Soil Science Journal Club : journal club

Next journal club meeting - carbon in China

Andrew.Rate — Wed, 01 Jul 2009 05:41:00 GMT

The next meeting (already notified by Talitha) is on Tuesday 7 July, 1pm, second-floor lunch area, Soil Science building, UWA.

The article to be mused upon is :
Piao S, Fang J, Ciais P, Peylin P, Huang Y, Sitch S, Wang T. 2009. Carbon balance of terrestrial ecosystems in China. Nature, 458:1009-1014.

Small data set, high impact

Andrew.Rate — Thu, 11 Jun 2009 01:52:00 GMT

[Musings by Talitha Santini]

The first article for the revived Journal Club was ‘Jarosite as an indicator of water-limited chemical weathering on Mars' (Elwood Madden et al. [2004] Nature, 431:821-823), chosen by Talitha because it was a short and reasonably simple article about soils on another planet. The authors used observations of jarosite and gypsum as alteration products of the basaltic parent rock at the Meridiani Planum landing site on Mars to argue a case for chemical weathering on Mars being water-limited. Using geochemical modelling software, a basaltic mineral assemblage (using data from Rosenbauer et al. [1983]) was titrated into a fluid containing SO₄^2-, Na⁺, K⁺, Ca²⁺, Fe²⁺, Mg²⁺, Al³⁺, and dissolved SiO₂, under current Martian atmospheric O₂ and CO₂ fugacities, at 298 K and 10⁴Pa total atmospheric pressure. The authors modelled both mineral assemblages as basalt weathering progressed, and the final mineral assemblages at different water:rock ratios. Modelling indicated that jarosite could only be present as a result of basalt weathering if (a) a large quantity of water reacted completely with a small amount of rock (for example, water creating an alteration rind on rock surfaces); or (b) a small amount of water reacted only partially with a large amount of rock. It was concluded that once jarosite formed, water must have been removed quickly in order to halt chemical weathering before pH increased and jarosite was converted to an iron (oxy)hydroxide - hence the article's title.

Once we started examining the article, we realized how little data were required to have an article published in Nature. The authors used only five pieces of information about Mars (the presence of a basaltic parent rock, the presence of jarosite and gypsum, and Martian atmospheric O₂ and CO₂ fugacities and atmospheric pressure) and a geochemical model designed for Earth surface conditions. This got us thinking about having a look at some Martian soil data from NASA (presented in Rieder et al. [1997]) and publishing our own articles. It's a good example of researchers considering data critically and extracting as much information as possible with the tools they have available to them. The tools we have available aren't perfect though, and one of the criticisms of this article was the ‘Earth-centric' modelling - that is, the use of Earth surface conditions to simulate Martian weathering processes. Where possible, the authors used (current) Martian conditions; however, in the case of temperature and pressure, current Earth conditions were used.

The ‘suppression of mineral phases...at the discretion of the operator' also raised debate about using geochemical models to simulate weathering. The problem is that models generally predict phase assemblages at thermodynamic equilibrium, which may not actually occur in the field. The authors cite the example of slow goethite formation hindering its occurrence in acid mine drainage environments despite being the thermodynamically stable iron phase. Kinetics were only included in this model ‘through the suppression of mineral phases unlikely to form in a geologically relevant time period.'

So why should we care about soils on Mars, anyway? We came up with a few answers to this: for the pure basic science objectives of understanding the properties and history of Martian surface materials and understanding how soils develop under different environmental conditions; because soil on another planet is inherently interesting; and because we may even want to annex Mars one day as a replacement Earth, in which case an understanding of its soils would be pretty important.

The next article will be chosen by Bree, with the next meeting scheduled for July 1.

Image from www.andersonfreepress.net

time for a little poetry

Andrew.Rate — Mon, 18 May 2009 03:21:00 GMT

FAREWELL TO THE EARTH

Christopher James

We buried him with a potato in each hand
on New Year’s Day when the ground was hard as luck,
wearing just cotton, his dancing shoes plus
a half bottle of pear cider to stave off the thirst.

In his *** pocket we left a taxi number
and a packet of sunflower seeds; at his feet was
the cricket bat he used to notch up a century
against the Fenstanton eleven.

We dropped in his trowel and a shower of rosettes
then let the lid fall on his willow casket.
The sky was hard as enamel; there was
a callus of frost on the face of the fields.

