Agricultural drainage : a retrospective of forty years experience / J. Bailey Denton.
- John Bailey Denton
- Date:
- 1883
Licence: Public Domain Mark
Credit: Agricultural drainage : a retrospective of forty years experience / J. Bailey Denton. Source: Wellcome Collection.
20/112 page 8
![Theory of under-drain- age. Depth of drains. the effects of drainage on clay soils to understand that water and air will penetrate their bulk. Their retentive powers, and their expanding and contracting qualities, always at work as water is absorbed and withdrawn, are pecuUarities which render them altogether dissimilar from free soils. The water that is instantly absorbed and percolates a free soil finds a check in clays which may not be broken up by deep cultivation; and were it not the fact that there are few clays that are not threaded with natural sand and gravel veins, more or less minute, and that there are none which do not crack as they contract, the believers in impermeability would gain ground. No water can be taken out of clay soils by drainage or by evaporation without contraction, and there can be no contraction laterally without cracks. The space the water has occupied in the soil is then claimed by the atmosphere, and the under-drains convert those cracks into constant channels fixed and secured by the minute particles of soil formed by disintegration which descend with the rain, and prevent the re-adhesion of their sides. The greedy capacity which enables clay soils to absorb water weighing from 40 to 70 per cent, of their own weight is thus counterbalanced by a natural law which imperceptibly obliges them to give it up again to drainage and the atmosphere. Each year after drainage the disintegration becomes more perfect, and the ramification of the cracks and fissures more and more minute, and thus the soil becomes more susceptible to the influences of gravitation downwards to the drains, and capillary attraction upwards to the surface. The best evidence of this gradual amelioration of clay subsoils is to be gained by the microscope, by which it will be seen that both their texture and colour undergo decided change in the course of a few years from the effects of air and water penetrating them.] The heads under which I shall divide the subject will be three in number, and may thus be taken—Depth of drains—Distance between drains—Arrangement and direction of drains. I. Depth of drains. The evidence I have collected is so condemnatory of shallow drainage, and with only one exception so much in favour of the deep system, that I consider the superiority of the latter incontestably proved. Of course I am now speaking simply of depth, irrespective of other considerations. Cases without number may be quoted in which the results of an indiscreet desire to economise have completely disproved the theory](https://iiif.wellcomecollection.org/image/b21782568_0020.jp2/full/800%2C/0/default.jpg)
