To till or not to till.
That's the tough question that I'm going to be addressing in this presentation.
It was the topic that I was asked to talk about
at the Ecological Farming Conference that was in California this past January
and also at this California Climate and Agriculture Summit
that was a UC Davis in February of this year.
It's important to keep in mind when I'm talking about this
that I actually have a lot of experience not in no- till systems
but in highly tilled systems. So in these two pictures here this is
more typical of what I work in.
This is a vegetable production system
and this system here's another one that I work in
which is strawberry production. And even in these we do a lot of tillage
so just keep that in mind as I go through his presentation that I actually have a lot more experience with highly
tilled systems than I do with no tilled systems.
I like this quote and I think it's an important one to kind of start a presentation like this because one of the reasons we're interested in reducing tillage
is because we want to make sure they were taking good care of our soil.
And I think it's important keep in mind that there really is just a thin layer on our planet that stands between us and starvation.
Now we also have to manage our water resources well.
This is a picture from California showing one of the reservoirs that was filled up with water this
past winter. So that's an important part of sustainability and preventing
major catastrophes in our agricultural systems. But also we need to keep in mind the
the climate. The thicker layer that surrounds our planet
which helps to allow us to farm productively. And we also need to acknowledge that us humans are having a
major effect on our climate. We're causing it to change and we need to carefully think about
that and figure ways so we can reduce our negative impacts on our climate.
I want to take you a little bit of a trip in his presentation, at least in the introduction. And what were going to do
is we're going to get onto this Hawaiian sailing canoe and sail over to Hawai'i.
This is actually a canoe which is on this voyage
and what the voyages is focused on is trying to set a course for a sustainable future.
This is something that I think is important for us to think about both in the water as well as on land.
And let's just assume that our canoe lands on this beach.
This is on the island of O'ahu.
It's a beach that I like quite a lot. It's over and the Kailua area. And you'll see these beautiful
scenes like this. But if you look carefully into the sand you'll see a lot of pieces of plastic
these are called micro plastics.
And they're clear evidence that us humans are having an effect on our environment.
And that's kind of an interesting analogy that I'd like to is draw on for this presentation.
What I'm going to do today is I'm going to show you little pieces of evidence to try to
get at this question of whether or not we should or should not be tilling in our agricultural systems.
So kind of keep that picture in your mind as we go through this.
Now an important thing that I often think of when I'm trying to understand a new area for
myself and I would consider
I wouldn't consider myself an expert and no-till at all. I would actually say that I'm pretty ignorant about it and so I went to the scientific
literature and here's a bunch of different titles that I read
and which I found helpful in understanding this. You might want to check these out as well.
One of the real interesting ones is this one is titled 'The soil carbon dilemma: shall we hoard it or use it?'
And it's kind of a neat idea because what the author Janzen
describes is thinking about soil carbon kind of like water in a dam. We can have that water be stored
or we can let that water out and it can actually generate some electricity, and some energy and do some work for us.
And the dilemma with soil carbon is that it's often most functional as it's being transformed
from solid carbon into...as it's decomposing really going back into CO2. And that's the dilemma we have is
should we hoard it or should we use it?
Well I think you may enjoy this paper where the author talks about that very eloquently.
Now before we talk about what may happen when we move from highly tilled systems like this in Salinas California into a
reduced tillage type system like this,
I think it's important to think about some of the benefits of tillage 'cause there are some benefits obviously.
It can reshape our landscape. These are two pictures one from Indonesia this is Bali Indonesia and this is Nepal.
And what you can notice in both of these is... people have put a lot of work into trying to transform these landscapes
to create these beautiful bench terraces which allowed them to reduce soil erosion and therefore farm those areas much more
sustainable than if it didn't have these structures.
So that's clearly a very intensive form of tillage and one which has allowed people to farm in
areas that they normally would not been able to farm.
Now another real important part of tillage is adding organic matter back to the soil and these three shots here show
some parts of that in Papua New Guinea where I grew up. So this man is making sweet potato mounds which will be filled with organic matter
like previous crop residue or weeds or different types of organic matter in the center of the mound.
And then as that material decomposes it will be releasing nutrients which are
helping subsequent crop like sweet potatoes to grow.
