Herbicide effects on soil biology and function


Ok everyone, good morning and welcome to the
October Soils network of knowledge webinar and our 6 monthly mark for these webinars. This month’s presenter is Mick Rose, and Mick
is a project officer on the Grains Research and Development Corporation project being
run by NSW DPI and in this project Mick is doing work to better understand how herbicides
might affect soil biology and grain production, hence the title of his presentation. Mick’s interest is the interaction between
plants, microorganisms and their environment and has led him to work in a diverse range
of projects and a diverse range of locations. He’s worked on the use of constructed wetlands
for improving water quality, plant growth promoting organisms, Abiotic stress tolerance
in plants and organics. Thanks to Abby for the opportunity today and
thanks to everyone for joining in. So this morning I’d like to talk to you about
our recently commenced GRDC funded project entitled: Does increased herbicide use impact
on key soil biological processes? This is a 5 year project and we started at
the beginning of the year and I guess really the first question that you might have is
why is GRDC and why are farmers interested in the effects of herbicides on soil biology
and processes and why now? Data about herbicide use is notoriously difficult
to come across. This graph here shows some data from the US that was recently compiled
by the author Benbrook. You can see here the start of the diamonds shows the amount of
herbicides applied per kilograms per hectare to the three major US crops, cotton, corn
and soybean and generally you can see an increasing trend so that we are getting more herbicide
applied per hectare. This is consistent with uptake in minimum till or no till practices
whereby more reliance is placed on herbicides for effective weed control. A similar trend you can see here in Australia
these white diamonds here. However data for the actually herbicide applied to crops is
not readily available so instead we’ve got here the value of the herbicide applied and
I’ve just scaled that per hectare of grain produced each year. So you can see a similar
trend here. The authors of this study put the decline of herbicides applied down to
the fact that herbicide chemistry is becoming a lot better and a lot more effective at lower
concentrations. But you can see that the trend is starting to turn upwards and we are getting
more and more herbicide applied. As well as that there is a lot of interest
from social groups from the public, largely driven by the fact that GM crops that have
been introduced have changed the spectrum of herbicides being applied to crops as you
can see here. You can see here, this is data from the US study showing the increase in
Glyphosate applied per hectare and you can see that as a proportion of total herbicide
applied it’s increasing a lot more rapidly. So there is a lot of focus on Glyphosate in
particular and chemicals being applied to GM crops. The second reason that GRDC and farmers are
interested in why herbicides might influence soil production is the increasing recognition
that soil biology and the functions they provide really give a lot of value that is kind of
not accounted for to agricultural systems and crop production, so recent estimates put
it down to between $300-500 per hectare of unaccounted value provided by soil and most
of these relate to functions provided by the soil biology. This slide is quite complex
but you can see here that many of these processes are driven by soil biology. In particular
nutrient availability, so the turnover of organic matter returned to the soil, transformation
and retention of fertilisers applied to soil and also the provision of nutrients from the
soil and atmosphere through biological processes. Secondly, the relationship of pathogens to
crop production and how the total soil biological balance relates to disease occurrence is also
of great interest. There is a lot of speculation about how herbicides might affect the soil
biology and how that can in turn influence crop productivity. Really we want to explore this over the next
5 years of our project, and in particular our aims are to define and identify the herbicide
concentrations at which significant negative effects occur. So many of the studies that
have been done to date work by conducting an eco-toxicological approach where by increasing
concentrations of herbicides are applied to soil and certain responses are measured. Usually these studies report certain negative
effects but whether or not they occur at herbicide concentrations which farmers are using in
the field is a different question. So we want to identify what is the relevance of any effects
that might occur and secondly we want to identify which processes and which soil biological
communities are most at risk. Following on from that we would then like to tease out
what kind of farm management practices might influence that risk, so what are the effects
of increasing the amount of organic matter in soil, does that provide more resilience
to the soil microbial population and the soil biology, how does water influence these processes
and with the effect of climate change how might heat and other stresses such as drought
impact on the risk posed by herbicides? So the first step of our project was to review
the literature which is what we have done over the last 6 months or so and that’s what
I’ll be talking about today, what data is already out there and what do we know already,
and further more where are the knowledge gaps and what do we need to know? So I’ll just quickly talk you through our
