Available or Not: The Nitrogen Guessing Game in Manure Planning

In this episode, Dan Andersen discusses nitrogen availability in livestock manure. He dives into PMR 1003, Using Manure Nutrients for Crop Production, which estimates nitrogen availability and the need for updated research to reflect changing manure handling methods and storage practices. 

Show Notes

PMR 1003 Using Manure Nutrients for Crop Production

Episode Transcript

Dan Andersen (00:06):
Hello, and welcome to Talkin' Crap, a podcast by
Iowa State University Extensionand Outreach. This institution
is an equal opportunity providerfor the full non discrimination
statement or accommodationinquiries, go to
www.extension.iastate.edu/legal.
In this podcast, we discussinsights into the science,

(00:27):
technology, and best practicessurrounding manure management.
Our objectives are to buildawareness about the challenges
farmers and the broaderagricultural industry face
around manure and to demonstratesolutions and areas of
innovation.
Hello, and welcome back foranother episode of Talkin' Crap.
I'm your host, Dan Andersen,associate professor and
extension specialist in the agand biosystems engineering

(00:48):
department and go by the nameDr. Manure. This month's episode
is Available or Not, theNitrogen Guessing Game in Manure
Planning. So this is a topicthat I really love. It's in
Manure Management 101, and thenwe get to zoom into maybe the
senior level version of whatavailability is, what we're

(01:08):
trying to talk about, where thescience is taking us. And what
the heck are we doing aboutthis, which is exactly what I
love. It seems simple,straightforward at the start.
And then we get to make itrocket science. And then
hopefully at the end, we canzoom back and say, alright, now
that we heard all that, thoughtabout it, tried to digest some
of that information, what doesit mean for us when we actually
make some of these decisions? SoI wanted to start out with, what

(01:30):
is nitrogen availability? Whatdo we mean when we say that? And
to me, I think the importantfirst thing is not all nitrogen
in manure acts like fertilizernitrogen. Available nitrogen
refers to how much N the cropcan use in the applied season or
in subsequent growing seasons.
So a definition I like isavailable N is nitrogen the

(01:51):
plant can use. Total N is mostlyorganic N and ammonium N, though
in some manure systems, nitratemay be present at relatively
small levels, organic N is slowreleasing nitrogen. Ammonium N
is basically what we're gettingin many commercial fertilizers,
and except for what is lost tothe air, can be used directly in

(02:12):
that application year. On theother hand, organic nitrogen
generally must be released orturned into smaller compounds
that plants can use, and the twowe think of most of the time are
ammonium and nitrate. Theremight be a few others you could
think of, like nitrites, but forthe most part, we're talking
ammonium and nitrate when wethink about what plants can use.

(02:33):
So historically, we've alwayssaid that organic nitrogen must
be mineralized to ammonium andnitrate, and I still pretty much
believe that. But I do want toadmit there has been some
research that say plants maytake up simple amino acids or
even short peptides. So smallparts of basically protein.
However, that is generally mostcommon in things like forest

(02:56):
tundra or extremely low nitrogensystems, not typical of
agricultural soils, probably notsomething we have to worry about
in less we we suddenly havebrilliant ideas about how to get
really specialized, operate atlow levels of nitrate in the
soil and still maintainproduction. In most agricultural
soils, microbes tend to be muchfaster than plants at finding

(03:18):
that nitrogen breaking it downbecause they're getting energy
from it and using it fornitrogen, so it's their entire
life support, whereas plants arereally thinking about it as I
just need it for nitrogen andthe rest is sort of a benefit.
So oftentimes microbes will outcompete plants. And that's going
to be a theme that I try andbring up a few times throughout
this when we think about, why isit available? Why does it get

(03:40):
tied up? So an opposite idea ofavailability, and I didn't use
the term yet, but one that Ithink is important as we set
this context, would beimmobilization. And what I mean
when I say immobilization isthat some portion of the
nitrogen that gets turned intoorganic compounds, whether that
be cellular biomass, enzymes,some people use it for plant

