Okay good morning everyone and welcome to
the April 2017 Soils Network of Knowledge webinar now I’d like to introduce Terry Rose
who’s from Southern Cross University up here in Lismore. Terry’s an agronomist who has
a strong interest in the mineral nutrition of crop plants particularly phosphorus and
the development of crop cultivars with tolerance to nutrient deficiency stress. So prior to
working with Southern Cross University Terry worked in both the public and private sector
he was an extension agronomist with New South Wales DPI in both Wagga and the Hunter valley
and has worked with private company in the UK and he’s also worked in the not-for-profit
sector risk Plant Health Australia in Canberra. So today Terry is going to talk about some
of his more recent work at Southern Cross University looking at the efficacy of nitrification
and urease inhibitors on nitrogen fertilizers in the wet subtopics.
Thanks Abby and good morning everyone. It’s interesting that I’ve called this topic nitrogen
in the wet sub tropics because our climate has been quite true to type of late and it
kind of highlights the difficulties we face so we had two months ago we had crops that
were well and truly drought stressed and some that wouldn’t even recover from that and following
that a lot of them went underwater and they just got their heads back out of the water
and now they’re fully underwater once again and so the wet subtropics is kind of unique
in there that way in that we don’t have a nice uniform rainfall pattern we face both
drought and we face deluge and that makes nitrogen management pretty difficult So why
are we interested in the nitrification and urease inhibitors or any nitrogen fertilizer
product really that can enhance the amount of nitrogen from the fertilizer the crops
take up. The main reason is because it’s estimated that about 50% of the nitrogen applied in
our region anyway. So I’m based on the north coast of New South Wales but there’s probably
regions in southeast Queensland are quite similar but we lose about 50 percent of the
nitrogen applied and that’s the results from the last review paper that was conducting
1994. So the main crops we grow are sugar cane or main field crops I should say we there’s
a lot of horticulture as well but most of our studies have been with broad acre crops
so we’ve got sugar cane which is often grown rotation with soybean then we’ve got tea tree
which is in the far right and that’s actually an inter-row crop of mung beans you can see
there that we were trailing to see if we can fix nitrogen and supply the main crop with
nitrogen that way as opposed to fertilisers but that’s a different story. And more recently
we’ve been toying around with rice in amongst the soybean and cane rotation. So that’s a
brief summary of the nitrogen cycle the main losses that we get in the subtropics here
tend to be through leaching of nitrate and it’s these big events or even just a good
storm following any application of fertilizer that tends to be the main driver however we
also can get and it’s estimated around up to 20% losses as denitrification in some of
our clay soils we also have it we can have especially with the use of poultry manure
we can get ammonia losses and we also get some nitrous oxide emissions although while
they’re important from greenhouse gas perspective they’re not generally a huge part of the nitrogen
budget so in order to address these problems there’s a fair few products on the market
at the moment that attempt to slow the supply of nitrate or they try to they try to reduce
the formation of a large pool of nitrate in the soils and it’s the formation of a nitrate
or these pools of nitrate that are susceptible to eat up oxygenand be nitrifying and causing
losses in N2O or then further to N2 or they’re susceptible to leaching. So there’s a number
of products out there there’s urease inhibitors that inhibit the first step. So if you apply
a urea they use a urease enzyme to convert it into ammonium and you have urease inhibitors
act here and then once it forms ammonium in the soil which can actually attach to the
soil because I have to cation exchange capacity so it is less likely to move in anywhere than
nitrate if you can hold the fertiliser in ammonium form that’s quite beneficial so the
nitrification inhibitors work on this and they try and hold it as ammonium and stop
it turning rapidly into nitrate and then you have polymer coatings and various kinds of
coatings on a range of products that simply try to slow the release of urea into the ammonia
stage as well. So we’ve conducted a fair few trials over the last few years in the Northern
Rivers mostly looking at nitrous oxides but also some agronomic studies just looking at
nitrogen efficiency and I’ll show you the results of some of those today. Now we used
commercial products for these trials we didn’t we didn’t use the actual inhibitors themselves
we just went out and bought off the shelf or were given by fertilizer companies products
that are currently sold the farmers and we tested them to see whether they could reduce
nitrous oxide emissions or whether we could put on lower application rates and get the
same yields. So from the literature we sort of expected that we might get up to 40 percent
reductions in nitrous oxide emissions by using these products and that’s from a couple of
recent meta analyses but when you look into those meta analyses most of the data are from
