Geoscience Reference
In-Depth Information
over warp. Moling is cheap, and the tunnels can last several years before collapsing
or becoming choked.
It is difficult to measure the benefit of drainage precisely - to estimate what B.G
Davies calls 'drainage worthwhileness'. Any experiment on classical lines needs large
areas with and without drains, but comparable conditions over large areas are difficult
to achieve so one cannot be sure whether other variables influence the results.
One such experiment in Cambridgeshire measured yields of winter wheat for six
years. The average yields from plots with drains was 33.7 cwt an acre (4,230 kg/ha)
while for the undrained plots it was 8.5 cwt an acre less; in 1960 this would have been
worth £8 10s an acre. Another experiment, by the Field Drainage Experimental Unit
of MAFF which was set up in 1962, measured liveweight gain in bullocks grazing
on drained and undrained grassland in Devon. There was a noticeable difference in
weights, and therefore in financial returns. (The market value of beef at the time was
ls 6d per lb!). However, the capital cost of drains, at 100 ft spacing plus subsoil cultiv-
ation, was £75 per acre, so it was doubtful if drainage would have been a worth while
investment for such a low value enterprise.
What was more likely was that the farmer would change to a more intensive form
of land use which drainage made possible, and which gave higher yields. The Min-
istry of Agriculture have classified land use under nine categories depending on the
intensity of use, and have recorded marked shifts in land use as a result of drainage
between 1971-1980. These are summarized in
Figure 59
which shows the especially
large gains in categories 3 and 5 - arable with roots, and mixed farming - largely at
the expense of extensive pasture and rough grazing. For example, of the 4268 hectares
of rough grazing in the south eastern region which were drained during this period,
only 28 hectares remained as rough grazing; and similarly in Wales, only 149 hectares
remained in this category after draining 21,041 hectares.
The draining of moorland in Britain has likewise been encouraged through 50
per cent grants since the 1940s, and by 70 per cent grants under the European Com-
munity's Common Agricultural Policy for improving the productivity of hill sheep
in 'less favoured areas'. No drainage statistics have been collected for hill land,
however, and there seems to be little hard evidence that the land has become markedly
more productive for sheep, red grouse or other game.
Open ditches are dug at 15-35 metre spacings but water is held so well by the
peat that the effect on the water table and on vegetation is confined to a few metres
on either side of the ditches. Afforestation may be the best way of lowering the water
table through transpiration, but this changes the land use entirely, and has other ef-
fects on the soil.
