Effective soil amelioration strategies offer growers significant yield benefits, but sometimes
things in the paddock just don’t go to plan.
So today I’ve put together a collection of grower experiences on soil amelioration.
At the Perth Grains research update event, Department of Primary Industries and Regional
Development researcher Bindi Isbister shared a range of soil amelioration lessons that
WA growers have learnt the hard way.
Over the last five years, we've done a lot of research on soil amelioration management
practices and we always tell the good things and the good stories about soil amelioration
and the yield benefits you can gain.
But actually it's not always as simple as it sounds, and not all soil amelioration techniques
are suited to all soil types.
Growers have found when they've gone to apply the research in their paddock that they can
actually be mistakes or bloopers that occur.
Now a blooper is defined as an embarrassing mistake.
I'm not sure that all of these examples I show in my presentation are embarrassing mistakes,
they are more just a result of what's happened.
But there's certainly some very good lessons that we can learn that will hopefully prevent
others from making the mistakes in the future.
The first blooper to kick things off is applying pre-emergent herbicides post amelioration.
One of the challenges that we've noticed post amelioration is that pre-emergent herbicides
can work too effectively.
So effectively in fact, they actually reduce plant establishment.
So you need to be really careful when you're going in to seed, newly ameliorated paddocks
that you actually consider what herbicides you're going to use just to make sure that
they're not going to impact on plant establishment.
Another lesson that’s been learnt I think that's quite common is mouldboarding or spading
dry isn't as good as wet.
And that's for two reasons.
So one is that you actually do a better job of inversion when the soil is wet.
So this is an example of ah topsoil slotted and spaded dry and you can see that it mixed
down to about here, the 30cm.
But when the same farmer, same process, same paddock even, but he did it when it was wet
you can actually see that we got much better inversion and mixing down to about 50 cm here.
The other aspect to why ameliorating soils wet is better than dry, is that the risk of
erosion in autumn is much higher.
So some growers have found when they ameliorated in autumn then they haven't had the rain and
the soil hasn't wet up enough and they get poor plant establishment that can be subjected
to erosion.
Now while that looks terrible and none of us want it to erode, what we do see very commonly
is that those erosion patches to actually recover and we get good plant establishment
when it finally does rain.
Sometimes they'll re-seed them, but not always.
And then we still see that there is a good benefit and in fact a yield increase from
the mouldboarding despite that initial soil erosion and setback early on.
But it is possible to have too much of a good thing, as some WA growers have found, it can
be too wet for ripping as well.
Bindi is quick to point out this is particularly problematic in heavier soil types.
You need to get out of the ripper if you're ripping in spring.
Grab a handful of soil and roll it and if you can make a soil sausage like the one I've
made over there, it's actually too wet for ripping and you'll just end up with slots
and the soils actually not going to fracture so you're not going to achieve what you want
to.
The next two bloopers are also related to deep ripping, but focused more on the ‘undesirable’
soil characteristics brought to the surface and the related return on investment.
It's commonly reported that you can get these big yield benefits from deep ripping up to
500kg/ha.
But in actual fact, you don't get this response in all soil types.
So another common blooper is actually deep ripping the heavy, loamy soils particularly
if it they're a calcareous loam that might be sodic and dispersive.
And in one of the GRDC-funded trials that we had and they tried to rip last autumn when
conditions but dry using a deep ripper with topsoil slotting plates, they actually found
that the soil was too dry and the topsoil slotting plates couldn't get in and the soil
came up really clumpy.
So when they took the topsoil slotting plates off, they then put the ripper in and were
able to dig a bit deeper.
So their target depth was 400mm about the soil was too dry and too hard.
So that had to go in two passes and they managed to get the ripping down to 300mm.
But surface that was left was really cloddy and actually impacted on plant establishment.
Bindi and the team went on to examine the impact on yield from this amelioration decision
in both 2018 and 2019.
So this is the trial results of that of two years of trial results.
And because it was sodic and dispersive, the treatments here did include gypsum, 5t/ha
gypsum.
We had a nil ripping depth, 200 which was mm ripping and 300mm.
And you can see that there was an impact on plant establishment in the ripping, so it
did reduce plant establishment by about 20 plant per square metre.
If we have a look at the yield in 2018 and 2019 which were also both dry years, you can
see that the crop in 2018, the ripping did actually recover so it actually yielded the
same as the control, but there was actually no benefit to the ripping.
And in 2019, again, we saw no benefit to the deeper ripping or the gypsum.
Not only was there no real yield increase, there was also a negative return on investment,
which Bindi says reflects the research findings there is no significant benefit to deep ripping
heavy, sodic, dispersive soils.
And it’s a similar story for delving duplex soils.
So this is the key one for today I think.
Bloopers commonly occur when the treatments not applicable for all soil types in a paddock.
So you might see a paddock where you've got water repellent soil and go out ploughing
or delving but actually you've underestimated that variability in the paddock and often
it is that in duplex soils so more commonly in the southern region, it does happen in
the north too.
But you've underestimated how that depth to clay there is.
