Hey everybody, welcome back! I want to do
a quick lecture on soil degradation and
conservation. It's kind of a good follow-up on the very last lecture that we did
which covered soil structure and plant
growth. These two lectures go very close...
hand-in-hand. In a lot of ways this is
kind of a part B or part 2 to that
lecture. So I wanted to continue going on
and if you haven't watched that lecture
yet, watch that one before you jump into
this one just to make sure that you're
fresh on the ideas that we're gonna be
talking about, OK. So we've been talking
about soil degradation and conservation.
That former lecture deals with the
origins of soils where they come from
what a healthy soil looks like and how
it operates. This talks about how these
things can be disrupted. Alright, so
let's jump into this lecture and I think
you're gonna really like it.
So damage to soil and land makes
conservation vital. Conservation of soils
that is. It turns out soils are a natural
resource that can be abused, it can be
damaged to the point where it becomes
non-renewable. It takes sometimes decades,
sometimes hundreds of years, sometimes
thousands of years for soils to return
after they've been improperly dealt with.
So let's talk about what soil
degradation is so. Soil degradation is a
decline in soil quality and productivity.
This can occur due to deforestation,
cropland agriculture, and overgrazing.
Those are things that we mentioned in
the last video which is the reason why I
was emphasizing you want to make sure
that you watched that before you watch
this one, okay. So over the past 50 years,
soil degradation has reduced potential
food crop production by about 13 percent.
OK. So soils do lose their ability to
give good, consistent, sustainable plant
growth if they are not treated properly.
OK. So land degradation is a general
deterioration of land, decreasing its
productivity and biodiversity. So this
could be due to erosion, nutrient
depletion, right. So you're growing the
same crop every single year and you're
not returning the nutrients that's going
to wind
causing the productivity of the land to
go down. Water scarcity. Right. If you take
the water and you funnel it off into a
different direction that can be a
problem. Salinization...this is something
you're going to learn a lot about today...
waterlogging and chemical pollution. OK.
So here we see a degraded...the soil is
very strongly degraded in this field. In
this case it's mainly due to erosion
where the nutrients are being washed off.
This fertile topsoil in the A-horizon
is being completely removed due to
the way that the water is running off
this field. There's no cover crop, there's
nothing to protect it. OK. We're gonna
talk about those things during this
lecture, over the next couple of slides.
So, what is erosion? So erosion is simply
the removal of material from one place
to another by wind or water. So here we
see deep erosion in these gullies right
here. Here's a creek of some sort. It's a
dry creek and in other words it only
probably has water in it when it rains
or whenever there's a major storm event
in the area. And then next to it we see
these deep erosion gullies that feed
sediment down into that particular creek
or river. OK.
Deposition is the arrival of eroded
material at a new location. So here we
see erosion, which is moving that
material down into this creek, this creek
is then going to transport this sediment...
it's either going to be to the right or
to the left, I'm not sure which direction
this creek goes, but it's going to move
it away from this location...and it's
going to deposit it at a new location. So
the nutrients that used to be here won't
be here for long. If it's eroded they'll
be transported elsewhere. As a
consequence, flowing water deposits
nutrient-rich sediment in river valleys
and deltas. So wherever it's going is
going to be the benefactor of the
erosion that's happening here. Now this
area here is not going to benefit
obviously. This is not a great place to
grow crops because of the high level of
erosion that happens here. As a
consequence, floodplains are excellent for farming and when we go to
many of the great floodplain areas of
the world,
whether it be in China or its in Egypt
or if it's in the Midwest or in the
Mississippi River Valley, we find a lot
of crops growing within these floodplains
largely because the nutrients that are
collected there, that nutrient-rich
sediment, is very good for farming. Now
erosion, today, occurs faster than soil is
formed and this is a major problem. So if
you're removing the soil faster than its
forming, you're gonna get an imbalance,
right. And it starts to become more
non-renewable of a resource than a
renewable one. It tends to remove the
topsoil which is of course the most
valuable layer for plant growth. And
again, we talked about that in the last
video. That's that valuable O and A
horizon right at the very top where all
of the vibrant activity happens in soil.
Now in terms of how erosion threatens
ecosystems and agriculture, there's a lot...
well, there's a lot of ways it could
happen. First off windy regions with
sparse plant cover suffer from wind
erosion. And so this is a common issue in
in deserts for example. Areas with steep
slopes, these are hillsides, right...high
precipitation, and little plant cover
suffer from water erosion as well. So if
it's raining all the time, you don't have
the plant growth to hold everything down,
you're going to get a huge amount of
things washing off those hills. This is a
common problem in places like the
Himalaya and northern India were you have high
mountains; even in parts of the Rocky
Mountains we have issues like this in
the United States. Land is made more
vulnerable to erosion through a couple
of different things that humans can do.
Over-cultivating fields through poor
planning or excessive tilling is one way.