project team and roles. It’s a national project based out of Wollongbar in NSW. We also have
collaborations with Qld, Nicky Seymour at QDAFF, Southern Cross University, Quick Test
Technologies in Sydney, Vic DEPI, University of SA and over in the west Craig Scanlon and
Gavin McGrath are contributing as well. As part of the project we’ll also be conducting
a number of field trials so we will be transferring from our literature review to undertaking
a number of studies in the glasshouse and in the laboratory to look at the effects of
herbicides on particular microbial processes then transferring that into the field and
seeing how practically relevant those results might be. So what do we know so far? This is just some
data from our initial review whereby we did a large literature search just to take in
as much knowledge as we could so we were searching for the effect of herbicides on soil biology
and function and these data represent the experimental evidence that is available already
in the literature. So it is a good check to see what kinds of herbicides are being focused
on in the literature and it’s quite similar to the spectrum of herbicides that are being
used around the world. So you can see here the most data that we have available is on
the Glycine group of herbicides, of which Glyphosate is the main chemical being used
and you can see that there is almost twice as much interest or more than twice as much
interest in Glyphosate than there is of any other herbicide. I’ve just got some chemical structures here,
I don’t want to go too much into the chemistry, but I’d just like to point out that many of
these herbicides as well as containing carbon also contain smaller amounts of macronutrients
such as Nitrogen and Phosphorus. So from the point of view of soil biology, certain microorganisms
can see these chemicals as a food source. So whether or not they interact detrimentally
or beneficially to the soil biology is hopefully something that we can tease out. We are also going to be looking at the sulfonlyureas,
not so much the second group here not so much the Chloroacetamides, most of this data comes
out of the US where herbicides such as Metalochlor and Alachlor are used for maize and soybean
production. We will also be looking at Atrazine which has had quite a bit of media attention
particularly in the US where it is highly mobile and has been detected in ground water
but we will be keeping the focus of this to soils. 2-4D, Trifluralin, Diuron and finally Diflufenican.
These are our focus model compounds that we’ll be conducting research on. Interestingly you
can see here that although Diflufenican is used quite a lot in the Australian grains
industry there is really very little data about it in the literature. So already we
can see that there is certain knowledge gaps where we are not sure what the affects of
some chemicals might be. Within all these classes I’d just like to make the point that
there is numerous different chemistries, so each class represents between 5 & 20 different
compounds. So there is myriad of products on the market and coming up with specific
recommendations for every single chemical will be quite difficult. Generally though
the chemistry within a class is quite similar and we assume that they will have a similar
function in soil and affect in soil. Before I go too much into the data, I’d just
like to point out that what we found from going through the literature preliminary , is
a bit of a disconnect between what happens in the field and what is done in the laboratory.
Farmers will apply their product at rates per hectare but in ecotoxicological studies
many of the dose response experiments look at herbicide concentration in terms of milligrams
of herbicide per kilogram of soil. So to come up with these concentrations that they are
testing in the laboratory many scientists need to make assumptions about how deep herbicide
applied at a certain rate will penetrate into the soil and also the bulk density of the
soil. So that for example a number of authors whose studies we have looked across suggest
that Glyphosate might only be distributed through the top centimetre of soil in which
case they come up with the concentration of 18 mg/kg. However, over time with rain, irrigation
and other soil processes we will get a distribution of movement of a herbicide through the soil
which will decrease the concentration. So that if we assume that a different herbicide
might distribute through the top 10cm of soil, if its more mobile than Glyphosate, herbicide
applied at 2.2kg/ha moving through top 10cm will then have a concentration 10 times lower
than what it might be in the top 1cm of soil So this has some practical implications for
conducting experiments in the laboratory. But also when we take that to the field and
we are trying to work out the relevance to crop productivity, if we are assuming that
the herbicide only has impacts in the top centimetre of soil what relevance does that
have to a plant that might grow through the top cm of soil and explore the rest of the
soil profile. Even if there are effects in the top cm will that impact on crop productivity? Secondly, herbicides dissipate over time.
So once a herbicide’s applied they start moving about and also breaking down. But importantly
this differs from farm to farm, between soils and also different environments. You can see
here from this graph that even within a single soil this data shows the breakdown of 2-4D
and most of the herbicide has disappeared from the A horizon by 2 weeks after application.
