Fig. 44 b. Untouched plot, many weeds
We have already seen (p. 69) that ordinary cultivated plants will not live in a water-logged soil. Wherever there is an excess of water it must be removed before satisfactory results can be obtained. Fig. 46 shows a field of wheat in May where the crop is all but killed and only certain weeds survive on a patch of undrained land that lay wet all the winter. Draining land is difficult and somewhat expensive; trenches are first cut to a proper depth, and drain pipes are laid on the bottom, taking care that there is a gentle slope all the way to the ditch. The rain soaks into the soil and gets into the pipes, for they are not joined together like gas or water pipes, but left with little spaces in between; it then runs out into the ditch. Usually only clay soils need drainage, but occasionally sandy soils do also (see pp. 30, 106). A great deal of drainage was carried out in England between 1840 and 1860, and it led to a marked improvement in agriculture and in country life generally. There is, however, a great deal that wants doing now.
Fig. 45. A plot of wheat left untouched since 1882 at Rothamsted has now become a dense thicket
The addition of chalk or lime to soil was found in Chap. III. to improve it very much by making it less sticky and less impervious to air and water. Chalk or lime does more than this. It puts out of action certain injurious substances or acids that may be formed, and thus makes the conditions more favourable for plants and for the useful micro-organisms; farmers and gardeners express this by saying that it "sweetens the soil." A United States proverb runs: "A lime country is a rich country." Very many soils in England are improved by adding lime or chalk. There are considerable areas in the south-eastern and eastern counties where the soil is very chalky; here you find a wonderfully rich assortment of flowers and shrubs. Where there is too much chalk the soil is not fertile, because it lets water through too easily, as was shown on p. 26: but for this very reason it is admirable for residential purposes.
There are some exceptions to the rule that plants need lime. Some plants will not tolerate it at all; such are rhododendrons, azaleas, foxgloves, spurrey, and broom; wherever you see these growing you may be sure that lime is absent.
Lime really differs from chalk, but changes into it so quickly in the soil that the action of both is almost, though not quite, the same.
