Question Re "Corn Sweat" and Evapotranspiration

[Judith D. Schwartz‏]

Hi Soil-Agers. There's some talk about midwest cornfields (densely-planted monocultures) as a factor in a "heat dome" that''s plaguing the midwest. As in: 

http://www.cnn.com/2016/07/17/weather/extreme-weather-heat-dome/index.html

I'm confused because evapotranspiration is generally a cooling mechanism. Is there something about corn or how it's planted that operates differently? Why wouldn't other planting regimes affect the dew point in such a way?

Thanks for helping me make sense of this!

Judy

Judith D. Schwartz

Bennington, Vermont
(802) 447-2413
www.judithdschwartz.com
Author: Cows Save the Planet: And Other Improbable Ways of Restoring Soil to Heal the Earth (Chelsea Green Publishing, May 2013)

Forthcoming: Water In Plain Sight: Hope for a Thirsty World (St. Martin's Press, July 2016)

 

[Walter Jehne‏]

Judith

While not on site actively transpiring green corn fields would normally transfer significant solar energy reaching the surface back up into the atmosphere thereby cooling those habitats. That is as long as they can access adequate soil water to sustain these latent heat fluxes. 

As we degrade our soil 'sponges' and engineer corn plants with fewer roots (breeding has been canabalizing roots to enhance shoot weights for 100 years) that are dependent on fertilizers rather than mycorrhizal symbionts to access essential nutrients we are both reducing the quantity of water able to be stored in our soils and the plants ability to access what there is. Drought stressed plants and soils dont cool but instead absorb the incident solar energy to increase surface temperatures that re-radiate it back up as heat. Such heat can readily create local high pressure heat domes that prevent cool moist low pressure air and rain inflows thereby further accentuating the local aridification. 

What we get is substantially up to us and how we manage and regenerate our soil carbon sponges and landscapes. Cheers

Walter 

---

From: Judith D. Schwartz <jud...@sover.net>
To: soil...@googlegroups.com
Sent: Tuesday, 19 July 2016, 4:59
Subject: [soil-age] Question Re "Corn Sweat" and Evapotranspiration

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[Judith D. Schwartz‏]

Thanks, Walter! This intrigued me enough that I pitched a little piece about it and looks like I'm doing it. 

I'd love to hear other comments--including observations from anyone sweltering under this heat dome. 

Walter, I'll send you a few questions for clarification.

Appreciatively,

Judy

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[Sally Dodge‏]

Thanks to you both for this fascinating info. What Walter describes certainly makes sense. Glad to hear you may get an article out on it Judy. 

Sent from my iPhone

--

[David Yarrow‏]

hello judith,

living just east of KC, i seem to be near the epicenter of this latest heat dome.  actually, thus far, not too bad, but temperatures are near 100 today, and forecast to hover in that range the rest of the week.  but i landed in the midwest for the intense 2012 drought, when temperatures went over 100 day after day after day, corn dried and died in fields, and hardly any farmers got a crop.  i didn't notice the extreme temperatures all that much because i was living in a basement with an outside entrance, and that kept temperatures inside lower, but i certainly was discouraged from taking long hikes during daylight.

however, this idea of "corn sweat" seems a bit off-target, even perverse -- a scapegoat for factors more directly triggered by the way industrial agriculture cultures corn.  personally, i think clean tillage monoculture contributes more to extreme heat & humidity than sweating corn.  yes, corn is a fast-growing plant that sucks up water rapidly from soil, and corn is quite good at scavenging water from dry soils.  and corn likes hot weather, and will grow in temperatures that cause other plant species to shut down, cut metabolism and close up it's stomata -- the breathing holes mostly on the underside of leaves.  so yes, growing corn can pump significant moisture into the atmosphere.

yet, seems to me, corn monoculture with clean tillage doesn't compare with the effects of a fully developed prairie ecosystem, which blankets the ground with a wide diversity of plants.  clean tillage corn monoculture renders soil bare and naked, and thus subject extreme heating.  bare, mineralized, low carbon soils will get much hotter and boil off much more moisture.  years of clean tillage and heavy doses of nitrogen fertilizers will deplete the soil of carbon, and C is a principal factor to increase soil macro-structure, porosity and water holding.

prairie soils, by comparison, are shaded by the thick tallgrass covers, which restrain soil temperatures, prevent soil surface crusts from forming, and keep soil open and porous so it can breathe and water can penetrate deeper.

david

--

[Erich Knight‏]

I thought that under such temps plants generally went dormant, Photosynthesis reduced.
Over 100 F the photosynthetic rate declines rapidly.
CO2 assimilation measures photosynthetic rates.
At temperatures above 20 degrees C (68 F) the rate of photosynthesis decreases as the enzymes do not work as efficiently.
Corn can achieve cO2 assimilation rates as high as 100 milligrams per decimeter per hour

Cheers,

Erich

Erich J. Knight
Shenandoah Gardens
1047 Dave Berry Rd. McGaheysville, VA. 22840
  540-289-9750   