So if you're not being careful about the
way that you're going about your tilling
you can absolutely destroy that field. A
lot of the time we think "well, if I come
out and I till this field I'm actually
tending it, I'm taking care of it" when in
fact we can be doing the exact opposite.
We'll explain that point in a little bit. We
can over graze rangelands and we can do
clearing a forest on steep slopes or
with large clear-cut. So if we're going
to go out and, say, collect a bunch of
wood because we need the wood for our
building buildings or whatever
it is we need it for as a raw material, and
we just cut all the wood down, that
suddenly leaves a bald spot that can
then be subjected to immense amounts of
erosion. Overall US croplands lose
about 2.5 centimeters, which is about one
inch, so it's about the width of your
thumb...if you have a large thumb it's
about one inch...of topsoil every fifteen
to thirty years. So that's a lot. Right. In
some places, like the Amazon rainforest,
you might...a thick A-horizon might
only be eight inches thick, right. So it
won't take you very long to work your
way through it. In some places the
A-horizon is completely missing so you
just have O sitting right on top of B.
When that happens, you wipe out what's
there very, very quickly. So you have to
be very, very careful with how erosion
works. Alright. So things that we can do
to prevent soil loss include the way
that we manage our agriculture
specifically how we grow our plants. So
plants prevent soil of loss by slowing
wind and water flow. So you can imagine
that if water's going to fall...and say
it's raining...the water is going to
hit these leaves, the velocity of that
water is going to be slowed dow, it's
gonna drip down these plants. The plants
are actually gonna absorb a large amount
of that water out of that field. But in addition
to that they're...and as a consequence it
won't run off as quickly it'll slow and
it'll actually soak into
the ground as opposed to running off the
surface.  In addition to that, it'll
actually break up wind erosion. So wind
can be whistling along here right across
the top of these crops, but it's not down
here where the soil is. If the wind
started moving quickly down near where
the soil is it would actually come into
contact with these plants, these corn
stalks would actually break up that wind
and slow it down. OK. So it turns out
roots hold soil in place...it's very
effective at doing that...keeps it from
moving. Plants have a vested interest, of
course, in not having the soil move
around on them because they're anchored
to it and as a consequence they bind
that soil. No-till agriculture leaves
plant residues on
crops, er...on fields. So one of the things
you could do is, instead of tilling the
field all the time which rips up the
soil and exposes it to the atmosphere,
what you can do is you can just let the
cuttings from the previous year...
you know let's imagine that we have
these corn stalks we're going to collect
all the corn and then we just cut the
corn down and we let it fall back down
into the field and decompose, that
creates a ground cover, okay, and that
ground cover helps prevent erosion.
Another thing we can do is cover crops. So
cover crops protects soil between crop
plantings. So here we see corn that is
growing, but there's a cover crop in here...
mainly radishes and turnips that are
growing in here as well...and what that
does is it helps bind the soil when
we're not growing corn which is the
primary agricultural product they're
growing here at this location. OK. So
that cover crop protects the soil
between crop plantings and US farmlands
lose about five tons...this is a big deal...
five tons of soil for each ton of grain
harvested. That's an immense amount of
expense to the topsoil. So, think
about that, for every ton of grain you're
losing five tons of soil. That's not
sustainable. That's not supposed to
happen. If you produce a ton of grain
you're not supposed to lose any soil.
That's the goal, right. You don't even
want it to be one to one. You want it to
be zero tons of soil loss for every ton
of food grown. Sustainable soils do not
have these problems. Alright, so what
are the consequences of mismanagement of
the soil. Well, desertification is one of
these things. So desertification is a
form of land degradation with more than
a 10 percent loss of productivity. So
this means that 10 percent of the
biomass is reduced. You can't grow nearly
as much food, you won't get as much plant
growth out of it, and you'll see that
once desertification starts to happen it
will accelerate and get worse and worse
and eventually the end game is it
becomes a desert. Right. So
desertification is the process of becoming a
desert. Commonly or caused primarily by
wind and water erosion,
but also by deforestation, soil
compaction and overgrazing as well.
Another common way of seeing this happen
is drought, right. So droughts are
actually pretty normal and desertification
will happen whenever there's a
drought, but the way that we manage the
conditions that drought can be a big
deal as well because if it's a very dry
drought...in other words, it's lack of
water but we go and use, maybe we force
water into the field, that normally
shouldn't be there during a drought
condition you can create something
called "salinization." You can actually
salt that field by accident. And another
thing that might happen is water
depletion, right. Those all will cause
desertification. And of course climate
change, any type of climate change. If you
raise the temperature up in an
area that is susceptible to desertification...and we're going to talk about
that here in a moment...these things
called drylands are especially prone to
this...you can create large amounts of
stress on that soil, on that field, and on
that land.
