This course will cover the agricultural and urban water quality issues in Florida, their bases, land and nutrient management strategies, and the science and policy behind the best management practices (BMPs). Students will learn to evaluate BMP research and analyze its role in determining practices and policies that protect water quality.
Irrigation Management, Part 1
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來自 University of Florida 的課程
农业可持续土地管理
45 個評分
從本節課中
Water for Agriculture
For week 7, we will wrap up nutrient management and then move to water for agriculture. We will dive deeper into the water of Florida and then begin the topic of irrigation management.
與講師見面
George J. Hochmuth, Ph.D.Professor
Urban and Agricultural Environmental Sciences
Hello everyone, and welcome back. Today I want to finish up Week 7 by
starting to talk a little bit about Irrigation Management.
If you remember last time we talked about water resources and some of the challenges
that we face. And today I want to start talking about
water management specifically irrigation. Those of us that are familiar with plants
and have had a garden. Or are familiar with farming know the
impacts of water stress on plants. For example, the, the wilted squash plants
in the top picture. And we also know what a timely rainfall or
a timely irrigation can do. To the health of our plants.
And to the yields and the quality of the of the end product.
So we know the value of, of having water on a timely basis for our crops.
If you look around the world it doesn't take long to find situations where water
has made a big impact on civilizations. I just want to illustrate one.
Here, the Nile River. In ancient times, the Nile river flooded
and farmers of those days took advantage of the floods to have water available for
crop production. And also took advantage of the sediment
the silt, and the organic matter that was deposited on their lands during those
flooding events. With time farmers figured out ways to get
water from the river to help, help provide water during in between those floods for
their crops. And they soon learned ways to actually,
instead of just letting the water come in through canals and ditches to actually
lift water out of the river and supply it through a canal system for irrigating
crops. And agriculture began to flourish.
This is a pretty spectacular picture taken from space that just illustrates how
important the river is and the water is to people growing living along the river.
And the importance of the water to agriculture and to food production along
the, the river. So we know and we can acknowledge that
irrigation is extremely important to crop production.
We see this in everyday life. And if you think back to some of the
earlier parts of the course, we talked about how agriculture is going to be
expected to increase productivity to meet the growing population on this globe.
And I think especially if we think about the challenges associated with increasing
food production. I think we will see, at least I would
expect that irrigation would be a major, major part and play a strong role in
increasing crop productivity. Irrigation is going to be very important.
And as we also learned a little while ago in the course, that agriculture is a major
user of water on this planet. So, we still have our job.
Our job is not going to go away. We just need to learn how to do it better
and better as we move forward, in terms of producing food.
Sustainable irrigation is going to play a role I firmly believe, in sustainable food
production and increasing food production in the future.
I've shown you a picture here of a potato field that is growing on very sandy soils
in Northern Florida. Even though we receive a lot of rain in
this state, as you learned earlier, sometimes it doesn't come during at
opportune time during the crop growing cycle.
And so, in this particular case, this farmer is supplementing the rainfall with
irrigation. So, we're going to be very concerned and
pay a lot of attention, as we move forward, to increase food production.
On making sure that we can assist and help, are farms do that with attention to
water conservation. And also as we've learned in the course,
water quality. Because farming and agriculture, in its
efforts to increase food production, Is going to rely a lot on irrigation.
But so will be the demands on water on this planet for the increasing population.
So there's going to be a, a, a conflict there is a conflict, and there will
continue to be a conflict. And so agriculture and farmers are always
looking for ways to become more efficient. And I think what the next two lectures I
want to try to illustrate some ways that we can improve the efficiency in our
irrigation. So that we can conserve as much of the
water as possible for agriculture. If we step back a little bit and take a
look at what water, how water is required in plants this little diagram here Is
really in effect a, a water cycle but on a plant basis.
So we have precipitation that comes in falls on the ground, on the soil.
This plant is going to take up water from the soil.
Some of that water will go to serve certain functions in the plant such as
photosynthesis where water is used through the in photosynthesis.
And photosynthesis is, is then the process that produces sugars that eventually
contribute to all of the biological functions in plants that result in growth
and, and productivity. So photosynthesis is very important.
But as you see that the amount of water that's used in photosynthesis of the total
that the plant takes up, is very, very small.
The other pathway for water or the other use for water is as it's absorbed, it
brings in nutrients and goes to the, the various parts and organs, and in this case
we see leaves. But we could have fruits on this plant,
and that water then serves to move nutrients.
