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.
Nutrient Fates, Part 1
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Del curso dictado por University of Florida
Sustainable Agricultural Land Management
47 calificaciones
De la lección
TMDLs & Nutrients
In week 3, we will discuss TMDLs and agriculture, agricultural soils, and the first part of nutrient fates.
Conoce a los instructores
George J. Hochmuth, Ph.D.Professor
Urban and Agricultural Environmental Sciences
Hello everyone, welcome to our third lecture in our third week.
If you recall, previously, we talked about soils.
Particularly in our agricultural systems and some of the roles soils may play in
nutrient management and environmental protection, and some of the things that
farmers might do to manage those soils. Today I want to dig a little deeper, as it
were, into nutrient cycles in the soils. Specifically, we want to take a look at
the idea of how nutrients enter our crop production systems on the farm, in our
soils, and some of the flows that these nutrients, some of the fates and, and
Transformations these nutrients undergo in these agricultural settings.
So we want to consider the cycling of nutrients in the environment, particuarly
on our farms. Where do these nutrients come from?
Where might they go on the farm? What are some of the processes they
undergo in terms of transforming from one form to another, become available to crop
use or not available for crop use. I think that it's very important to
understand these processes, these cycles, cycles on the farm.
If we're ever going to understand where we might deal with nutrient management on the
farm in an effective way. In other words how might we develop best
management practices and focus on the important parts of the nutrient cycle so
that we can achieve goals. That we want.
I like these presentations of the different cycles.
This is the nitrogen cycle. I like them particularly because the
different colors show you the different pools of in this case, nitrogen.
For example the green colored items identify those important components of
nitrogen, so for example the top of the picture you see nitrogen from the air,
atmospheric nitrogen. You also see some other pools of nitrogen
that would appear in the soil. For example, we have organic forms of
nitrogen in our soil from organic matter. Maybe even crop refuse from the previous
crop. We also have mineral forms of nitrogen,
ammonium, and nitrate. We have the blue-colored portions that
depict the sources of nitrogen that might come into this production system.
For example, over to the right here we have the industrial fixation we know as
fertilizers. We'll talk a little bit about this
process. We use fertilizers, we apply fertilizers
into the system, into the cycle to help grow crops.
Then those crops can, as we harvest, there's crop refuse that might be left in
the field behind after harvest. Those residues then decompose and enter
into the organic pool. Cycle back into the organic pool in the
soil. We also may apply manures.
In terms of increasing organic matter or supplying nitrogen to crops.
There's also atmospheric forms, other atmospheric forms of nitrogen.
For example, that fixed by electrical storms.
Also an important source of nitrogen in. Production systems would be the biological
fixation process. This happens in certain types of crops we
call legumes, and they can actually fix atmospheric nitrogen in forms of nitrogen
that can be utilized by plants. Sorry let's not.
Let's look at the red the crop harvest is a pool of nitrogen that shows up in our
crops. This is actually the pool of nitrogen that
we want to focus on. Most, we want to maximize the amount of
our Nitrogen fertilizers that we put on getting into the crop and resulting in
im-, improved crop growth and yields. There are also some pathways of Nitrogen
loss from the system. For example, we'll learn a little bit
later today about volatilization. We'll learn a little bit about runoff and
erosion as ways that nitrogen can be lost from the system.
There are other ways that nitrogen can be lost from the system.
For example, gaseous losses from denitrification.
We'll take a look at that process. And then finally, we can lose nitrogen.
Mostly in the form of nitrate through the leeching process.
And this might be a negative implicatoin in the cycle because nitrates can result
in eutrophication that we've already talked a little bit about.
The nutrient phosphorus is important in plant growth and we supply it in
fertilizers to achieve crop growth and good yields And there is a parallel
process or cycle for phosphorus and our agricultural systems.
This particular diagram shows the same kinds of pools of phosphorus in terms of
the forms of phosphorus that are in the soils, the way that we might apply or
introduce phosphorus into the system, and then the red being the ways that
phosphorus might leave the system. In the case of phosphorus, Phosphorus
enters into a lot of different transformations in the, the soil.
And can become fixed in unavailable forms or at least not easily available forms for
plant use. And I've given you some of the different
ways that Phosphorus can be transformed in the, in the soil.
Again, phosphorus can be introduced into the system from fertilizers.
From plant residues from animal manures, and also from atmospheric deposition, for
example dust or smoke. We become very concerned about the
pathways for loss of phosphorus from the system.
