Despite the significant negative impact soil
compaction has on Western Australian grain growing operations, little is being done by
farmers, particularly on the south coast, to manage the issue. However that is set to change with work being
conducted by local farmers and the Department of Agriculture and Food WA in South Stirling. Soil compaction often constricts roots to
a depth of around 35 centimetres, meaning plants can’t always access the water and
nutrients needed to maximise growth. The issue is of particular concern on Western
Australia’s deeper sandy soil types. Subsoil compaction is an increasing problem
in all crop areas, especially in Western Australia with some of our sandy soils. It’s a problem because machinery size is
increasing and there’s a lot more passes over the paddock than used to be and, together
with continuous cropping, there’s a lot of pressure being applied to soils. The impact of subsoil compaction is to restrict
the root growth into the subsoil, and we need roots deep into the soil so that the plants
can pick up as much water as possible at the end of the growing season to finish the crop
off, and during the growing season mobile nutrients, particularly nitrogen, is readily
leached through the soil beyond the root zone. The impact of subsoil compaction on productivity
can be quite dramatic, but seasonally dependent. In a year with a good finish it’s not so
noticeable, but if a plant is mostly dependent on subsoil moisture at the end of the season,
then it can reduce yields significantly. Jeremy Lemon says every farm has some level
of subsoil compaction to manage. The main cause of subsoil compaction is wheeled
implements trafficking over the paddock. As a rough rule of thumb the compaction occurs
at about half the width of the width of the tyre. Even when people have dual wheels on, there’s
compaction under each of the duals, but they also work together to give you compaction
as if it was a much wider wheel and so we’re finding the depth of compaction is much deeper than it used to be with smaller implements and less tyres. While many farmers recognise they do have
subsoil compaction, they are unsure of the severity of the problem and the resulting
impact on their yields. Jeremy Lemon says it needs to be diagnosed
and managed correctly. Largely it’s tackled by deep ripping and
deep cultivation and we’re finding that given maximum compaction is down to 50 or
60 centimetres, it is quite an expensive process to loosen a paddock to depth so that the roots
can explore the full potential soil. Jeremy Lemon says farmers need to get a better
handle on how soil compaction is impacting their farming operation by firstly identifying
the extent of the problem, before working on a management solution. Investigation involves using a penetrometer
on suitable soils and certainly digging holes, maybe with a backhoe, looking at root growth,
where those roots are going, whether they’re going to depth, and if possible, do some test
strips of deep ripping across the paddock and see if there are benefits, and if you’ve
got yield mapping then you can quantify those benefits in what the yield advantage is.