However if the herbicide moves to the B horizon you can see here that it takes almost 50 days
for this herbicide to dissipate. So even within the same soil you can get different rates
of dissipation of a herbicide. This study looked at the application of herbicide degrading
micro-organisms. And you can see that when genes are present that can degrade the herbicide
then the lifetime of the herbicide is a lot shorter. So what this suggests is that herbicides will
probably have the largest affect immediately after application but over time we might see
that this affect is attenuated, so that there might be a short duration affect that doesn’t
continue over time. This graph is a little bit complicated but
what I just wanted to do here is point out the different modes of actions of the different
herbicide classes. And what we can do from this is speculate which of these herbicide
classes may impact on the soil micro-biota through their mode of action. So what we have
here is this red colour indicates that it’s highly likely that that mode of action will
affect that particular biological group within the soil. And of course algae being photosynthetic
organisms are generally pretty well impacted by all herbicides. That has large implications
for river and marine environments where algae form the basis of primary productivity but
for the soil environment and crop production it’s probably no as important. So although
there is not too much data out there about that we’re more concerned with the fungi,
the bacteria and the meso-fauna. So what you can see is that Glycine which
incorporates Glyphosate, the Sulfonylureas and the Immies all have a kind of medium,
what we would guess is a medium hazard towards fungi and bacteria, and that’s because this
enzyme, the different enzymes that these chemicals inhibit are also present in these organisms.
So Glyphosate for example inhibits the synthesis of branched chain amino-acids, fungi and bacteria
also rely on this pathway to produce their own branched chain amino-acids. Glycine impacts
aromatic amino-acid synthesis. They’re responsible for a lot of secondary compounds in plants
that have a role in plant protection but this pathway is also present in fungi and bacteria. Similarly, the Sulfonylureas that’s where
the pathway for branched chain amino-acid synthesis is inhibited and that is also present
in fungi and bacteria. The Immies also impact on that pathway and
we expect them to have slightly higher activity towards those groups. I’ll just point here as well that the Triazines,
the phenylureas and some of the other herbicides that impact on photosynthesis, because those
pathway aren’t present in the majority of the meso-fauna and the micro-biota, we are
presuming that they probably won’t have as great an effect as some of the other classes. The Dinitroanilines may have an effect on
protozoa. These micro-tubules the same pathway that is in plants is not present in animals,
fungi and bacteria, however there is some evidence that it may exist in protozoa. And
these protozoa are responsible for regulating the ecological balance by feeding on fungi
and bacteria so there might be a slight impact there as well. So what I’d like to do in this talk is just
focus on some of the chemical classes that we anticipate may have a greater affect on
the soil biology and function. And that’s Glyphosate and the Sulfonylureas. Glyphosate is highly contentious at the moment;
there is a lot of talk about Glyphosate in the public arena. Much of that’s probably
to do with big business and Monsanto but also the increasing use of Glyphosate also I think
has played into the minds of the public. But also farmers as well who are worried that
if they are relying too much on the Glyphosate aside from possible resistance in weeds species,
what is that doing to the soil. So from our review of the literature I’ve
just put together this table here as a bit of a broad-brush approach to suggest which
effects might be possible, the magnitude of any possible effects, so how far will it push
a particular function and how long will that affect last? So here I’ve got listed the two
main biological groups that we have classified in soil, the micro-biota and the meso-fauna,
and down here I have some of the major functions that contribute to crop productivity. So what we have found in terms of Glyphosate
with respect to Nitrogen cycling and Phosphorus availability there is not much data to suggest
that Glyphosate applied at label rates on broad-acre crops will have any impact on Nitrogen
availability and Phosphorus availability. There is some evidence to suggest that it
can shift the balance of the soil micro-biota, however this is just in a few studies and
generally speaking the effect will not last for more than 1 month. Interestingly I’ve
got here the direction of the effect, so is it a negative effects is it a suppression
of the micro-biota or a stimulation. Some studies have observed suppression and some
studies have observed stimulation. So this is really important as well, and what
does that mean for crop productivity. In terms of the meso-fauna, also some studies have
shown a few effects but overall most studies show that at label rates we have not seen