temperate regions and we didn’t find much from the subtropics so we were pretty keen
to see whether our results were the same or whether we sort of contrasted what was reported
in those analyses in those meta analyses so we use static chamber methodology whereas
which is essentially whacking those chambers you can see on screen in the field You have
the lids off most the time when you want to sample nitrous oxide you come in usually between
8 and 11 in the morning put the lid on take a sample with a syringe put it into a vial
and bring it back to the lab and they our samples for analysed at Wollongbar DPI. You
then come back one hour exactly one hour later and take another sample and the nitrous oxide
that’s fluxed out of the soil in that time will be within the chamber and as long as
you pump it a few times to get it the air mixed inside you can get a pretty representative
sample of the gas composition in there and we find out what nitrous oxide fluxes there
were. So this is one of our trials on a rice crop that we’ve also done work with sugarcane
but to be honest rice is a lot more easy to manage and anyone who’s been into a sugarcane
paddock and tried to sample will appreciate why. So we sowed a local cultivar, Tachiminori
that’s sown by most the farmers around here we throw on 80 kilos per hectare of nitrogen
and the reason we use that rate is because trials over the past few years have shown
that’s roughly about the rate that gets us our maximum yield obviously that depends slightly
on the paddock in the history but around 80 kilos seems to max this out and that gets
us five to seven tonnes a hectare of rice The previous crop was sugarcane and there’d
been a seven-month fallow So over here you can see the nitrous oxide production across
the season so we go from January up to May when harvest was and you can see it was relatively
speaking for our area reasonably dry in February / March then we had a big rainfall event in
April and then another little one in May Urea was the control then we have Urea DMPP which
is actually the commercial product Entech and then we had a blend of the two So because
a lot of farmers say the price of Entech is prohibitive we split We had 50 percent urea
50 percent Entech urea to see what results that gave So these the fluxes have been modelled
by Steve Morris the biometrician at Wollongbar and it’s much easier to see than that if we
just presented raw data where there’s a lot of noise because measurements vary within
a couple of metres in a field and so you get a lot of error associated But this graph shows
the urea in the black line and then the grey area around it is the LSD if you like sides
at P equals 0.05 anything outside of that grey area is significantly different So you
can see in this main flux period here so fertilizer was applied back here then you get the big
flux following application and a bit of rainfall and during that time the Entech and the Entech
plus urea the 50/50 blend were actually significantly lower in that flux period Beyond that there
were very little emission so that pretty much after that first month nothing happens even
with these big rainfall events down here there’s no nitrogen left in the system to actually
turn into N2o So that looks promising back here but then beyond that nothing happens
so if we go over to the total seasonal emissions when you analyse it you find that there’s
actually no difference statistically So urea gave off 0.42 kilograms of N2o N per hectare
and as you can see as a percent of the total amount of nitrogen applied it’s not huge but
as a greenhouse gas it is significant There was no difference across the season and that
simply because you can see the error over here and it’s all this tail where not much
is happening the error created here means you don’t find significant differences but
this little part of the curve here was quite promising so in that early period it did look
quite good The next season we grew the same type of rice different paddock 80 kilos of
N again and this time because the blend appeared to have a similar trajectory as the Entech
in the first one we used urea we used urea DMPP which is the Entech and this time I threw
in a polymer coat to see what happened So in this season we had a big rainfall event
up front another one about a month later then a relatively dry period after that so we actually
had two flux events here after the first rainfall event emissions are quite high but you can
see the urea and the urea DMPP which is Entech they’re pretty much sitting on top of each
other so there was no difference between those two this line down the bottom is the polymer
coat So the polymer coat urea it wasn’t significantly different at P=0.05 it was pretty close
so in that main flux event the polymer coat looked like it may have been effective beyond
that they tend to merge and nothing’s going on So again if we come over here to look at
the total amount emitted across the season there’s no difference and the emissions were
roughly the same across the season as the year before So one season the Entech appeared
to do pretty well in the next season it mimicked what Urea did and the polymer coat urea seemed
to have some efficacy in reducing nitrous oxide emissions So that’s two of our trials
we had three other ones over the past a couple of years we had a repeat with the Entech and
the polymer coat on a peat soil The last two trials I showed were on a fairly clayey profile
