Tolerance to salinity of pasture plants suited to waterlogged areas
Highly tolerant:
saltwater couch
Moderately tolerant Grasses:
, phalaris, fescue, kikuyu, puccinellia, tall wheat grass couch, wimmera ryegrass
Legumes:
strawberry clover balansa clover, Lotus spp.
For non-saline areas, the tolerance of pastures to waterlogging is shown in Table 1.
Sowing:
Sowing pastures early in areas that are susceptible to waterlogging and salinity is very important. Late sowing should be avoided even if the species have some tolerance to waterlogging and salinity.
Grazing management and weed control:
Grazing pastures until they are short will increase the likelihood of the pasture being submerged during periods of inundation. Even short periods of inundation can kill some pasture species. Manage grazing to make sure that pastures are tall and leafy.
Waterlogged soils also have little strength and sheep and cattle can easily destroy the soil structure by pugging them. This further restricts water infiltration and so inundation becomes more serious.
Farms with a large percentage of soils prone to pugging need special grazing management. Stock can also uproot plants from waterlogged soils. The ability of pastures to recover after waterlogging is greatly affected by the number of weeds, such as dock and rush (more weeds make recovery more difficult).
The pastures and weeds compete for the small amounts of nitrogen and shallow water. Weed seed banks can be reduced by selective spraying before seed set and by managing grazing pressures to encourage the seeds of desirable species to set.
Weeds may also have to be killed in autumn, when pasture species that can tolerate waterlogging should be sown.
Pastures that are still green in late spring and early summer can increase problems such as stomach worms and footrot in sheep. Rotational grazing with cattle can help overcome these problems.
Cattle also graze less closely than sheep so the tops of the pastures are less likely to become inundated. However, cattle pug waterlogged soils more severely than sheep.
Desirable pasture species that grow well late in the season are an advantage if the area is sufficient to provide late feed for stock. However, on many farms in high rainfall areas, some of the wet parts should be drained to increase early pasture production, which is usually more useful.
Fertiliser requirements:
Pastures will be less stressed if they have a high nitrogen status before they become waterlogged. A high nitrogen status will also help the pasture recover from waterlogging more quickly.
Strategic applications of nitrogen in late-break seasons can stimulate grass response and provide early feed; they also increase the likelihood that the pastures will enter a period of waterlogging with sufficient dry matter and nitrogen to continue growing.
Late applications of nitrogen can be an advantage where nitrogen has been lost by denitrification and leaching. However, nitrogen is often difficult to apply when the soils are waterlogged. Sulphur is also leached from waterlogged pastures that have shallow roots.
Adding superphosphate can replace sulphur but it is an expensive and environmentally-unfriendly source if the levels of phosphate are already adequate. Gypsum and sulphate of ammonia can be added in early spring to provide sulphur for the period of maximum growth; slow release forms of sulphur can be applied before winter.
Waterlogging restricts root development and this severely reduces potassium uptake. Potassium may be applied to sandy and sandy-surfaced duplex soils to increase growth and the number of seeds set by legumes.
Disease control:
Root and leaf diseases are often more severe in waterlogged areas because the pasture is already stressed and humid conditions favour the growth of pathogens. Drain away as much excess water as possible, reduce weed competition and correct any nutrient deficiencies.
Farm planning:
Drains can greatly reduce the variability in pasture growth in a paddock. However, it may be necessary to separate those parts of the paddocks that are most susceptible to waterlogging and inundation. Fertilising or spraying areas that cannot respond to treatment is wasteful.
Separating wet areas also means they can be spelled in winter, when close grazing and pugging can be a problem. These areas can be grazed heavily in late spring and summer when other pastures have hayed off or have been reserved for hay.
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