too many effects on the meso-fauna. Generally speaking if they don’t like it they will avoid
it, so they will move through the soil to areas where there is lower concentrations
of it. Again there this short duration of effect. What I’d like to focus on is these 2 aspects
here, Carbon turnover and disease. There is really quite a lot of data on the effects
of Glyphosate on Carbon turnover and there has also been a lot of attention on whether
or not Glyphosate impacts on the occurrence of disease, the likelihood of disease when
crops are being sprayed with Glyphosate. So this data here comes from about 40 different
papers, so all the data points have just been thrown together and what you’re looking at
is the effect of a Glyphosate application to soil on respiration, so CO2 emissions from
soil. On the X axis here we’ve got the concentration in soil and I’ve just put it on a log scale
because some people are interested in what happens if you spill some pure chemical on
the soil, so these are very high concentrations. 1 represents 10mg/kg, 3 represents 1000mg/kg
so here we are getting very high concentrations in soil unlikely to be seen out on the farm
when you’re applying Glyphosate to a crop or a fallow. This here represents approximate the label
application rate. And what we have on the Y axis is the effect ratio. That means the
effect of Glyphosate compared to a control that does not receive Glyphosate. So a ratio
of 1 means that the respiration from a pot receiving Glyphosate is exactly the same as
the respiration from a control that has not received Glyphosate. If the data is above 1 that means that Glyphosate
has increased respiration relative to the control. If the number is less than 1 that
means that Glyphosate is suppressing respiration. I guess what is most noticeable here is the
scatter of data. So some studies observe suppression some studies observe an increase. But generally
speaking there is few significant effects and if there is an effect it’s usually not
more than 50% either way. At concentrations higher than label application
rates you can see here a stimulation of respiration. And generally this is put down to the fact
that Glyphosate contains both Phosphorus and Nitrogen and therefore provides additional
nutrients to stimulate Carbon Turnover. But really the take home message from this graph
is that at label application rates there is not much of an effect on Carbon turnover and
respiration from soil. This is the same data but looking at a duration
effect. So how does the effect change after Glyphosate has been applied to soil? And what’s
most noticeable here is that you get a large pulse of CO2 emitted soon after application
but this is attenuated over time so we get a drop off and after say a month there is
no real trend with respect to respiration. So you can see here pretty clearly that any
effect of the herbicide is strongly observed in the short term but over time the effect
dies down and this could be due to a number of factors but probably mostly likely is the
fact that with respect to Glyphosate at least it has a strong affinity to soil and becomes
less bio-available over time. Most herbicides are also transformed, so degraded over time,
and herbicides won’t have such a strong effect once their concentrations are reduced in the
soil. So just moving onto the impact of Glyphosate
on disease. This is a recent review that has summarised much of the data on the impacts
of Glyphosate on pathogens and plant disease and the authors conclude that most of the
available data supports the view that neither Glyphosate resistance trans-genes nor Glyphosate
use in Glyphosate resistance crops increases crop disease. However they also point out
that there may be effects of Glyphosate in transgenic crops to do with mineral, nutrition
and or disease under particular but uncommon conditions eg specific soil, environmental
conditions, particular crops or Glyphosate formulations. So this really highlights the
complexity in teasing out systematic affects of any chemical and note that here we are
just looking at Glyphosate we are not looking at the entire spectrum of herbicides that
may be used on crops. The reason that Glyphosate could have particular
impacts in certain systems and in certain soil types is that the ecology of pathogens
is highly complex and Glyphosate might interact with any component of that interaction. So
you can see here that not only can a herbicide increase the incidence of disease but in some
circumstances the herbicide can also assist in reducing disease. So herbicides can have
direct impacts on the pathogen and like we saw Glyphosate has an impact on amino-acid
synthesis in micro-organisms and depending on the particular microbial species if they
have an enzyme that is sensitive to Glyphosate they may be inhibited. So whether or not that
occurs to a pathogen or it may occur to a plant growth promoting micro-organism, can
change the balance of the microbial species in the soil and that could be for the worse
or it could be for the better. Herbicides applied to the plant may also have an indirect
through the plant. So if there are low level impacts on the plant that may not be visible
