-: My name is Javed Iqbal, and I am a nutrient management
and water quality specialist
at the University of Nebraska-Lincoln.
So in this presentation, I am going to share with you
how the nitrogen moves and transforms
into different nitrogen pools, into the soil,
and this will give you a kind of sense,
as which nitrogen sources or fertilizers
are good for the soil, for your crop,
and for (indistinct).
So, to start this presentation,
I will be sharing the nitrogen transformation
when nitrogen from two different sources of fertilizer
is applied into the soil.
So in the first example,
(indistinct) when commercial fertilizer,
in the form of ammonium nitrate, is applied into the soil,
it provides nitrogen in the form of nitrate and ammonium.
This uptake of nitrate is rapid,
because of its mobility.
However, ammonium uptake is slow,
because ammonium is bound to the soil,
and roots have to reach it.
So, most of the plants, they prefer nitrate over ammonium,
however this ammonium is, most of it,
it is converted through soil bacteria to nitrate pool,
which is then taken up by the plant.
However, some of this nitrate
also leeches down into the groundwater,
especially when this nitrate pool
is in excess of plant nitrogen needs.
'Kay, we have different sets of nitrogen transformation
when we applied manure into the soil.
For example, when we are applying manure,
this provides nitrogen in two forms,
organic nitrogen and ammonium nitrogen.
Organic nitrogen is not mobile,
and is not directly taken up by plants,
however it transforms into ammonium pool
through the process of mineralization.
This process speeds up as the soils get warmer,
for example in July.
In the next step,
this ammonium is again nitrified into nitrate pool,
and this process again speeds up
as the temperature exceeds 50 degree Fahrenheit.
Among these two pools again,
ammonium uptake is slow,
because it is bound to the soil,
while nitrate uptake is faster than ammonium nitrogen pool.
Here it is important to note
that when you're applying manure,
then this nitrate pool is comparatively small,
when you apply nitrogen
in the form of commercial nitrogen fertilizer.
So this small nitrate pool
is, though, replenished through mineralization
and nitrification processes,
and provides the (indistinct) nitrogen of the crop uptake.
Because of small size,
this reduces the nitrate leaching potential,
compared to commercial fertilizer.
(man sings in background)
All right, okay.
So, in the previous slides,
we have talked about the nitrogen transformation
and the pools,
but now we are going to see how these chemicals move
within the soil profile.
And actually, soil does a great job
of absorbing all different kind of chemicals,
which are added to the soil profile.
However, not all those chemicals
can be absorbed by the soil particles.
Some of those chemicals usually can move
through the soil profile along with the water,
and contaminate groundwater.
As an example, nitrate, when it's not intercepted
by the crop roots or by soil bacteria,
it usually leeches down into the groundwater
through irrigation water or through rainfall,
which results in contamination of groundwater.
And this problem is usually severe
where we have sandy soils
or we have shallow groundwater table,
and then some evidences have also shown that
this high nitrate contamination also occurs in wells
which are near to the animal feeding operations,
or at home septic tanks,
or the fertilizer dealerships.
Another question is, why does nitrate move into the soil
and ammonium, which is another form of nitrogen,
doesn't move into the soil?
And where does this ammonium nitrogen end up,
and where does this nitrate nitrogen move?
So to see this chemical movement,
we did an experiment to illustrate
what happens when different chemicals
which are water-soluble are added into the soil,
with different ionic charges.
So here in this example, you will see,
we filled up the soil columns, our tubes, with sandy soil,
and so there are some holes at the bottom of these columns
to allow the percolation of the water into the container
that you are seeing below these tubes.
In the left soil column,
we added a red solution containing nitrate nitrogen
which has negative charges.
And then, on the right column,
we added a blue solution
containing ammonium form of nitrogen,
with positive charges.
In the middle column,
we added a mixed solution of nitrate and ammonium
containing both negative and positive charges.
Now we will see how these solutions
containing nitrate and ammonium
move through this soil profile
into the container below.
So, as you have seen,
the solution moved into the container below,
and as you see on the left column,
all the nitrate that was poured into the soil column
has moved into the container,
as you can see the color, which is red.
So this indicated that nitrate
didn't stay into the soil profile,
and it moved through the soil into the container.
However, when you see on the right side column,
the blue solution containing ammonium form of nitrogen
was retained by the soil,
that didn't move into the container.
So now the question is, why did nitrate move
through the soil profile into the container below,
and ammonium did not move?
And then you can see also in the middle column
that nitrate also moved through the soil
into the container below.
So this nitrate moved through the soil
because this nitrate had negative charges,
and these negative charges were repelled
by the negative charges on the soil.
But when you see on the right column,
ammonium nitrogen, which has positive charges,
was attracted and retained by the soil profile,
which had negative charges.