(04:00):
biomass. I tend to not do that.
I just call that plant uptake,but it's getting turned into a
type of nitrogen that isn't justsitting in the soil mineral
pool, and it can't be used,right? It has to re break down.
And there's sort of contrastingideas. The more that's
available, the less that we'vehad immobilized. If we're
getting mobilization, that meanswe don't have as much

(04:22):
availability at the moment. Theother thing that I wanted to
talk a little bit about, andwe'll get to this in more detail
as we get to PMR 1003, is sortof the idea of availability
versus supply. And some statesuse this differently than I do,
and that's why I wanted to bringit up. When in Iowa, we say the
word availability what we reallyare trying to refer to is that

(04:45):
it's in a form that plants canuse. That is it's available to
help support plant growth, notthat it will. When we say
supply, we're really talkingabout how much nitrogen is in
that soil altogether, right?
It's, it's related to thisaddition loss question. So
supplies related to things likeleaching, losses,
denitrification, maybe ammonia,volatilization. When we talk
about availability, at least inthe context of Iowa, we're

(05:07):
saying it's in a form thatplants can use, other things can
happen to it too. But thatdoesn't ultimately change what
was available in the manure. Itchanges how much that manure
might be capable of supplying.
All right, in my notes here, itsays I'm supposed to talk a
little bit more about forms ofnitrogen. I feel like we've been
hitting on that pretty good. Butreally, when we think about
manure, there's three types ofnitrogen. There's ammonium

(05:29):
nitrogen, so that acts just likemost ammonia fertilizers. I want
to say, like most ammoniafertilizers, it's not perfectly
similar. For instance, if you'reusing anhydrous ammonia and
inject that into the soil, youget a zone that's really basic
in pH. Maybe I've killed somemicrobes in that, that near
vicinity with manure. We don'ttend to see that reaction. We
might still inject the manure,get it into a zone, but we don't

(05:51):
get the same PH effect, right?
We don't get nearly as basic.
We're probably not killingmicrobes in the soil. We might
even be firing up or inspiringthem to do a little bit more
activity, because I fed them areally nice, available carbon
source. But for the most part,it's at least relatively similar
to something like urea. Theother form that we think about
the most is organic nitrogen,and that's tied to some sort of

(06:12):
organic matter. It's coming withcarbon attached to it, and that
means it needs some time tobreak down. The final form is
nitrate, and in most manuresources, there's extremely low
levels of nitrate. Oftentimes, Idon't even think about it or
consider it every now and then,if you're working with the
solidmanure system, one thatmight get aerobic, you can
sometimes see some nitrate, butit does tend to be a relatively

(06:33):
minimal portion of the nitrogenthat we're putting on the soil.
Now that isn't to say it staysthat way once we put it on the
soil, once we're putting it inthe soil, and those aerobic
conditions, all bets are off. Sowhy this matters, or at least
why I think about it a lot, isit's complicated. It really
changes our fertility picture.
And what we're trying to do istake advantage of manure as a
resource on every acre we havethat in the state. So avoid over

(06:54):
applying. So trying to avoidplaces where man, that yield,
that corn, looks terriblebecause I didn't have enough
nitrogen there, and also toavoid over applying right,
because that leads to moreleaching losses, volatilization
losses, or at least ways thatit's getting into the
atmosphere, whether that bedenitrification or movement with
water. We have a great historyof knowing that matching manure

(07:14):
and crop demand and trying toget those two numbers right
improves nutrient use efficiencyand environmental outcomes. So
we're on the same page, right?
If we're doing the best by ourcrop, that also probably means
we're doing the best by waterand air quality. But it is
complicated. Every year isdifferent, and I don't want to
make light of that. And when wethink about how variable manure

