calendar. Its called Roe Hill, sometimes spelt Row Hill and Rough Hill. Those nice people at Rural Payments Agency know it by the intimate and romantic name of Field Data Printout One, Line Two. It is long and narrow, on the south side of a little valley, and like most of the fields here, runs the full range of soils from gravely loam, through chalk, up to the clay cap on the ridge at the top.
So just how big is this patch of finest Hampshire earth? The 15 farmers in the country who think only in hectares will have to excuse this bit for being in acres. According to the 1909 map, its 27.069 acres. The 1971 maps gave it as 26.99 acres, and when the National Trust swiped a bit off one end for tree planting, the figure on the first IACS form was 25.60 acres.
Then we put a strip of maize in, and this years IACS area is 25.03 acres. But for general planning such as seed ordering and sprayer filling, 24 acres usually works out about right. For seed calibration, The old Bamlett and the newer Amazone drills both give consistently high acreage figures at around 27 acres, so that figure is used for calibration.
Im happy using those figures, the RPA seemed happy with the figures; everyones happy. Can we abandon the cartography and get on with the farming? Not a chance. Over the horizon – quite literally – comes the latest little wheeze to enforce a lot more awkwardness. New ministry maps are coming, using "spy-in-the-sky" technology: A whole new set of areas to argue about, and the RPA reckons 10% of fields will need correcting. Its lucky weve hours of spare time to help out the government with its latest Doomsday Book, and fortunate, too, that we are so adept at paperwork; it is what makes us farmers.
There seems to be a little mathematical problem with "spy-in-the-sky" technology. Lets switch to metres: Roe Hill runs up the side of a valley, and it is quite steep for these parts – steep enough to make it hard work avoiding overlaps when drilling. According to my map reading, it drops 10m in 100m, about 6 degrees. Some basic trigonometry will tell you that a 100m line on that slope will look like a line 99.45m long when viewed from above. (Remember cosines?) So a 100m x 100m square might read one hectare on the ground, but our friendly "spy-in-the-sky" will argue that it is 0.9945ha. Not a huge variation, admittedly, but parts of the countryside are far steeper than Roe Hill. A 10ha field with a twenty-degree slope will only read 9.397ha when viewed from above, enough discrepancy to start causing problems.
Dont worry, new software no doubt will take this sort of thing into account, and problems will be minimal. Lets hope it doesnt come from the same department responsible for producing error-free IACS forms, thats all.