[ASC-media] DEAD PAN NOT A GOOD LOOK: Crop Doctor

BRENDON CANT brendon at iinet.net.au
Wed Apr 16 03:56:39 CEST 2008

DEAD PAN NOT A GOOD LOOK 16/4/08<?xml:namespace prefix = o ns =
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WA soils challenge growers in many respects, including salinity, high
alkalinity or acidity, boron toxicity, aluminium toxicity, waterlogging and
micronutrient deficiency.


Further, an estimated 13 million hectares, or approximately 70 per cent, of
WA’s agricultural soils have moderate to high susceptibility to subsurface
compaction, which is a soil structural problem.


A fact sheet written by GRDC supported researcher, Dr Stephen Davies of
DAFWA and available from HYPERLINK
outlines how to identify and assess soil compaction.


A recent study by Dr Imma Farre and fellow DAFWA researchers, as part of the
GRDC funded WA Soil Constraints Project, indicates that ameliorating
anything but severe or moderate subsoil constraints on heavy textured soil
is probably not worth the effort, unless the constraints are in high
rainfall zones.


Compaction decreases pore space around the root zone of plants, which can
reduce soil water holding capacity in heavier textured soils. Also, plant
roots can’t grow into or through compacted soil to access water.


While the main cause of subsurface compaction is machinery traffic, others
are tillage, stock trampling and pressure of overlying soil.


The resulting layer of soil with high strength beneath the surface is known
as a hardpan. Traffic hardpans, common on sand to sandy loam soils, occur
10cm to 40cm beneath the surface and generally allow water and nutrients
through, but slow and restrict root growth.


Ploughpan, commonly occurring on finer textured or clay soils, results from
tillage of wet soil that’s been tilled for many years at the same depth and
inhibits the passage of roots, water and nutrients through the profile.


How much crops are affected by compaction is determined by climate, extent
and depth of compaction and root growth patterns.


Where moisture and nutrients in the layer above the pan are adequate there
may be no yield penalty, but in dry years crops may not have access to vital
subsoil moisture.


Severe subsoil compaction, in heavier textured subsoils, can create a
barrier to water and waterlogging and increased runoff can occur above the
compacted layer. Waterlogged plants have restricted access to nutrients.


Dr Davies says there is limited opportunity to physically improve compacted
layers, except through deep ripping to 30cm or 40cm to break the hard pan.


In high and medium rainfall areas this has been successful, with average
yield increases of 22 to 37 per cent for wheat on the deep sand and sandy
earth soils common to WA’s wheatbelt.


However, Dr Davies noted negative responses with a dry finish and when
bigger, deep ripped crops have used the available soil water faster, leaving
little water for grain filling.




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

Further Information: Dr Stephen Davies, Tel 08 9956 8515

                              Dr Imma Farre, Tel 08 9441 8111

GRDC REF: CDFeb083.doc/GRDC CODE SIP08/Blumenthal


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


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