(07:35):
is, how uncertain manure is,it's a difficult, difficult
subject, one that I'm 10 yearsin 12 years into this job, and
still wake up every day excited.
And get to say there are a lotof things that I don't know
enough about to really giveeveryone the recommendations
they want, but I do think we'relearning more about how to point
in the right direction. So allthat to say it's not just about
how much nitrogen is in themanure, it's whether the

(07:56):
microbes want to share it withyour crop.
The other day, I was sitting ina defense and it was about
nitrogen mineralization. Soinspiring. This this talk a
little bit, but he talked abouthow fertilizers are often
feeding the plant and manuresare feeding the soil. And I like
that analogy to some level. Butreally, with manures, we're

(08:16):
doing some of both, right, andthat makes it more complicated.
And when he says that it's notso much for necessarily feeding
the soil, when we think of justabout the nitrogen forms that
has more to do with carbon. Butit is an analogy that I think
does some justice here, thatthis is really, really
complicated. So when we thinkabout nitrogen availability, or
what's happening in soils,generally, soil microbes tend to

(08:37):
run the show. Right when itcomes to breaking down organic
matter in soils, we're prettydependent on microbes. When it
comes to nitrogen processing,the microbes are determining
what's happening. So when youthink about what microbes are
doing when they find thatorganic matter, they're breaking
the carbon down. Some of it getsconverted into CO2and some of it
gets converted into microbialbiomass. Oftentimes we think of

(08:58):
that as cell biomass, but itcould be other things, like
enzymes that they're making orwhatever, right? And then the
nitrogen was just there alongfor the ride for the first part.
But then they have a choice. NowI've broken down this carbon. I
freed up this molecule ofnitrogen. If I'm growing cell
biomass, making proteins, makingenzymes, I might need that
nitrogen. I'm gonna say, oh,that's precious to me. Gonna

(09:18):
hold on to it, put it in my celland use it if I have more than
what I need, well, then it's awaste product, and I start
throwing it back into theenvironment, right? Essentially
throwing it away. Now that's agood thing for us. It's not a
waste, right? We still want itto help support crop production.
That tends to be how we'rereally using a lot of the
organic nitrogen in the manure.
It gets cycled through thatmicrobe, and they make a
decision of, should I turn itinto microbial biomass, or put
it back in the soil? And it's awaste to me, and then when it's

(09:41):
a waste of them, it becomes ourcrop food. So some rules of
thumb on this, the C to N ratioof things often, are a nice
first indicator of how themicrobial pendulum of whether
release or mobilization is goingto occur. And this isn't
perfect, especially when I talkcoarsely about carbon to

(10:02):
nitrogen ratio. What I'm reallytalking about is bioavailable
carbon to nitrogen ratio. Butthat gets complicated to say
every time, so it's sort ofimplied. And then, because of
that, we use some rules of thumbto understand maybe how
bioavailable that carbon mightbe in general. So if we're
talking about low carbon tonitrogen ratios, and by that, I
tend to mean something below 15carbons to 1 nitrogen. That

(10:24):
really means there's enough andthere for the microbes to have
excess. So as they break downstuff, some of that nitrogen is
released in the form ofammonium, back into the
environment. They'remineralizing that nitrogen,
taking it from an organic form,turning it into a mineral form.
So essentially that they'reconsuming that carbon, they're
releasing CO2 and they can't useit all for cell mass and

(10:47):
enzymes. Something has to go andthey get rid of it. And that's
really typical for many of ourliquid manure systems, swine
manure, liquid dairy manure,liquid beef manure. When we get
the opposite of that, somethingwith a high C to N ratio. And to
me, that's generally above 30 to1. The microbes need to pull
nitrogen from the environment tosupport themselves, so there's

(11:10):
not enough carbon to handle sortof what cell mass they're going
to make as they're breaking thismaterial down, and they're like,
I need more nitrogen. I'm in agood environment. I'm growing
well, I have plenty of energy.
There's one. Take it in, I'mgoing to turn that into
something. So they're reallyscavenging for nitrogen in the
environment. And that's thatsituation where we think about
immobilization. Now, microbesdon't last forever, right?