So, for example, one place that we found down in Esperance, it was a farmer delved his duplex
soil that varies in depth from 10cm to 60cm and this was done back in 2009 when delving
was just emerging.
And what he found is he actually brought up to the surface this sodic, grey clay that
was dispersive and actually was high in boron.
10 years on and this grower is still seeing a negative yield impact from delving the
shallow duplex areas of his paddock, up to one t/ha in fact.
How can we learn from this mistake?
So initially when they went to delve the paddock, they knew that the variable depth to clay
was a problem and they looked at EM and the gamma radiometrics to try and zone out those
those areas.
But they found that the background salinity and soil moisture were too high so they
didn’t get an accurate delving map.
So now the farmer has actually gone on and because he keeps to the risk of, I guess,
turning up this sodic soil and having this yield impact, he now is claying out his poor
sand areas and he’s developed a good seeding system that is good in the non-wetting soils,
it’s something that he can apply across the whole paddock without having to worry
that bring up soils that he’s not able to manage or have an impact on production.
Mouldboard ploughing can also turn up some unwanted soil constraints in duplex soils,
in the form of cloddy patches.
For this blooper, Bindi shares an example of this experience at a trial site in Ravensthorpe.
So this is another example down at Ravensthorpe and this is a large scale trial and this is
the mouldboard and spading treatment.
And you can see here that it's really variable spatially across the paddock this soil type.
So this is actually about 12m in that distance so the soil is varying every 10-12m so that's
really hard to find something you can map that depth.
What they found, the mouldboarding here it did reduce plant establishment compared to
the control.
What the farmer's seen is that there is still lumps and this is after four or five years.
In fact he says they are still there today.
And it's been rolled every year and speed tilled in 2007 and they're still seeing poor
plant establishment in those areas.
Coming to end of the presentation, Bindi shifted the focus to a challenges that can come with
liming acid soils at depth.
So the research has shown to ameliorate those deeply acidic sands that we need to apply
lime, we need to mix it deeper, and then if they have compaction you need to deep rip
out that compaction.
But what does this mean in the paddock?
Well actually, in some of those soils that have never been deep ripped it means we find
rocks and they can be huge rocks and they can actually bend the hydraulic arm on the
ripper.
Oops, break the ripper.
So apparently this is the super-size toughest hydraulic arm you can buy.
But um yeah that's a bit of a problem.
Now I did get asked to put the economics onto this but I reckon you guys can figure that
out better than I can.
So what's happened is the paddock has been zoned up into these rock warning zones so
that the driver knows when he comes into these ones he has to pay a bit more attention and
listen to the ripper or start to lift it a bit shallower.
The final blooper?
Soil after amelioration is soft… very soft.
So trafficability is a really big challenge as well in these soft soils so after amelioration
the soil is soft, and you can see this is one of the CTF after ploughing and they've
fallen off the wheel tracks and got a bit bogged and then it can happen after deep ripping
as well.
One strategy to deal with this risk is using a roller behind a deep ripper, which helps
firm the soil surface for machinery and also aids plant establishment.
So another way to help manage the soft soil post soil amelioration is to actually consider
your seeder.
So using a seeder that has independent depth control, farmers have found is particularly
good in ameliorated soils because you can tend to get sinking of the bar.
So this means that we just maintain good plant establishment.
Another really important way to manage this soft soil post amelioration is actually to
match your wheel tracks and move into controlled traffic.
Because if you’re going to invest all this money in soil amelioration, really the last
thing you want to do is run over it.
So in conclusion Bindi has three key messages for all growers to keep in mind when it comes
to soil amelioration.
The most important thing is that you need to know what your soil is, what are the soil
properties to depth and we recommend every 10cm, and also how it can vary spatially.
Because especially with strategic tillage methods, the last thing you want to do is
turn up a sodic or a toxic subsoil that's going to impact on your plant establishment.
And you also want to be able to choose the right tool for the job, because in some of
these cases, they're probably not bloopers and the technique doesn't work, it's just
it doesn't work for that soil type.
So it's really critical that you actually know what you're targeting and choose the
right machine.
The second key message is that you ameliorate conditions not to the calendar.
So it's really tempting to chase that half a tonne or a tonne benefit from soil amelioration.
The key is, before you go ripping or ploughing make sure the soil profile is fully wet to
get the technique working and consider that erosion.
So growers have found that if you ameliorate it when it's half wet and half dry, that can
actually be more of a problem.
So make sure that you go on the conditions and don't just go because it'll fit into your
calendar at that time.
Maybe you better to pull up and wait for a bit.
The third and final key message is If in doubt, leave it out.
It’s really important when you’re doing amelioration to get out of the tractor, get
your spade, have a look and have a dig, is it doing what it wants, is it coming up too
cloddy and if it is, stop.
Make it a trial, have a strip that you can monitor and then see how that goes or perhaps
just pull up and wait and look for other opportunities to do it.
Alright thank you very much.Bindi Isbister, Research scientist at DPIRD.
And this video is one in a series of update videos recorded at the 2020 GRDC grains research
updates.