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For most of my life, I've given little thought to the soil.
To me it was the flat surface that I walked on.
I've been thinking a lot more about it these days and what I learned has
surprised me.
I learned that soil is like the earth's skin
that lies between the
sky and it's rock core.
It's where plants keep tenuous grip with their roots,
as they harvest the sun's energy with their leaves.
I begin to realize that soil is alive.
That a handful of good soil contains more living things than all the human
beings that were ever born.
It dawned on me that without soil
life as we know it would not exist.
If soil is alive
I wondered if soil could die.
I visited with Pam Thomas and spoke to her about this.
A recent historical example is the Dust Bowl.
In the early part of the 1900's homesteaders plowed
millions of acres of prairie lands in order to plant crops, mostly wheat, because
wheat was bringing very high prices during the
World War one wheat boom.
Well because of this intensive cultivation
uh... the delicate balance - the ecosystem- was essentially destroyed - you know you
had the plants, the animals and the micro-organisms
to the point of where the soil no longer was able to function.
So as the wet years of the twenties gave away to the
drought of the
thirties,
the soil, which
no longer had the natural anchors to keep the soil in place, became very
susceptible to wind erosion.
In fact in the nineteen thirties
dust storms would start the great plains and would move cross-country to places like
Boston and DC....
Meanwhile in the southern US piedmont,
plowing and monoculture crops destroyed soil,
causing massive gully erosion.
Some of these gullies are still visible today.
No wonder FDR said that
"the nation that destroys its soil, destroys itself."
These were dramatic examples of soil destruction,
and I got to thinking how we were doing today.
We're still losing soil today. It's not as obvious to us today as it was in the Dust
Bowl thirties
but it's an ongoing crisis because....
the bottom line is, we are feeding more and more people on fewer and
fewer acres.
We're literally losing ground.
The nationalist Aldo Leopold warned us that one of the dangers of
living away from the land
is that we are inclined to think that our breakfast comes from the grocery store ...or a carton.
This got me to wondering how much soil we had to feed
our planet.
My soil scientist friend Jackie helped me understand this. Imagine for a moment
that the earth is this apple... seventy-five percent of the earth is covered by water...
Now half of the dry land on our planet is too hot or too cold
to produce food for humans.
Of this amount, about half is too rocky, steep or too shallow to produce
food.
It doesn't take a rocket scientist to figure that there's not much left
over.
And then what we have left is under pressure from things like urban sprawl
and erosion.
It takes five
hundred years to form an inch of soil,
something that can be destroyed in a few minutes,
and that worries me.
Leonardo DaVinci said that we know more about the movement of celestial bodies
than about the soil underfoot...
I'm guilty as charged
but i'm not going to leave it that way.
Join me in the rest of the series to find out what soil really is and what it
means to us...
perhaps if we learned more about soil we'd be better eqiupped to take care of the
planet.
If life is we know it depends on the soil,
it stands to reason that what happens below the soil's surface has a profound
influenced on what happens above the surface.
My knowledge of soils needed to run deeper.
The people that could help me do this were the soil scientists -
their work is to look beneath the surface into this life-giving, yet unseen
world.
Each day in the field is an adventure of discovery for them -
they have their own vocabulary and they love the feel of dirt in their hands.
this was the soils dream team, and they would be my teachers for the
next few weeks.
Dennis is a veteran who has mapped over a million acres of soils in his lifetime.
Lance and Emory are also seasoned soil explorers who have discovered a new soil
series that bears their respective names.
This was going to be fun.
the first thing they showed me was how the soil was formed.
This happens when weather and living plants and animals breakdown loose rock,
called parent material.
Parent material is typically weathered bedrock that over time becomes the main
mineral component of the soil.
It looks like rock when you dig it out, but as you can see
it's very fragile
massive structure, breaks easily.
Dennis took me to a road cut to show me that overtime, soil is formed in layers called horizons.
These horizons tell us about their history
and they can also give us clues about their future.
This is the A Horizon or the surface layer.
Look at all those roots in there.
That's wonderful.
Dark colors caused by the organic matter in there.
In here we have what's called the E Horizon, capital E.
Fairly light in color,
more sandy in texture
and down below it,
is our B Horizon
that contains much more clay and you can see
it's much more red down here, too.
Each soil horizon has unique properties
like depth, color or clay content.
When these horizons are layered on top of each other over time,
they form soil
profiles which can be identified by name.
they are often named for the place they were first identified, like Norfolk
or Durham.
When it comes to looking below the soil's surface, nothing is as effective as a
good old-fashioned soil auger.
You'll never find these guys in the field without one-
I guarantee it.