(11:32):
They're going to break down.
Enzymes are going to break down.
So just because it wasimmobilized doesn't mean it no
longer can ever be plantavailable again. It just means
it needs to go through a cyclewhere that cell dies.
Eventually, something else comesalong and breaks that cellular
material down, and eventually itmight lead to some release. Now
you might notice that I had agap in there 15 to 1 to 30 to 1
What happens in between? And theanswer is, I don't know. That's

(11:54):
when sort of thatbioavailability of the carbon
question gets to matter a lot,or what sort of conditions do we
have, and how rapid can themicrobes process these things?
And that really is an unknownzone, right? We could really
dive in and try and do better,but essentially, to me, what
it's saying is, well, weprobably won't see a lot of
nitrogen release, a lot ofavailability. We probably won't
see a lot of immobilization.
We're sort of hanging out inSo you've all probably had some

(12:16):
experience with this. And if webetween.
think through some of our manuretypes, it's probably pretty easy
to say, why? So when we talkedabout swine manure earlier, I
said, Well, that's a low C to Nratio. It's broken down pretty
good in the pit and we put it onthe soil. And oftentimes we're

(12:36):
putting it on the soil, about80% of the nitrogen is already
in the ammonium form, and only20% in the organic form. So
that's one easy to say, well,even if I have some tie up from
breaking down those organicsolids, I probably don't. They
have low C to N ratios, probablyin the neighborhood of 10 to 1,
12, to 1, generally in soymanure. So we're probably
getting even released fromthose. But even if I wasn't,
there's enough ammonium thatI've added to the soil to really
cover what I'm breaking down.
Corn is gonna look green, gonnalook good. I don't have to worry

(12:58):
as much about early season eventand availability. If you
contrast that with somethinglike solid beef cattle manure,
maybe you've had this experiencewhere, wherever the chunks of
bedding fall, my corn looks theworst in that part of the field,
and that's really because ofthat N high up, right? We're
getting an immobilization. Andthat's the rule of thumb that we
really want to think about andremember, from this section high

(13:22):
carbon to nitrogen ratio manurestend to lead to nitrogen tie up
early in the season. Maybe we'llget some release later low
carbon manures, especially lowcarbon nitrogen ratio manures,
we tend to get that nitrogenrelease. And that's why two
manure samples with the sametotal N can behave very, very
differently in practice, right?
It's all about thatavailability. So if one's high
with bedding or straw, you mightactually be getting some

(13:44):
immobilization or tie up tostart, even though you're like,
I put on how much nitrogen Iactually think the crop needs?
Well, it might not be availableat the right times.
All right. That takes us to thenext portion of what my notes
say I'm supposed to talk about,and that's really the Iowa guide
to this discussion, or at leastthe starting point to the Iowa
guide to this discussion, that'sPMR 1003, Using Manure Nutrients

(14:07):
for Crop Production. And it'snot the end all be all, right,
but it's a great starting pointfor what we're doing. And a
couple things on this. Therecommendations here are based
on limited field and lab datathat was collected quite a
while, a while ago, now, in theearly 2000s and the data is
probably getting more dated.
Storage message methods arechanging. For instance, in

(14:28):
poultry litter, we went fromhigh rise facilities to maybe
belt facilities where we'redoing some manure drying. Well,
hopefully that system is holdingon to more of the urea, ammonia
nitrogen in the manure. And onewould think that increases
availability. I think we'veprobably seen that. I think I've
seen that on some of the trialsthat I do with poultry litter,
but that's one example. We'vealso seen a lot more people
looking towards bed pack anddeep pit beef barns rather than

(14:51):
open lot facilities. And whileas a starting point that one
says all beef manures are thesame, I think when you look at
the samples, you do. See somedifferentiation, and it's
probably about time that westart catching up with that. And
that's before I get into well,manure processing has really
taken off. We see many dairyfarmers doing different types of
solid liquid separation forvarious reasons. We've seen some
farms think about anaerobicdigestion systems. There's just