that gets extremely boggy after a big rainfall event And sorry this is in 2012 and 13 it
wasn’t in 2015 /16 there We had no significant difference in the main flux period there so
the lines set on top of each other and across the season no significant difference Another
one last season where we tried Entech we tried polymer coat urea we threw in green urea which
has the urease inhibitor MBPT and we’ve tried a black urea which is a carbon-based product
and they’re all sold commercially around the place This is back on the clay soil again
The curve set on top of each other even in the main flux period so no difference there
and no difference across the whole season Same treatment on the peat soil last year
and exactly the same result So no difference in that peak flux period and no difference
across the season So all in all there’s a fair bit of variability across our trials
and there was no clear evidence that any inhibitor products can actually reduce seasonal emissions
from a statistical point of view We had one and possibly two trials where there was a
hint towards reduced emissions in the peak flux but then three trials where absolutely
nothing happened So moving on from those nitrous oxide trials and probably of more interest
to growers is what happens with grain yields So in all our trials at the rate of 80 kilos
per hectare there was no difference in grain yields. However you wouldn’t expect there
to be because we’ve just put on the rate of urea which is the control that we expect to
get maximum yield so it would be silly to expect that giving more nitrogen to the system
is going to increase yields On that note if you look at recent papers in the literature
and there’s five have come out in the last few years but I’m going to pick on Abalos,
they all conclude the same thing they all look at studies and find very few yield increases
or very little yield increase from either DMPP that’s one using Entech or NBPT the one
using green urea or another nitrification inhibitor called DCD So they find you get
these tiny yield increases even though you do get up to 40 percent reduction in nitrous
oxide However if you actually look into those studies they’re all conducted at or most them
are conducted at a single rate of nitrogen and that single rate of nitrogen is usually
the recommended rate for that region so I would argue that those papers are somewhat
flawed in that you shouldn’t expect a nitrogen response if your control is the rate of nitrogen
that’s non limiting So we, bearing that in mind what is needed to actually test these
products is a nitrogen rate response trial where you try five or six rates so you can
derive a fertilizer response curve and you test that against urea. Now to the best of
our knowledge the only published studies that we found using Entech that have actually gone
and bothered to do the work and the reason presumably is because it costs a lot to run
such trials is some work on sorghum up in Queensland and they had five trials over a
couple of seasons and they didn’t find any large response or they didn’t find that you
could reduce the amount of Entech fertilizer applied and get the same yields as urea but
that’s one study in the whole of the literature that we found which was quite surprising given
what a hot topic it is So we ran our own This trial was on the clay soil that we ran the
rice nitrous oxide trail on in 2015-16 We’ve shown, the data here are not means they’re
actually the individual replicates there’s three replicates and we’ve got the black dots
are our control urea and we had six application rates including a zero N control but you can
see the zero N control still yielded three ton of rice per hectare and then we’ve got
in the blue was Entech. We actually ran this with four other products as well but I’m just
showing you the Entech verse urea because essentially we’ve got the same result with
all of them So there’s a reasonable amount of noise but it’s the same sort of noise that
you see in most field trials What we have in the black line is that if the key is the
fitted curve for the urea response the blue line is the fitted curve for the Entech response
The dotted lines the dotted black line is the 95% confidence interval for that fit for
the urea and ditto for the 95% confidence interval for the Entech and so you can see
the confidence intervals overlap and there’s there’s no signal difference in those response
curves now even if you get picky and decided that points too high this points too low and
you toss them out which we didn’t in the end because we had the biometrician look and he
said no they’re not outliers But even if you do and we toyed around with it you don’t get
a huge difference in the response the shape of the response curve So from this season
what you can conclude is the products behaved exactly the same and you couldn’t reduce the
rate of the inhibitor product and get the same yields and that in that trial was the
same for green urea for black area and for polymer coated urea we couldn’t reduce the
rate of any of them and get the same yields compared to urea So that’s only one season
we’ve got another trial in this year looking at the same thing and I’ll probably throw
in a couple more in the next few years because given the lack of data out there on it I think
it’s time we started even though it’s expensive running proper trials to see whether these
products can be used at a lower rate So one of the reasons we thought we might be getting