Now I began to see how soil profiles can tell their story,
layer by layer.
this is a soil profile
put into a long tray so we can look at it a little
easier that pulling it out with the auger.
In this hand here
you'll see this is the A Horizon
and you'll see it is much darker cause it contains
organic matter in here.
This is the A Horizon or the surface layer. This is eight or ten inches below the surface
and see how red this is?
All soils contain iron and we
know if we put a piece of iron
outside for two weeks it turns rusty.
This is rusty soil.
Rusty soil, how about that?
So each color has a different meaning-
bright reds and yellows mean that a soil is well-drained
there's more oxygen
in the soil to oxidize or rust the iron in the soils.
Grey colors on the other hand, mean the soil is waterlogged for most of the year
because there is less oxygen to get at the iron.
A dark brown color means more organic matter
which is mostly in the A Horizon or topsoil.
we can use the Munsell Color book to classify the exact color of the soil.
We take the
soil ped
and put it behind the book
and find the colorship that it most resembles.
I'm going to say that it's that color there
2.5 YR 4 8
2.5 YR 4 8 by the way
is a more precise way of saying "red".
Dennis also pointed out to me that soil depth is another way
to identify soils.
This is the "Cecil series" because the clay content
extends below a thirty inch depth.
If this clay content decreased above a a thirty inch depth
it's called the "Pacolet series".
They're kissing cousins.
Whoa! kissing cousins?
It turns out that if two soils have similar color and clay content,
but different depths,
they'd be named differently.
At this point I knew enough to see how you could identify a specific soil series.
I was now ready for Lance and Emory to show me their newly discovered soil -
it's named the Brewback series.
Right there, about 22 inches
we just starting to barely nip on the CR material.
You can hear the grind and feel it in the auger.
Right here we have the A Horizon.
It's about six inches thick and it's a fine, sandy loam.
Then we get into the B Horizon, which is a heavy clay.
And here, about
twelve or fifteen inches, we have the uh...
the grey colors
coming in, and for a Brewback soil we have to have the grey colors within
the top ten inches of the B Horzion.
As we move on down the profile about twenty inches, we get the sandy, clay loam,
which is the B-C horizon, which is a transition between the B Horizon and the parent material.
By this time, I had seen a few soil series,
each with its on color, depth, and clay content -
each with its own personality if you will. It turns out that soil scientists have
identified and mapped over nineteen thousand different soil series in the
country.
That sounds like a huge effort -
I had to find out who was doing the work
and why it is so important.
I found out that the massive effort of identifying and mapping soils
is known as the soil survey.
The body of information resulting from this ongoing effort, also known as
the soil survey,
is available in hard copy and online at the web soil survey.
It's an inventory of soil maps, soil properties, suitabilities and
limitations.
I was reminded that what happens beneath the surface of the soil ultimately
affects everything above its surface.
Everything.
That's what makes the soil surveys
so important to any land management decision, from farming to disaster
recovery planning.
I drove out to Lee County to find out
who the people were behind all this work,
and how soils were mapped.
Charlie is a soil scientist who is responsible for the upkeep of about
eleven million acres of soil survey.
Most of this...all of
South Carolina has been mapped,
so what we're doing is updating all
the older soil surveys.
He offered to take us through the process of making a soils map in the
field,
and I asked him to sketch out the day for us.
One of the things we do,
when we go through the process of making the soil map
is to stand and just look at the area
and take in the whole landscape itself. and you can see out in this part of the world,
that some areas of it are concave, some of it are more convex.
So essentially what we do
is to stand out here and note where these areas are,
dig the holes,
identify the soils,
and label them on the map using alpha-numeric symbols.
The finished product looks like this.
This is the same area that we're standing in, and
we can see that these soil lines delineate the different tones on the map.
The first hole we dug was on a slight rise...
we then moved over to a slightly lower area only three hundred feet away and dug another hole.
Charlie showed me the
difference between the two soils that was so close to one
another, and how
land form influenced them.
This soil in the front,
is the "Rains Series".
This soil in the back is the "Nolfork Series" that we looked at earlier.
One of the first things we notice is that the surface of the "Rains" is darker
and that is reflected by the tones on the map.
The other obvious thing is that the subsoil is much grayer.
Where the "Norfolk" series is dominately brown, the "Rains" is dominantly gray.
The grayer
colors immediately below the surface means that this soil formed and still at times
will have a water table
at or near the soils surface.
And although these soils are only 300 feet apart, the
water table is a limiting factor on land management here in the Coastal Plains.
Part of the process of making a map
is to ask the questions
and then to go get the answers.
And once we've identifed some soils in the area,
we begin to understand
that the same soils
more than likely will be occurring in that area.