this does not mean that they haven’t been changed, that their biochemistry has not changed
in response. And they may signal this change within the plant through the roots to the
microbial community and again this can result in increased disease or could actually reduce
disease. So again you can see the complexity of the interaction and the fact that we really
need to tease out under what circumstances we might be seeing more disease or not. Moving onto the Sulfonylureas, you can see
here that there is a lot less data than there is for Glyphosate and not many studies are
focused on disease or the meso-fauna. What we have found though is that there appears
to be quite an interesting effect on Nitrogen cycling. So I’ve put here as a possible effect
on Nitrogen cycling. Again the duration of the effect doesn’t seem to be more than 1
month in the short term but unlike Glyphosate where we are seeing some increases and some
decreases of impacts on functions here generally the Sulfonylureas seem to have a negative
impact. So this slide shows an accumulation of data
from 4 different studies. 1 of which looked at the long term impacts of Sulfonylureas
on soybean, which I have here the 5 year study and in this diagram CR stands for Conventional
Rate and these arrows represent whether or not the herbicide has an impact and which
direction that impact might be on particular process. So here we have Nitrogen fixation
and in 1 study it was shown that repeated applications of Chlormuronethyl. Over 5 years
had a consistent negative impact on nitrogen fixation it reduced the diversity of nitrogen
fixing organisms and also reduced the amount of nitrogen fixation in soybean plants. Some short term impacts have also been observed
in other studies to do with mineralisation of organic N so conversion to ammonium and
also nitrification the conversion of ammonium to nitrate. But in these studies, for example
here, these effects did not occur until the concentration reached 10 times the label application
rate. So as you can see the duration of the effect was less than a week, so that microbial
populations and that process returned to normal in a period of less than 1 week. In terms
of nitrification though, there seems to be more of an impact at conventional rates. Again
the affect is temporary, but it is happening at conventional rates in these studies. Interestingly here although there is a negative
impact on nitrification depending on what the farmer wants this may actually be beneficial
to crop production. So many farmers now are applying synthetic nitrification inhibitors
to slow down that process and draw out the conversion of ammonium to nitrate to give
a longer term supply of nitrate to the crop. So even though there might be this effect
on the soil whether or not that’s a bad thing may depend on the situation. So I just wanted to focus a bit more on this
effect here of the repeated applications of Chlormuronethyl to soybean. The reason that
they saw depressed functional responses there over a long term was put down to the fact
that they also found residues of this herbicide were accumulating over time. So here you can
see the treatment with no herbicide treatment of the herbicide for 5 years and application
of the herbicide for 10 years annually. And what you can see in the corner here is the
level of Chlormuronethyl at the start of the experiment using soil from those treatments.
And you can see an increasing amount of the residue in the soil over time. So that then
any additional applications of herbicide are lifting the residue level above what it would
be had that herbicide not been applied to the fields before. So what we are getting
is an accumulation of herbicide residues and they are not breaking down fast enough in
that soil. Quite a bit of work has been done in Australia
looking at the degradation of Sulfonylureas in soils and there is a strong pH affect,
such that at neutral and alkaline pH these herbicides tend to persist a lot longer whereas
if they are being applied in quite acid soils, so less than pH 5, then they will degrade
a lot faster. So as you can see the magnitude and duration of the response of any soil biota
will depend a lot on the concentration of the herbicide remaining in the soil. So just to wrap it up: Overall in our literature
review we didn’t come across any red flags to suggest that there are some irreversible
detrimental impacts to soil function in the short term. What we did find though is that
the ALS inhibitor group, group B, the Sulfonylureas in particular, could pose a relatively higher
risk than some of the other classes especially with regard to nitrogen cycling. In terms
of Glyphosate despite the increased use there is no systematic evidence for enduring impacts
of Glyphosate across soils but this doesn’t rule out the fact there could be some less
common site specific effects, particularly with respect to disease interactions. But I guess overall what we did find is that
there is a lot of knowledge gaps particularly regarding the chronic affects of long term
repeat application. And I think anecdotally that is what farmers are most interested in.