(15:13):
more variation in the types ofsystems that we're building. And
it's not manures, manures,manure, it really is time to
dive into some of the sciencethat and start trying to maybe
refine some of these estimates alittle bit more to meet what
production systems are actuallydoing these days. One thing I do
want to talk about, and werarely state this when we talk
about that availability tablefrom PMR 1003, but it's true is

(15:35):
this method was at least pickedin part for simplicity. It only
needs to know the total nitrogencontent of the manure, and you
simply apply a coefficient, andboom, you get your answer. The
method was picked in at least inpart because many labs at the
time weren't measuring ammonicalnitrogen. They were only
reporting total nitrogen back tothe user. And if you only have

(15:56):
total nitrogen, it's nice tohave one coefficient to measure.
It, say that's good and move onwith life. But I think a lot of
the more recent work, one thatcomes to mind is some work that
I saw out of Wisconsin has shownthat generally, by having both
the ammonium nitrogen and thetotal total nitrogen, organic
nitrogen fraction, you can do abetter job of estimating because
we know that or that inorganicthat ammonium fraction is plant

(16:18):
available, and we can focus onrefining maybe for that organic
fraction estimate. So when wethink about what that PMR 1003,
says, I just wanted to give yousome ranges. When we're dealing
with cattle manures, whetherliquid or solid, beef or dairy,
we're grouping them all thesame. And I don't particularly
love that, especially as we'vewe've learned to feed different
it probably matters, right? Abeef cow probably gets fed a

(16:41):
fair amount different than afinishing steer. Dairy cattle
probably have the proteincranked through them, and
they're not eating maybe theforage that they were when we
developed this, or at least inthe same form, right? They're
eating a lot more corn silage, alot less alfalfa hay, and that
means it's probably time toupdate. But for the for the
starting point on this, at leastit estimated 30 to 50% first
year available. With our pigmanures, we were at that 90 to

(17:03):
100% first year available. Andthen with poultry, all the
species got grouped together. Itwas at 50 to 60% first year
availability. And then it doesprovide some mineralization
coefficients for year two and insome cases, year three, as
footnotes on that. I'm not goingto take the time to read them
out, but it does put them inthere. I think the important

(17:23):
part to note is that they don'talways add up to 100% and
there's reasons for that, andwe'll try and talk to some of
those a little bit later.
A second way to estimateavailability, and one that in
many ways I'm partial to, is theold Midwest Plan Service method.
And it starts out moresophisticated. It says, Hey,

(17:44):
that ammonium is already plantavailable. We don't have to do
much about that. Just take theamount you have there and say
that's 100% available bydefinition. It's in a plant
available form. And then itsays, let's focus on the organic
and fraction next, right? So howmuch of this is going to
mineralize is related to how themanure has been previously
stored and handled, at least tosome respect, because it's kind

(18:04):
of about the losses or breakdownthat it's had during the
storage. And I'm not trying tosay we should treat these
methods, these numbers, likegospel, but I think that first
breakdown, it at leastintuitively, tells us that
there's some reasons to believethat it might be a little bit
better, at least pointing us inthe right direction. One thing
in particular I enjoy is it'ssort of a tuning factor for for

(18:25):
the variation of manure, right?
So if I go get a swine manurethat comes back with only 50% of
the nitrogen in the ammoniumform, I might say, well, that
doesn't look quite like atypical manure. And if I'm just
applying that Iowa number, I'mstill gonna say 90 - 100% first
year availability, whereas inthis case, I get to say, well,
something was weird about thatmanure. Let's think about it a
little bit more deeply. How isit stored? How is it used? And

(18:45):
go from there. Now what theytend to do is they came up with
a table that basically has twofactors to it, the manure type,
so basically the animal speciesthat you're using, and then a
manure handling system. And youcan find what those numbers are
in the show notes, and they'renot the gospel truths. As a
matter of fact, I can't findwhere much of that number, how
they derived it comes from, butit does fit at least relatively

