Symptoms of poor drainage

Symptoms of poor drainage include:

  • grey or mottled soil colours;
  • restricted rooting;
  • reduced working days for cultivation;
  • weed problems;
  • pest and disease problems;

Timeliness is the cultivation of the soil when it is at the right consistency.

Drainage is the removal of gravitational (excess) water from the root zone.

  • excess fertilizer requirements;
  • topsoils water-logged for long periods in warm conditions have a smell of bad eggs (see sulphur cycle p325).

Soil pits dug in appropriate places reveal the extent of the drainage problem and help pinpoint the cause, which is the basis of finding the solution. The level of water that develops in the pit indicates the current water table. Further indications of poor drainage are the presence of high organic matter levels (see organic soils) and small black nodules of manganese dioxide.

Soil colours show the history of water-logging in the soil. Whereas free drainage is indicated by uniform red, brown or yellow soil throughout the subsoil, the iron oxide which gives soil these colours in the presence of oxygen is reduced to grey or blue forms in anaerobic conditions, i.e. when no oxygen is present. Zones of soil that are saturated for prolonged periods have a dull grey appearance, referred to as gleying (see Figure 17.7). Reliance on colour alone as an indication of drainage conditions is not recommended, because it persists for a long time after efficient drainage is established (see also soil types p301-3).

Structural damage, whether caused by water (see stability), machinery (see cultivation), or by accumulations of iron (see natural pans), is an obstruction to water flow in the soil profile. Pans or platy structures near the surface can be broken with cultivating equipment on arable land or spiking on grassland; but subsoiling is used to burst those deeper in the soil. If water cannot soak away from well-structured rooting zones, artificial drainage is required.

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  • niko
    Can horticulture help with poor draining soil?
    3 months ago

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