For example, our phosphorus and nitrogen that we've talked about in the course to
these leaves. Again, to support growth and, and
productivity. Much of this water that moves is taken up
and moves through the plant, exits the plant as water vapor through a process
called transporation. And as I've illustrated here, most 95 to
98% of the plant water that's taken up by the plant Is eventually lost back to the
atmosphere through the s the, the stomates in the leaves as, as water vapor.
In fact, if you look here, a corn plant can transpire as much as three to 4,000
gallons per acre per day that is, so that's a lot of water that's taken up by
the plant. That goes in, it moves nutrients and it
serves many functions in the plant and then exits as water vapor.
This whole process here also includes losses of water from the surface for
example, from our soils. We'll set aside, for the time being The
fact that we already know about other losses of water from the field from our
agricultural operations, such as leeching and runoff, but evaporation from the soil
surface is another large exit or loss of water from the production system.
These two processes are taken together, what we call evapotranspiration.
Now, I've also illustrated here, if precipitation cannot supply enough water
to support these processes that are important for plant growth and development
and for our economic yields. Then the farmer supplements with
irrigation. So irrigation should always be thought of
as a supplement to natural rainfall. So just a, a couple pictures of, some
drought stress on plants. The top picture here, many of us that
garden, probably recognize blossom end rot of tomato.
It just so happens that the fruits of tomatoes do not, are not a large
transpiring area surface. So as the water moves up through the
plants, it, under mild water stress, most of that water, then, is going to go to the
leaves and not to the fruits. It just so happens that calcium moves
preferentially in this water stream. And so, when the water is bypassing the
fruits when these fruits are young, as these are.
And expanding very rapidly, they need a, a, a constant ample supply of calcium.
And under mild water stress, calcium is moving preferentially with the water to
the leaves, and the fruits suffer a mild deficiency, which is illustrated as loss
of meenra. Usually, it's temporary, and the fruits
will develop normally when the water stress is removed.
In the lower picture, I've shown you a fairly prolonged water stress on corn
plants. And you can see that eventually even
though the leaves have wilted, they have progressed to the stage where they've
actually died from lack of, of water. So water stress is very, very important
and very critical. To our crop plants.
So how do we supply water to avoid these stressful situations?
I've given you just a few of the various kinds of irrigation systems that we use
around the world. Some of, many of these are used in this
country and some of which we've already at least pointed to through the course.
But I want to just, just take a look at, at each one of these and, and just kind a
illustrate some ways that farmers have or some techniques technologies that farmers
have to supply water. Now, irrigation as a system supplying
water to crop plants is not brand new. In fact this is an example of a irrigation
system that is quite old called the Qanat. Originating in, in Persia and has been
spread to many areas, of the world. It's still used to some degree in, in some
places like I believe Syria. For example, and you can see in this
picture the ingenious nature of this whole set up.
Because these farmers figured out that there was water here, the water table in
the hills. And if they could tap into this water
table, they could make it flow by gravity down to the areas, the lower areas, where
the crops were. And so, these vertical shafts were dug.
To facilitate digging this horizontal tunnel.
That eventually intersected the water table and provided a way to get water to,
to run out from the water table out to the, the to the production areas.
Also along with irrigation of course we have to have a way to, to move.
Now, in the Qanat the water moved by gravitation from the water table out to
the, the production areas. But man also has figured out how to move
water particularly from a lower level to a higher level of elevation.
To satisfy irrigation demands. The pump, has been around for, in various
fashions for a long, long time. For example, the shaduf, has been around
since 3000 BCs. And then, Archimedes' screw pump, the
windmill pump that you used wind. Now the shaduf and the screw pump use
manpower to bring the water from the water body to a higher level.
And maybe into a ditch or a canal to take out to the agricultural field.
Obviously, wind, the windmill pumps use wind.
And then eventually the internal combustion engine and electrical engines
to drive the pumping mechanism to move the water from a well or from a water body.
Up to a, a level where we can move it then to the fields.
Today through, usually through a series of pipes.
So here's the shaduf. It's a dipping bucket with a counterweight
on the other side. A pretty ingenious way of moving water.
Dipping water out of the river, in this case.
And depositing it, into a canal that, will, move it out to the, to the fields to
irrigate the crops. Portable pipe.
Now, this is something that goes back to brings back, memories.
We use portable pipe on the vegetable farm that I grew up on.
And so, I remember the pipe wagons very, very well.