(19:08):
well with some of the data wesee from some of the
mineralization studies that youcan find in literature, and it
seems directionally correct. Sofor example, you might look at
the swine manure. And for swine,they have basically three
different types of manure. Theyhave fresh manure, anaerobic
liquid and aerobic liquid, andfor the organic nitrogen in
those they give them threedifferent mineralization
factors. For first yearavailability for the fresh

(19:30):
manure, it says 50% first yearavailable for anaerobic liquid,
it says 35% of the organicnitrogen will break down. And
for the aerobic liquid, it says30%. So why those numbers? And
in many cases, it's sort of whatyou'd expect with fresh manure,
it hasn't broken down much yet,but there are more compounds
that are easy to break downstill remaining in the manure.

(19:51):
So because of that, they'resaying, well, it has to break
down. It didn't break down if Istored it, it's going to break
down when I put it in the soil.
That availability has to be.
Higher. And the same sort offollows for that anaerobic
liquid being higher than theaerobic liquid. In this case, I
often will tell students,there's a reason elephants
breathe oxygen, right? And it'sthat oxygen reactions tend to be

(20:11):
exothermic. They make lots ofenergy. That's why fires are
cool and fun, also dangerous,but cool and fun, right? And so
that means that when I go froman anaerobic environment and put
that thing in an aerobicenvironment, like soil, those
microbes are going to get afterit and get stuff that in an
anaerobic environment, therejust wasn't enough energy
available to keep chasing do thesame reaction. In an aerobic

(20:33):
environment, it's worth yourwhile to get that last juice
from the squeeze, all right. Andthen after that, we sort of hit
the, my favorite part of thismethod, and that's the part
where it looks like we needed tocome up with an answer and and
they said, That'll do because wedon't actually have the data we
need. So they also give you amethod to estimate availability
in years two, three and four.

(20:56):
And it does feel a little bit tome like they said, who knows,
but it'd be nice to have asequence like, how about 50% 25%
and then 12.5% of what wasavailable in year one, sort of a
curve that's slowly gettingtowards that 100% saying you
don't have to take as muchcredit for what's left. And then
someone else at the meetingprobably said, I don't know
either, but that at least soundslike a reasonable first

(21:18):
approximation. And given thatnot that much of the nitrogen is
organic, probably minimizes someof what we're doing. It also
means that if I have a manurethat had a lot of organic
nitrogen,I might have less of it becoming
available, and it'll take along, long time to get to 100%
and they said, you get to stopat four years. You don't have to
keep doing this, right? And atsome point that nitrogen just

(21:38):
acts like it's in the soilnitrogen pool. Now, at this
point, my show notes say I amsupposed to talk a little bit
about how you'd do someexperience experiments to figure
out how to measure nitrogenavailability, or how to figure
it out. And there's a coupleapproaches to this, but the one
I wanted to highlight first wasdoing it at a field scale, and
why getting those numbers fromyear two and year three and year

(21:59):
four might be really tough todo, or not, something that we've
done enough of in the past. Soto do this type of work, what
you do is you put a manure ontoa plot at some reasonable rate,
or two reasonable rates. Now ithas to be reasonable, because if
I put on too much manure, toomuch nitrogen, it won't work for
me. I have to be a little shorton nitrogen. If I'm if I'm
optimal to short, I'm probablyokay, if I put on too much

(22:21):
nitrogen I don't get anyinformation out of the study at
all. And you'll see why in asecond. And then, right next to
where I did that manure trial, Ihave to generate a nitrogen
response curve. So I have to goand say, What happens if I had
no nitrogen? What happens if Iput on 25, 50, 75, 100 pounds an
acre, all the way up to whateverI think is optimal. And ideally
I'd say one more rate or twomore rates, so that we really

(22:43):
see that we've maximized yield,and we know the shape of that
curve. And then what we do is welook back at the yield of that
manured plot and say, Well, ifthat would have been commercial
fertilizer, we'd fall right hereon the yield response curve. And
then you read the x axis andsay, Well, that was worth 170
units of nitrogen. And in theplot, I put on 200 units of
total nitrogen from the manure.

