A 15-year trial has proved the value of lucerne in reducing recharge and lowering groundwater levels under a hillside environment from the top to lower slopes.

The research updates previous studies which indicated the effectiveness of lucerne as a salinity control measure was dependant on landform and groundwater flow systems.

The latest work will be presented at the Department of Agriculture and Food’s Agribusiness Crop Updates next week, supported by the Grains Research and Development Corporation.

Department researcher Ruhi Ferdowsian and Jerramungup landholder Geoff Bee will discuss the role of groundwater depth on the hydrological benefits of lucerne and the subsequent recharge values.

Mr Ferdowsian said the study was particularly important with secondary dryland salinity and rising groundwater levels now affecting an increasing area of cleared land in Western Australia.

“To effectively reduce land and water salinity, a deep-rooted perennial is needed to mimic the extent and distribution of the leaf area that existed prior to clearing,” Mr Ferdowsian said.

“This research explores the recharge processes operating during 15 years of crop-lucerne-crop-lucerne periods in a phase farming system in the Jerramungup district on Western Australia’s south coast. 

“The data shows lucerne lowered groundwater levels under a whole hillside and under unfavourable conditions.”

Mr Ferdowsian said the time lag between rainfall and its impact on groundwater increased as lucerne became effective and groundwater levels dropped.

In turn, he said the increased time lag resulted in a longer period for the lucerne roots and soil profile to absorb excess rainfall and reduce recharge.

The study site had very saline groundwater (25,000 mg/L) that was close to soil surface (0.5m and 1.6m below soil surface), high sodium chloride chemistry and high groundwater levels.

“The data found that as groundwater levels dropped, lucerne became more effective in reducing or preventing recharge.  It demonstrated that the beneficial impact of lucerne extended beyond its life span and into the cropping phase that followed.”

Mr Ferdowsian said lucerne reduced and lowered groundwater levels from the top of the hill to lower slopes.

“The hydrological impacts of lucerne was realised during the first four to five years, and the lucerne intercepted more of the rainfall as the saline watertable dropped,” he said. 

“The lucerne roots also extended into the depths previously occupied by saline groundwater.”