different results to the literature at least for nitrous oxides while we aren’t seeing
the big drops in nitrous oxide and possibly why we didn’t see a response last year in
our rice trial while we couldn’t use less we thought maybe the warm temperatures of
the subtropics are different to a lot of the published studies from temperate areas in
that it causes the, there’s a different dynamic between the bacteria in the soil the microbes
in the soil and the inhibitor you put on so here’s some data here’s some data from a paper
from Deli Chen from 2010 where they’ve done some incubations and incubation is where you
just put a bit of soil and known amount of soil in say a test tube or a falcon tube you
put in a known amount of fertilizer and you put it in the dark at a given temperature
and over time you can measure changes in anything but in this case they measured changes in
ammonium and nitrate production so this is ammonium and this is at five degrees so this
is at a cold temperature so what happens is you’ve put the fertilizer in after day naught
you get production of ammonium up here and it stays pretty constant and doesn’t drop
off and the reason presumably is because it’s quite cold and the bugs aren’t doing much
so they don’t convert it into nitrate and this is at 40% water filled pore space 60%
water filled pore space is sort of optimum for nitrous oxide production but even at 60%
not much is going on When you increase the temperature to 15 degrees the urea treatment
which is this black one after about 28 days starts to convert to nitrate well, you can’t
actually say it from this graph all you can say is the ammonium is disappearing but if
you go over to the other graph over here which is nitrate they match each other quite well
the nitrate starts to go up the products so that triangle is DMPP that’s Entech, this
other one’s called N serve and that is the basis of a lot of products sold over in the
U.S. at the moment although they are creeping into Australia as well So the Entech can hold
it as ammonium the urea starts to turn to nitrate as the temperature increases again
after seven days the microbes quickly start turning the urea from ammonium into nitrate
over here so you get this big increase in nitrate and that’s what we’re looking to avoid
so over here at 25 if you can hold the nitrogen in the form of ammonia for this extra from
7 to 42 days then it’s not susceptible to leaching it’s less susceptible to forming
nitrous oxide and the plants can still get it and it’ll adhere to the soil cation exchange
so that is a good outcome Interestingly at 60% water filled pore space these guys found
that the Entech starts to drop off but it was better than sorry the Entech starts to
drop off whereas the Nserve which is the one that forms the basis of a lot of American
products doesn’t drop off Anyway onwards to our data so we use some soils from around
here we’ve got the clay loam soil or it’s clay loam topsoil it gets to pretty clayey
beneath that with a pH of 5.6, 2.3% carbon from down in our rice trials so we do the
same We incubated them in Falcon tubes with 15 grams we added a big wallop of fertilizer
N because we actually added the product the fertilizers as bought from the shop so we
actually When I say we it’s a royal we, my technician weighed out individual grams of
fertilizer it took him three days to set this up he got the exact weight of all the granules
and found granules of the same weight and added one to each and that was a rate of 400
kilograms of n which might seem high to some people from that who aren’t from around here
but it’s not it’s not that high you know you can get 200 to 300 kilograms of N thrown on
a big cane crop so it’s not that unrealistic and we incubated them at 3 moisture contents
at 30 degrees instead of 25 So let’s start with the nitrate production over here and
we’ve got 40% water filled pore space where usually not much happens 60% which is optimum
for nitrous oxide and a lot more action and we put 90% in because reasonably frequently
our soil topsail can be up at 90% or above whenever we get a decent rain event on these
clay soils it’ll stay for a few days quite saturated so we tried that as well what you
can see and here’s our, so urea is this little guy green urea which is the NBPT is the circle
and then the Entech is the square but regardless not much difference you come up to 60% not
much difference now the Entech here seemingly has a bit less nitrous sorry nitrate production
we’re going to check that because I would have expected if it’s going to start separating
here then when the nitrate started to form back here that it should still have been active
so that’s a bit of an anomaly that we’re going to repeat and see we get the same result over
at 90 percent water fill pore space at 30 degrees they’re all the same so we don’t see
we didn’t see the same results as the Chen paper what we hypothesize is that A we’re
at 30 degrees not 25 so the bugs are a lot more active and B we think our soil is probably
or it has more labile carbon and food sources for the bugs and it’s just a more biologically
active soil so when you put these fertilizer products in it’s the competition the inhibitors
are trying to inhibit the microbes that can do nitrification or have urease activity while
the rest of the bugs are just trying to eat these products and use them as a food source
and we suspect that at the rate of inhibitor used on these products in our soils that are