Dust to dust; but this was no ordinary muck.
The burial plot was by his allotment, where
the water butt brimmed with algae and the shed door
swung and slammed as we shook back the soil.

During the service, my mother asked
the funeral director to leave; take away some hair
and the resemblance was too close; and yet
my father never looked so smart.

I kept expecting him to walk in, his brow
steaming with rain, soil under his fingernails
smelling of hot ashes and compost;
looking for fresh tea in the pot.

One of an occasional series of poems (this is No. 3) selected simply because they mention the word 'soil'.

In this poem soil helps to signify death, most likely drawing from the biblical creation story:

"By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return." (Genesis 3:19)

The second mention of soil perhaps tells us about the character of the dead man; earthy, with few pretensions.

But never mind the references to soil, and biblical allusion - it's a beautiful poem.

Journal club revived

Andrew.Rate — Mon, 18 May 2009 03:05:00 GMT

[Edit at 29 May 2009 - the date has been shifted to Wednesday 3 June]

The poster at right was prepared by Talitha to publicise the first meeting of the Soil Science Journal Club for 2009...

...we'll be discussing the article: Madden MEE, Bodnar RJ, Rimstidt JD. 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. Nature, 431:821-823.

Maybe we'll see you there?

[The second-floor lunch area is on the top floor of the School of Earth & Environment (South) building (i.e. the Soil Science building).]

Renewable energy

Andrew.Rate — Fri, 24 Apr 2009 07:48:00 GMT

It may be that we see a bit more activity on this blog, following Talitha's suggestion to crank up the old-style journal club. That is, a club with more than one person in it, who actually read and discuss journal articles, and post their musings on this site (formerly created for that very purpose).

I'd be very keen on this sort of development, particulary as I thought I heard an offer for participants to take charge of at least some of the selection of articles and the blogging. As Talitha put it, a bit like a book club, but with less reading. Less work for me? - sounds very worthwhile.

Partly, this springs from my newly acquired role as one of the Graduate Research Coordinators in the School of Earth and Environment. Lots of this role is administrative, to be sure, but the opportuntity to interact with many of the School's motivated and scarily smart graduate research students is inspiring (and a lot of fun).

(Image from www.hardbacker.com)

Urban Soils

Andrew.Rate — Wed, 25 Feb 2009 02:20:00 GMT

The journal Urban Ecosystems has just published a Special Issue on Soils. As our planet and its human populations become increasingly urbanised, this would seem to be a growth area for the earth and ecological sciences.

Some of the articles from this issue of the journal:

A comparison of soil organic carbon stocks between residential turf grass and native soil
Richard V. Pouyat, Ian D. Yesilonis and Nancy E. Golubiewski
Altered resources, disturbance, and heterogeneity: A framework for comparing urban and non-urban soils
S. T. A. Pickett and M. L. Cadenasso
Scratching the surface and digging deeper: exploring ecological theories in urban soils
Mitchell A. Pavao-Zuckerman and Loren B. Byrne
Urban soil ecology as a focal point for environmental education
E. A. Johnson and K. M. Catley

I'm definitely looking forward to reading some of these.

Science and sustainability

Andrew.Rate — Thu, 19 Feb 2009 03:18:00 GMT

A recent article in Environmental Science and Technology identifies scientific facilities as high energy users.

Mills, Evan. 2009. Sustainable scientists.Environ. Sci. Technol., 43:979-985.

University sustainability, as rightly pointed out by Sky elsewhere in myResearchSpace ("A Sustainable Campus"), commonly focuses on 'green' or ecological issues . Dr Mills makes the point that "much can be done to enhance sustainability within the scientific enterprise itself". The diagram at left, from Mills' article, suggests that the practice of science can result in comparatively high energy usage.

The main contributors to high energy use are identified as laboratories, computing, and clean environments.

Mills goes so fas as to suggest that sustainability, or at least energy usage, issues should be amongst the criteria against which research grants are assessed (pity the poor folks in space research).

It would definitely be interesting to analyse the energy use of earth science projects. Many (especially involving remote area or ocean travel, drilling or remote sensing) could come in fairly high.

