Why waterlogging needs to be managed
Waterlogging can lead to:
- crop and pasture production loss
- poor trafficability
- loss of nutrients
- soil structure decline.
Waterlogging plus salinity is much worse
Under saline conditions, waterlogging inhibits the ability of roots to screen out salt at the root surface. This results in large increases of salt uptake, concentration of salt in shoots, and reduced plant growth or death. More information is available on the Dryland salinity in Western Australia page. Reducing waterlogging is the first step in managing saline sites.
Management options for waterlogging
Suitable options depend on the severity, position in the landscape and land use (type of crops or pastures):
- do nothing: just avoid waterlogged areas when seeding, spraying, and harvesting. This is only recommended on small areas
- use more-tolerant crops or pastures, sow early and increase seed rate
- alter nitrogen management to suit the waterlogged situation
- use shallow surface drainage on waterlogged or inundated areas
- use surface water management upslope to prevent waterlogging occurring or reducing the period of waterlogging
- use raised beds on high susceptibility flats, with shallow surface drainage.
Choose tolerant crop species
Some species of grain crop are more tolerant than others. Most grain legumes and canola are generally more susceptible to waterlogging than cereals and faba beans. Grain legumes in decreasing order of tolerance are: faba bean, yellow lupin, grass pea, narrow-leafed lupin, chickpea, lentil , then field pea.
Oats tends to recover better from waterlogging than wheat and barley. Wheat and barley varieties have a large genetic range of waterlogging tolerance.
To avoid crop damage from waterlogging:
- seed crops early
- use long-season varieties
- plant waterlogging-susceptible paddocks first and early; crop damage is particularly severe if plants are waterlogged between germination and emergence
- resow the crop if waterlogging delays emergence and reduces cereal plant density to fewer than 50 plants per square metre, if accessible and if waterlogging has ended
- increase sowing rates in areas susceptible to waterlogging – waterlogging depresses tillering (not sure what this means in this sentence); high sowing rates will also allow crops to compete with weeds that take advantage of stressed crops.
Crops tolerate waterlogging better with good nitrogen status before waterlogging occurs. Waterlogging usually results in nitrogen being leached beyond the root zone, and crops may be nitrogen deficient after waterlogging.
- on moderately waterlogged sites (7–30 days waterlogging to the soil surface - not sure what this wording (and same wording in next point) means), apply nitrogen after waterlogging when the crop is actively growing where basal nitrogen applications were 0–50 kilograms per hectare.
- on severely waterlogged sites (greater than 30 days to the soil surface), the benefits of nitrogen application after waterlogging are questionable; seek agronomic advice.
Applying nitrogen at the end of a waterlogging period avoids loss by leaching or denitrification. However, nitrogen cannot usually be applied from vehicles when soils are wet, so consider aerial applications.
Weed density affects a crop's ability to recover from waterlogging. Weeds compete for water and the small amount of remaining nitrogen, hence the waterlogged parts of a paddock are often weedy. If herbicide resistance is not a problem, spray the weedy areas with a post-emergent herbicide when the paddock is dry enough to allow access, provided the crop is at an appropriate growth stage. Aerial spraying is an alternative when ground-based sprays cannot be used.
Control root diseases
Diseases, particularly take-all, of wheat and barley are often more severe in waterlogged crops because the pathogens tolerate waterlogging and low oxygen levels better than the crops. Eliminating grasses from the preceding crops or pastures will reduce the severity of take-all in well-drained and waterlogged areas. Leaf diseases are likely to be more severe in waterlogged crops because the crop is already stressed. Spraying may be an option after the site has dried, but only in crops with a high yield potential.
Use shallow surface drainage on waterlogged areas
Shallow relief drains remove ponded and run-off water from areas affected by inundation, waterlogging or flooding. For more information, see the shallow relief drains page. All drainage should be part of a whole farm water management system.
Use surface water management upslope of waterlogging
Prevention is better than cure: prevent water from flowing downslope where it can lead to erosion, waterlogging and inundation. Options are on the Surface water management page.
Use raised beds on waterlogged flats
See the Design, layout and installation of raised beds page.
For more information, refer to the contact below.