The gradual loss of farm and grazing land to rising salt, is a massive problem worldwide. Native ecosystems have evolved to be salt resistant through the use of woodland species. For example, trees are deep rooted and have a higher demand for water. This kept the system in balance, the salt stayed put. But due to the adoption of European farming practices, the native vegetation was replaced with crops and pastures. These new crops having shorter roots and needing less water, the inevitable happens. With every rain fall, unused water "leaks" down to the water table, this in turn raises the water table, bringing the salt up with it. (Leakage rate under native vegetation is 1-10 mm/year why under annual crops and pastures 10-150mm/year). In an irrigated farm land system this process is increased as most crops, only use about 30% of the water and fertilizer applied the rest ends up in the water table. In the past deep rooted trees have keep the system in balance. By removing trees from the environment, we have destroyed this balance which has been in place for tens of thousands of years.
In the development of any salinity control program you first need to understand the key features of the catchment area you are planning on regenerating. This would include:
- Weather including rain distribution and average temperatures.
- Soil and aquifer properties
- Catchment size
- Landscape gradient
- Salt storage capacity of the catchment
- Aquifer discharge capacity - maximum amount of water it can discharge when full
- Variations of discharge rates across the catchment
- Salinity of the ground water
- Scale of the ground water and were it is situated within the catchment.
Once the above information is compiled and in collaboration with local farmers a model can be designed which fits both the needs of the farmers and the needs of the catchment. Farming models can have a diverse agricultural range from annuals and pastures for cattle to orchards including nut trees and wood lots. While any remediation system will need to produce a long term removal of salts from the ground. Why in the shorter turn be able to address the need to develop salt tolerant crop species so farming can recommence.
Example of some components in a restoration of a degraded catchment.
- Development of salt tolerant crop species (eg; strawberry’s) which can be planted in the short term and will be able to tolerate the saline conditions, long term we would like to see non salt tolerance crops being reintroduce back into the catchment areas.
- Strategic planting of nut trees. Examples depending on location Macadamia, Almonds or chestnuts just to name a few. In the medium term these trees could bring good returns to farmers, while greatly helping in the long term remediation of the land.
- Strategic planting of high value timber lots, these could be rotated with pastures. As trees not only take up excess salt and lower the water table. They also repair soil structure and improve biological activity within the soil. Which has been slowly destroyed through current farming practises or from constant over crazing by cattle or sheep. Even the most prolific grass species, when grazed continually, become visibly smaller and smaller, their root zones also reduce in depth and becomes unable to reach minerals and moisture deeper down. Compaction results through absence of roots and microbial activity. The compressed soil acts like blotting paper and through capillary action draws salt to the surface. In the past these effects were not noticeable as the soil biology and structure were still intact preventing the capillary action from taking place.