The major threat to the sustainability of irrigated agriculture in the rice growing regions of the southern
Australia is secondary salinisation as a result of rising watertables. Rice growing contributes about half
of the accessions to the groundwater in these regions. A range of strategies for reducing the accessions
from rice are applied, including restricting rice growing to soil assessed as suitable for rice. In the past
this was based on soil texture, but increasingly EM-31 survey is being used, and the inclusion of soil
sodicity constraints will further improve the ability to predict suitable soils. The net evaporative demand
for rice growing over the whole season is well-approximated by reference evapotranspiration (ETo),
which is used to calculate the seasonal rice paddock water use limit.
Potential methods for increasing rice water use efficiency and reducing recharge include shorter duration
varieties and a range of water and soil management strategies. Intermittent and sprinkler irrigation can
significantly reduce water use, however yields are also reduced due to cold temperature damage during
early pollen microspore. Small areas of leaky soils can greatly increase total accessions to the watertable,
and EM-31 surveys show that many “suitable” rice paddocks have leaky areas. Recharge from leaky
areas can be reduced by puddling or by impact compaction. After rice harvest, soil water content is high,
and recharge may continue, especially under the influence of winter rainfall and low evaporation.
Research is underway to quantify the effect on accessions to the watertable of growing a winter crop
immediately after rice harvest. Future work will investigate the conjunctive use of groundwater and
surface water to promote watertable control while maximising agricultural productivity by making more
water available for irrigation.
The SWAGMAN (Salt Water And Groundwater MANagement) series of computer models has been
developed to determine the impacts of management and climate on watertables, salinisation and yield,
and the tradeoffs between environmental objectives and profitability. These models include SWAGMAN
Destiny, a point scale crop model that can be run for up to 30 years of climatic data. SWAGMAN Farm
is a farm scale optimisation model which predicts the most economic cropping mixes that meet specified
net recharge and root zone salinity objectives, taking into account farmer preferences. Regional
groundwater models have been developed to evaluate the impacts of climate and management on
The development of shallow saline watertables results in the generation of saline drainage waters.
Numerous evaporation basins ranging in size from a couple of hectares to a few hundred hectares have
been created in recent years to receive saline drainage. Investigations into the salt and water balance of
evaporation basins, the development of the model BASINMAN, and economic analyses have led to
guidelines for the siting, design and management of evaporation basins. A pilot trial is also underway to
investigate the feasibility of serial biological concentration, with the production of high value crops in the
first 2 stages, followed by salt tolerant crops (stage 3), fish farming (4), evaporation basins (5) and a solar
pond to generate energy.