The revoluTion in agriCulTure^111John Bailey Denton, for example, thought that ‘floods are more quickly
precipitated into the valleys, in proportion to the extent of under-drainage
in the various river basins’, and urged that if yet more agricultural land was
drained, rivers would need to be extensively engineered.^100
High farming brought a host of other changes. Seed drills came into more
widespread use, so too did mechanized hay mowers. The former allowed for a
further intensification of weeding, often now carried out with a horse-drawn
hoe; both ensured greater disturbance of ground-nesting birds, probably
accounting for the marked decline in the numbers of corncrake recorded in
nineteenth-century avifaunas in the period after c.1850.^101 Threshing machines,
from the 1860s fitted with both winnowing mechanisms and rotary screens,
removed weed seeds more effectively from the threshed crop, including that
part of it destined for use as seed the following year, something which may
have led to declines in cereal weeds like common corncockle (Agrostemma
githago), thorow wax (Burpleurum rotundifolium) and cornflower (Centaurea
cyanus).^102 Above all, the use of imported or manufactured fertilisers, and
of cattle cake, raised the quantities of nitrogen in the farm environment
to unprecedented levels. Already there are signs that watercourses were
suffering from eutrophication – that is, the build-up of nutrients (nitrogen
and phosphorous) which promotes the excessive growth of plants, favouring
the development of simple algae and plankton over more complex species. As
this proceeds the water becomes cloudy, reducing the amount of light reaching
the bottom; as the algae die, moreover, their decomposition by bacteria
figure 22 Ridge and furrow in Northamptonshire. The progressive grassing-down
of the Midland ‘shires’ in the course of the post-medieval period served to fossilize
under pasture the former plough-ridges of the open fields. The expansion of arable
farming in the Midlands since the Second World War, combined with widespread re-
seeding of established pastures, has rendered views like this increasingly rare.