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Moderate deep drainage

Deep drainage is the hardest element of the water cycle to understand and manage - it is impossible to observe, difficult to measure and has a range of potentially positive and negative impacts.

From a pasture growth perspective, deep drainage should be minimised, as it is rainfall that is ‘lost’ to the pasture system. Deep drainage needs to be reduced in catchments where groundwaters are rising, bringing salt nearer to the surface and causing dryland salinity.

On the other hand, deep drainage often contributes to a catchment’s water supply through springs and base-flow into streams.

It is difficult to determine what is ‘good’ deep drainage and what is ‘bad’, on a paddock-by-paddock basis. However, the extensive spread of dryland salinity across the farming and grazing areas of southern Australia is strong evidence that our major focus should be to reduce deep drainage.

Maximise pasture water use to utilise as much rainfall as possible, leaving less for deep drainage.

Increase the number of trees and shrubs, especially in deep drainage ‘hot spots’. Use native species indigenous to the area, unless planting for commercial forestry, and focus on revegetating areas of the farm likely to have high natural recharge because of porous/sandy subsoils, or shallow soils over fractured rock, and where pasture productivity is low.

Revegetate riparian zones to increase water use, stabilise stream banks and restore habitat.

Use tactical grazing management and strategic fertiliser application to maintain perennial grass content, and to ensure ground cover of green leaf is maintained on paddocks for as much of the year as possible.

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