OK. So arid and semiarid lands, called
drylands, are the most prone to desertification and they're not a small part of
the earth. It's about 40% of the Earth's
land surface, okay. That's a lot. How much
of it is caused by wind erosion? About
forty-one point eight percent according
to this plot that we have here, and
water erosion about forty-five point two.
We also have chemical problems...this is your
salinization and soil structure problems
that also happen. This could also be
caused by the way that we're pulling
plows through the soil and
ripping up that A-horizon...which normally
have good structure in it...we ripped
that structure up and it will actually
make it susceptible to erosion. Ao we
should be very careful about what we're
doing. Alright, so how do we come to learn
about this stuff? Why do we care so much
about soil degradation? Well when we
really had the biggest eye-opening
experience about soil degradation was
when something called the Dust Bowl
happened, especially in the United States,
in the 1930s. The Great Depression was
already happening and during the middle
of the Great Depression suddenly a large
series of dust storms starting to form
throughout the Midwest of the United
States.
This was a complete shock [compared] to anything that had
happened prior to that. In the
late-1800s, early-1900s, farmers and
ranchers, they grew wheat, they graze
cattle, they used unsuitable land, and
removed native grasses, but they didn't
think there was anything wrong with that,
right. There had never been a problem
before. They just saw the soil as this
limitless bounty that would always
produce the grasses that they needed to
take care of all of their life. And what
happened was, out of the blue, something
called the Dust Bowl. Massive dust storms
from erosion of millions of tons of
topsoil in 1930s. Drought also came in and
it worsened the human impacts and dust
storms travel up to 2,000 kilometers
which is about 1,250 miles. Thousands
of farmers left their land, many of
them went from...in the case of the United
States...from Oklahoma, many of them moved
to California. So California begin to
become very settled by people from the
Midwest right about that time in
response to that and there's several
great novels about that. So study your
American history and you'll come up with
that information. Of course, the Dust Bowl
did only happen here, there were dust
events that happened worldwide, but what
was really interesting was it happened
in the United States in an area where it
had never happened before and it opened
people's eyes to the fact that we can
abuse the earth so badly that it
basically collapses on us, okay. So what
we did was...we in the United States did...was to establish a soil conservation
service. So that happened in 1935.
The service works with farmers to
develop conservation plans for
individual farms. So basically the idea
is to come out and prevent this from
ever happening again and you do it
through education and by showing better
ways of these things happening, taking
into consideration the risks of
activities that we're doing, and where
that might lead. Ultimately we developed
a series of conservation districts, these
are districts that promote soil
conservation practices at the county
level, and they operate with federal
direction, authority, and funding and are
organized by the state. So this is a
state,
local, federal collaboration that's
designed to bring people together to
worry about the soil, to come to be
concerned about the soil, and to try to
conserve the soil. And in 1994, the
service was renamed the Natural
Resources Conservation Service and the
responsibilities expanded to also
include water quality, protection, and
pollution control. And this became a
model for a lot of the services that we
see across the world. OK. Soil is not
something we could take
advantage of and take for granted,
this is a resource that can be
absolutely devastated if we don't pay
attention to what we're doing. So some of
the ways that we can protect soils,
some of them are pretty innovative and
some are kind of obvious. One thing
that's been around for a very long time
is crop rotation. So crop rotation is
where we're growing different crops from
one year to the next. So this returns
nutrients to the soil because instead of
growing corn, which might extract certain
nutrients preferentially but leave the
others, which then depletes it...what you
do is you're constantly rotating
different plants in the areas that use
different nutrients and different
amounts and therefore it gives the soil
the opportunity to rest between
plantings. OK. It prevents erosion and
reduces pests. If you have a lot of the
same thing in an area you're gonna
attract the pests of that thing. So if
you're always growing corn in a field
every single year then if...say in year
one you're gonna grow up corn you might
not have a problem; by year two, year
three, year four the pests are going
to start to build up to the point where
you maybe have to use pesticides to be
able to deal the problem. Through crop
rotation it's possible that you might
have a little bit of pest problem maybe
in year one or year two, but then as you
rotate that back out then the pests,
who've maybe...let's say it's a pest that
that is attracted to corn...and then you
rotate in instead of corn soybeans, you
might not get as many pests in that
field because they haven't established
themselves to that location yet. Like
crop rotation no-till farmers may
alternate wheat or corn with nitrogen-fixing soybeans.
And that's, that's actually a pretty
common practice in a large, in a lot of
places that engage in crop rotation.
Contour farming is another kind of
interesting thing. This is really
designed for stopping erosion. So here we
see contour farming. And so we
see these these furrows going around and
around and around, and what they're doing
is they're plowing furrows sideways
across the hillside perpendicular to its
slope. And the reason why is they don't
want the water to run right off the hill
and create water erosion and hillside
erosion. What they're doing is they're
actually trapping the water and forcing it
into the soil so the water has value to
those crops while at the same time
preventing erosion. So contour farming is
another way that we can do this. And
another thing that's been going on for a
very long time that's a very old
practice is terracing. Terracing is
cutting level platforms into steep hill
sides. So here we see terracing here.