(23:05):
So that means it's 85%available. And that's great.
Year one went fantastic. We gother done. Now I say that's great
and easy. There's a lot ofvariability in some of those
numbers, so deciding where youare on the curve can be
difficult. And lead to saying, Ishould just pick it was in this
range. But that also means thatif I want to do this for year
two, three or four availability,I have to take that same manure

(23:26):
plot and then the next yeargenerate a nitrogen response
curve near that plot, puttingnothing on my manure plot, and
say, Well, where did I fall onthat curve now? And as you might
guess, some of that corn mightlook a little yellow because
there isn't much nitrogen supplythere, but that's what we'd have
to do. And then year three andyear four get even tougher,
right? Because we're gettingless and less nitrogen

(23:47):
essentially back from thatmanure. But if you want to get
good carry over numbers, that'sreally the experiment you're
going to do, or you have to workwith some modeling to try and
get at that number.
The other way to look at it is,if I had a manure with really

(24:36):
high C to N ratio, if I apply inthe fall, maybe I had some time

(25:16):
for that stuff to break down. Iwent through that initial

(25:52):
immobilization cycle, and by thetime I get to next spring, I

(26:31):
hope we haven't lost a wholelot, but I've already done that

(27:09):
tie up, and we're starting toget on the lower nitrogen at

(27:46):
least portion of that leg,because it effectively changed

(28:22):
the carbon nitrogen ratio of themanure by the time the crop will

(29:03):
be growing. All that to saythey're complicated things,

(29:38):
right? But I think sometimesthis nuance matters, and

(30:12):
oftentimes when we have thediscussion at manure 101 level,

(30:49):
we don't get into some of thosedetails, and I think they're

(31:27):
worth having. They're worththinking about, how do they

(32:02):
impact how we're makingdecisions? Where do we go from

(32:36):
here? And I think that's that'simportant for Iowa. It's

(33:12):
important for better manuremanagement and better

(33:43):
environmental outcomes. So atakeaway, when you apply affects

(34:22):
not how much nitrogen it.
Affects how much nitrogen isavailable, in theory, but to a

(34:56):
small level, what we reallyprobably need to focus on is how

(35:33):
much is actually sticking aroundto be available or supplied to

(36:14):
that plant. Alright, so at theend of the day, not all nitrogen

(36:52):
and manure is created equal.

(37:31):
Some of it feeds the crop rightaway. Some of it feeds the soil.

(38:12):
And microbial activity has a pitstop essentially, along the way,

(38:53):
and some of it we never reallysee show up. Maybe it stabilizes

(39:33):
soil organic nitrogen. Maybe itis lost during those shoulder

(40:11):
seasons. It remains to be seen,the carbon to nitrogen ratio,

(40:50):
the ammonium content and how weapply the manure all shape

(41:27):
whether the manure becomes anutrient that we can use, or if

(42:05):
it's lost to the environment.
Tools like PMR 1003, give us aplace to start, but we need

(42:43):
better more current data toguide real world decisions. That

(43:18):
means more research, more fieldtrials, and better ways to

(43:58):
predict nitrogen behavior inmodern systems. If we want to

(44:33):
unlock the full value of manure,we've got to keep digging into

(45:12):
the science, into the field andinto the soil.

(46:02):
Thank you for joining thisinstallment of Talkin' Crap. Be
sure to take a look at the shownotes on our website for links
and materials mentioned in theepisode. For more information,
or to get in touch, go to ourwebsite,
www.extension.iastate.edu/immag.
If you found what you heardtoday useful, or it made you
think, we hope you subscribe tothe show on your podcast app of

(46:23):
choice. Signing off from a jobthat sometimes smells but never
stinks, keep on talking crap.