So these were short sections of, in this case, aluminum pipe.
That are put together connected together. And in the bottom picture you see how
they're lined up in the field, and they're hooked up to a main line that comes from
the water source, a well or a river or a canal.
And the water is then dispensed out through the pipes and through these
sprinkler heads. And so when you were finished irrigating
this particular area then you un, you unhook the, the pipes from the, this
particular header and move it over to another area.
And you had to walk these pipes across the field.
And as a child I re, a teenager I remember many, many summers moving pipes across
crops to irrigate. And it's not very it, it's not very easy
dealing with full-grown crops to walk through.
But anyway that's the portable pipe. It just simply means that we have pipe.
That we move, we can move around in the field and position it where we want to, to
execute the irrigation. Here's a couple illustrations of
travelling guns. This is called a cable tow.
Essentially, it's a, it's a small cart with a gun on it and you have this cart
hooked to this tractor. This tractor is nothing more than an
anchor. And the cable is stretched out to the cart
and then the cart pulls itself back towards the tractor along that cable and
drags a water supply hose with it. In this particular case here, the, the
cart with the gun is stretched out into to the field and then is reeled back as it
irrigates. And so, again, another way to irrigate
large areas with a single with a single sprinkler system.
And as we go through these, you can kind of imagine some of the advantages and
disadvantages of these various irrigation systems.
Center pivot, probably most everyone whose familiar with agriculture has probably
heard about the center pivot. As its name implies it irrigates in a
circular fashion. The pivot in this one is back here, in the
corner, if I can point to it. And then this whole system then with these
wheels revolves around in circular fashion in that field, irrigating as it goes.
And you can see the result of irrigation with center pivots here in this very dry
climate in southwestern part of the United States.
And all these green circles are probably about 140 or 50 acres of irrigated crop
and each of 'em would have one of these irrigation systems to it.
Center pivots have come a long way. We had center pivots on our farm.
And in the old days they had sprinklers, impact sprinklers on the top of this pipe.
And that was a rather inefficient way of distributing water because it threw the
water up into the air where you could have evaporative losses of the water.
And then the idea of dropping the water down through these tubes and through a
low. A low pressure sprinkler emitter put the
water closer to the crop and reduced the evaporation losses from that water.
So, the efficiency of center pivots can actually be quite high because of these
innovations. Sometimes the center pivot is not exactly
the right choice. They are good for square fields but if you
have rectangular fields sometimes the center pivot is not exactly the most,
doesn't cover most of the, the area. And so, in that case, you might choose
what's called a lateral. In this case, it operates very similar to
a center pivot except it moves in lateral fashion instead of around in a circle.
But nonetheless is a, again has most of the same kinds of amenities such as those
low pressure drop nozzles as the center pivot would have.
I wonder, you know, here is a, here is a irrigation system that we might we might
label the modern day qanat. Furrow irrigation.
This is furrow irrigation. It happens to be in California on
processing tomatoes. But you can see how the water is being
distributed into this field at the head of the field from a canal through the siphon
pipes. And then the water is moved down the field
in these furrows. And here's another example.
It's usually a canal that brings the water to the fields from a larger canal and
water distribution system. And these siphon tubes are put into the
canal and go into the field into each of the furrows.
And this show basically how it works. So the furrows receive the water.
And the water runs from one end of the field down to the end.
These fields are lasered so that one end is a little bit higher than the other.
And the water in the furrow then, by capillarity, soaks into the soil and
eventually wets the roots uniformly. So, with furrow irrigation it's very
effective on soils that have fine texture, recall back to our discussion about soils
and soil texture. So if you have a soil that has clay and
silt in it, then you can move that water very effectively laterally from that
distribution. Furrow, and here's some other pictures of
a canal with the syphon tubing in 'em and here's a, another field that's being
irrigated the same way. You can imagine that with furrow
irrigation, with all of this open water that the evaporation losses from the water
surface can be quite large. Here in Florida, we have kind of an
interesting example. I thought I'd bring this up It's not used
in many, many places. But remember back when we talked about
spodosols. Those were very, very sandy soils.
They happen to have that organic clay. Horizon in them, but those soils were
formed under very wet conditions with a high water table.
And in this particular case we used canals and ditches to bring water into the field.
But in this case, it's not to, it's not, it, it's not on every, single row, you'll
there's just an occasional ditch. And you, I think you might be able to make
out an area over here where there's another one of these, field ditches.