So how does their herbicide application schedule and regime over a number of years start to
impact on soil function? And if farmers are applying similar herbicides that are not degrading
in soil then that could really pose some problems down the track. But what we really need is
to undertake a lot more modelling to work out how the herbicides move and are transformed
in soil so that we can predict effects over time and work out whether these effects are
going to be a short term impact that may fix itself overtime or whether they will have
some longer lasting impacts on the capacity of soil for crop production. So I’ll leave it there. I’d just like to acknowledge as well Abby
for organising the webinar series and also the project team members for contributing
to this presentation and the work that’s been done so far and also to GRDC in particularly
Martin Blumenthal for his assistance. I’ll leave it there and happy to take questions. Thanks very much Mick that was really great
and I suspect that lots of people will be interested in the research that’s going to
come out of the next part of the project as well. Janelle Jenkins wanted to know if the review
has been published Mick. Not yet Janelle. It’s nearing the point where
we can send it in to GRDC for comment, but should be published soon and I’m sure it would
be OK if you are really keen to have a read then I’m sure we could send you a draft. So it’s best to get in contact with you about
that. Yes. The next person to ask a question is Steve
Kimber, off you go Steve Mick can you make a comment on how many of
the studies enabled you to discriminate the difference between the affect of the active
ingredient on the function versus formulation effects? Yeah, that’s a very good question. Probably
about half the studies used the active ingredient alone and probably about half the studies
applied the, or 1 or more, commercial formulations. However very few studies actually compare,
within an experiment, the active to a commercial formulation. From the few studies that are
available, and this includes insecticides and fungicides as well, generally speaking
it appears that the formulation will have more of an impact than the active ingredient
alone. Whether or not that’s a synergistic effect of both the active ingredient and other
compounds with in the formulation or whether its an impact mainly due to the other compounds
in the formulation is really yet to be determined. So as part of the project I think that will
be something we’re really targeting. From a regulatory point of view APVMA are probably
most interested in the actives however from a practical point of view I think most farmers
won’t really care about the actives so much as to whether the products they’re using are
having an impact. Mick can you just clarify that when you say
formulations you mean the added things that are put within the herbicides to make them
stick to soil or whatever. Just to clarify that for everyone. That’s right. So there is a number of different
compounds that could be in the herbicide formulations that could be having that effect. Our next question is from Rai Kookhana. Off
you go. Hello Mick. Thanks for the webinar it was
really enjoyable and also it confirms, we did a study a few years ago for Rural Industries
Research and Development Corporation for the impact of herbicides and we found similar
things, in fact for herbicide generally you don’t find much impact on the soil microbial
health as far as that’s the way that review was concerned and your findings kind of confirm
that. The one technical point was that particularly for the Glyphosate data when you see, when
you were looking at the respiration data and particularly increased respiration, sometimes
increased respiration is also an indicator of stress, so under stress the micro-organisms
can respire more and so that’s not necessarily just kind of conclusive of that, just that
it doesn’t have an effect and may not necessarily be driven by the nutrients because the nutrient
fraction if you like addition coming through the Glyphosate is not likely to be that significant
to convert into. But that’s an element worth looking at. I assume the focus of this project is purely
on herbicides and I was wondering because probably any concern about the potential impact
on soil health or microbial health is likely to emerge from insecticides and obviously
grain industry, certain grain production systems use insecticides, and I just wonder whether
that is excluded from this current project? Thanks Rai. I’ll just quickly address the
first comment. I completely agree with the respiration data and the fact that that might
indicate a stress to the organisms. I didn’t show it there but we also have pulled out
some data from the microbial biomass in some of those studies so that together with the
respiration and the actual microbial biomass we can start to address whether those respiration
effects are a stress related effect or whether it is resulting from an increased biomass
within the soil. It’s a really good point and something that we need to keep in consideration. With respect to the second question: This
project is focused solely on herbicides and I think for the grains industry that’s mainly
because of the volume of herbicide that’s used relative to insecticides and fungicides.
So I think there is probably about 4 times as much herbicide used as insecticide or perhaps
even more and similarly 5-10 times as much herbicides as fungicide, but I agree that
fungicides in particular that are targeted to kill fungi that may or may not impact on
plant health for beneficial reasons is also of great interest. So hopefully we can look
at some aspects of that down the track, but really this current project is just looking
at herbicides. Thanks Rai Our next question is from, Lukas, would you
like to ask your question Mick how many of the studies looked at herbicide
mixtures, cause I certainly know that in the eco-toxicological assessment of other pollutants
it’s often found that mixtures of chemicals can be far more toxic I guess than the sum
of the individual parts. Can you comment on that and whether you’ve found the same results
for herbicides? I guess as with the formulation vs the active
there’s actually not that much data about herbicide mixtures out there and the data
that is available is often from studies that have been conducted in the field that have
perhaps not put in places many experimental controls as other studies so that it is really
difficult to interpret what might be happening in terms of effects of herbicide mixtures.