The steps of the staircase do hold
large amounts of water. Now, on the one
hand you can...this allows you to go grow
a tremendous amount of food right here
in these terraces, and you can feed a lot
of people in this way. On the flip side
of this, it's also extremely dangerous
because now you have water and mud
sitting on these terraces on these
hillsides and if it fails...
remember this is a lot of water so it's
a lot of weight, a lot of soil, a lot of
weight's gonna be there...and if it fails
it's going to catastrophically
go down into the valley and it could
cause a mudslide that would take many
lives. So terracing has its ups and downs
but for the most part it's a good way to
begin feeding large numbers of people
using land that is normally not
available to us; because hillsides, you
know, they erode easily. It's hard to
access. Terracing seams to correct that
problem. Another process that we've
picked up is intercropping. So instead,
you know, sometimes you might say "well, I
don't want to just grow corn this year
and I don't want to just grow soybeans,
I want to grow several things" and so we
can intercrop which is of course a form
of polyculture. So intercropping is
planting different crops in alternating
bands or mixed arrangements. This
increases the ground cover and it
prevents
erosion by doing so. It decreases pests and
disease because you're bringing in so
many things that the pests don't really
build up on one thing and even then
those pests might compete with each
other for that particular area. So
there's a natural suppression of the
pests in that area. And then you'll also
get the replenishment of the
soil over time because you might move
these crops
year after year to different spots in
the farm all the same time growing all
of these things at the same time.
Shelterbelts are, also known as wind
breaks in the western part of the United
States, but shelterbelts are rows of
trees that are planted along the edges
of fields to slow the wind. When I was
growing up in Southern California, wind
brakes were all over the place. They were
usually planted with eucalyptus trees
which were imported from Australia...so
they're non-native to the United States
but it turns out they're very effective
at stopping the wind and it's not
uncommon to see them. This is...these are shelter belts right here, and
so here's the farm or the field and then
the wind is blocked by these tall trees
that  hedge in or block in that field.
And it can be combined with
intercropping. So you can take
intercropping, you can take a field like
this one here and you could shelter belt
it. You could put these tall trees all
around it. Another thing that you can do
to stop a lot of the erosion and the
degradation is conservation tillage. This is strategies that reduce the
amount of tilling relative to
conventional farming. So this
usually entails leaving at least 30% of
crop residues in the field, and then of
course if you did no-till farming, this
is where you're leaving all the residues
in the field and then you don't till it,
you don't plow that field year after
year. You just come back and you grow it
again. So what we see here is
conservation tillage happening here
where there's still some of that old
material from the previous year's growth
is still in that field. It is now part of
the O-horizon that's
decomposing and it's becoming part of the
fertility of that field in the next year.
OK. A lot of fields and a lot of
farmers, they remove all of that stuff
and so the fertility has to be returned
through fertilizers which can be quite expensive.
And, of course, if you don't put some type
of cover crop or something that's going
to protect that field, it might be
subjected to erosion during the winter-
time.
Sometimes no-till farming...where you just
let the material die after you've
harvested the fruit part of it, let's
say it's corn you're going to remove the
corn...let the stock fall into the field
and become part of that O-horizon which
then introduces the fulvic and humic
acids and decomposition and all the
nutrients back into that soil, and you
need minimal amounts of fertilizer when
you're doing that type of thing. So
that's what we mean by conservation
tillage. So, in fact here's a
nice diagram or a nice image of a
no-till farmer that's growing corn. So
no-till farming has many
benefits. It increases the organic matter
and soil biota, it reduces erosion and
improve soil quality. So it...this
field by most people's guess or most
people's estimate of how fields should
look, looks like a mess. Right. There's all
the stock down here. It's almost like the
farmer didn't clean up after himself. And
in fact here's the farmer. It's almost
looks like he's lazy. But what's really
happening here is it's actually a
concerted effort...it's actually quite
intelligent. While we're doing is we're
growing corn, last year's corn crop is
dead, it's falling in here. The corn was
harvested off this and now it is part of the fertility into that field.
It uses less labour, right. You don't have
to go cut that stuff down, bale it up and
haul it out of the field. It saves time,
right. Because all you have to worry
about and focus on is growing that corn
and getting the corn...the actual
corn itself...removed where the
stock can remain behind. And it causes
less wear on machinery. In a lot of cases
all you need to do is come and pick the
corn and then you leave the stocks in
the field and you go past it. You don't
have to come in and till it up, you don't
have to change it, you just leave it as
it is. And we have a wonderful film that
I'm going to recommend at the end of it
that it gets into why no-till farming 
is actually better than coming in and
plowing that field every single year and
I highly recommend that you watch it.
