[Garden] Fertilizers and soil health

[J. Rochon]

Gardeners, Preppers and Armchair Economists,
 
                It seems that there's a small group of academics 
contesting the notion that artificial nitrogen fertilizer results in 
carbon sequestration. If they are right then artificial nitrogen 
actually reduces soil fertility, and locks farmers into using ever 
increasing amounts of fertilizer to offset the damage done by 
fertilizer. Sadly, they have repeatable results to back up their 
position.Clearly, we have gone a long time with artificial nitrogen, 
itself a product of WWI research, and it has put a lot of food on our 
plates. The point of diminishing returns remains unknown.
   

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Fairly used facts from from: http://www.energybulletin.net/print/51697
Most photos removed to keep your mailbox from swelling.
san
*New research: synthetic nitrogen destroys soil carbon, undermines soil 
health*
Published Tue, 02/23/2010 - 08:00
by Grist


/Just precisely what does all of that nitrogen ferilizer /do/ to the soil?

"Fertilizer is good for the father and bad for the sons." ---Dutch saying/

For all of its ecological baggage, synthetic nitrogen does one good deed 
for the environment: it helps build carbon in soil. At least, that's 
what scientists have assumed for decades.

If that were true, it would count as a major environmental benefit of 
synthetic N use. At a time of climate chaos and ever-growing global 
greenhouse gas emissions, anything that helps vast swaths of farmland 
sponge up carbon would be a stabilizing force. Moreover, carbon-rich 
soils store nutrients and have the potential to remain fertile over 
time---a boon for future generations.

The case for synthetic N as a climate stabilizer goes like this. Dousing 
farm fields with synthetic nitrogen makes plants grow bigger and faster. 
As plants grow, they pull carbon dioxide from the air. Some of the plant 
is harvested as crop, but the rest---the residue---stays in the field 
and ultimately becomes soil. In this way, some of the carbon gobbled up 
by those N-enhanced plants stays in the ground and out of the atmosphere.

Well, that logic has come under fierce challenge from a team of 
University of Illinois researchers led by professors Richard Mulvaney, 
Saeed Khan, and Tim Ellsworth. In two recent papers (see here 
<http://jeq.scijournals.org/cgi/content/abstract/36/6/1821> and here 
<http://jeq.scijournals.org/cgi/content/full/38/6/2295>) the trio argues 
that the net effect of synthetic nitrogen use is to reduce soil's 
organic matter content. Why? Because, they posit, nitrogen fertilizer 
stimulates soil microbes, which feast on organic matter. Over time, the 
impact of this enhanced microbial appetite outweighs the benefits of 
more crop residues.

And their analysis gets more alarming. Synthetic nitrogen use, they 
argue, creates a kind of treadmill effect. As organic matter dissipates, 
soil's ability to store organic nitrogen declines. A large amount of 
nitrogen then leeches away, fouling ground water in the form of 
nitrates, and entering the atmosphere as nitrous oxide (N2O), a 
greenhouse gas with some 300 times the heat-trapping power of carbon 
dioxide. In turn, with its ability to store organic nitrogen 
compromised, only one thing can help heavily fertilized farmland keep 
cranking out monster yields: more additions of synthetic N.

The loss of organic matter has other ill effects, the researchers say. 
Injured soil becomes prone to compaction, which makes it vulnerable to 
runoff and erosion and limits the growth of stabilizing plant roots. 
Worse yet, soil has a harder time holding water, making it ever more 
reliant on irrigation. As water becomes scarcer, this consequence of 
widespread synthetic N use will become more and more challenging.

In short, "the soil is bleeding," Mulvaney told me in an interview.

If the Illinois team is correct, synthetic nitrogen's effect on carbon 
sequestration swings from being an important ecological advantage to 
perhaps its gravest liability. Not only would nitrogen fertilizer be 
contributing to climate change in a way not previously taken into 
account, but it would also be undermining the long-term productivity of 
the soil.


/Getting their hands dirty: Saeed Khan, Richard Mulvaney, and Tim 
Ellsworth (l.-r.), in front of the Morrow Plots, University of Illinois. /

*An Old Idea Germinates Anew*
While their research bucks decades of received wisdom, the Illinois 
researchers know they aren't breaking new ground here. "The fact is, the 
message we're delivering in our papers really is a rediscovery of a 
message that appeared in the '20s and '30s," Mulvaney says. In their 
latest paper, "Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A 
Global Dilemma for Sustainable Cereal Production," which appeared last 
year in the /Journal of Environmental Quality,/ the researchers point to 
two pre-war academic papers that, according to Mulvaney, "state clearly 
and simply that synthetic nitrogen fertilizers were promoting the loss 
of soil carbon and organic nitrogen."

That idea also appears prominently in /The Soil and Health /(1947), a 
founding text of modern organic agriculture. In that book, the British 
agronomist Sir Albert Howard stated the case clearly:

    The use of artificial manure, particularly [synthetic nitrogen] ...
    does untold harm. The presence of additional combined nitrogen in an
    easily assimilable form stimulates the growth of fungi and other
    organisms which, in the search for organic matter needed for energy
    and for building up microbial tissue, use up first the reserve of
    soil hummus and then the more resistant organic matter which cements
    soil particles.