It looked like Charlie asked and answered a lot of questions -
I don't know how many miles he walked, but he mapped 300 acres that day.
Many of my conservationist friends
tell me that a bad day in the field is better than a good day in the office.
I began to reflect on my new-found appreciation for the work that Charlie and
his colleagues do in the soil survey.
My knowledge of the big picture was taking shape,
but I wanted to see the area we had mapped in the Web Soil Survey for myself.
Back at the office, I went to the Web Soil survey and found the place we had
mapped in Lee county. I drew my area of interest boundary and went to the soils map tab.
All the familiar soils - Goldsboro, Noboco,
Norfolk and Rains appeared.
I was in the right place.
Charlie had told me that depth to the water table was the limiting factor here,
so I went to the soils data explorer to look at the soils properties.
Sure enough, the Goldsboro and Rains soil had shallow water tables as we had seen in the field.
I then had a look at the soils suitabilities and limitations for land use
to see where the best place to, say,
build a house would be.
It turns out that if I were to do that,
it is better on a Norfolk soil and maybe on a Goldsboro -
all of the other soils were going to be too wet.
I used the shopping cart feature, which was free by the way,
to get a custom soil survey report....
a little memento of my day in Lee county.
What I had learned so far
showed me the broad brush strokes of soils in the landscape
and how they affect so many of our above- ground land management decisions.
I now wanted to see the soil from a different perspective.
To get really upclose and personal with soils,
I visited with my good friend Richard in his garden.
We moved into our house about 1984,
and we have always had the hopes of having a garden. We've tried a whole different
groups that things, We've always had tomatoes and squash, diffferent
kinds of squash, zuchinni, yellow squash,
and uh...
melons, cucumbers. That's been the basis.
Now we've gone from about half an inch of topsoil, to about eight and half, nine inches.
So
it'll be good for the next people who will be moving in.
uh... they'll be able to use the soil well,
..and now we're trying to do a no-till
garden. So that's a new step in our direction.
To take a close look at Richard's soil,
we took a sample and put it under a microscope.
The first thing we noticed was that the soil was made up of both
mineral and organic particles.
The next thing we noticed was how much mineral particles size varied.
It turns out
that mineral particles can be classified by size,
sands being the largest and clays the smallest.
Sand is gritty to the touch, while clay has a sticky feel to it.
Pure silt, not very common in the southeast,
feels like talcum powder between the fingers.
The mix of these sand, silt and clay particles in a soil is known as
soil texture.
Clayey soils are fertile
but they don't always drain well.
Sandy soils on the other hand
drained very well but are generally not fertile.
The soil in Richard's garden contains about 40% sand,
40% silt
and only 20% clay.
This would make it a loam -
the soil texture that combines both good drainage and fertility.
If you hold Richard's soil in your hand,
you can see that it clumps together nicely into soil aggregates.
Soil scientists call this aggregation property soil structure -
keep in mind that structure is a different soil property to texture.
Soil aggregates, or soil peds, can
be classified by size,
shape and strength.
Good soil structure is important in soils because water, air,
nutrients and roots will find it easier to move between soil aggregates than through them.
One of the surprising discoveries I recently made
was that in an undisturbed soil, about half of the soil's volume is made up of spaces.
These spaces are vital to the health of the soil
because they contain air or water-
it's in these spaces where soil chemistry and biology are at work.
Soil scientists tell me
that these are called pore spaces.
If they are between sand, silt and clay particles, we call them micropores.
The much larger spaces we found between soil aggregates are called macropores.
Macropores are especially important
because they become the superhighways for air,
water and nutrients to reach plant roots.
Richard put his rototiller away a few years ago.
Less disturbance by rototilling
has benefited his soil by preserving those pore spaces.
More spaces for air, water
and roots in the soil
means more vegetables on the table for Richard and his family.
I had always thought of pH as a property of water and not soil.
Lemon juice has a pH of about three - that's acidic,
and baking soda has a pH of about nine -
that's basic.
Pure water, which is neutral,
has a pH of seven.
Now that I realized that more than a quarter of the volume of soil is water,
this make sense.
The water chemistry in those pore spaces is
critical to how plants absorb nutrients from the soil.
Richard usually gets his soil tested at the local extension,
but pH test kits like this
are available online or at local stores.
...between six and seven...
His soil is slightly acidic but, it's in the range from most of his plants
thrive.
If the pH is too low his plants will not be able to take up
nutrients like nitrogen and potassium.
If the pH gets too high
his plants would have problems absorbing iron,
manganese and zinc.
So keeping that pH in the 6-7 range is really critical.
As we finished up our visit,
Richard shared some of his land philosophy with me.
