From ETH Zurich , something that actually makes sense.
Straw albedo mitigates extreme heat
Wheat fields are often tilled immediately after the crop is harvested, removing the light-coloured stubble and crop residues from the soil surface and bringing dark bare earth to the top. Post-harvest tilling is a widely practised and common management technique in Europe. However, ploughed fields can have a negative effect on the local climate during a heat wave. This effect was addressed in a recent study conducted by researchers at ETH Zurich led by Edouard Davin, senior lecturer at the Institute for Atmospheric and Climate Science, and Sonia Seneviratne, professor of land-climate dynamics, which has now been published in the scientific journal PNAS.
Unploughed stubble is lighter in colour and reflects more solar radiation than tilled surfaces. Measurements taken show that approximately 30% of sunlight is reflected back due to the albedo effect – the albedo is a measure of the reflectance capacity of reflective surfaces. Ploughed fields reflect only 20% of incoming solar radiation. Model simulations have shown that this difference results in a 50% higher level of reflection in unploughed fields and that this in turn has a significant effect in extreme heat. In the event of a heat wave, such as the one in Europe in 2003, unploughed farm fields could reduce the local temperature by as much as 2 °C.
Regional effect
The hotter it becomes, the greater the albedo effect and the resulting temperature reduction. “Cropland albedo management has more effect during heat waves because there is almost no clouds during these events and more radiation can be reflected back into space”, says first author Edouard Davin. However, this effect is only short term and local — perhaps at the most regional, but never trans-regional. “In other words, if all French farmers were to stop ploughing up their fields in summer, the impact on temperatures in Germany would be negligible,” says Seneviratne. Leaving fields untilled would also have no noticeable effect over the long term on global warming trends and more frequent heat waves. Nevertheless, as Seneviratne points out, the local impact is important and could help break peak temperatures on extremely hot days.
Overall, says Seneviratne, no-till farming makes more sense in regions where summers are regularly very hot due to high levels of sun exposure e.g. in areas around the Mediterranean. Nonetheless, on heat days, the effect is also relevant in Central and Northern Europe. As part of the study, which was carried out jointly by the ETH researchers and French scientists, Davin analysed solar radiation measurements on farmland near the southern French city of Avignon. The researchers also conducted model simulations for Europe that incorporated the projected effect of unploughed cropland.
The scientists also report that the cooling effect of an unploughed field cannot be attributed solely to changes in albedo values. Crop residue acts as an insulating layer that holds back moisture from deeper soil strata and releases it only slowly — this long process of evaporation also helps reduce the air temperature during a heat wave. In a ploughed field, on the other hand, moisture evaporates more rapidly and almost completely in extreme heat. Thus, there is an additional cooling effect of no-till farming through slow evaporation.
No-till farming common in the Americas
The researchers believe no-till farming is a useful option in order to mitigate the local effects of climate change — for example, on extremely hot days in summer. “It is important that cropland albedo management can dampen heat waves because these events, although rare by definition, have a large impact on humans and ecosystems,” Seneviratne explains. Even though the rise in average global temperatures has stagnated in recent years, there has been an increase in extreme heat events over land areas.
Europe in particular has sufficient potential to use no-till farming as a tool to lower temperatures on hot days. Until now, European farmers have left only an extremely small portion of their fields unploughed after a harvest and globally the region accounts for only 2% of all unploughed cropland. The situation is very different in the US and South America, which account for 85% of the world’s unploughed farmland.
References
Davin EL, Seneviratne SI, Ciais P, Olioso A and Wang T. Preferential cooling of hot extremes from cropland albedo management. PNAS Early Edition, published online 23 June 2014. DOI: 10.1073/pnas.1317323111
Michael Palmer wrote, “I truly find this baffling. Before the advent of farm machines, tilling used to be hard work – why was it invented if it is superfluous?”
http://research.wsu.edu/resources/files/no-till.pdf
There is something magical and satisfying about a freshly plowed, disked and seeded field that isn’t present when seed is drilled into last years stubble.
One would think that these people had never heard of the “dirty thirties” and the steps taken by the agriculture industry to avoid its re occurrence.
I have to apologize for subjecting your readers to another of my comments but the following is just flat out wrong:
‘Unploughed stubble is lighter in colour and reflects more solar radiation than tilled surfaces.’
Now, the last time I shaved my dear niece said to me, “Uncle Tom, you look like a chipmunk.” So, for understandable reasons I haven’t shaved again for decades. But, I can assure you, the stubble that was on my face back then could not possibly have reflected more solar radiation than the rather lengthy (I use a rubber band on it sometimes), and far lighter coloured surface that replaced that stubble. To prove this point may I point out that young girls have tugged at their mother’s sleeves, pointed slyly in my direction and whispered, “Mommy, it’s Santa Claus.”
