Geoscience Reference
In-Depth Information
or insecticides. A good farmer knows the subtle differences that every field can have
in its 'timeliness' for cultivation, but nowadays he may be constrained by the need
to spray against wild oats or take-all disease at very precise times notwithstanding
whether the soil conditions are good or not. The use of tramlines was introduced from
Germany relatively recently; that is, the re-use of the first set of wheel marks for sub-
sequent passes. The original purpose of this was to ensure accurate spraying, without
gaps or overlaps, but it has since been adopted for cultivation as well as it greatly re-
duces the amount of overall compaction. This is because the first pass causes 70% of
the compaction produced by several passes. The benefit to the rest of the field greatly
outweighs the loss of crops in the tramlines.
Soils containing a high proportion of clay or silt are particularly prone to com-
paction when wet. The basic fabric of the soil is something the farmer has to live with
but he can greatly reduce the risk of compaction by improving the drainage. He can
also improve the resilience of the soil by introducing a grass ley into the rotation to
increase the organic matter content - a return to 19th century husbandry.
The main function of ploughing, as Russell showed, is to control weeds, but
ploughing also loosens the soil and creates the need for one or more cultivations be-
fore drilling. In the past, this often meant a delay of 4-6 weeks, at least on heavy land,
so it was only possible to drill some of the fields on a farm before winter set in. If
the winter was wet, and the land was not well drained, considerable difficulties and
delays could be expected in the spring which would be reflected in lower yields. This
happened in 1969 after the exceptionally wet conditions of the previous summer and
autumn mentioned earlier. In terms of energy, ploughing is also very demanding and
therefore expensive; it has been calculated that ploughing a nine inch deep furrow
turns 1000 cubic yards of soil for every acre - 1900 cubic metres per hectare.
Really heavy, 'four-horse', land would always have been problematical for the
farmer; the economic returns on his labour would be lower than on more easily
worked land. This applies even in more recent times. A vivid example of the relative
cost of cultivation was seen in about 1970 in the Woolley area of west Cambridgeshire
where two crawler tractors were harnessed together to draw a plough: maximum trac-
tion with minimum compaction.
The introduction of heavy cultivators or chisel ploughs, instead of the conven-
tional mouldboard plough, was a partial answer, but it was the bipyridyl weedkillers
paraquat and diquat that opened the way to a new farming revolution in the late
1960s. These chemicals killed all green foliage but were inactivated on contact with
the soil. They therefore made it feasible to eliminate competition from most weeds
and self-sown crops after the last harvest by spraying, and then to drill directly into
the undisturbed stubble. Perennial weeds, particularly couch grass, were still a prob-
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