And so what we're doing with this water is, we're distributing it into the field,
but we are raising the water table, so that we have similar kinds of, ditches and
canals to bring the water in. And then field ditches to distribute water
more uniformly across and about the field. But we're trying to raise the water table.
And so this has some unique aspects compared to really true furrow irrigation
that I just showed you. Before, but we're raising the water table
and we're sub-irrigating the crops from this raised water table.
Again, when you have a lot of open ditches and canals, as we are showing in this
picture, this particular irrigation system does not have the greatest efficiency.
So we'll talk a little bit about efficiency in a bit.
We've already introduced to you the aspect the drip technology the irrigation
technology that we call drip irrigation. And we talked about it being a
distribution system, with small plastic tubes that have.
Emitters or orifices spaced along that tube that emit water in very, very small
streams and, and amounts. That's why it's called drip irrigation.
Some people, an older term for it was trickle irrigation.
So the water drips out of this pipe. And you can see, it's very effective
because it only wets a small portion of the soil around the plant, and not the
whole bed. If you can just think back to the furrow
and the seepage systems, those systems are going to irrigate all of the soil in that,
in that field. They're going to wet the entire soil
laterally. So here's just a littel artist's diagram
of how drip irrigation is laid out. And so the water comes in from, usually, a
well into maybe a filter or something like that to get the, some of the organic
matter if it's coming from a surface or maybe some.
Limestone particles if it's coming out a well for example here in Florida.
And then that water is distributed out into the field and you can see the, the
tubes here that are along the, the rows of plants.
And this particular case, I've illustrated also the, you know, the capability of
Remember we learned about fertigation, injecting fertilizers into irrigation
systems. And drip irrigation is, is ideal for
practicing fertigation. Here's a picture of some footage that I
took of one of our research farms with plastic mulch.
This happens to be squash. And I'm illustrating here a line, you
might call it a main line or a submain. And the drip irrigation tubing as you can
see there is plugged in to this line and that's the way the water is distributed
out and down the row. Here you see the drip irrigation tubing in
that crack of soil. Typically drip irrigation tubes are buried
to sort of keep them from, keep them stable from moving around on the surface
of the bed. But also to protect them from damage from
insects or birds for example, can be a major issue with drip irrigation.
Here's drip irrigation. It's very, very adaptable to small farms.
These are some pictures from Haiti and Africa showing how, you know, if you have
a source of water, it could be just a container at a raised level to give it
some head. So that the pressure can push the water
out and down the row through the drip irrigation system.
So drip irrigation has been around for a long time, probably since the late 50s.
And has been used commercially more and more, particularly on high-value crops,
like vegetables and fruit crops. And highly adaptable to small farms as
opposed to just think about some of the, the other systems that we looked at.
They're not very adaptable to very small land holdings for irrigation.
Irrigation systems have a lot of differences about them.
There's advantages and disadvantages And not all irrigation systems can be used in,
in all situations. If you think back to some of the pictures,
the center pivot the traveling guns they require high amounts of energy.
A large pump that can generate high pressure to push the water long distances
through those tubes. And with frictional losses on the way.
And then to force it out through that gun to great distances across the field.
So some systems require large amounts of energy.
Drip irrigation is a little different because we're using very small volumes of
water and we do not need the high pressure that we would with a cable toe, for
example. There are issues with design and
maintenance of these systems, just like anything else that we, we deal with that's
mechanical in nature. There's the chances for leaks in the pipes
bringing water to the fields or distributing water in the fields.
Certain systems that have open ditches to convey water to the fields would suffer
evaporational losses of water. So we've, we've made the expense to put
the water in the ditch and convey it, and we would like to minimize, the loses as
much as possible. And of course deep percalation, or loses
of water, through running are systems too long, would be a potential issue, even
with drip irrigation you can have leaching if you run it too long.
So there's differences in the overall irrigation efficiency of different
irrigation systems, not to mention the cost of all of these systems, the
variation in cost to, to purchase a system and to, to operate it.
So irrigation efficiency is usually thought of in, in two ways.
The first one, I've illustrated here as the irrigation and I, I put in
parentheses, supply efficiency which is the ratio.
The amount of water that's delivered to the field relative to the amount of water
that was input into the system. And usually things that affect irrigation
efficiency would be, leakage and evaporation, So leakage obviously would be
a problem where we're using pipes to convey water, to the field and evaporation
would be a problem with some of the open ditches.