highly active and in summer crops where the soil temperature’s warm the soil microbes
can destroy and eat the inhibitors before the inhibitors can act on the bugs that do
the nitrifying The other reason we think that ourselves might be more active is because
if you look at the soil ammonium concentrations they don’t drop off and so over let’s look
down here at 90% pore space even while nitrate is increasing over here we don’t see the same
drop-off in ammonium over here they’re not concomitant. What that suggests is as ammonia
is turning to nitrate through the nitrification process bugs are also active on soil organic
matter and are turning organic nitrogen sources into ammonium and so that in itself when you
look at these results compared to Chens results here where it drops off suggest that we have
quite an active soil so that’s our current hypothesis as to why we may not may not be
getting the results and we are going to continue looking at different soil types and look at
some different concentrations of these inhibitors to see whether that is the reason so in summary
we didn’t find any significant lowering of seasonal nitrous oxide emissions consistently
in five rice trials Both Entech and polymer coat showed some evidence during peak flux
events in one season each that they could reduce nitrous oxide fluxes at that time but
it didn’t translate into lower seasonal emissions and we need to better understand what is happening
with these inhibitors whether or not we need to increase the concentration of the inhibited
weather we need to try a new inhibitors I’m not sure but we need to try to work out what’s
going on so that we can improve it So our current data suggests that given the extra
cost of the fertilizers with inhibitors they don’t appear economically valid based on our
current trials but we obviously that was just a few seasons and we need to do more work
to see whether in some seasons they can be used to reduce rates to produce maximum yields
and finally I say it’s not good enough to simply go and tell farmers Oh you know our
trials show they’re ineffective we actually need given that we’re losing 50% of our nitrogen
from fertilizers to the environment and we live in a pretty environmentally sensitive
area we actually need to do some hard work and find products that do work otherwise we’re
going to find ourselves as an agricultural industry under a lot of pressure and I dare
say it’s the same in Queensland where you’ve got crops growing near the barrier reef the
social licence to farm it’s going to come under pressure so it’s not good enough to
say don’t work we actually need to work with companies and find products or modify products
to make them work and make them work at an economically viable cost to farmers so I’ll
leave it there thank you for listening and I think Abby has a way that you can send in
any questions. Yeah okay thank you very much Terry that’s fantastic as I said we’ve got
now time for questions Steve Kimber yeah that’s a great presentation Terry We went through
quite a complex story I think you’re really pushing things uphill because you’ve got so
many challenging conditions and mechanisms that vary wasn’t soil moisture and temperature
that with one or two trials it’s very difficult to show what’s going on and also making a
comment on the polymer coat I think there’s a need to three or four different levels of
resistance or release resistance for the fertilizer so you get some sort of coverage of nitrogen
release right across the season. Yep I agree with that and I think that’s something it’s
been meeting from polymer coat trials at the moment too is different blends even a 25%
urea 75% polymer coat or as you say there’s different polymer coats that have a different
release pattern trying different blends I think we need to do it the problem as always
is that when you start running decent sized replicated field trials and you start mixing
things up it gets expensive that doesn’t mean they don’t need to be done they do but you
know you need you need funding to do it and it would be nice if this sort of work was
prioritized I think because you know there’s a lot of study a lot nitrous oxide stuff out
there is fairly pointless for growers it does represent a big end loss pathway and I think
as you say a lot of these product combinations need to be tested and I need to be tested
in an agronomic sense over multiple seasons so we can actually try and work out in what
seasons they might be effective If a price has put on nitrous oxide emissions that’d
change the economics of it too This is true yeah There’s a few other questions that have
come in that are typed so I’m going to read those out Justine Cox is interested Terry
to know what the individual company’s response to your data has been? So far I’ve only presented
parts of the data at a conference and I’ve flicked off some of the results to one of
the companies but it’s been it’s taken me until about a month ago to actually get all
the data together and there’s actually a couple of other data sets that I haven’t finalized
yet that I want to put all together before I actually go and talk to them because I think
it’s much as they were interested to see the preliminary data and sort of see the data
as it was coming in I think for a proper discussion I’d like to take all the data we’ve got which
is all the field trials all the incubations with different soil types and look at it as