That has happened more than once. Honest. And, due to the fact that I weigh a svelte 128 lbs., I know it’s the beard.
Michael Palmer: When a field has used up nutrients close to the ground, plowing was the only answer. Plowing digs pretty deep and brings that deeper soil with its nutrients (like worm castings) to the surface. Then you had to slice through the rather large clods with disks to change the plowed ground into a finer layer of top soil for drilling (the final process that plants the seed in the ground). It was a pain to plow every year, so even back in the old days, it did not happen every year unless absolutely necessary. And some crops were never plowed until they needed to be completely reseeded because the crop was a perennial.
The albedo from no-till won’t help global warming. Deforestation, concrete, and blacktop doesn’t contribute to global warming. Nope, it’s just that bad CO2 caused by those mean old energy companies.
There are many conflicting positions and policies regarding tilling in Europe and – it seems to me – this is just some ag scientists trying to get a ‘climate change” link into theirt research – good on ’em!
Tilling is about weed control and when you have a selective herbicide (one that kills weeds and not your crop plant) people have been using no-till because it is much much more effective. The problem was the lack of and expense of selective herbicides and so plant breeders have been selecting for tolerance cheap broad spectrum herbicides for many many years. Mutation breeding has been very successful for one class of herbicides (sulfonyl-ureas), but when companies developed engineered lines tolerant to glyphosate and glufosinate (both very cheap and environmentally nice as they break down quickly in the soil) farmers leaped on them wherever they were allowed to.
However, leaving stubble in a field is not the same as no-till. No till is about how you prepare before planting, not what you do after harvest, unless you are talking about winter sown crops (which is something relatively rare in North America, which has snow cover at much lower latitudes). Stubble retention is often about soil structure and can be both a good and a bad thing depending on what soil you happen to be working with. There is also an issue with an increase in a group of fungal diseases referred to as necrotrophic – that is, they live on dead plant material as opposed to living plants. Burning stubble was employed as a pretty effective control mechanism for these necrotrophs, but that had other environmental issues and is pretty much banned now.
The other issue with European agriculture which has recently (10-20 years) come up is the consideration of nitrate run-off from agricultural fields left bare over the winter. When crops are growing in spring and summer there is almost no leaching of nitrate from the top soil into the water table. However, over the winter when the soil is bare, microbial action breaks down organic nitrogen in plant matter to nitrates, which leach during winter rainfall. In order to prevent this, countries have put in place requirements for planting of a catch crop over the winter – often referred to as “anti-brown field” policies. Stubble is not a living plant and so to plant a nitrogen catch crop often involved getting rid of the stubble before you can get your seeders in there.
Thus we have a complicated mixture of agronomic and policy issues to consider here. As I said at the top, kudos to this group fotr getting a climate change angle in there – this should ensure their funding for a few more years.
There is a noticeable darkening of wheat stubble with time in sunny inland Australia due to oxidation. It is not a constant light colour.
How many people, and gas tanks, could we feed without GMO farming?
Just sayin,,,,,, Math?
Zeke says:
June 23, 2014 at 2:28 pm
We used to burn fields to reduce fungus. Natural and sustainable practice. But people don’t like all the smoke. Boo hoo. Ok, so then you can be slowly poisoned by RoundUp residues. Why don’t we just ban farming? All food comes from Safeway anyway.
From what I see in the US mid-Atlantic states, no-till farming is the norm now for some yrs.
Theyouk says:
June 23, 2014 at 2:34 pm
“Have any of these people ever talked with a glider pilot? My understanding is that the dark ploughed fields warm more quickly and generate thermals under the hot sun”
Many years ago I learned to fly a microlight (generally known as ultralights elsewhere) from a site in the middle of the East Anglian Fens in the UK. The soil there is not just dark, but black (it’s dried out peat, and the most productive soil in the country). I can confirm that ploughed fields generate VERY powerful thermals on a sunny, summer day!
Interesting, there could be a ploughed field heat island effect. Wheat from Texas to Canada is harvested from June to July respectively, just as summer heat waves arrive.
I wonder if this shows up in the temperature record via night time temperatures increasing more near cropland that is harvested early summer, i.e. wheat, versus rangeland and cropland that is harvested late summer, i.e. corn.
Here in SE Missouri there is an interesting local phenomena associated with post-harvested wheat fields: It’s called the “Oopsy! grass fire!”. It’s simply amazing how many farm machines, tossed cigarettes, and lens-shaped pieces of broken glass “accidentally” light off the stubble, reduce it to carbon, and make it easier to plow under and return to the soil.
I chuckle every time I see one. Like last week.
Is the next step a campaign to ‘preserve the albedo’ by letting the stubble lay in the fields to nourish the weeds, and then to till only after first snowfall?