Geoscience Reference
In-Depth Information
F
IG. 58
Percentage loss in crop yields due to 7 days waterlogging occurring in specific months as shown. Water-
logging in other months has no effect. (Data from B.D.Trafford 1970.)
This last effect was nicely shown by some Hungarian work on various crops sub-
jected to waterlogging for 3, 7 and 15 days in each month of the year. Grass, as one
would expect, was least affected; that is why grassland predominates over arable land
in areas of higher rainfall. But even with grass, the yield was halved if it experien-
ced a fortnight of waterlogging in May, June or July. Potato tubers drown easily, and
even one week's waterlogging between June and August could lead to the total loss
of the crop. Winter wheat was intermediate but could suffer substantial losses from
prolonged waterlogging during the winter months; which would not be unlikely on
poorly drained soils. These results are perhaps not exactly transferable to British con-
Partly because of the loss in crop vigour that occurs in badly drained soils, the
competition from weed grasses is increased, and diseases can take hold where they
could not on healthy plants. Poorer crops also extract less water from the soil in tran-
spiration, and so it does not dry out so quickly. These various effects exacerbate each
other, thereby reducing productivity and thus the income which the farmer has to in-
vest in improving soil conditions.
More than half the agricultural land in Britain needs artificial drainage to shed
excess rainfall and maximize crop yields. A survey in 1969 suggested that a quarter of
the 27.3 million acres (11 million hectares) of agricultural land in England and Wales
had already been drained, and another quarter would benefit from tile drainage. The
Ministry of Agriculture, Fisheries and Food (MAFF) offered grants of 50-60 per cent
towards the capital costs of approved drainage schemes during and after the war, with
the result that there was a sustained effort for over 40 years. Rates of drainage in-
stallation increased from about 15,000 acres a year in 1944 to 105,000 acres a year
in 1960, and then levelled out at about 250,000 acres a year between 1970 and 1980.
At this rate, it was estimated that all the land thought to need draining in 1970 would
be drained by 1990. However, drainage grants have now virtually ceased, with the
change in agricultural emphasis towards reduced rather than increased output, so this
target may never be reached.
