Welcome everyone to the May Soils Network of Knowledge Webinar and thank you for turning
up this morning and I would like to introduce Steve Kimber who is presenting today's webinar
which is Stubble, fertiliser and water management options to reduce Greenhouse gas emissions
from Australian rice.
Steve has been part of the soils research team at Wollongbar since 1997.
He is an Environmental Scientist working on the degradation and movement of pesticides
and analytical residue chemistry.
Steve has studied how to reduce off-site movement of pesticides, enhance pesticide degradation
and risk assessment of contaminated sites.
His current research is focused on management options to improve fertiliser use efficiency
and reduce Greenhouse gas emissions from cotton, rice, sugar cane and horticulture systems.
The management options being evaluated in the work include nitrogen management, irrigation
management, the use of biochar and other organic amendments.
Thank you everyone.
We'll jump straight into it.
This was a collaborative project between the NSW DPI, Southern Cross University and Rice
Growers Association of Australia and was co-funded by the Australian Government Department of
Agriculture.
It is an Action on the Ground Project from the Carbon Farming Futures program and as
it is an Action on the Ground project it has implication on how the work is carried out
i.e. it's got to be on real farmers' properties.
The project aims, were to quantify greenhouse emissions from Australian rice production,
something that up until now has not been done properly.
To determine the impact of water management on greenhouse gas emissions, now there are
water use efficiency gains but we won't discuss them fully here.
Determine the impact of stubble management options on emissions and this is an area of
quite some interest in the industry.
And determine the impacts on soil carbon stores, this is a part of the project but it will
not be discussed at all today.
The greenhouse gases we're interested in are nitrous oxide, which has 300 times global
warming potential to that of carbon dioxide.
So that very small quantities of produced nitrous oxide can have a profound impact on
the overall greenhouse gas balance of a crop.
Methane, which has 23 times the radiated forcing index, and similarly small emissions of methane
have a large impact, and methane is of particular interest because rice fields around the world
are implicated as being major methane emitters, but good Australian data is lacking.
So how important is methane?
This is ABARE's data from 2012 and you can see that rice cultivation produced about 480
giga-tonnes carbon dioxide equivalent.
Now I believe this data is produced from IPCC default values and not really based on field
data, so this is one of the important assumptions that we are testing.
So what sort of stubble treatments can the industry adopt?
Traditionally stubble is burnt, rice produces a large quantity of biomass, and leaving the
biomass in the field can prove difficult for subsequent agricultural operations, so burning
is a convenient way of getting rid of it.
We are looking at non-standard methods of treating the stubble, that's removing the
stubble and composting it off-site, in this case with cow manure.
We are also looking at producing a biochar through the pyrolysis of stubble.
Once again this involves removing the stubble, producing the biochar and bringing it back
to the field.
And lastly just baling the stubble and removing it and using it for other purposes.
So in our small plot work, the burning was a little bit problematic because we are only
dealing with 10m wide plots, but a few hands on deck and the process went pretty smoothly.
Fertiliser treatments that we are looking at: All plots received 125kg of MAP with Zinc
drilled prior to sewing and where the stubble was baled and removed the plots received 225kg
of Urea prior to flooding.
This is fairly standard fertiliser practice for the industry but when we get to the biochar
amended plots they received also 225kg/ha of Urea prior to flooding.
This is due to the biochar having a fairly low available nitrogen content whereas the
composted amended plots only received 160kg of urea per hectare because the nitrogen availability
of this product was moderately higher than the biochar.
Water treatments: The first one is a fully flooded system where the rice is aerially
sown so there is no cultivation involved after the initial bed preparation.
We then have full flood drill sown, so before the flooding takes place the rice seed is
drill sown into the paddy.
Delayed permanent water; this is one of the water saving options we are looking at and
the field is just left a longer time before flooding up.
And early drain where the field is drill sown but it's drained after flowering and grown
aerobically after flowering whereas normally the paddy would be left full.
So as I said, small plots, establishment of the crop in one of the compost treatments.
Once you start flooding up.
And then as we get into the mature rice, you can see dotted throughout the field are these
white circles, they are the top of our static chambers which we're using to test greenhouse
gases, which we'll go to in a minute.
Before flooding up, a base for a static chamber is installed into the field.
This chamber will protrude 150mm into the ground and as the crop grows extra rings will
be added on top of this so that when we put the lid on to measure the gases we are not
interfering with the crop.
So once the crop is up they will have 3 rings on, the lid will be left off during most of
the period except for the 1 or 2 hours when Greenhouse gas samples are being taken.
So here you can see one of our helpers from Rice Research Australia, Katrina, installing
the lid on one of the chambers.
The procedure will be she will install the lid, take a gas sample and exactly 1 hour
later or exactly 2 hours later depending on how many collars on the chambers we have she
will take another sample and we will determine the greenhouse gas flux mathematically by
difference.