I believe in stewardship. If..if you're given something can you make it..improve it or
can it be better for the next person?
So we've done everything we can to
help it be someplace that people will enjoy later.
That got me to thinking.
Richard's soil is a Cecil -
that won't change.
But it was clear that there were some properties in the top six to nine inches
of Cecil soil that he had improved through good management.
It means that a Cecil soil could be healthy or unhealthy, depending on how
it's managed.
A healthy or unhealthy soil?
This was a fascinating concept that I had to explore further.
I spoke to Pam and told her about my experience and asked her if management made
a difference to the soils.
She replied with a story from the famous soil scientist and father of
soil conservation Hugh Hammond Bennett.
In the early part of his career, in the 1900s, he and a colleague were wandering around,
when they noticed two pieces of land side by side.
These two pieces of land looked vastly different, in terms of soil quality.
It was obvious that these two areas, at one time, had been identical. They had the
same geology, the same slope, and the same climate.
However, in one area the soil was soft.
It was loamy and moist enough that they could dig it with their hands, even in
dry weather.
The other area,
in contrast, was very hard and dry.
It was almost like a brick. They could not dig it at all.
The difference between these two was that the soft one, the mellow one, was under
a dense forest,
while the other one had been continuously cultivated for decades.
Mr. Bennett, or Big Hugh, called this his epiphany.
Big Hugh's epiphany was about how management can change soil function.
Put in the simplest terms,
soil function is its ability to moderate water flow and storage,
to store and recycle nutrients
and to sustain life.
In the spirit of Big Hugh's epiphany, I did a simple test to see how well
soil structure holds together in water,
it's called teh slake test.
I took two soils -
both from the same soils series,
one was continuously cultivated
and the other had been under no-till and cover crops for years.
The no-till soil measured out
at 3% of carbon-rich soil organic matter,
the paler, tilled soil at less than
half a percent.
It didn't take me long to figure which soil was healthy.
It's no wonder so many of our Piedmont reservoirs are the color they are.
The difference in the way the two soils behaved is about glue
and string. Soil-life... roots,
earthworms, fungi and bacteria,
secrete biotic glues. Roots and fungi also form biotic string,
which works with the glues to form a sticky network that holds soil
particles together.
The glue and string is what keeps the pore spaces between the particles open,
to provide a place for water storage and flow, and to provide a habitat for all of
the soil organisms.
This allows water be stored and to move through the soil when it's
needed.
The easiest way of damaging the glue and string is by disturbing
the soil.
Soil disturbance chops up the
biotic string
and allows piranha-like bacteria to gobble up the carbon-rich
string and the glues,
turning them into carbon dioxide and releasing them into the atmosphere.
When i removed the soil organic matter the pore spaces collapsed and I was left
with empty dirt.
Any kind of soil disturbance will do this, the more intense, the more of the soil
will be damaged.
If Big Hugh were still around he'd have a
fascinating conversation with today's soil ecologists.
They'd tell him that the glue and string are part of soil organic matter, which
consists of decomposable organic material, humus and living things.
The decomposable organic material is like the pantry for many soil organisms.
Humus, dark and sponge-like, is a very stable organic substance that remains
after many soil organisms have used and transformed
the original decomposable material.
One of the functions of humus
is to be a sponge that holds water for drier weather.
About 5% of the soil organic matter's mass is made up of living things,
microscopic soil bugs or soil microbes,
and animals that we can see without a microscope.
The weight of the microbes alone under one acre of this soil's surface
is more than this cow-calf pair.
That's a lot of microbes.
It's the soil biology that regulates about 90% of the
soil's function
of moderating the flow and storage of water, nutrients and energy
....in your backyard,
in the farm field,
on our planet.
I still worry about urban sprawl and erosion,
and the amount of fuel and fertilizer we use to make food.
But there's good news.
Soils are resilient and forgiving!
From the Carolinas to the Dakotas,
farmers and gardeners are restoring soil health
by working with nature, not against it...
they've stopped tilling.
Completely.
They've started growing multi-species cover crops
that feed and cover the soil...
it's growing them more
and costing them far less.
In the cities, they're planting trees and rain gardens,
restoring old buildings instead of breaking new ground.
School kids are learning more about soils....
that's huge.
In these last few months, I have come such a long way,and yet
where i stand now, I see how much more I have to learn.
Sometimes I feel all of this can be overwhelming, but when i think of
Big Hugh and what he went through,
I think he'd tell me that there's hope.
I bet he'd like us to call it "humic hope".
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土壤層 (Soil Stories - The Whole Story)

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Akki 發佈於 2015 年 2 月 1 日
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