a whole so the short answer is I haven’t actually shown them the full data sets yet but I intend
to and hopefully we can have some interesting discussions Okay thank you Next we have a
question from Rob Norton and he said have you got any comment to make about the losses
of nitrogen as dinitrogen Good question Rob and it’s something that we are just starting
to set up some incubation studies now looking at following some work from David Rowling’s
up at QUT where they had they looked at some dairy soils where they’re quite puggy and
they were getting I think I think it was 20 plus percent losses as dinitrogen in those
soils they were that was irrigated dairy soils We suspect and particularly given the weather
events we’ve had this year where even without these giant flooding events when we get it
if you get a good storm with you know 50 or 60 mms in it a lot of these soils the topsoil
gets wet enough we think to fully denitrify so I don’t have any data on that at the moment
I apologize but we are setting up incubation studies at the moment to actually work out
with our soils when it might occur and then if we look at some historical rainfall data
we can then try and model when we think it might have occurred and try and get some idea
of what the losses might be but if the data from Queensland is anything to go by I think
we will be getting reasonable amounts of dinitrogen losses more than ammonia losses put it that
way we I don’t think we’re losing much as ammonia we’ve got fairly acid soils and a
lot of the guys put the nitrogen to the ground and anyway so I think dinitrogen losses are
going to be a much bigger loss pathway than loss as ammonia gas Thank You Terry and further
to that I think I just heard you mentioned some work that was done in pastures is that
right Neil Griffith was wondering if you have looked at the pasture work that Warwick Dougherty
has done that seem to show similar results and he said not enough yield to cover the
extra cost of the product I haven’t seen that I’ve only heard I’ve had a few people talk
to me about that but I haven’t actually seen any of the data in either a report or paper
yet but that’s interesting that there was similar results that you know you can’t lower
rates or the degree to which you can lower rate doesn’t justify the cost at present yeah
and further to that Robert Guy also said that they’ve had they’ve got similar thinking to
how things are working in southern pastures but they need they would like better efficiency
of nitrogen used. So it’s obviously a common issue. Did you want to comment on that or?
Yeah I will because you hear of you know you had a few conference of being you get a few
academic types saying Oh you know these doesn’t work this is rubbish blah blah but I think
Robert makes a good point the fact is we still having low efficiencies in nitrogen use so
it’s not it’s not good enough to just poopoo things and so they don’t work the reality
is we actually need to work at what’s going on and keep working to find products that
are economically viable for farmers to use that actually do increase the efficiency of
use because otherwise I think we’re going to get in strife at some point particularly
in environmentally sensitive areas where the locals aren’t going to put up with poor water
quality and so I yeah I think we have to keep plugging away and find ways to increase the
efficiencies Yeah good point I think Now a slightly different question from Phil Hirst
he said with the temperature regimes is it worth considering soil temperatures over the
year and therefore adjust the application of fertilizer according to that? In the end
the application, the fertilizer rates you’re going to apply should be based on trials nitrogen
rate trials over many seasons for that crop in that season so I don’t think for example
so there’s a bit of barley grown out towards Casino around here I don’t think there’ll
be any way we can say ok soil temperatures are going to be lower over that winter period
and we can change our nitrogen rates according to that I think we simply need to go and do
nitrogen trials out there rate trials and come up with recommended rates that are suitable
for the that crop in that season I think that’s the better way to go about it even though
what you’re saying is probably true we might find better efficiencies because of that during
those seasons but in the end I still think to come up with valid recommendations you’ve
just got to run the trials get enough data to do some models and then possibly even run
an economic model over the top in the same way that state governments have been doing
it for years and years I think that’s still the best way to do it Ok thank you for that
Phil and Rob Norton says he’s given a comment on the value of inhibitors is that they generally
have a short residual time maybe less than 40 days and they will only be effective if
the loss process is operating at the period when the inhibitor is active which makes sense
and this is difficult in cane as the opportunity for interventions is limited and the duration
of crop growth is long so you probably only get one shot for it to work so thank you very
much for that comment Did you want to say anything? That’s it in a nut shell. Good point
Rob. OK I will take this opportunity to thank Terry I took the liberty of putting his email
address up there on that slide that you can see so if you do have any other questions
that occur to you afterwards you could forward them there thanks very much Terry