Water Balance - Workshop shows there is no simple answer on salinity
GroundCover™ Issue: 50
By Cathy Nicoll
Too much water at the wrong time or a missed opportunity? That"s the dilemma faced by growers and researchers battling dryland salinity.
According to Dr Phil Price, researchers at a GRDC water balance workshop identified the potential for a win-win solution to dryland salinity for some growers.
"In situations where the problem is driven by local (shallow) groundwater systems, growers might find their best option is to change cropping practices to try to take advantage of the extra water and maximise production and profits," says Dr Price.
In this situation, losing income by replacing profitable crops with less-profitable perennials might not be the best option, even if it would otherwise mean a smaller area of salinity.
The water balance workshop brought together leading scientists from all grain-growing areas. It sought to work out "where to next" for researchers and growers in manipulating on-farm groundwater and surface water to control dryland salinity (some initial findings were reported in Ground Cover 44).
The workshop revealed that the best mix of management options is likely to vary widely from place to place. Growers and communities need tested methods and tools to consider the full range of options for particular situations.
Growers will already know about many of the intervention options. They include biological solutions (planting lucerne, alley farming, agroforestry), and engineering solutions (drains or raised beds).
Some of these are expensive, in terms of upfront cost and forgone income. Some involve a major change in land use such as cropping to agroforestry.
The issue at the workshop was that it has not been convincingly demonstrated in Australia that major changes in land use will achieve the desired results on a landscape scale.
For many growers, most intervention options will never be as profitable as annual crops. This means it is essential to identify where exactly in the landscape that intervention will be most effective, and over what time period.
"The workshop identified some major risks with some biological interventions, such as the early death of tree plantations which run out of stored soil moisture, the over-drying of soil profiles by lucerne, and lucerne-induced bypass flow," says Dr Price.
Engineering solutions, he adds, also have their problems. Some soil types are not suited to drains because the rate of lateral flow is too low; and there is the ongoing issue of managing drainage waters which may contain not only salt but other contaminants.
Despite these concerns, data presented at the workshop showed that some significant increases in water use can be achieved through improved crop agronomy. Even better, the workshop was able to provide several examples where changing land use had reversed an earlier "problem" associated with small-scale, local processes.
This was considered to be most effective at managing salinity where cause-and-effect relationships between increased recharge and increased discharge operate within a single sub-catchment or even a single property.
It is in these smaller, local groundwater systems that groundwater levels may respond to changes in land management over a few years.
"But if it has taken 50 to100 years to raise groundwater levels, it may take an equivalent or greater time of reduced recharge to reverse this effect," says Dr Price.
The story for areas with salinity driven by regional (deep) groundwater systems is, unfortunately, very different. Growers in these areas will have to work with others in the groundwater catchment to minimise the damage caused by rising water levels and salt.
"The problem for growers dealing with regional groundwater systems is that even the highest long-term water use by annual cropping systems is significantly less than that of native plant communities," says Dr Price.
Another problem is that causes and effects are often separated by large distances in these landscapes, and there are few practical methods to achieve equitable sharing of the costs and benefits of remedial action.
Dr Price says that communities in these areas will have to consider the full range of options using the best possible knowledge to try to manage their farming systems in the context of the landscape.
Bringing together specialists in soils, groundwater, water use modelling, crop agronomy and even agroforestry, was an important first step to further develop some of these methods and link paddocks to entire catchments and landscapes.
For more information:
Dr Phil Price, 02 6251 4669
GRDC program 4