Look out for that recommendation at the
end of the film. It also prevents carbon
from entering the atmosphere. So it's a
carbon storage, right. So all of this...the
old corn stalks here...remain in place.
They haven't burned, they haven't been
turned into fuel, they haven't been turned into food,
and they're therefore not radiated back
into the atmosphere through the metabolic processes of
decomposition...er, sorry...of the cattle that might be eating it or whatever. OK.
Reduces fuel, fossil fuel use due to less
use of tractors. You can see that there's
not a lot of tractor use here. Adds
organic matter to soils that is kept
from the atmosphere. It's got a little
reference here to the science of soil
health which is something that you can
google up and it should have a little
bullet point over here. If you're
interested in soil health, no-till is one
of those things that comes up right away.
Alright, so from the previous slides I
think it's pretty clear that plant cover
is the key to erosion control. There's a
lot of methods that we can use to reduce
erosion, and the main key,...er the main
point of a lot of the stuff is simply to
keep the plant cover in place. If you
keep it there you don't get the erosion.
Things stabilized very easily and very
quickly.
So what you can do is you can move
livestock to prevent overgrazing. So if
you have cattle coming through and
eating everything in the area and eating all the vegetation down to just a
little, maybe a little nub maybe about an
inch tall, and that does happen in places
I'll actually show you an image where
that's happened, you'll realize very
rapidly that erosion can very easily
take root and wash all that soil
away.
You cut fewer trees in an area rather
than clear-cut. So if you're going to
remove wood which does happen when we
have to harvest certain areas and
there's different reasons why that might
happen...might happen for forestry reasons,
for fire safety I should say in forestry...
but there's also just the natural
resource needs of people. Sometimes it's
better to go ahead and take a couple of
trees out of an area rather than take
them all. If you just take select trees
you can reduce that erosion and then
when you grow back new growth you won't
have the erosion, you can actually have
sustainable forest that's constantly
giving you that natural resource. You can
also plant vegetation along riverbanks
and roadsides, and you frequently do see
that. And you can imagine a road, when it
rains, it collects a lot of rain water
that runs off to the edges and there's a
tremendous amount of erosion that
usually happens along roadsides. That's
the reason why you usually see either a
gully or some type of gutter that's
installed there, because the erosion can
be extremely intense. Well if you don't
have those things in place, it's best to
have some kind of vegetation there in
place to prevent the erosion from taking
root and wiping out the road. So it's
actually a very good way to do it.
Here we're seeing plants being
intentionally grown in rows on this hill
slope, and this is designed to keep the
hill slope from failing due to erosion,
sliding things down.
Alright, so we just talked about the way
that animals can graze things down to
almost nothing. What we're seeing here in
this picture is an overgrazed and under-
grazed area. So let's talk about this.
So grazing animals on rangeland can be
sustainable if the total number of
grazing animals is kept below the
rangelands carrying capacity. And you
remember, we talked about carrying
capacity in one of our previous
lectures. Overgrazing occurs when too
many animals eat too much of the plant
cover and it impedes plant growth. And so
when we look over here we could see this,
right. The left side of this place, this
is in the Carrizo Plain ecological
reserve, this left side of the image has
clearly been eaten down, right. It's been
overgrazed. On the right this is what it
would look like how the cattle not come
through it all. This is ungrazed,
completely ungrazed over here. So here we
see it's basically a flat desert with no
vegetation at all, and here we still see
some low-level vegetation...that's not a
whole lot that normally grows out here
anyway, but what is here is holding the
soil in place [but] on the other side the
soil's changed color, it's going to erode
at some point, it's gonna be a major
problem. This soil is exposed allowing
erosion, less regrowth, and positive
feedback of more erosion. So non-native
invasive species also tend to invade,
right. So you're gonna get non-native
species that come in. Livestock do not
like to eat these weeds or these
non-native species. And so as a
consequence, they'll eat the native and
not the non-native and
therefore the non-native are then
completely allowed to take over the area.
This will out-compete the native
vegetation. Trampling is another thing
that happens. It compacts the soil and
prevents water infiltration. And that
prevention of water infiltration goes
back to erosion again, so the water can't
soak in, it runs off it carries the soil
with it. It's just basically what we call
a bad-all-around, right. It's a bad
all-around situation. So overgrazing can
degrade soil...we just kind of showed you
that, that's the name of the slide here.