Image from pubs.acs.org

Digging for gold

Andrew.Rate — Thu, 06 Nov 2008 05:36:00 GMT

Musings on:
Anand RR, Cornelius M, Phang C, 2007. Use of vegetation and soil in mineral exploration in areas of transported overburden, Yilgarn Craton, Western Australia: a contribution towards understanding metal transportation processes.Geochemistry-Exploration Environment Analysis, 7: 267-288.

The use of soils and vegetation as sample media for geochemical exploration is not new. In recent years there seems to have been a resurgence of interest in sampling soils, and particularly plants, with the expectation that these media carry a signature of underlying ore bodies. In many cases the rock or regolith which hosts the ore body may be masked by transported sediments, so that even the weathered ghostly imprint of an ore may lie well below the surface.

Several mechanisms may allow the formation of signatures of ore bodies in surface soils, even in a transported overburden. In addition to purely chemical or physical processes, it is possible that plants can access ore-forming elements at depth, as deep roots search the regolith for water. Not only can this give anomalous concentrations of trace elements in plant tissues, but biological re-cycling can subsequently enrich surface soils with a signature of what lies beneath.

These ideas are the basis for Anand et al's. article. They took vegetation (mulga; Acacia aneura and related species) and soil samples across known but unexploited gold and/or base-metal (Cu, Zn, Ag) deposits in Western Australia, where much of the bedrock is covered by deeply weathered regolith profiles and, in many cases, transported sediments as well. They found that analysis of soils did not clearly delineate the vertical projection of underlying ores (even using selective extractions for trace elements which commonly improve signal:noise ratios). In contrast the living plant tissues, and particularly the litter layer, showed clear signatures of underlying mineralization, with peak concentrations in both media vertically over the ore body.

These results are of obviously practical importance to exploration geochemists, demonstrating that (at least in some instances) vegetation sampling and analysis offers an additional tool to "see through" weathered and/or transported material to ore bodies beneath. It is possibly more generally significant, from an "understanding the Earth" point of view, that vegetation may be important in redistributing trace elements in earth surface environments, particularly in arid regions where plants' search for water requires root growth to great depth. In such environments, geochemical signatures in soils may well be the result of millennia of plant uptake.

Image of the Moolart Well prospect from www.regisresources.com

New Comment on A Soil Scientist's Lament

Andrew.Rate — Fri, 24 Oct 2008 07:19:00 GMT

A new Comment has been posted in reply to A soil scientist's lament, by Professor Philippe Baveye (the author of the article mused upon in the original post).

It's well worth reading. You can get to it by clicking here, too (scroll down to the bottom of the page).

the soil on Mars

Andrew.Rate — Tue, 02 Sep 2008 03:15:00 GMT

...musings on Amundson R, Ewing S, Dietrich W, Sutter B, Owen J, Chadwick OA, Nishiizumi K, Walvoord M, McKay C. 2008. On the in situ aqueous alteration of soils on Mars. Geochimica et Cosmochimica Acta 72:3845-3864.

It's great when an article related to one's own discipline is about something exotic, and it would be hard to imagine a more exotic environment than the surface of Mars. I enjoy highlighting interesting developments to students, so this year's Introduction to Geochemistry students had the data from this article as an example when we learned about mass balance during weathering. And this was my first crack at teaching this geochemical topic to students as well, so I learned a lot too. We used the subject matter, if not the Martian data, in a prac class, using an excellent dataset published by Oh & Richter (2005).

Amundson et al.'s hypothesis is that liquid water must have existed on Mars at some stage in that planet's history, based on the mineralogical record (minerals which need water to form, such as smectites and jarosite, have been identified on the Martian surface). Amundson et al. further tested this hypothesis by using elemental analysis data from conveniently exposed "soil profiles" on Mars, within the Gusev and Endurance craters investigated by the Mars Exploration Rover (Opportunity) mission. They were looking for evidence of absolute loss or gain of elements which might reflect transport by liquid water - and they found exactly that. Soils were depleted in major rock-forming elements (Si, Al, Mg, Ca, Fe, etc.) relative to the likely parent materials (Gusev basalt, or aeolian dust), probably representing earlier weathering mediated by water. A key result was the enrichment in the soil profiles of sulfur, chlorine and bromine, consistent with the aqueous transport of sulfate, chloride and bromide salts followed by drying.