So incorporating organic matter into the soil allows that to decompose and then provide a lot of benefits for us.
Now another real obvious benefit of tillage is to reduce compaction
This picture down here shows a lettuce harvest in Salinas and you can see how we've got these big ruts left in the fields from the harvest operation.
And here's another example of this and a broccoli field. So after harvesting broccoli or lettuce we often have real rutted up fields
and we need to try to get rid of this compaction in these areas so that it doesn't create problems for our next crops.
Another reason that we would incorporate or use tillage in the systems would be.... say you have a crop failure.
For some reason this spinach crop wasn't harvested
It could be several reasons maybe it had disease in it that that wasn't... didn't make the crop marketable. And so they need to quickly
turn this field around and the easiest way to do that is to come in and till out this spinach so they
can get this field ready for the next crop of vegetables.
Now very obvious reason for tillage that I'm sure a lot of people think about is reducing weeds. What we don't to have is we don't want
a situation like this in romaine lettuce where we've got a lot of weeds. The weed here is burning nettle
and this is a real challenging weed to work with because it will actually sting you and your hands
or on any of your sensitive skin. And so we don't want situations like this and therefore we put a
lot of time and effort into tilling those systems with a
special cultivator like this and also using hoes to take out those weeds.
Those are forms of tillage that are very important in these vegetables systems.
Now there are many problems with tillage and these four pictures show some of those problems.
When we till the soil we can create a lot of dust and that
degrades the air quality. Also when we've got bare fields from tillage
we can have a lot of soil erosion, a lot of nutrient loss, and that's not very good. And that can lead to fields like this in Thailand where I
worked where you lost yields because so much of this topsoil had eroded off.
And of course when we till our agricultural soils
it takes a lot of energy and that actually can create problems
because we're actually letting a lot of CO2 backup into the air from the use of the fossil fuels, the excessive use of fossil fuels.
One of the publications that are listed on the reading list has is very nice figure that talks about some milestones in agriculture
and the development of different tillage tools and tillage practices over time. I think you might enjoy checking this out.
I've been interested in tillage tools for quite a long time and here's three that I've collected in
different parts of the world where I've either lived and traveled. The first one here this is a
hoe from Nepal. This would have been what they might have used to make some of those bench terraces. This over here is a
short handled hoe from Zambia. They also make longer handled versions of this. This is in Southern Africa.
And this center one this is a digging stick from Papua New Guinea where I grew up.
And this would have been used for harvesting sweet potatoes.
In general I think that when people were using these types of tillage tools where all the energy to make the tool work
came from food that they had eaten. It's unlikely that they were tilling excessively.
I generally think that when we started sitting on tractors and using fossil fuels
that's probably when the excessive tillage began. Just something to keep in mind as we think about tillage in different parts of the world
and whether or not we should or should not be tilling.
Let's look at a little bit of data here. So this is
a graph taken from a paper that describes changes in soil organic of carbon, on the Y axis
and how the changed over a period of intensive vegetable production. So you can see early on
before that field had been cultivated when it was just naturally
left on its own, the soil organic carbon levels were quite high and that over time they've dropped
especially during say the first 10 to 20 years... big drop there.
And they slowly start to kind of stabilize but
there's a big decline. And that just shows how intense vegetable production can be quite challenging or
have a real negative effect on soil organic carbon levels in these fields.
This is a very dramatic shot that shows that in a different way.
So this picture was taken from this publication here
and this pipe in the center, this white pipe was actually... the soil surface was up here
in about 1923 when this pipe was installed. The pipe goes right down to the bedrock and this soil in this farmed area
had been drained. So it was a very high organic matter soil and it had been drained and then put
into sugar cane cultivation. And you can see that about 1.5 m
several feet of topsoil had subsided here. So a lot of that subsidence has to do with the fact that
in this soil, carbon was being burned up through the drainage of the soil and then the
cultivation of the sugar cane that followed.
Okay so now that we've seen very clearly that intensive tillage as you can see in this graph here has a
major negative effect on soil carbon or soil organic matter,
I want to move on to talk and show you some data on how conventional tillage would compare with say no-till.
