Effectiveness of Current Farming Systems in the Control of Dryland Salinity

Conclusions

The large mismatch between the leakage below current farming systems and the capacity for groundwater systems to accept this leakage is the fundamental cause of our expanding dryland salinity problem.

Many of the best management practices for our current agricultural systems cannot reduce current leakage rates at a catchment scale to anything approaching leakage rates under native vegetation. Some of our groundwater systems of most concern can only accept leakage comparable to that of native vegetation.

If we are to use biological measures alone to control salinity we need to significantly modify agricultural practices. We can only achieve the necessary level of control in some local situations. In the higher rainfall parts of the Basin, a high proportion of trees needs to be incorporated into the landscape to significantly reduce leakage. In the medium rainfall zones, the variation in leakage rates between different grazing and cropping systems may have potential to slow salinisation.

However, there is little evidence that there are current farming systems that can reduce leakage to levels similar to those of native vegetation. Other farming systems that have large leakage reductions, such as opportunity cropping, need to be targeted at those groundwater systems with the greater capacity for leakage. That will control leakage and hence salinity for a wider range of conditions. With intensive focus on redesign of new farming systems it may be possible to build systems that will control leakage, and thus salinity.

Even if we were to find and adopt suitable practices immediately, we cannot return to conditions identical to the natural system. In many cases, improvements in dryland salinity would occur very slowly, if at all. Although smaller, local scale catchments may respond to best management practice within several years, the larger regional and intermediate systems may take much longer.

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