Degraded rangeland costs over $23 billion
worldwide. So there is a very
strong economic cost to us. We feel that
in the price of our food, we feel that in
the availability of certain
meats, things that would normally be
available to us at the market are
suddenly more expensive. Grazing exceeds
the sustainable supply...sustainable
supply...of grass in India by 30%
and in parts of China by up to 50%. In
terms of the US, the US government
subsidies increase harm because ranchers
pay little to graze their animals on
public lands. You would say "Well, what
difference does that make If it's a
public land and the ranchers are out
there?" What that does is it creates
something called the "Tragedy of the
Commons." Tragedy of the Commons is the
phenomenon that people tend to use
common land or common use things very
differently than they would use their
own, right. It's the old adage
that people spend other people's money
differently than they spend their own
and that's exactly what we deal with
when we're dealing with ranchers. When
ranchers have the chance to put
their cattle into their own pasture or
out on government pasture where it's free,
they always put it on government pasture
until that resource is used up and then
they'll bring it onto their own pasture.
The consequence of this is that you see
the tragedy of the commons. Public areas
or publicly or commonly owned areas tend
to get degraded very rapidly, whereas if
a rancher has the cattle on
their own land they have a very high
motivation to make sure that over
grazing doesn't happen because they want
their farms to operate sustainably. OK.
And so here we see a large amount of
this happening. This is a grazing operation,
Happy Canyon is the name of this in Los
Padres National Forest, and they're
basically running out here this is on a
public land. And here we could see the
cattle, while it's eating grass down here,
there's not a whole lot of stuff around
these trees. Pretty much anything that is
up high has to be above the height of
the cow's neck to be able to grow.
Everything else has been completely
chewed down. Ranchers are now working with
environmental scientists on ways to
raise livestock more sustainably.
And one of the ways that we could do
that is get involved in grass-fed beef
production, that's a growing area
in the meat market. People are demanding
it. [For] one, it's healthier not only for
humans but it's also healthier for the
animal, it's also healthier for the land,
and there's different ways that we're
doing this. Another culprit in the
degradation of soils is irrigation. So
irrigation is the artificially providing,
providing water to support agriculture.
And so here we see an agricultural field
and here we see it's being...it's
undergoing some type of irrigation. What
this does is it makes unproductive
regions become productive farmland, right.
So if this was in the middle of the
desert, which normally couldn't grow
anything, suddenly if you irrigated with
with water from say a local river, then
all of a sudden you can grow a
tremendous amount of food in an area
that used to not be productive at all.
You can grow water-intensive crops like
rice and cotton. You'd be surprised at
how much rice and cotton for example is
grown in the deserts of the United
States. It's incredible. If you have
good fertile soil but without water you
can't grow anything. But if you're able
to get the water to the right places you
can grow a tremendous amount of crops
like rice and cotton which take a large
amount of water. 70% of all freshwater used
by humans...70% of all...goes to irrigation.
It's not for drinking, it's not for
toilets, not for brushing your teeth, it's
not from doing any of that stuff. It's
for putting out into these fields and
growing the things that we eat, OK. And
as a consequence it can deplete aquifers
and dry up rivers and lakes, and we've
seen this happen worldwide. If you take
the water out,
for example the Colorado River in the
United States...there are definitely times
that the Colorado River of the United
States does not make it all the way to
the Pacific Ocean or to the Gulf of California which then
feeds into the Pacific Ocean
because the water is siphoned off and
diverted into agricultural fields in the
United States...so it creates tremendous
problems.
So one of the ways that we can deal with
this is to look at alternative
irrigation systems. In other words, match
irrigation to whatever the need is. So
what we can do is we can match crops to
the climate...so instead of growing cotton
for example in Arizona in California,
let's try growing these crops in Georgia
or Florida or Texas...where they grow
normally anyway, right. So we don't need
to necessarily grow them in dry climates,
but that doesn't mean we're not doing it
anyway.
We are growing cotton in very, very, very
dry and water-intense areas where
it's not readily available. California
produces a tremendous
amount of cotton. Growing cotton in dry
climates requires extensive irrigation
while wheat does not. Okay. In
conventional irrigation, like flood and
furrow...and by the way this is flood and
furrow...let me go back to this...this is flood and furrow, so these are
the furrows and basically they flood
this entire field with water. In
conventional irrigation like flood and
furrow and sprinklers...so here's a
sprinkler down here...as little as 43% of the water applied is
used by the crops. So that's a lot of
water to put out for less than half of
it to actually get into the crops. By
contrast, drip irrigation...and here we see
drip irrigation, this is a pipe right
here and there's a little spot, here's
the plant that it's watering...come back
to here in a moment...the water is coming
out, it's falling right directly on that
plant. So drip irrigation targets water
directly to plants and plants use as
much as 90% of that water. So that
means that you don't have a whole bunch
of wasted water as a resource but
additionally you're not degrading the
soils as intensely as you would with
doing a flood and furrow style
irrigation. And if you tend to use too
much water you can get something that's
also very bad. It's called water logging
So water-logging is experienced by over-irrigating soils when the water table rises
to cover and suffocates the roots. This
is the kind of field that nothing is
going to grow in effectively. In fact, you
can see where the waterlogged soils are.