So to help to understand what I mean by no-till let me show you this nice graphic. This graphic I think provides a
very clear illustration of the differences between no-till agriculture
conservation tillage and then conventional tillage.
So the data that I'm going to show you is comparing
conventional tillage with no-till. So these are on opposite sides of this spectrum
with conservation tillage being somewhere in the middle. So in a conventional tillage system in this
case this would be an example with corn-soybean crop rotations
in the U.S. you can see there's many many different tillage passes, one with the moldboard plow then with a disc
then a field cultivator and then different harrows and things like that.
Whereas with a no-till system
the only real tillage that occurs, and there is a small amount of tillage that does occur,
and that's when you plant the seeds in just a small slot where the seed is drilled into the soil
that's the only
time that the soil is disturbed. Other than that you just apply an herbicide to kill the weeds, you
you plant the crop with a no-till seeder, you apply an herbicide
in this case this would be in a conventional situation to control weeds again
and then you come in and harvest.
So as you can imagine there's a lot more crop residue on the surface here in this no till system.
Now in a conservation tillage system there's generally about 30% or more surface residue
there still is tillage in it but it's far less than say in the conventionally tilled system.
So if you're interested in understanding these differences I suggest that you have a closer look
at this nice illustration because I think it really
it does a good job of, in a nutshell, showing the differences between these different systems.
Okay so what happens when you move from a convention tilled system like this
into a no-till or a reduced tillage system?
Well there's a lot of things that can change
Let's look a little bit at some more data.
So this shows long-term organic soil carbon level changes
as we go from say
taking an area into cultivation
and then going into some kind of an improved management practice.
So you can see this is the soil organic cabon level at the beginning
its natural level it would not have been changing very much
and then we start doing some kind of cultivation and right away just like I showed you on that previous slide it drops down.
This is because the input of carbon is less than the decomposition rate
so you're getting a quick loss of organic matter in these system.
And then eventually the levels of input of soil carbon and the decomposition rate kind of equal each other so that we get a steady state system.
And then we start some new practice, maybe its cover cropping
and we start to get an increase in soil organic carbon levels.
But notice it never really, kind of gets back up to this level here it stabilizes at some other level.
So keep in mind early on there is a quick decline or relatively quick decline and
before we get to another steady state it takes quite a bit of time
and the steady state that we reach generally does not usually go back to the original state when the system was not in agriculture.
Okay, now I'm going to show you several different graphs that provide some interesting data on what happens
in a conventionally tilled system versus a no-till system.
And all the graphs are going to look somewhat similar to this, so I need to explain a few things here.
So this paper that this comes from they conducted a meta-analysis which is where they've taken the results of many many
different studies and they've combined them to try to get a whole bunch of information that's very robust.
This is the average point right here in this error bar right here represents a 95% confidence interval.
So this means that we can essentially be 95% confident
that the real number falls within this range here.
So it's a good way to estimate where an effect is.
Also I should point out that this 'n' here this indicates the number of observations
that went in to make this mean or this average and it's 95% confidence interval.
Now in these graphs if the average like this falls on this side, then this would mean that conventional tillage is better
And if the average falls on this side than it would mean that no-till is better.
So this first one we're looking at the mean difference in soil organic carbon
in conventional versus no-tilled systems. And you can see that...
oh actually I should point out what the zero is. So the zero would indicate
no change, okay, so no change there. Let's look at what's happening in say the top of top say 5 centimeters of depth of the soil.
So at 5 cm it's very clear that there's an increase in the
mega grams of carbon per hectare. So we've got about 3 Mg of carbon per hectare more in the no-till system.
This makes sense because there's a lot of residue on the soil surface.
Now when you look say 25 centimeters down, the situations not that clear, well actually it's the opposite it is relatively clear here
in this data. So we can see further down actually the the conventionally tilled systems
have got more carbon stocks at that depth.
What I want you to just kind of take away from this graph is that the sampling depth at which you
measure the effects of a conventional tilled system or a no-till system has a huge effect on how you would interpret
the data. When were looking near the soil surface no-till looks better.
But when we go a little bit deeper, conventional till looks better.
And actually when we go really deep say 45 to 55 cm
it doesn't look like there's much of a difference.
So I hope this is helping to you to understand the complexity of this issue of soil carbon sequestration.