In other words, synthetic nitrogen degrades soil.

That conclusion has been current in organic-farming circles since Sir 
Albert's time. In an essay in the important 2002 anthology /Fatal 
Harvest Reader, /the California organic farmer Jason McKenney puts it 
like this:

    Fertilizer application begins the destruction of soil biodiversity
    by diminishing the role of nitrogen-fixing bacteria and amplifying
    the role of everything that feeds on nitrogen. These feeders then
    speed up the decomposition of organic matter and humus. As organic
    matter decreases, the physical structure of soil changes. With less
    pore space and less of their sponge-like qualities, soils are less
    efficient at storing water and air. More irrigation is needed. Water
    leeches through soils, draining away nutrients that no longer have
    an effective substrate on which to cling. With less available oxygen
    the growth of soil microbiology slows, and the intricate ecosystem
    of biological exchanges breaks down.

Although those ideas flourished in organic-ag circles, they withered to 
dust among soil scientists at the big research universities. Mulvaney 
told me that in his academic training---he holds a PhD in soil fertility 
and chemistry from the University of Illinois, where he is now a 
professor in the Department of Natural Resources and Environmental 
Sciences---he was never exposed to the idea that synthetic nitrogen 
degrades soil. "It was completely overlooked," he says. "I had never 
heard of it, personally, until we dug into the literature."

What sets the Illinois scientists apart from other critics of synthetic 
nitrogen is their provenance. Sir Albert's denouncement sits in a dusty 
old tome that's pretty obscure even within the organic-agriculture world 
<http://www.grist.org//article/soil/>; Jason McKenney is an organic 
farmer who operates near Berkeley 
<http://www.hiddenvilla.org/>---considered la-la land by mainstream soil 
scientists. Both can be---and, indeed have been---ignored by 
policymakers and large-scale farmers. By contrast, Mulvaney and his 
colleagues are living, credentialed scientists working at the premier 
research university in one of the nation's most prodigious 
corn-producing---and nitrogen-consuming---states.

morrow plots

/Abandon all hope, all fertilizer execs who enter here. /

*The Dirt on Nitrogen, Soil, and Carbon *
To come to their conclusions, the researchers studied data from the 
Morrow plots on the University of Illinois' Urbana-Champaign campus, 
which comprise the "the world's oldest experimental site under 
continuous corn" cultivation. The Morrow plots were first planted in 1876.

Mulvaney and his collaborators analyzed annual soil-test data in test 
plots that were planted with three crop rotations: continuous corn, 
corn-soy, and corn-oats-hay. Some of the plots received moderate amounts 
of fertilizer application; some received high amounts; and some received 
no fertilizer at all. The crops in question, particularly corn, generate 
tremendous amounts of residue. Picture a Midwestern field in high 
summer, packed with towering corn plants. Only the cobs are harvested; 
the rest of the plant is left in the field. If synthetic nitrogen use 
really does promote carbon sequestration, you'd expect these fields to 
show clear gains in soil organic carbon over time.

Instead, the researchers found, all three systems showed a "net decline 
occurred in soil [carbon] despite increasingly massive residue [carbon] 
incorporation." (They published their findings, "The Myth of Nitrogen 
Fertilization for Soil Carbon Sequestration," 
<http://jeq.scijournals.org/cgi/content/abstract/36/6/1821>in the/ 
Journal of Environmental Quality/ in 2007.) In other words, synthetic 
nitrogen broke down organic matter faster than plant residue could 
create it.

A particularly stark set of graphs traces soil organic carbon (SOC) in 
the surface layer of soil in the Morrow plots from 1904 to 2005. SOC 
rises steadily over the first several decades, when the fields were 
fertilized with livestock manure. After 1967, when synthetic nitrogen 
became the fertilizer of choice, SOC steadily drops.

In their other major paper, "Synthetic Nitrogen Fertilizers Deplete Soil 
Nitrogen: A Global Dilemma for Sustainable Cereal Production" 
<http://jeq.scijournals.org/cgi/content/full/38/6/2295>(2009), the 
authors looked at nitrogen retention in the soil. Given that the test 
plots received annual lashings of synthetic nitrogen, conventional ag 
science would predict a buildup of nitrogen. Sure, some nitrogen would 
be removed with the harvesting of crops, and some would be lost to 
runoff. But healthy, fertile soil should be capable of storing nitrogen.

In fact, the researchers found just the opposite. "Instead of 
accumulating," they wrote, "soil nitrogen declined significantly in 
every subplot sampled." The only explanation, they conclude, is that the 
loss of organic matter depleted the soil's ability to store nitrogen. 
The practice of year-after-year fertilization had pushed the Morrow 
plots onto the chemical treadmill: unable to efficiently store nitrogen, 
they became reliant on the next fix.

The researchers found similar data from other test plots. "Such evidence 
is common in the scientific literature but has seldom been acknowledged, 
perhaps because N fertilizer practices have been predicated largely on 
short-term economic gain rather than long-term sustainability," they 
write, citing some two dozen other studies which mirrored the patterns 
of the Morrow plots.