And again the data’s really inconsistent some of the studies that I have actually read have
shown that some mixtures negate the effects of each other so that when the compounds are
placed individually they might come across with a negative impact but when they are put
together that negative impact disappears. Again it’s very inconsistent but there is
a big lack of data and particularly quality data I think from that point of view. I guess one of the things that needs to be
pointed out as well with the herbicides is that the other key mechanisms for weed control
is mechanical tillage and what would the relative destruction of soil processes be from herbicide
compared to mechanical tillage. Yeah that’s right. I suggest it would be quite
high. But again I’m not sure there has been too many studies looking directly at that
as well. There has also been a few studies looking at the relative effect of pesticides
vs fertilisers and interestingly a few of those studies have shown that some fertiliser
will have a more severe effect in the short term than the pesticides will. I guess it just raises the point that these
types of studies we shouldn’t just be looking at purely at a laboratory study at the impact
of Glyphosate on a particular soil function, it has to be taken into consideration in a
farming system. So what’s the overall impact of these particular practices? Sure. Thanks Lukas, they are good comments. Douglas
Fox has a question. I look at soil function and it’s a medium
to stand a plant but it is actually a home of microbial life. And it seems we know less
than 20% of what the microbial life does in the soil I feel it is very difficult to understand
what effect it has on the percentage we do not know. Thankyou. I would agree entirely with that comment and
I think that’s really something that we’ll have a lot of difficulty coming to terms with.
I guess there is kind of 2 ways of looking at the problem whether we work from the top
down or the bottom up so whether we drill right in and try and work out what’s happening
to individual microbial species or taxa and then try to work out how that all fits together
to have an impact on crop function or whether we keep an eye out in the field to whether
we are seeing a particular effect and then try and tease out what might be causing that
effect but I agree that its going to be very difficult to work that out. Thanks Douglas. Our last question comes from
Carol Rose. So I have unmuted you Carol and you can ask your several questions I notice. I’ll only ask one of them. Mick, in the experiment,
is the carbon that is the result of the death of the plant, which is the way you’re using
the herbicide in the first place, is that taken into account? No. Many studies that have been done in the
laboratories focus solely on a bare soil with a herbicide being applied to that soil. Whereas
in the field, there have been good field studies done, particularly from David Wardal who is
originally NZ, and they have done a lot of longer term field studies and they point out
that has a large impact so rather than the herbicide having direct impacts on soil biology
the effects that they have observed they put down more to the indirect effects in the larger
system. So the removal of weeds from a system, although in the short term, you know that
that has a carbon input into the soil if the weeds were left there and allowed to grow
there is a lot more carbon goes into the system in that kind of natural state. So the question
of direct vs indirect effects is also another challenge. Carol do you want to ask your other question,
I thought it was a good one. The experiments looking at herbicide and nutrient
interaction. So if for instance farmers don’t do herbicides alone, they do fertiliser applications
at the same time. I have not come across one study looking at
that. But it is an excellent point. The studies I have seen with regards to fertilisers generally
keep them separate so that they are looking at the impact of a fertiliser vs an impact
of a pesticide. But I guess a lot of the studies would use agricultural soils that have a reasonable
level of nutrition inherently through past fertiliser practices but in terms of controlled
experiments I no, haven’t really come across many. You made that point that the nutrient within
the herbicide could be having an effect so if you got urea put on at the same time there
is a whole compounding issue. Yeah that’s right. I think the point that
Rai made as well is quite important there that some of these studies where they do see
an effect of nutrients from herbicides are those studies where the herbicide has been
applied 10-100 times the label rate, so when the herbicides are applied at the label rate
really the amounts are quite small and they may, those nutrients might be available to
a select component of the micro-biota but in terms of the greater context how much impact
that’s having is another good question. It could also be a solution for farmers if
you can show something will ameliorate an affect. Yeah that’s right. From the point of view
of herbicides having kind of fungicidal activity that was something of interest that I hadn’t
anticipated but some of the herbicides also counteracting pathogens and the impact of
for example the SU’s on nitrification if its working as a nitrification inhibitor. There
is kind of some unintended consequences that might be more beneficial than detrimental. OK thanks again Mick for your time, I think
it was really interesting and useful and as we see there is many more questions to be
answered which should keep people busy for a long term. Thank you very much again and
thank you everyone who attended and hopefully we’ll see you again next month for the next
webinar which is slightly different. It’s all about the new espade platform from the
OEH and how to integrate that for soils information so if you are interested in that look out
for the invitation. Thank you once again everyone and we’ll see you again
Bye

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