The point is also made that comparable environments (very dry and cold; e.g., some of Antarctica) exist on Earth, and similar soil-forming processes have occurred here (on Earth, that is!) as well. The authors refer to such terrestrial soils as being "abiotic"; a bit of a misnomer, I thought, where perhaps they meant the absence of higher organisms (surely some microorganisms were present in all the Earth examples - were they there on Mars?). Plus there is the usual issue with mass-balance approaches (fully acknowledged) of matching the weathered/altered material to its assumed parent material.

This was a fun article to read. It's not often that I get to read and use a publication that contains so much language usually reserved (in my reading experience) for science fiction - Mars landers, differences in gravity - all wonderful stuff.

Image from www.nasa.gov

Occasional poetry No. 2

Andrew.Rate — Tue, 12 Feb 2008 07:32:00 GMT

Hiking the Summit

by Simmons B. Buntin

from Riverfall (Salmon Poetry, 2005) http://salmonpoetry.com/riverfall.html

Reprinted in Salmon: A Journey in Poetry 1981 - 2007(http://www.salmonpoetry.com/anthology.html)

_______________________________________________________________________

Hiking the Summit

Thirteen miles have passed beneath
these broken boots, though I
have been lost since the first step.
I cannot see snow-crowned
peaks or a canyon gone crazy
upon itself, but only my breath, thick
as frost on the evening ridge. As
the trail grows twisted, I lose level
ground and fall into a rushing spring,
the water drowning my call
with the taste of panic,
sweetness. I work the current
like a cutter through ice, reach
the bank to dream of sleep,
and fall upon the hardened earth.
As the moon slides across the frozen
sky, distant wolves hurl their calls
against my camp. Waking, I spur
simmering coals and return
the howls, watching as my fire
grows. When the flames
form a ladder, a straight line
of smoke opens the night. I climb in, and the trail is gone.

______________________________________________________________________

About the poet

_______________________________________________________________________

Simmons B. Buntin is the founding editor of Terrain.org: A Journal of the Built & Natural Environments. With a master's degree in urban and regional planning, he is-logically-a web program manager for the University of Arizona in Tucson, Arizona. He has published in Canadian Bulletin of Medical History, Sou'wester, Southern Humanities Review, The Manhattan Review, and elsewhere and is a recipient of the Colorado Artist's Fellowship for Poetry.

Urban soil habitats

Andrew.Rate — Wed, 06 Feb 2008 02:24:00 GMT

Musings on:
Byrne LB, 2007. Habitat structure: A fundamental concept and framework for urban soil ecology. Urban Ecosystems, 10:255-274.

The title's claim of a "fundamental concept and framework" are ambitious, and this paper has a few shortcomings that leave it falling somewhat short of such lofty goals. Despite this, the stated overall objective to ". . .stimulate interdisciplinary interest in, and research about . . . urbanized ecosystems" does seem to be achieved by a paper that, refreshingly, emphasises ideas over activity. And there's nothing wrong with an article having shortcomings, especially if it encourages further thought and debate.

Quotable
quote:

"In general, very little is known about the effects of
urbanization on the ecology of soils"

The article itself is an odd hybrid of original empirical data and review-based analysis and conceptualisation (but perhaps it is only an odd hybrid for soil science, a discipline whose journals seldom publish conceptual articles). The original data are used to support the concept of habitat structure in urban soil systems, by measuring various soil parameters under four treatments, which are all (lawn, old field, bark mulch, gravel mulch) manipulations of the soil surface. This is all very well . . . IF these four treatments are really types of urban habitat structure. The challenge is then to describe and preferably quantify the "habitat structure" sufficiently to be able to relate it to habitat conditions, such as soil physical and chemical properties, or to biological responses, such as species abundances or biotic fluxes such as soil respiration. Later in the article it is suggested that surface are to volume ratio is ". . .can be an appropriate description of habitat complexity", but this seems simplistic; the assumption appears to be that "complexity" is a key component of "structure". I wonder if fractal geometry might have a role in more quantitatively describing habitat complexity?

Loren Byrne makes some useful observations in this article. Like Tim Low, the point is made that ". . .human-designed plant communities may have unique and perhaps unexpected effects on urban soil biodiversity." It would certainly be interesting to test this hypothesis across a range of contrasting soils. On the other hand, there are some less-than-useful implications; the paragraph at the bottom of page 264 implies that soils are separate from "habitat structure", being ". . .beneath the different types of habitat structure. . .". A more useful approach might have been to consider soils as part of the habitat structure continuum, as soils contain spatially arranged entities of their own.

