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Ministry of Agriculture, Food and Rural Affairs

DRAINAGE

Drainage patterns in the field have a big impact on crop growth and pest susceptibility. Poorly drained areas of the field are often more prone to diseases such as Phytophthora, damping-off and root rots.

Water drains through the soil through large pores, cracks and earthworm channels. Drainage is influenced by several factors including: topography, soil texture, soil structure, compaction, tillage and even buried layers of crop residues. The texture of the sub-soil layers can play a large role in soil drainage. For example, a coarse sandy-loam soil with a clay sub-soil may experience slow drainage and waterlogged conditions, despite its surface texture.

Identification
Crops may appear yellow or dead in waterlogged areas. Crop growth may be stunted and plants may be more susceptible to disease. Plants grown in wet soils often have unusually shallow root systems.

Use a soil probe or auger to look at the full soil profile and feel the soil at various depths. Look for changes in soil texture and moisture with depth. Soil colour and the colour patterns are good indicators of natural drainage characteristics. Well-aerated or well-drained soils are usually red, yellow or brown in colour. Grey or blue soils indicate a that it has been saturated for extended periods of time and is usually poorly drained. Mottled areas (orange or red streaks on a dull background) indicate soils that are saturated or nearly saturated for shorter periods of time (usually seasonal variations) so these are imperfectly drained.

Management Notes

  • Consider the cause of the poor drainage, some factors like soil texture can not be changed.
  • Tile drains, grassed waterways and other types of surface drains, can help improve internal drainage.
  • Drainage can also be improved through good crop rotation. Rotate between a variety of crops with different types of root systems.
  • Additions of organic amendments like manure and compost can help to build better soil structure, improving the network of macropores.
  • Timely and reduced tillage can also aid in the building of soil structure.

Poorly drained compacted soil in vineyard Poor drainage in a vineyardClick to enlarge.