The groundwater is so high and is so
saturated the water can't even soak in
it's just over-irrigated. There might
have been a couple storm events that
came in and exacerbated the problem, but
here it is and you'll notice that right
where the water is, nothing's growing.
This is a dead zone.
Here's another dead zone right out over
there. This field is essentially dealing
with some real problems. This is water
logging and plants can drown in water. And
kind of on the flip side of that
is salinization. So salinization is where
you can get buildup of salts, and this
happens when you have a large amount of
water that is being used in an area
improperly, and then what happens the
heat in an area...in a very arid
environment in particular...evaporates off
the water and it leaves the salt that's
been drawn out of these waterlogged
soils and it basically crusts everything
with salt. And of course we all know
nothing grows in salt. So evaporation
pulls salts up from the lower soil
horizons. It is easier and cheaper
to prevent salinization than to fix it.
So just don't make the mistakes, right. Do
not plant water-guzzling
crops in sensitive areas. Irrigate with
low-salt water, ok. Irrigate efficiently
and only as much as needed. This is due
to over-irrigation. This is too much
water that causes this. Fixing requires
flushing soils with large amounts of
water. So then you got to take fresh
water, you're gonna dump it in, you got to flush
it out, and even then you're not guaranteed a
result. Most of the time, farmers just
walk away from it and they hope that
eventually the rains over a period of
time will wash it out, ok. But here we see
this salt has encrusted this soil and you
can see there's a tremendous amount of
difficulty for these plants to grow and
survive here. Alright, so the other thing
that can happen is we can apply
fertilizers to these fields, right. So
we've got damaging effects of the
topsoil, and so one of the things we have
to do is we've got to come in and add
nutrients. So a fertilizer is a substance
containing essential nutrients.
So remember, plants require nitrogen,
phosphorus, and potassium and remove
them from the soil possibly limiting
their growth. So if, you know, that's the
reason why you don't have an unlimited
amount of forest in an area. Because
there's only so many nutrients at that
location, there's a lot of competition
for those nutrients. They're getting
drawn away. Now there's two different
ways that we generally return
fertilizers...er, we fertilize the soil.
Inorganic fertilizers, which are usually
mined ore synthetically manufactured
mineral supplements, these are produced
by chemical companies and they're
sprayed around in the field...in fact this
is what we see here. This is a gentleman
that's spraying a chemical fertilizer in
this field probably trying to introduce
nitrogen out there but I'm not exactly
sure what it is he spraying. It's usually
nitrogen. And it's from some chemical
plant or there's organic fertilizers
which is the remains or wastes of
organisms. This includes manure, crop
residues...remember those little corn
stalks I was showing you earlier...fresh
vegetation could be an organic
fertilizer, and of course compost is
another thing. A lot of people really
like to get involved in composting...and
here we see compost right over here...this is organic compost...it's a mixture
produced when decomposers break down
organic matter. You can take that compost
and you can turn it into the field. And
so that's what's happening here is this
is being used to grow stuff. So this is a
fertilizer, a natural organic fertilizer.
So fertilizers do have their benefits,
right. They...and whether they be organic
or they're inorganic...they do have their
benefits of increasing plant growth by
putting the nutrients into the soil. Now
traditional agriculture relied on
organic fertilizers, but the Green
Revolution brought on increased use of
inorganic fertilizers. And we talked
about the Green Revolution in the last
video. So again, if you haven't watched
that you need to watch that video before
you trudge through this one here.
Inorganic fertilizers are more
susceptible to leaching and runoff. They don't absorb into the soil as
well. They're not kind of part of the
ecosystem already, they're kind of more
like chemical pellets that are thrown
out in the field or sprayed out there.
And as a consequence it can wind up in
the runoff,
right. It can runoff into surface waters far
from the point of application causing
dead zones in water bodies. So here we
can have a tractor that spraying their
inorganic fertilizer,
the result is you might have nitrous
oxides that are coming straight off the
field. The inorganic fertilizers are
gonna wash off and become runoff. These
are things that you don't necessarily
want in your bodies. There's things in there
that you don't necessarily want in the
food that you eat. So if it goes
into a lake or a river where you're
collecting fish, that's something that
should be a concern to you. And it can
get into there, not just over the surface,
but it could also get into the
groundwater system. It can contaminate
the groundwater. That's what these blue
dots here in this diagram are
representing. So it's gonna get down here and
it'll wind up in the lake that way. So
possibly too many fertilizers can be a
major problem. Inorganic is worse, right.
But you still don't want to use too much
of any type of fertilizer, you want the
right amount.