The definition of habitat structure itself, although given quite comprehensively in Table 1, may also need some work. The phrase "patterns of habitat structure", seemingly containing another level of abstraction, appears to be used synonymously with "habitat structure" in the paragraph at the bottom of p.265.

Reading back through this, I seem too critical. There is great value in this article's presentation and application of the habitat structure concept to urban soil ecosystems. There is also considerable benefit to readers, particularly postgraduate students in soil science, in examining the way the author develops and justifies arguments to present a coherent concept. As I have maintained before, the discipline of soil science and its practitioners have much to gain from a true dialogue with disciplines such as ecology and geography.

Image from "Jack and The Beanstalk" by Richard Walker and Niamh Sharkey; Barefoot Paperbacks

Briefs

Andrew.Rate — Thu, 20 Dec 2007 03:52:00 GMT

Trevors, J.T. and Saier, M.H., Jr. (2007). Academics and their knowledge are underutilized. Water, Air and Soil Pollution, 186:1-2.

"Scientists and other academics are generally underutilized in numerous ways. For example, many scientists who also serve as instructors are not provided with the best infrastructure for use in teaching courses."

"While some academicians are utilized for governmental decision-making purposes, too often political allies are used, and almost never is a major segment of the scientific community consulted."

Schnoor, J.L. (2007). World water woes. Environmental Science & Technology, 41:7953.

"Everyone wants to live “on the edge” where seawater beckons, but it doesn’t quench our thirst. Eighty percent of Australians and more than half of all people worldwide live along the coast."
"...global warming will produce greater worldwide precipitation. But if rainfall patterns shift and floods increase, we will not benefit. By 2025, 1.8 billion people will live in countries with absolute water scarcity, according to UN estimates. Rich countries can adapt. But the future of developing countries is at stake."

A soil scientist's lament

Andrew.Rate — Fri, 14 Dec 2007 02:26:00 GMT

Musings on:
Baveye, P. C. & Jacobson A. R. (2008). Soil science education and the "age of money": reflections and concerns for the near future. Water, Air and Soil Pollution 187:1-4.

This was a guest editorial in Water, Air and Soil Pollution, and I decided it to be worth reading; there's much to be said for a catchy title. The topic summarised in the title seems to be a consistent point of angst for the first author; this editorial self-cites two other articles (Baveye, 2006; Baveye et al., 2006) with similar themes.

Baveye & Jacobson start off by emphasising the importance of soils. Ironically, given the title, this is framed in terms of climate change and the role of soils in carbon cycling. (The irony I perceive is that while the authors decry the inevitable money chasing activity by researchers, any mention of climate change - "big money" science, in anyone's terms - implies a fair amount of money-chasing pragmatism itself. Maybe I'm wrong.) Next, the question is asked about who will be around to conduct the soil science research humanity will need given the pervasive background of climate change. The answer: not many scientists, if the authors' concerns about declining graduates in soil science (and indeed declining numbers of soil science departments themselves) are founded.

There is an assumption in these concerns that only soil science (post)graduates are adequately trained to conduct soil science research, a point made more insistently in another paper (Baveye, 2006). This may be true, but my observation is that in soil science academia, not many soil scientists actually have a first degree (or in some cases, a postgraduate degree) in soil science. Certainly at my University, I can not think of any academic within the soil science discipline who has a first degree in soil science, and only two who have soil science-related PhDs. So Baveye & Jacobson's contention, that only "pure" soil scientists will do, seems unsupported by hard evidence (or, at least, will be subject to many exceptions).

The decline in soil science is attributed to a few factors. One seems reasonable; an insistence on teaching soil science in the context of crop production (where soil science has many of its traditional roots) is probably outdated, especially with " ...the open intention of a majority of students to pursue careers dealing predominantly with environmental issues.". It's hard to argue with that - but not the second point, that "... the fact that soil science faculty do not seem to find that their craft is really exciting any more..." (a point also made in Baveye, 2006). Baveye & Jacobson's evidence for this seems to be the re-naming of many former soil science departments as "earth" or "environmental" something-or-other; we've seen that trend over this way as well, but still soil science research (and teaching!) gets done. The authors are also worried about soil science departments being subsumed into physical geography (or whatever); again, my own discipline may be heading that way, and my interactions with the new discipline have only served to increase my interest in my discipline. Opening up new ideas, and developing new relationships (interpersonal, and between ideas), is exciting too!

