Soils webinar: Stubble fertiliser and water management to reduce greenhouse gas emissions in rice


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.

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