So I hope this is helping to you to understand the complexity of this issue of soil carbon sequestration.
If were interested in sequestering carbon in the soil we have to really look carefully at different depths within the soil
and this paper really helped me to understand that complexity.
In that reading this I also listed this paper which is another one that kind of opened up my eyes to a new
way of thinking about stabilizing soil organic carbon in the soil
So let me try to walk you through this a little bit and hopefully I'll be able to explain this kind of new way of thinking about
soil carbon sequestration.
So let's start with this middle section here
as you I'm sure are aware there's many different qualities of soil or of plant litter that one can add to the soil.
You can add say leaves of legumes, things that are very easily decomposed. And then you can also add, on the other end of the spectrum
things like wood chips or more lignified material
And my initial way of thinking about carbon additions to the soil was that this type of material that decomposed slowly
would tend to increase soil organic matter more than
this material that would decompose more quickly.
However, this paper talks about... sort of a different way of thinking about this.
When plant litter that decomposes easily which we call 'labile' organic matter
When that decomposition process is occurring
there's a lot of decomposition products that are being produced
and those decomposition products are actually what's leading then down to more stable forms of soil organic matter in certain situations.
And this is compared to say the more lignified or the more woody materials
those don't have as many decomposition products and therefore their ability to
build up stable forms of soil organic matter
is not as great as say this material here.
The other thing that's intriguing is that these more labile or easily decomposed forms of organic matter or plant litter also tend to cause
less carbon fluxes or releases compared with these materials.
So as you think about soil carbon sequestration
I want you to try to keep this model in mind, or this framework
and I encourage you to go and check out this paper. I found it very intriguing.
I want to now move on and talk a little bit about how
no-till versus conventional till systems affect yield.
Okay let's look at another one of these graphs from another meta-analysis.
So we're looking at the effects of conventional till versus no-till on yield.
And this is taken from a large number of studies .... so 678 studies and about 6000 observations.
within those studies were what's used to make up this first data point.
So overall, over a whole bunch of different crops
generally, you can see this this dot here indicates the average,
generally what the data is showing is that
averaged across many different crops
conventional tilled systems
have about say 5 percent greater yield then no tilled systems.
Now if you look down say for oilseed or cotton type systems
the difference doesn't seem to be very much.
Maybe a slight indication that no-till might be a little bit better but this average this middle point is pretty much right on zero.
With legumes there's pretty much a clear difference or indication that
conventional tilled systems are better than no-tilled systems.
With root crops it's very dramatic say about 20% yield loss or greater yield
in a conventional tilled system versus a no tilled system.
So this really does show that the type of crop that you're talking about responds differently to no-till or tilled systems.
Here's another graph. Now we're going to look at the duration of the effect on yield.
So we've got here some studies that went for 1 to 2 years,
3 to 4 years, 5 to 10 years and then more than 10 years.
Again this is the the number of studies and then the number of studies...
I'm sorry this is the number of studies here, and this is the number of observations.
So studies that happened for say 1 to 2 years only, conventional did better
but over time if a study goes on for a longer period of time
the differences between tilled and no-tilled systems start to become less obvious.
So this data, the fact that the average is relatively close to zero would suggest that over time
averaged over many different crops
no-till and conventionally tilled systems may not have very big differences in their in their yield.
Okay let's look at one more graph from this meta-analysis and how no-till affects yield.
So what were going to look at here is the effect of climate.
In this graph what they've got is they're showing
tropical latitudes in the world, subtropical ones and then temperate latitudes.
And it should be quite clear right away that in tropical latitudes
conventional tillage generally yields quite a bit better than no-till does.
Whereas in temperate latitudes the differences between
conventional till and no-till are closer to zero. They still are generally favoring conventional till
but not near as much as is occurring in tropical latitudes.
So this just shows very clearly that where the tillage practices are done can have a huge effect on how the yields respond.
So just to kind of summarize a little bit, I've talked about two different meta-analyses
this first one where looked at whether or not no-till can stimulate carbon sequestration.
So generally what it showed me was it's a lot more complicated than just saying 'yes no-till is sequestering carbon.'