So, let's look into this concept by another example,
so here we have a play with magnetic characters in the soil.
So in this cast today we have six characters,
our first character is ammonium nitrogen,
which has positive charge.
The second character which is nitrate nitrogen
has negative charges.
Our third and fourth character,
which is clay particle and organic matter,
which are found in the soil,
both of them, they have negative charges.
Our fifth character is ammonium nitrate,
which contains both ammonium and nitrate,
but it has together, these have neutral charge.
Our last character, which is water,
also has a neutral charge.
Now, let's start this play and see our first character,
which is ammonium nitrate,
you can see that ammonium and nitrate,
they are bonded together by their ionic strength.
So this ammonium nitrate, it's just like a magnet,
and it has a neutral charge.
However, when this ammonium nitrate
comes in contact with water,
water dissolves this ammonium nitrate
into two different ions, nitrate nitrogen ion
containing negative charges,
and ammonium nitrogen ion containing positive charges.
So let's look into our other two characters,
those are found into the soil,
clay particle, and organic matter,
and both of these are negatively charged.
So which form of nitrogen that we saw in the previous slide
is going to be attracted
by these negative charges in the soil?
The answer is ammonium.
So this ammonium is just like,
you know you might have heard, opposites attract,
so this ammonium nitrogen form
contain positive charges,
so that's why it is attracted by the negative charges
on the soil particles.
So because of this form,
this ammonium nitrogen does not move into the soil profile
until it is taken up by the plant
or until it is nitrified by the soil bacteria.
But what happens with the nitrate nitrogen form?
So this nitrate nitrogen form also has negative charges.
So, will this be attracted by this clay
and organic matter particle?
Probably not,
because those clay and organic matter particle,
they have negative charges,
and negative charges on the nitrate nitrogen,
so this nitrate nitrogen
is repelled by these negative charges
on the clay particle and organic matter,
which results in the movement of this nitrate nitrogen down
through the soil profile into the groundwater,
if this nitrate nitrogen is not taken up by the plants.
So in this play, finally, the ammonium nitrogen is adsorbed,
or held by the soil,
while nitrate nitrogen,
it keeps moving down into the soil profile
and it leeches down through the soil profile
into the groundwater, again,
this happens only if this nitrate nitrogen
is not uptaken by the crops,
which is the case when excess nitrate nitrogen
is present into the soil.
All right, so, we have seen two forms of nitrogen,
ammonium and nitrate nitrogen in our previous slides.
So the question here is,
what happens to the organic nitrogen,
does the organic nitrogen move in the soil profile?
And actually, this organic nitrogen does not move,
because in this pool,
nitrogen is attached to the organic matter particles,
that doesn't move in the soil profile,
neither it is taken up by the plant,
nor it leeches down into the groundwater,
rather it is transformed into ammonium and nitrate pool,
which is then taken up by the plants.
And again, this transformation speeds up
as the soil gets warm.
So otherwise, you can also say that this organic nitrogen
also acts as Mother Nature's nitrogen inhibitor.
So you may have heard about nitrogen stabilizers,
which are used to prevent nitrogen loss
with commercial fertilizer.
So, this organic nitrogen, or manure,
is an alternative product that acts
as Mother Nature's nitrogen inhibitor.
Okay, so now to wrap up,
here I have a summary of 141 studies,
so in this study, they compare the effect of manure
and commercial fertilizer on nitrogen losses.
So what they found,
that when you substitute commercial fertilizer with manure,
it provides some benefits.
For example, it adds nitrogen into the soil profile,
it increases nitrogen pooled by 22%.
And this substitution decreases
ammonia volatilization by 27%,
it also decreases nitrogen runoff by 26%,
decreases nitrate leeching by 29%.
From crops perspective,
this substitution increases nitrogen uptake by 4%,
and crop yield by 7.8%,
which indicates that this replacement
is really a win-win situation,
not only for decreasing the nitrogen lost,
but also enhancing the crop's yield.
So now we'll just wrap up with a take home message,
that these ammonium-based nitrogen fertilizers,
they are good for retaining nitrogen into the soil,
which ultimately increases the nitrogen uptake,
when there is a better synchronization
between nitrogen uptake and nitrogen availability.
And we have seen some bad years in Nebraska,
which increases the nitrogen loss,
so when you are using this ammonium-based nitrogen sources,
these provide good insurance
under heavy precipitation events,
which eventually reduces nitrate
leeching into the groundwater,
and as I mentioned earlier,
these ammonium-based fertilizers of organic nitrogen,
especially this manure-based fertilizer,
they are good alternative to nitrogen stabilizers
that are used with commercial fertilizers.
'Kay, so with this I will end my presentation.
If you have any questions,
you can reach out to me through my email or phone.