Leeching is in most agricultural soils a relatively minor pathway for loss of
phosphorus. Most often, we find phosphorus being lost
from the system through runoff, particularly from erosion, and we've
looked at a few pictures of erosion from our fields, and as that soil is moved off
of the field it can take the phosphorus is associated with the soil, and if you look
at the green colored portions of this diagram you can see how phosphorus becomes
closely associated with the soil particles and therefore your erosion can be a
particularly troubling avenue for losses of phosphorus from the system.
So what we might ask ourselves when we look at these cycles, which of these
inputs and losses might be the largest issue that we might deal with, knowing a
little bit about our soils and our topography and the cropping systems that
we're using. Which of these nutrient sources might be
the easiest to manage? Is it easy to manage for example, our
manure or fertilizer inputs into the system?
And what role may the soil play itself for example sandy soils we've already learned
that sandy soils are highly prone to leaching.
So in managing nitrogen in those systems, consideration of the type of soil that we
have might be important. If we are on rolling land, we might be
very concerned about the loss of phosphorus from those fields through
erosion. Phosphorus has a long list of different
pools and fates, and I've provided a list. You'll see these same ones on that
diagram. I don't have time enough to go through
both phosphorus and nitrogen in detail. We'll focus on nitrogen.
But I think it might help you to take a look at this list and maybe write out some
definitions and descriptions of these different processes and think about in
your particular maybe perhaps farming scenario.
Which of these processes would be important to, to consider, particularly
from a economic standpoint of increasing crop productivity, but also from an
environmental A standpoint. Which ones of these sources can you manage
most appropriately and effectively? And which ones might be causing you the
greatest concern for losses of Phosphorus from the system?
Because remember, the triple bottom line tells us that we need to be concerned
about both the economic ramifications of nutrient use as well as the environmental
aspects. Just as an aside in the case of phosphorus
the USDA has developed what is called a phosphorus index.
And this is simply a tool to help A land manager determined a risk associated with
certain soils in terms of, as it relates to phosphorus loss.
And so it can predict the likelihood as phosphorus loss from a particular soil.
Most of the states had developed their own P index.
And the P index is simply an approach to embody variables, measurements of
variables, in an approach to synthesize all of these different kinds of variables
and come up with a factor that might predict the risk of phosphorus loss from
that particular form or soil. So for example variables such as soil
tests, some kind of measurements of the soil tests, phosphorus value, P
application rate as manure or fertilizer, something about the topography of the
fields in the proximities to water bodies. So all of these variables are, are
assigned point values and then the greater sum of the, the points would equal a great
risk to the environment. So it's a way to do an evaluation of a
particular field and, and the soil and the farming system.
And come up with a risk that might be associated with phosphorus management on
that land and it's relation to potentially pollution of a nearby water body.
I want to spend a little more time today and the next lecture or two on, on the,
the nitrogen cycle. Keeping in mind that there is a parallel
cycle for phosphorus and these are the two nutrients that we're most concerned with
as it relates to farming profitability or economics and, and the environment.
I want to go through these items and talk a little bit about their importance in
terms of the cropping system and the farming productivity and also the
environment. First of all, take a look at some of the
nitrogen inputs into the system and there are several of these.
We probably think of fertilizer as the first and most important nitrogen input
into a farming situation and in most cases we would be right.
I've given you two pictures here of different kinds of crop production
scenarios, each involving fertilizer inputs into the plant production system to
increase plant productivity. The industrial form of nitrogen fixation.
The so called Haber-Bosch process is our main way that we form fertilizers.
This is where our fertilizer industry, our nitrogen fertilizer industry is based.
This particular process was developed and taken to an industrialized level by these
two German individuals shortly before World War 1.
In fact, some people consider this to be one of the most import and scientific and
industrial discoveries in history. It's the basis of today's fertilizer
industry and some writers and scientists would estimate that 50% of today's
population on this planet exist because of this process.
And this is because the, this shows the importance of nitrogen fertilizer and its
many fracturing to increases and crop productivity.
So the fact that we can develop and manufacture nitrogen fertilizers and use
them, hopefully efficiently, on the farm has led to an increase of food production
that has allowed a lot more people to, to live.
There are many sources of synthetic nitrogen fertilizers that in one way or
another relates to this process and I've given you a few of these.
Anhydrous ammonia urea those are two important sources of nitrogen fertilizer
for crops but there are a lot of other materials that combine nitrogen and
phosphorus, for example, or nitrogen and potassium.
Nitrogen fixation can also occur in a biological path and this is done by
nitrogen fixing plant such as legumes or some people might call pulses.
This process is due to the fact that symbiotic nitrogen fixing bacteria live in
association with the roots of these specific plants.