The most recent bit of evidence for the Mulvaney team's nitrogen thesis 
comes from a team of researchers at Iowa State University and the USDA. 
In a 2009 paper <http://www.grist.org/i/assets/2/Russell_2009_paper.pdf> 
(PDF), this group looked at data from two long-term experimental sites 
in Iowa. And they, too, found that soil carbon had declined after 
decades of synthetic nitrogen applications. They write: "Increases in 
decay rates with N fertilization apparently offset gains in carbon 
inputs to the soil in such a way that soil C sequestration was virtually 
nil in 78% of the systems studied, despite up to 48 years of N additions."


/Fertile ground for research: the Morrow Plots at the University of 
Illinois. Photo:brianholsclaw <http://www.flickr.com/photos/brianholsclaw/>/

/*Slinging Dirt*/
Mulvaney and Khan laughed when I asked them what sort of response their 
work was getting in the soil-science world. "You can bet the fertilizer 
industry is aware of our work, and they aren't too pleased," Mulvaney 
said. "It's all about sales, and our conclusions aren't real good for 
sales."

As for the soil-science community, Mulvaney said with a chuckle, "the 
response is still building." There has been negative word-of-mouth 
reaction, he added, but so far, only two responses have been published: 
a remarkable fact, given that the first paper came out in 2007.

Both published responses fall into the 
those-data-don't-say-what-you-say-they category. The first, published as 
a letter to the editor 
<http://www.grist.org/i/assets/2/reidletter.pdf>(PDF) in the /Journal of 
Environmental Quality, /came from D. Keith Reid, a soil fertility 
specialist with the Ontario Ministry of Agriculture, Food and Rural 
Affairs. Reid writes that the Mulvaney team's conclusion about synthetic 
nitrogen and soil carbon is "sensational" and "would be incredibly 
important if it was true."

Reid acknowledges the drop in soil organic carbon, but argues that it 
was caused not by synthetic nitrogen itself, but rather by the 
difference in composition between manure and synthetic nitrogen. Manure 
is a mix of slow-release organic nitrogen and organic matter; synthetic 
nitrogen fertilizer is pure, readily available nitrogen. "It is much 
more likely that the decline in SOC is due to the change in the form of 
fertilizer than to the rate of fertilizer applied," Reid writes.

Then he makes a startling concession:

     From the evidence presented in this paper, it would be fair to
    conclude that modern annual crop management systems are associated
    with declines in SOC concentrations and that increased residue
    inputs from high nitrogen applications do not mitigate this decline
    as much as we might hope.

In other words, modern farming---i.e., the kind practiced on nearly all 
farmland in the United States---destroys soil carbon. (The Mulvaney 
team's response to Reid's critique can be found in the above-linked 
document.)

The second second critique 
<http://www.grist.org/i/assets/2/PowlsonreMulvaneypaper.pdf>(PDF) came 
from a team led by D.S. Powlson at the Department of Soil Science and 
Centre for Soils and Ecosystem Function at the Rothamsted Research 
Station in the United Kingdom. Powlson and colleagues attack the 
Mulvaney team's contention that synthetic nitrogen depletes the soil's 
ability to store nitrogen.

"We propose that the conclusion drawn by Mulvaney et al. (2009), that 
inorganic N fertilizer causes a decline in soil organic N concentration, 
is false and not supported by the data from the Morrow Plots or from 
numerous studies worldwide," they write.

Then they, too, make a major concession: "the observation of significant 
soil C and N declines in subsoil layers is interesting and deserves 
further consideration." That is, they don't challenge Mulvaney team's 
contention that synthetic nitrogen destroys organic carbon in the subsoil.

In their response 
<http://www.grist.org/i/assets/2/mulvaneyreplypowlson.pdf> (PDF), 
Mulvaney and his colleagues mount a vigorous defense of their 
methodology. And then they conclude:

    In the modern era of intensified agriculture, soils are generally
    managed as a commodity to maximize short-term economic gain.
    Unfortunately, this concept entirely ignores the consequences for a
    vast array of biotic and abiotic soil processes that aff ect air and
    water quality and most important, the soil itself.

So who's right? For now, we know that the Illinois team has presented a 
robust cache of evidence that turns 50 years of conventional soil 
science on its head---and an analysis that conventional soil scientists 
acknowledge is "sensational" and "incredibly important" if true. We also 
know that their analysis is consistent with the founding principles of 
organic agriculture: that properly applied manure and nitrogen-fixing 
cover crops, not synthetic nitrogen, are key to long-term soil health 
and fertility.

The subject demands more study and fierce debate. But if Mulvaney and 
his team are correct, the future health of our farmland hinges on a 
dramatic shift away from reliance on synthetic nitrogen fertilizer.

Content on this site is subject to our fair use notice 
<http://www.energybulletin.net/fair-use-notice>.

-- 
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Jason Rochon
Campus Tech, Student Life Centre
Monday to Friday: 9:00 am to 5:00 pm
Shop 24/7 at campustech.uwaterloo.ca.

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