Policy & Community Chairman
2013 North American Biochar Symposium
Harvesting Hope: The Science & Synergies of Biochar
October 13-16, 2013 at UMASS Amherst
http://pvbiochar.org/2013-symposium/

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[David Yarrow‏]

yep, eric.  as temperatures rise into the 90s, plant metabolism slows.  above 100, most common photosynthesis shuts down, and even the stomata of leaves close.  i've seen squash vines "wilt" and their leaves fold up in extreme heat to reduce surface area and conserve water.  corn likes hot weather and functions well in 90s,  but i suspect at over 100, even corn starts to shut down.

david

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[Russ Conser‏]

Judith, David, Eric,

Seems to me that put simply, if he corn is sweating, the air is, by definition, cooling (i.e. evaporation of water consumes heat) .  Weather wise, this will indeed mean warmer mornings (due to higher dew point), but also cooler afternoons (harder to heat humid air).  The heat dome would only seem to accelerate when the sweating stops - either because a) water supply couldn’t keep up (drought, poor soil), or b) it just got too hot (photosynthetic shut-down).  Like many native prairie grasses, corn is a C4 photosynthesis plant so it actually thrives in the higher temps (compared to soy beans that are C3’s), but it too will stop growing and thus sweating due to a) or b) at some point and thus the drier air will get hotter.  As it gets warmer, this would seem to form a positive feedback loop - i.e. the warmer it gets, the less growth/sweating happens, which leads to faster heating of drier air - and thus logically a heat dome.  Maybe put differently, growing life cools the environment - right up until it stops.

Russ

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[Thomas Goreau‏]

The key is to realize that around 90% of the water vapor entering the atmosphere from soil goes through plants, transpiration rather than physical evaporation. So when we reduce total photosynthesis by habitat degradation we reduce the heat transfer from soil to air nearly in proportion. The opportunities for cooling lie anywhere that plant growth can be increased! 

But it is important to recognize that the vast bulk of atmospheric water vapor comes from physical evaporation from the oceans, which we can’t affect, and so the local cooling effects will be greatest in continental interiors and not near coasts.

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.

Coordinator, Soil Carbon Alliance

Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies

37 Pleasant Street, Cambridge, MA 02139

gor...@bestweb.net
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

The Green Disc, New Technologies for a New Future: Innovative Methods for Sustainable Development

http://www.greenthindisc.org

No one can change the past, everyone can change the future

To view this discussion on the web visit https://groups.google.com/d/msgid/soil-age/EC782EC9-3D00-44BF-BE01-7C2027ECFE97%40sover.net.

[Thomas Goreau‏]

Monocrop cultivation hits species-specific temperature limits much sooner than a diverse natural flora!

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.

Coordinator, Soil Carbon Alliance

Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies

37 Pleasant Street, Cambridge, MA 02139

gor...@bestweb.net
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

The Green Disc, New Technologies for a New Future: Innovative Methods for Sustainable Development

http://www.greenthindisc.org

No one can change the past, everyone can change the future

To view this discussion on the web visit https://groups.google.com/d/msgid/soil-age/CAB5EiYA5O9vt4Oects2AmcmHmJ2tHxFtQRW3qZ8zW%3D_mbm7wWw%40mail.gmail.com.

[Walter Jehne‏]

Erich

Yes most photosynthesis declines rapidly above 38oC due to bio-chemical/enzyme limits but that does not always mean that transpiration and latent heat transfers cease as plants have to try to prevent their leaves from 'cooking' permanently. Cheers

Walter

---

From: Erich Knight <erichj...@gmail.com>
To: Soil Age <soil...@googlegroups.com>
Sent: Wednesday, 20 July 2016, 15:53
Subject: Re: [soil-age] More comments on the corn/heat dome connection?

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[Richard Hatfield‏]

Dear all –

 

Appreciating the ongoing discussion.  As a non-expert, designing and implementing land-and-water management projects in Africa, I am finding it very useful in the context of ‘climate change literacy’ – which is something we see must start to be articulated and disseminated widely, including in schools.

 

Thomas answered below a question that was forming in my mind of evapo vs transpiration.  I am trying to appreciate the difference in terms of cooling effect, in laymans terms.  Can someone help to interpret Walter’s piece below, in terms of the big picture air conditioner? IE grams of soil water taken up by plants, significance of 590 calories in terms of cooling, etc.

 

Meanwhile two overarching messages seem to be:  1. Plants cool the planet (until some point) and 2. We need to look after water levels in the soil (the ‘tank’) to ensure plants have the supply they need (not to mention people and rivers etc) eg in the corn belt example, one contributor seems to be the tank is not being well looked after due to tilled soils..

 

every extra gram of soil water that is transpired can transfer up to 590 calories of heat from the soil surface back up into the atmosphere thereby cooling that habitat and region. As that transpired water condenses to forms clouds with high albedo that can reflect up to 80% of the incident solar energy back out to space this can also further cool that habitat and regions. As these cloud droplets are coalesced on precipitation nuclei to form raindrops most of this transpired water can be returned to the soil to be again transpired and recycled continually enhancing the productivity, cooling and resilience of that landscape and the communities dependent on it.