OK. So nitrates volatilize into the
air and contaminate groundwater. Nitrates
and phosphates and drinking water can
cause cancer and blue baby syndrome in
infants. So, you know, these fertilizers
don't come without a cost. There's an
absolute cost imposed on us if we use
them and it's imposed on the environment
as well. Now one of the goals that we
have is sustainable fertilization of the
soils, right. So self-sustaining soils
should have sustainable fertilizers. So
sustainable fertilizer use involves
targeting and monitoring nutrients. So
nutrients can be added to the drip
irrigation and are delivered directly to
plants as opposed just spraying it out into
the field behind a tractor, right. Just
add it straight to the water supply. You're
already using a very smart drip
irrigation system. put it directly into
the water. No-till planting allows the
application of fertilizers with seeds
rather than spreading it across the soil,
right. So then you can just put it right
where you need it if you need it at all.
You might not even need it at all.
Monitoring of soil nutrients can prevent
unneeded applications. And this is what
we see here. This is a soil core that can
be used for doing soil chemistry. So if
you were in one of my face-to-face
classes where you were actually on my
campus...I take my students out frequently
and we collect
soil cores and we do soil chemistry to see how
much...what the nitrates
are, the nitrites are, how much ammonia is in there,
what the pH is, soil color...you name it,
we're working on it. Phosphates is another thing
we look at and several other parameters.
And potassium is another one. So that's
something that we can do. And it turns
out you could actually do this pretty
easily and effectively yourself. Soil
testing kits are quite cheap these days,
you can order them online and you can
have them shipped to you and you can
find out what the soil quality of your
home or wherever you work or whatever
your field is, you can get that checked
very quickly and very cheaply. Organic
fertilizers provide needed nutrients as
well as improving the soil, improving
soil structure, increasing nutrient
holding capacity, and increasing the
water-retaining capacity. Remember, it's that organic
material that's in there that does that.
Alright, so one of the other things
that we've given up in our pursuit of
agriculture are our wetlands. So wetlands
are defined as swamps, marshes, bogs, river
flood plains, and in the United States
over fifty percent have been drained for
agriculture. And there's reasons that go
beyond that, but agriculture is the main
reason. And in other countries it's
actually worse in some situations. Some
countries it's not as bad. But it turns
out these wetlands are almost always
looked at as a great place for growing
things. Government policy in the United
States led to something called the swamp lands acts in 1849, 1850, and
1860. And what they were doing was
draining and converting wetlands to
control floods and malaria. So here we
see a wetland over here and we can
imagine there's a large number of
mosquitoes in the area and mosquitoes
carrying malaria. So they would wipe out
these wetlands, turn them into agricultural
fields, and they would kind of pat
themselves on the back. The problem is is
that it turns out these wetlands are very,
very good at cleaning soils and cleaning
water. They're natural
cleaning systems. They're natural filter
systems in the environment. And so
they're extremely important. Wetlands are
now seen as vital ecosystems for
habitat, they control flooding, they
recharge water supplies. It's amazing how
clean a wetland can make water. You can
take a bunch of dirty water in one end of
the wetland it'll come out perfectly
clean on the other side if you have a
vibrant ecosystem working there. Now the
wetland biomass quickly
removes fertilizer from water. When we say
fertilizer, we mean all those fertilizers
that come in artificially but it also
includes all the manure and animal waste
that comes out of people's backyards and
things like this.
Trust me...it's pretty crazy what
you'll find flowing into the river
systems of many cities and what a
wetland can do with that material once
it gets to it. So it's impressive. In
the United States we have something
called the Wetlands Reserve Program
which is where landowners are paid to
protect restore and enhance wetlands. So
it's a way to make money. And we're
starting to see the restoration, even the
creation of new, wetlands for the
purposes of cleaning water. And as that
experiment happens in the United States
we're starting to see that experiment
also happened in other places
independently, and we're starting to see
in some countries where we thought water
quality was going to not recover anytime
soon that it's making a very rapid
turnaround in natural ecosystems. But we
have to be on our guard because there's
a tremendous amount of waste still going
into the natural environment and we're
still losing the soils, we're still
losing the rivers, and we have to be
vigilant, OK. Now if you're interested in
soil conservation and if
you're interested in soil structure
or any of this stuff, the master of all
of this is Dr. Ray Weil. His interview,
which he gave at this YouTube link
right here and I'll also put it down in the
above the...I guess it's in the comments...
down below this video, I'll put a link
there, you should check him out. It's a
very short I think 11-12 minutes, but if
you're interested in soils again he's
the master and he can absolutely open
your eyes on this question of no-till,
and, you know, for example why is
no-till...not actually plowing a field...
better than plowing it? Right. That seems
contradictory
to what we were raised with. He goes into
the exact reasons why that happens. OK.
So our next lecture's gonna be on
agriculture, biotechnology, and food and
I think you're gonna really like where
this is going. I have a deep interest in
food and agriculture and biotechnology
and the way that soils kind of feed into
the growing of crops and the taking care
of people and the way that our whole
ecosystem operates and our interaction
with it, is really through the
agricultural system. So I think you're
gonna really like where this goes. If you
have any thing that you would like to
add, put it in the comments down below
and I'll see you in the next video. Take
care!
