BRENDON CANT brendon at iinet.net.au
Wed Dec 5 01:07:39 CET 2007


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Dryland salinity is a major environmental issue facing agriculture and six
per cent of the WA wheatbelt has saline soil.


Where native vegetation has been replaced with annual crops and pastures,
leading to reduced evapo-transpiration and increasing runoff and recharge,
groundwater levels rise and salt held within the soil profile is mobilised.


In a time of drought and with current predictions regarding climate change,
it may seem absurd to talk about ‘water excess’.


However, water excess from run-off, as well as drainage below the root zone,
is a challenge facing some farmers in southern WA that may be solved by
planting lucerne.


Perennial pastures, such as lucerne, dry the soil and lower the input of
water from run-off into groundwater, which assists in combating salinity.


A GRDC supported collaborative study by scientists from the Department of
Agriculture and Food WA (DAFWA), CSIRO and The CRC for Future Farm
Industries showed lucerne significantly and rapidly reduced long term excess


According to Dr Perry Dolling of DAFWA, phase farming using three to four
years of lucerne, followed by one to four years of wheat, is one way of
implementing a mixed farming enterprise and generally three to four years of
lucerne will dry the soil and lower the input of water from run-off into


Farming systems can be structured to use different configurations of lucerne
and crop use to minimise water excess where this contributes to salinity, he


For each 10 per cent increase in the time lucerne is in a rotation, mean
water excess decreased 7-9 per cent at Kojonup, compared with water excess
associated with continuous wheat.


Simulation models using historical rainfall data support this experimental


Both annual rainfall and soil water deficit influence water excess.


Run-off in the eastern wheatbelt of WA is generally very low at 1-5 per cent
of annual rainfall, so drainage below the root zone is the major excess


At the end of summer, the soil has a water deficit or a buffer against
drainage and in a Mediterranean-type climate the size of the drainage buffer
established by autumn influences water excess.


The higher the soil water deficit, the greater the soil’s capacity to store
water and prevent it draining away below the root zone.


Other factors influencing drainage buffer size are rainfall, soil type,
stage of lucerne development and root depth, as well as the soil water
extraction of lucerne and wheat.


While lucerne needs care to establish and maintain, it can provide long term
environmental advantages and contribute to the economy of mixed farming




The Crop Doctor is GRDC Managing Director, Peter Reading, Tel 02 6166 4500

Further Information: Dr Perry Dolling, Tel 08 9821 3261

GRDC REF: CDOct074.doc/CSP293/Blumenthal


Brendon Cant & Associates
Public Relations & Marketing 
Suite 5
4 Gugeri St
Claremont WA 6010
Tel 08 9384 1122


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