 

Thanks,

Richard Hatfield,

Kenya & S Africa

 

From: soil...@googlegroups.com [mailto:soil...@googlegroups.com] On Behalf Of Thomas Goreau
Sent: Wednesday, July 20, 2016 5:53 PM
To: soil...@googlegroups.com
Subject: Re: [soil-age] More comments on the corn/heat dome connection?

 

The key is to realize that around 90% of the water vapor entering the atmosphere from soil goes through plants, transpiration rather than physical evaporation. So when we reduce total photosynthesis by habitat degradation we reduce the heat transfer from soil to air nearly in proportion. The opportunities for cooling lie anywhere that plant growth can be increased! 

To view this discussion on the web visit https://groups.google.com/d/msgid/soil-age/C805278C-0B3E-49B0-A379-515D87A96161%40bestweb.net.

[Judith D. Schwartz‏]

Thanks everyone for contributing your thoughts and questions. The piece posted today on Ag Insider: https://thefern.org/ag_insider/summer-heat-wave-corn-sweat-part-problem/

I quoted David Yarrow from his comment on this list.

Of course, with 600 words I could hardly take on the bigger questions, but hope this at least raises some.

Richard, your point on plants cooling the planet is apt. That theme kept coming up more and more as I researched and wrote my book on water (which will be out on Tuesday!) I recommend delving into Walter's Regenerate Australia papers on the Healthy Soils Australia website. I take pieces of that and explain them in terms accessible to the general public. Here's the publisher's page on my book: http://us.macmillan.com/waterinplainsight/judithdschwartz

I'm also doing some NPR-level interviews, which give me the opportunity to articulate how water influences climate and soil determines what happens to water.

J.

On Jul 21, 2016, at 8:36 AM, Richard Hatfield wrote:

Dear all –

 

Appreciating the ongoing discussion.  As a non-expert, designing and implementing land-and-water management projects in Africa, I am finding it very useful in the context of ‘climate change literacy’ – which is something we see must start to be articulated and disseminated widely, including in schools.

 

Thomas answered below a question that was forming in my mind of evapo vs transpiration.  I am trying to appreciate the difference in terms of cooling effect, in laymans terms.  Can someone help to interpret Walter’s piece below, in terms of the big picture air conditioner? IE grams of soil water taken up by plants, significance of 590 calories in terms of cooling, etc.

 

Meanwhile two overarching messages seem to be:  1. Plants cool the planet (until some point) and 2. We need to look after water levels in the soil (the ‘tank’) to ensure plants have the supply they need (not to mention people and rivers etc) eg in the corn belt example, one contributor seems to be the tank is not being well looked after due to tilled soils..

 

every extra gram of soil water that is transpired can transfer up to 590 calories of heat from the soil surface back up into the atmosphere thereby cooling that habitat and region. As that transpired water condenses to forms clouds with high albedo that can reflect up to 80% of the incident solar energy back out to space this can also further cool that habitat and regions. As these cloud droplets are coalesced on precipitation nuclei to form raindrops most of this transpired water can be returned to the soil to be again transpired and recycled continually enhancing the productivity, cooling and resilience of that landscape and the communities dependent on it.

 

Thanks,

Richard Hatfield,

Kenya & S Africa

 

Judy

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[Thomas Goreau‏]

Your point about keeping the tank full is absolutely right. In a drought plants stop transpiring!

That’s why managing runoff to maximize infiltration and prevent surface runoff is the key to minimizing loss of water, soil, and nutrients, and the best way to do that is to keep the land vegetated. Too often our land management has the opposite effect!

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.

Coordinator, Soil Carbon Alliance

Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies

37 Pleasant Street, Cambridge, MA 02139

gor...@bestweb.net
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

The Green Disc, New Technologies for a New Future: Innovative Methods for Sustainable Development

http://www.greenthindisc.org

No one can change the past, everyone can change the future

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[Philip Bogdonoff‏]

Correct me if my thinking is off, but as average temperatures rise around the world such that plants increasingly experience temps that cause them to close their stomata and stop transpiration, it would seem that having both mixes of C3 and C4 species, as well as multiple layers of plants (canopy trees, understory trees, bushes, typical crops, and ground cover plants) would be an important strategy to allow shaded plants to experience below shut-off temps longer than they would in a monocropped system.  Such mixed systems would presumably be able to keep transpiration going for longer, right?

And transpiration sounds like it is our friend in the short term to try to cool the planet.

-- Philip

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[Thomas Goreau‏]

Transpiration is indeed our friend, as long as we don’t let the tank run dry (i.e. add more carbon to soil). 

More C-4 plants will inevitably come to dominate, but it can’t hurt to speed them along by planting more for future extreme heat spells.

CAM plants play a similar role in desert habitats, the Sonoran Desert, for example, has an astonishing plant biomass for so little rain.

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.

Coordinator, Soil Carbon Alliance

Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies

37 Pleasant Street, Cambridge, MA 02139

gor...@bestweb.net
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

The Green Disc, New Technologies for a New Future: Innovative Methods for Sustainable Development

http://www.greenthindisc.org

No one can change the past, everyone can change the future

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