And canals with those irrigation systems. And then there is another irrigation
efficiency that we can discuss and that's, that's the ratio the amount of water that
actually arrives in the root zone for the plants to use.
And is, and is maintained in the root zone for the plants to use.
Versus the relative amount the total amount of water that's delivered.
So here we think about poor efficiency in application would be due to loses due to
deep percolation or, or leaching or even non-uniform application.
So here are some leaks. The one on left obviously this pipe has
been leaking for a long, long time. These are, these represent losses in not
only a, a resource, but also in expense. Because somebody had to pay to get that
water pumped and put into those pipes and then lost water due to the leaking.
And so irrigation efficiencies then can be described, application efficiencies can be
described for these systems. And you can see that depending on the
system, system there's a lot of variation, in, the efficiencies of these systems.
And it ranges all the way from maybe a low of 20, up to, drip irrigation, and, and
some of are very advanced center pivots that might be 85 or 90%, efficient.
You probably won't get 100% always, because there's always going to be some
losses, particularly to evaporation, even with drip irrigation.
So but, but we do have irrigation systems now that have, have developed over the
years to become very, very efficient in water.
Now, here's an example that you sometimes and you're watching this you would wonder
What does it take for a manager to get the picture that non-uniform water application
is happening. It is very simple to understand and see
non-uniform, obviously this is happening here.
You don't need to go out and measure to see that there's a lot wasted water or
poor water management. And some of the plants, in this case, turf
grass, are suffering or they're not getting enough water due to lack of
uniformity. And all it takes is just some simple
measurements of the water application. And you can set up catch cans under a
sprinkler system, or you can catch from drip irrigation emitters.
And then you can measure the amount of water that you caught in those containers.
And you can decide what area you're interested in evaluating and you can
calculate up how uniform that system is. And these are very important tests to run
with an irrigation system periodically. And I might add, this is especially
important if you're applying fertilizer through that irrigation system.
Because in, in fertigation, you're not only having non-uniform water application,
but you're having non-uniform nutrient application as well.
So just to tie up a few take-home messages from this part of the irrigation lectures.
We've seen that agriculture has many, many ways to use water and I'm talking about
the crops here. We've looked at, early in this lecture we
looked at the utilization of water. In processes in the plant such as
photosynthesis and transporation. We also in the previous lecture we looked
at other places where water is used in agriculture, for freeze protection, for
example. For cooling vegetables after harvest and
processing so water is very important, not only in just producing our crops but in
many other ways. So agriculture uses water in various,
various ways. Irrigation as we've also learned has been
around a very long time. People have, farmers have learned how to
take advantage of water. That's available to them to be able to
take care of crops, and make them perform better in periods of low rainfall.
The pump, of course, had a big impact on this whole process.
Irrigation has allowed people to live in dry places around this planet.
And in fact you know there are some concerns about irrigating and using a lot
of water from ground water particularly in very dry areas.
And now that we have the capacity with irrigation systems and large pumps to
withdraw massive amounts of water from an aquifer there are situations where people,
farmers and, and also. General society that has concerns about
the level of water in, in some of our aquifers.
So, that's an example of how we need to really work very closely with growers so
that while they're using large amounts of water, they're doing it in a most
efficient way. And using the best management practices.
We'll talk a little bit about that later. There are many types of irrigations.
Each, irrigation systems, each with its own pluses and minuses.
And even though we didn't harp on a lot of these pluses and minuses as we went
through those irrigation systems, I think, we highlighted a few.
And maybe you can add. More if you go back and look at, and, and
think about how those systems are used. And think about some of the advantages
and, and challenges, with using a particular irrigation system.
So irrigation system design, also. We just touched on a, a couple things,
about irrigation. And, Looked at, you know, just this, sort
of efficiency, aspect to it. But design and, and management of those
systems are, are very critical to achieving, the maximum.
Some level of efficiency. I want to back up.
So a couple more take-homes. What about management?
That's going to be the other question that we'll talk about.
And I'm fond of the, the little saying here.
That I put here for you to ponder. It's the water, folks.
If we teach em how to manage irrigation then they'll be able to manage fertilizer.
And I think if you think through the course, when we get finished and you look
at nutrient management and you look at water management through irrigation I hope
you'll agree that we need to really focus on water management.
Because water is the driver of where those nutrients are going to be in the soil.
In the root zone of below the root zone. And so irrigation has a major impact on,
on water quality. Irrigation management.
And so next time, we're going to focus a little bit more on some specifics about,
irrigation management. So we'll see you next time.
