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Resource Management Technical Report no 196
Louise Hopgood
December 2003
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- Technical report 196 with the exception of Section 3. Farm planning [481kb pdf file]
- Section 3. Farm planning [905 kb pdf file]
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Summary
Esperance Downs Research Station (EDRS) was established in 1949 as an experimental farm. Knowledge from trials on the station has been instrumental in development of agriculture throughout the Esperance region. However, land degradation and in particular secondary salinity became widespread by the 1980s. With potential for similar problems to develop in the region, the EDRS rehabilitation program began in 1990/91. This report details the objectives of this project along with implementation procedures and an assessment of its achievements.
The stated aim of the rehabilitation was 'To research and demonstrate economic methods of obtaining production from land affected by salinity, waterlogging and wind erosion' (Anonymous, 1990). To achieve this objective a system was designed to reduce groundwater recharge through more efficient drainage systems, increased plant water use and improved water-holding capacity of the soil. Accordingly, the project was based on a farm plan, which arranged the station into defined land management units (LMU) in terms of broad soil characteristics and associated suitable land uses.
A system of shallow surface drains had already been constructed prior to addressing the increasingly degraded land on the station. While the siting of the drains was correct the drains had high and low points causing puddling, with other parts operating inadequately through insufficient depth or even degraded sections.
Appropriate amendments were therefore carried out, as were additional installations to improve the entire system. The completion of these works during the early stages of the rehabilitation enabled appropriate siting of perennials and realignment of fencing consistent with future land use.
Development of dryland salinity in Western Australia has been widely attributed to the removal of native perennial vegetation and replacement by shallow-rooted annual crop and pasture species for agriculture. Therefore, revegetation was an important component of the rehabilitation program on EDRS. The bulk of trees and shrubs were planted on degraded land with windbreaks and alley planting on a smaller area but widely distributed over the station.
Perennial pastures were also included as an integral part of the rehabilitation program for the station. The sowing program began in 1991 using temperate perennial grass species with good salt and waterlogging tolerance. There were also areas planted to lucerne. Although plant density declined in all perennial paddocks after sowing, the majority of the perennial paddocks were successfully established. With respect to livestock carrying capacity the perennials did not affect winter grazed stocking rates. However, it was noticed that compared to annual pastures the perennials, particularly tall wheat grass, provided a buffer that delayed waterlogging.
The cropping program at EDRS aims to fit in with the rehabilitation program by maximising crop water use along with using best practice rotations. The rotations employed depend on land class and drainage as well as position within the overall farm plan. As the soils are only medium depth the most common cause of poor crop performance is waterlogging. However, flexibility is the key to maintaining cropping rotations as weeds, diseases, soil conditions, economics and techniques change.
Investigation of hydrology characteristics across EDRS was done to identify causes of land degradation and assess performance of the rehabilitation strategy. There was a continuous discharge of water through the deeper basement layer to the drainage lines. However the removal of native perennial vegetation allowed an excess of water to saturate the regolith to the surface. Ground-based electromagnetic conductivity (EM 31 and EM 38) surveys showed that mobile salts can be flushed from the soil profiles. However, this may only be occurring when watertables have been lowered.
The program to monitor effectiveness of rehabilitation examined attributes such as depth to watertable, surface and subsoil salinity and groundwater quality. In addition, an economic assessment estimated the impact of rehabilitation on the past and future financial performances of EDRS. The benefits were based on extrapolating future contraction in surface salinity in pasture areas. During the 1990s salinity as measured by EM 38 was ameliorated on 60 ha of pasture.
In areas under annual crops or pastures bore hydrographs showed rising trends. The rising trend of groundwater levels was generally lower under the perennials than annual pastures and crops. Perennial vegetation including shrubs and pastures that allowed for buffering of seasonal high rainfall events was vital to decrease salinity trends. Surface drainage is also likely to have had a positive effect. However, the groundwater level is still rising at a relatively high rate in some areas where perennial pastures were sown into shallow soils. Modelling the solute and water flows would help to give a complete picture of the processes involved and the linkages with farm practices.
The rehabilitation project required substantial expenditure and foregone profits during its eight years of implementation. However, these costs are expected to be recovered through the prevention of secondary salinity. This involves both livestock and cropping being essential components of the farming system. Within twenty years from the program's completion the cumulative discounted profit (net present value) is expected to be greater than had the program not been carried out. There is likely to be scope for reducing this break-even period if some areas where salinity is ameliorated could include annual cropping or be managed using enhanced stocking rates.
In addition, external developments including the creation of market mechanisms which value environmental characteristics could provide an incentive for development of profitable farming systems which are sustainable over the long-term. These market structures would need to be fair and reflect the link between farm production and environmental outcomes. In particular technologies are needed to utilise saline conditions and prevent hydrological consequences such as watertables rising and excessive discharge of saline groundwater and surface drainage into the environment.