As the chambers get quite high in height, there is danger of getting stratification
of the gases, so in each of the chambers we have installed a small battery powered fan
to ensure we are getting accurate measurements of the greenhouse gases being emitted from
the soil.
So some results: Methane emissions from the treatments.
Now the pink shaded line represents an area of no significant difference.
What you can see in this plot is the fully flooded paddy shows up as being quite significantly
different in methane emissions very early in the season.
Now if you will remember, the fully flooded system was aerially sown whereas these other
treatments were drill sown.
What we are hypothesising is happening is that with the drill sown you are disturbing
the soil, you're ripping the soil open and you're exposing the roots from the last rice
crop which are easily degraded and they are being oxidised to carbon dioxide.
Where you get the aerially sown crop that disturbance isn't happening and once flooding
occurs, that root material, that really decomposable, root material is degraded anaerobically and
you get methane produced.
What we need to do to confirm this is to look at some stable isotope studies so we can label
up some rice roots with carbon-13 and we will be able to definitively say where the methane
is coming from in this peak.
When we go over to the nitrous oxide emissions once again there is very little difference,
most of the treatments fall inside this pink shaded line.
The delayed permanent water treatment however displays this pronounced peak in nitrous oxide
moderately late in the season and we are at a bit of a loss to explain this.
It's quite repeatable; it's a real effect we are seeing.
We are hypothesising there's some difference occurring in the redox of the sediments and
this is data from last year and in this year's crop we have been endeavouring to monitor
the redox conditions in all of these treatments across the season so that we can see what
impact the difference in water treatments has on the redox potential of the soil, the
electrical potential of the soil which tends to drive some of these processes so that we
can tease out exactly why we are seeing these differences and we can target treatments that
might take advantage of these differences that we are seeing occurring.
So how do we compare?
Overall in spite of that large peak in nitrous oxide that we saw in the last slide, that
we saw in the delayed permanent water, over the season the nitrous oxide balance was not
significantly different amongst the treatments.
However, the early peak of methane in the full flood treatment meant that the full flood
produced significantly more methane over the season.
Even with this higher methane value, how do we compare with the rest of the world?
If you look at the median values our high value fits within the range we'd expect globally,
but some of the other treatments are getting significantly lower than the world medians.
So the Australian industry is probably not in too bad a position as it stands and with
room to improve.
So, small plot harvesting: This is typical of the harvesting you'll see in Japan for
their commercial work but we are using these small plot harvesters because we are working
on a small scale.
Conclusions from the first season are that greenhouse gas emissions from Australian rice
fields; they have not been quantified properly in the past.
Preliminary data that we have suggests that methane is the dominant Greenhouse gas.
It's contributing about 7t/ha of carbon dioxide equivalent under full flood production whereas
the nitrous oxide by comparison has a fairly minor contribution.
The drill sown systems, more than half the methane emissions and we believe that's due
to the oxidation of labile carbon present in root material from the previous crop and
as I said, we will be moving in this season to do labelled studies to investigate that.
We have some redox data to investigate what's happening with the late peak in the nitrous
oxide emissions.
Although we didn't talk about this in the presentation, adding straw back to the fields
as either compost or biochar did not increase methane emissions compared to plots that had
stubble baled and removed altogether, and this is an indication, definitely in the case
of the biochar, that the labile carbon has been converted to a more recalcitrant form
and similarly with the compost.
What we need to do this season and into the next season is really pinpoint the cause of
the delayed nitrous oxide peak that we saw in the delayed permanent water.
We are using stable isotope studies to measure nitrogen use efficiency.
There is anecdotal evidence that some of these treatments as well as reducing emissions increase
the nitrogen use efficiency of the crop.
And we are looking at stable isotope studies to trace the origin of the methane peak early
in the season.
Some early work we are doing with some labelled nitrogen to determine the nitrogen use efficiency.
Thank you and I'll take questions.
Thank you very much Steve, that was really good, it's always nice to hear about a project
as it goes along, so we can learn as you learn.
Now I'm happy to open the floor for questions, so if people have questions.
Steve, Ashley asked if there is any indication of emissions from dryland rice in comparison.
We haven't started the dryland rice component of the project yet, that will be in this coming
season.
So you will have to stand by on that one Ashley.
And Andrew Docking has asked a question about dryland rice.
So that will be part of the project but as yet there is no data on it.
Yes
Steve, talking of aerial sown rice, is it actually sown from an aircraft?
Yeah, they will.
In the commercial world yes they will sow it by aircraft but we've just sown by hand
because the plots are quite small, necessarily small for the amendment work.
So both the urea and the rice can be put on by air.
Just like to thank Steve again for his time in presenting and thank you all for attending
and hopefully I'll see you next month.