It really depends on the depth, and we probably ought to be sampling our soils much more deeply
like down to a meter so to see if the overall difference between tilled systems and no-till systems
really is that big of a difference.
Now the other meta-analysis that I talked about was this one where we looked at the effect of yield. We looked it overall a bunch of different
crops and then the effect of duration of the tillage practices and then also climate.
And I also encourage you to go and look at that paper in more detail.
Hopefully what this has shown you is that this question 'To till or not to till?' is a little more complicated
once you really get into the scientific literature and start looking at the data.
Now what I really want to focus on for the rest of this presentation is
some experiences that I've had with trying to reduce tillage in vegetables systems.
It's something that I think is really worthwhile trying to do but it's also pretty challenging.
So I'm going to talk about some of our experience with a roller-crimper and then with a mowed type system.
I want to explain the roller-crimper type system that we've been trying out at the USDA.
On the front 3 point hitch we've got a standard roller-crimper.
We've got that mounted on the front, we can raise and lower this as we need to
and that does a really good job of
crimping cover crops as we drive across the beds, and it crimps the cover crop that falls in the same direction as we're traveling.
Now one challenge that we have had sometimes is that
sometimes the cover crop falls parallel to these crimper blades and therefore
that material is not crimped very well by the front crimper.
So what we've done is we've taken a
tow attachment that can be used for say a grain drill
and we mounted a toolbar on the back of that
and so right now the tow attachment wheels are lifted off the ground and all the pressure is on these
this toolbar, and toolbar's got a series of
coulters, flutted coulters that are attached to that which have dulled blades. So the blades of these coulters have been dulled
and we're just towing this. And this allows us to crimp any material that falls perpendicular to the direction of the tractor's travel.
So between the front crimper
and then this rear tow type crimping system we're able to pretty much crimp material that falls in any direction.
So the idea in the system was that we would grow cover crops on beds like you can see here
and then we'd come in with our roller crimper
and we would crimp that down and then ideally we'd get this beautiful layer of mulch
right over the soil surface which would be suppressing weeds
and doing a bunch of other good things. And then we would be able to transplant say a romaine lettuce crop
into that and have a beautiful system.
So let me describe that in a little bit more detail.
In our systems these beds from center of this furrow to the center of this one would be about 80 inches wide.
And because our crimper works very well on the bed top we actually had to plant
something a little bit different in the furrow. We planted mustard.
And the mustard variety that we use has hollow stems and when we drive our tractors
in these furrows to crimp the bed top, the wheels are very effective at crimping the furrow mustard.
So here's a picture that shows our cover crop with the mustard in the furrows.
This is in January, the cover crop would have been planted in the previous year in the fall.
And you can see the rye has grown up quite nicely and the the mustard is here in the furrows.
Now let me show you what happens when we get in there and we crimp it.
So here's the tractor.
We don't have the rear crimper on there right now but we do use that.
So we've got the front crimper that's pushing down the cover crops on the beds
and then the wheels are crimping in the furrows and crimping off the mustard plants.
So this looked pretty good when we crimped it down.
But this is where we started to get concerned. About 54 days after we crimped this cover crop
we had all this green in the field and that green is essentially regrowth of a cover crop.
So the mustard in the furrows died very nicely
but the rye on the bed top
didn't die very well. Even though it was flowering when we crimped it we still had lots and lots of regrowth of our rye cover crop.
This really kind of got us concerned during the first year of the trial.
Now when we went to the second year
we tried this again and we actually had even worse results.
This time we got not just regrowth of cover crop but a massive amount of weed growth on these bed tops.
So these two experiences, that is the regrowth of the cover crop on the bed top and then massive amounts of weed growth coming up
through the cover crop mulch
really made us realize that the roller crimper
may not be the best tool for us to try to do a reduced tillage system in our vegetable systems.
So what we're trying now is a different system where we're
focusing on killing or controlling a cover crop's growth using a mower and then trying to kill it with another tool.
Let me kind of describe that.
So I've been working with my good friend Jim Leap on this. Jim is very good at understanding how different tillage tools work
and great at trying to innovate different methods.
And what we've been doing is we've been planting the rye on the bed top, these are again those 80 inch wide beds
and this case we're actually cultivating the furrows of the cover crop
and once the rye gets up, you know a certain height
we then start mowing it repeatedly.