The "age of money" referred to by Baveye & Jacobson is linked to their premise that the success of an academic discipline depends on its adherence to the following criteria (reproduced unchanged here):

"A Promise of Money. The field is popularly linked (even if erroneously) to improved chances of securing an occupation or profession that promises above-average lifetime earnings.
A Knowledge of Money. The field itself studies money, whether practically or more theoretically, i.e., fiscal, business, financial, or economic matters and markets.
A Source of Money. The field receives significant external money, i.e., research contracts, federal grants or funding support, or corporate underwriting."

In Baveye & Jacobson's view, soil science departments only do reasonably well at 3.; it's possible that the Australian resources boom may see some success in 1. in this part of the world. Admittedly, the constant focus on money is tiresome for many academics. In the current milieu, it may not be something we can address, so we all (somewhat reluctantly) have to live with it, or so my Head of School tells me from time to time.

Another intriguing issue raised, not in this editorial but in Baveye (2006) , is that scholarly journals (and conferences, apparently) in many cases suppress vigorous academic debate. In addition, many academics (and I can heartily relate to this) are simply too busy to have stimulating discussions about their science any more. It certainly would make for more interesting reading if journal editors took some risks and published more "edgy" material. One journal I sit on the editorial board of is concerned about its low impact factor. My view of the problem for that journal: in most cases, the articles are simply boring. Scientifically sound, they may be, but I think it is true, especially for many of the applied sciences, that much our science gets bogged down in activity and loses the passion for ideas. Perhaps making space for risky thinking and learning from disciplines, such as [some of] geography, which still seem to favour truly creative thinking, will inject some life into soil science. If we get the time.

Baveye, P. (2006). A future for soil science. Journal of Soil and Water Conservation, 61:148A-151A.

Baveye, P., Jacobson, A. R., Allaire, S. E., Tandarich, J., & Bryant, R. (2006). Whither goes soil science in the US and Canada? Survey results and analysis. Soil Science, 171:501-518.

The image is not related to any of the papers discussed!

Too much carbon... in soils, now?

Andrew.Rate — Thu, 01 Nov 2007 03:21:00 GMT

Musings on:
Stewart CE, Paustian K, Conant RT, Plant AF, Six A. 2007. Soil carbon saturation: concept, evidence and evaluation. Biogeochemistry 86:19-31.

On first glance I thought that this was too obvious to be significant - if carbon input fluxes (e.g. litter fall) are increased (in a single step), then of course soil carbon will increase, but asymptotically to a new maximum, caused by establishment of a new steady state with increased losses due to mineralisation, etc.
I was wrong; this simplistic understanding assumes, as Stewart et al. point out, that every increase in input flux will eventually increase soil C content. In fact, with this assumption the relationship between input flux and new equilibrium soil carbon concentration turns out to be linear; this is what most models of soil organic carbon dynamics (e.g. CENTURY or RothC) do.

Stewart et al.'s hypothesis is that with increasing input fluxes to soil, the soil C content does not keep increasing but reaches a maximum value. Using sites having a range of annual carbon inputs (0-6 Mg C/ha/y), with treatments ranging in duration from 12-51 years, they find that the data as a whole are described best by a model that assumes that soil carbon content, or at least one pool of soil carbon, reaches a limiting value.

Clearly (if correct) Stewart et al.'s findings have implications for carbon sequestration in soils for controlling CO₂ concentrations in Earth's atmosphere (again, the authors make a point of emphasising this). Soils, then, behave the same way as reforestation/revegetation in terms of carbon sequestration (ecosystems reach steady states eventually in terms of productivity vs. loss). Soil is not an infinite sink for carbon; neither is the biomass growing on it.

It's early days before this hypothesis is fully evaluated across a range of biomes, but it needs to be taken notice of. There may be some issues with the treatment of data; it wasn't clear, for example, whether clustering of data for different sites affected the fitting procedure for the carbon saturation model. But we'd better understand stuff like this if we're to be serious about exploiting the role of soils in global carbon dynamics.

Soil image from Australian Society of Soil Science Inc.