The signs are everywhere on the roads and across the land.
This high rainfall zone north of Albany, is part of 3-million
hectares across Western Australia s southwest agricultural region, prone to waterlogging.
And this year's rainfall is well above average.
On the eastern side of the membership zone, some members have had up to 800 mills of rain
since August last year and some of that land is actually 25% under water and then obviously on
the western side there's waterlogging and yellow patches as we can see in the paddock behind.
The yield effects of un-managed waterlogging can be significant including soil structure decline.
It can create issues around nutrient deficiencies or toxicities within the plants as soil
conditions become anaerobic without free oxygen within the soil
and that ultimately ends up with yield penalties either reduced yield, or complete yield loss.
Contour banks are routinely used around this region to remove surface water.
But GRDC s sub-surface drainage trials, west of Cranbrook,
aim to offer growers an additional tool to help manage the effects of waterlogging.
What we're doing is we're implementing sub-surface drainage which is a process of burying a pipe at
approximately sort of that 500 mil down and more
and we bury that pipe with like a chainsaw type machine and it digs a trench in there
drops the pipe and then we put a limestone rubble over the top and then cover it up
with a bit of dirt. And what we're trying to do is we're trying to look at the economics
behind implementing sub-surface drainage. We want to be able to determine what that
return-on-investment is and is it actually effective.
A big advantage of sub-surface drains is that machinery is able to traffic over them,
freeing up spraying operations and improving productivity.
It has definitely relieved the pressure in the areas of the paddock that we've put it in.
It's traditionally been the wettest part of that paddock
and we've had trouble with trafficability in the past where so far this year
it's definitely a long way in front of what we considered it used to be.
So this is where the pipe's laid, it comes from the creek up all the way
up and then it's got a numbers of spurs off going to catch the
water as it comes down on different profiles and from different layers of the land and slopes.
Surveys show growers believe it might take up to 3 years for an investment
return on sub-surface drainage, which can be expensive to install depending on soil types
and how far apart pipes are laid. But the Preston family installed
just over a kilometre of pipe in February, with immediate effect.
Massive amount of water coming out. It's good isn't it.
The contour drains are very good at getting rid of the surface water but in summer they're quite
often dry. We installed this drain in February and it hasn't stopped since there's always been
a drip to a trickle to gushing out the end of the pipe since so it shows you with a
drain that is completely dry an open drain that's completely dry it's not addressing that sub soil
where in the sub-surface drainage is relieving pressure all year round, which I think is great.
Comprehensive data monitoring of the drainage system is being recorded via satellite imagery
and on-site weather stations which help to monitor plant establishment and biomass,
as well as weed and disease pressures.
Also the leaf wetness over there to monitor disease risk and make
sure that at the end of the day this crop is doing the best that it can.
Growers are encouraged to consider sub-surface freshwater drainage
in conjunction with other waterlogging management techniques.
It's also important to check regulations and approvals with your local government authority
before embarking on any drainage solutions. But the sub-surface trial,
in its first of three years is already returning promising early results.
We are hopeful we'll get great results out of it, and we've already got members investigating it,
potentially implementing it as early as next year based off what we're already seeing here.
Stirlings to Coast Farmers are producing project publications on the trial
and offering field walks through areas where sub-surface drainage is installed.
It's not something you'd want to do just for a one in 10-year event but if you've got areas
that would be wet consistently, I think it's definitely worth looking at and definitely
so far I think it would be a good investment to consider.