So, for example, alfalfa, soy beans, or clovers would be called nitrogen fixing
crops and this is due to the bacteria that live in association within root nodules on
these plants. And you can see that there are some
significant amounts of nitrogen that can be fixed from the air.
From the nitrogen gas in the air and made N forms that are available for plant
assimilation. The fixed nitrogen that's provided by this
process though converts nitrogen gas into forms eventually into forms ammonium and,
and nitrate that then enter this nitrogen cycle and thus must be now managed.
So we have it, in effect taking an inert gas and put it into our crop production
system and our management system so that now just like fertilizer sources of
ammonium and nitrate. We must now manage to keep it in our
production system, benefiting crop productivity and not ending up in the
environment in a negative fashion. Here's a picture of clover crops that fix
large amounts of, of nitrogen, sometimes we'll learn, well will learn little later
on in the course about how these kinds of crops can be used not only to provide
nitrogen for a subsequent crop but also to be used as cover crops.
Here's a here's a legume that shows the, the particular nodules in which the
bacteria live and fix nitrogen. That is then assimilated by, by that
plant. We also can provide nitrogen to our crops
from animal wastes, manure. I've given you a list of, of various
manures that we typically use in, in crop production systems.
Poultry manure would be one of the more common sources of nitrogen from an animal
waste, but all of these different sources can be used and they supply nitrogen and
also other nutrients. Phosphorus in particular can be supplied
by animal waste and be a significant source of phosphorus on the farm.
Animal wastes are in effect a low analysis fertilizer.
They have a relatively percentage of these nutrients in them.
They are an organic matter. It's, can be or should be thought of as a
mixed fertilizer because these manures do supply a suite of nutrients that are
important for crop productivity. Nitrogen phosphorus and potassium in
particular. So, if we're going to use manures as
sources of nutrients on the farm, we really need to know the content of these
nutrients in these manures so that we don't over apply the manure as an attempt
to supply enough nutrition. An important part of this whole process is
understanding how fast those nutrients are going to be released not organic matter or
that manure. It takes a while for this nutrients to be
mineralized from that manure. So we need to understand a little bit
about how fast that process works because we want to apply enough of these manures
and understand that how long it takes for those nutrients to be released so that we
benefit from them. And that most of the release for example,
does not occur late in the cropping cycle or even after the crop has been harvested.
So animal wastes can be used as fertilizer.
Here are a couple pictures, one on the top of poultry manure that has been piled at
the end of the, the field while it's being while it's being applied, and at the
bottom compost from cattle manure is being applied to a cover crop in preparation for
tillage and planting of, of a major economic crop.
There are, also some other sources of nitrogen that can come into our system.
For example, atmospheric deposition. As I mentioned before, electrical storms
can fix nitrogen. Combustion, automobiles, industrial
sources can also put nitrogen in the air, then they eventually Be deposited on our
land. I've given you the website for the
Naitonal Atmospheric Deposition Program which calculates and presents data for
various places in this country for nitrogen potentional for nitrogen
deposition. And it varies greatly so in some areas of
the. The country.
Their are significant amounts of nitrogen that can come from this source, and as a
mentioned before atmospheric fixation by lighting, this is a relatively small only
a few percent of total fixed N that would be applied or be deposited on our crop
land by this, this particular method. So if we just summarize a, a few aspects
about Nitrogen and Phosphorus and, and the cycles.
Both of these nutrients are involved in relatively complex cycles in the soil.
These are not trivial to understand and even More difficult for scientists to
measure and it, it becomes, it becomes a very difficult exercise to really
understand and quantify the amounts of nutrients that are being put into a system
and how they cycle in the system and the amounts and the methods by which they
might be lost from the system. We looked at nitrogen and, and phosphorus
in this regard. Our major inputs of these two nutrients,
they are important plant nutrients, but the major inputs in most farming
situations would be from fertilizers and, And in some cases, manures.
There are several fertilizer sources that we might apply.
For example, an organic farmer might be supplying phosphorous from rock phosphate,
and a, other farmers might supply it from synthetic forms of fertilizers.
So there is various forms of fertilizers and farmers need to determine what is the
best source and material to use in their production system I want to take a little
bit in the next lecture, a little bit of time, to take a look at some of these
fates. We sort of have an idea now of where some
of the sources of nitrogen and phosphorus inputs into the system.
Would be so after we've introduced them into the system or had them introduced, if
it's in a natural fashion,then what happens to those nutrients once they're in
the systems. And we'll take a look at some of the fates
of these nutrients in our soils and in our farming systems in the next lecture.
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