And this kind of keeps the biomass under control so that it never kind of gets out of hand.
So here we're mowing the rye cover crop.
And then the idea is after we've mowed it several times as it's been growing
we then come in with this tool which is.. it's got rippers here in the furrow
there's actually a residue manager to clean out some of the furrow area
and there's a large flat coulter which cuts through some of that residue and then there's a large ripper shank which
rips into the furrow bottom and that allows us to take this next tool which is an undercutter and undercut this entire bed so we're basically
cutting off the root systems of this rye cover crop on the bed using his undercutter.
The shanks of these under cutters extend down and then somewhere down into the soil here
about say 3 to 4 to 6 inches or so deep we've got our blade of the undercutter which extends underneath here
and basically cuts off the root systems of the rye.
I'm going to show you a little video clip of this working.
Okay so you can see the undercover is moving along very nicely and is undercutting
that residue or those rye cover crops on the surface
and leaving the rye right in place but undercutting it. So hopefully it we'll kill it.
Now in this situation this is rye planted on 40 inch beds, we had two lines on a 40 inch bed
but the same basic idea could also work potentially with rye planted on an 80 inch bed.
I'd like to conclude by answering the question to till or not to till in high value vegetable systems.
and I'd like to do that by bringing in a few more images. So at the beginning of the presentation
I talked about this need for us to set a course for sustainable future
We looked at some evidence from the scientific literature
and hopefully that's inspired you to go and look at some of that evidence for yourself.
I find this image to be one that I think is helpful to answer the question of whether or not we should or should not be tilling.
So this is a sailboat, I love sailing, and
if we turn the sailboat around what you'll see in the back of the sailboat is this
part of the sailboat right here which I'm holding in my right hand. This part of the boat is called the tiller.
And the tiller is one the most important parts of the sailboat because it controls the rudder.
And when I'm sailing a sailboat if I don't have access to the tiller, the boats completely out of control.
You have to very carefully use that tiller and by doing that you can set a course and get to where you want to efficiently.
Without a tiller the sailboat is pretty worthless.
I tend to think that in high value vegetable systems
we need to still need to be using tillage. I don't think we should be abandoning tillage.
But I think we do need to be careful with how we use it.
Make sure that we're using it in a thoughtful way.
And also move towards reducing tillage where possible.
I do however think that there's some real low hanging fruit in our vegetable systems
that we should focus more on then just completely eliminating tillage.
And probably the most obvious low hanging fruit that I can think of is
the need for us to increase cover cropping.
And that's true in both conventional as well as organic vegetable systems.
So this picture shows two different ways that we can add carbon
into these high-value, high-input vegetable systems.
One way to do it would be by bringing in carbon from an outside source such as using yard waste compost
that's a very convenient way to add carbon to our systems.
But the other way which is one that I think we actually should be focusing much more on
is on-farm carbon production.
The reason that I think we need to do that is that these on-farm sources of carbon
provide so many more benefits to maintain a healthy soil and these vegetables systems.
When we grow cover crops there's a whole bunch of other benefits and that's kind of
well described in this paper that was published in 2010.
And in that paper the authors talk about carbon friendly farming practices.
So when you grow a winter cover crop you are adding large amounts of carbon to the soil
but in addition to that you're also reducing nitrate leaching
You're increasing the infiltration of winter rainfall
and that will hopefully increase our groundwater recharge
and were also providing habitat for beneficial insects
so because of all these co-benefits from cover cropping
I think that cover cropping is such an obvious low hanging fruit, it's one that we really need
to focus more on in our agricultural systems.
And try to help farmers come up with ways that they can incorporate these as often as possible.
I think that will do a lot to improve the sustainability of these systems even if they have a fair bit of tillage in them.
Now if you have any questions or comments to free to send me e-mail.
You also may enjoy checking out some of my publications that are all available for free on this web site.
take care
For more infomation >> Where is my mind? (2K) - Duration: 3:51. 
For more infomation >> 0017 - Duration: 8:02. 
For more infomation >> 0018 - Duration: 10:45. 
Không có nhận xét nào:
Đăng nhận xét