Toxic Algae and No-Till—The Environmental Darling of Industrial Agriculture and Genetic Engineering Looks Less Attractive

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Read attempts to defend the sustainability of industrial agriculture and genetic engineering, and you will soon encounter no-till, or more generally, conservation tillage. Now it appears that no-till may be contributing to some serious environmental problems.


Huge algal bloom, in green, spreading across Lake Erie. NASA photo.

Tillage, or plowing, is the age-old practice of turning the soil to kill weeds or incorporate plant matter or manure. But tillage often leads to increased soil erosion and loss of fertility. Erosion also contributes to silting of streams with soil carrying phosphorus, a major cause of freshwater pollution. So conservation tillage, and no-till in particular, which eliminates tillage, have some real benefits. This is especially true for industrial agriculture, which otherwise can contribute to erosion and reduced soil fertility.

And soil fertility, in turn, is critically important for ensuring the productivity and resilience of crops.

We already know that, while providing some real benefits, conservation tillage also has substantial limitations compared to agroecological approaches that reduce erosion, such as growing cover crops. Cover crops are grown to protect soil when cash crops like corn are not present in fall, winter and spring. They not only greatly reduce erosion and improve soil fertility, they also substantially reduce nitrogen loss which causes water pollution, such as dead zones in coastal areas. They can also suppress weeds and other pests, and reduce the need for synthetic fertilizers and pesticides. Conservation tillage does not provide any of these other benefits.

Another possible benefit of conservation tillage, increased carbon sequestration, is unproven. It may still turn out that it provides some additional carbon sequestration in some soil types and climates compared to conventional tillage, but that remains to be seen. On the other hand, organic and related methods probably do reliably increase soil carbon sequestration.

Toxic Green Slime

And now, new research reveals a darker side of no-till—it may actually exacerbate phosphorus pollution of waterways.

I grew up in Michigan, the heart of the Great Lakes region. These lakes, the biggest in the world, are a natural wonder that are more like fresh-water seas. Lakes are a terrific resource for recreation—from swimming to fishing to boating. The Great Lakes also have had substantial commercial fisheries of whitefish and other species. There have even been Great Lakes cruise ships. The presence of lakes, including the smaller lakes of the region stretching from the Canadian prairies through the upper Midwest to upstate New York, greatly enhances the quality of life and supports tourism.

So learning that the green slime of cyanobacteria (sometimes called blue-green algae) was back with a vengeance was a shock. Efforts to reduce phosphorus from sewage treatment plants and laundry detergents in the 60s and 70s resulted in one of the real successes of the environmental movement. Lake Erie is particularly susceptible because it is relatively shallow. But lakes in general are vulnerable, smaller lakes and reservoirs possibly even more so. So although detected in Lake Erie, it is also happening elsewhere. For example, Lake Winnipeg, a Canadian Great Lake, is also seeing increased eutrophication.

And the problems go beyond causing an eyesore or foul odors or fish kills. Two of the main species of cyanobacteria produce liver or neurotoxins, which were found in the lake at alarming levels.

The Lake Erie algal bloom of 2011 set records, eventually reaching about 5,000 square kilometers, or about 3 times larger than the next-biggest bloom. But records show that algal blooms have been increasing since the mid-1990s, after several decades of progress.

What happened? Why was the momentum toward cleaner water reversed?

No-till and Climate Change: A Bad Combination

The increase in harmful algal blooms coincides with increasing use of no-till in the Corn Belt. It turns out that without tillage, applied phosphorus fertilizer or phosphorous in manure becomes concentrated in the surface layer of the soil. Even though no-till reduces soil runoff and erosion—which carries phosphorus bound to soil particles into waterways—the resulting high phosphorus concentration at the soil surface leads to runoff of dissolved reactive phosphorus. The algal blooms that result from this are exacerbated by heavy rainfalls, which wash more phosphorus into the lake, and which are predicted to become more frequent in the region as global warming proceeds.

On top of that, phosphorous may become scarce in the future. Large deposits are found in only a few locations globally. So the loss of phosphorus from agricultural soils is also the waste of a valuable resource.

It is possible that occasional tillage will help alleviate this problem, by burying the phosphorus. But it is unclear whether many forms of tillage, such as the use of cultivators or chisel plows that do not invert the soil, or methods such as rotational tillage or ridge till, and so on, will effectively address the problem. And data are sparse about whether the other benefits of no-till would also be reduced in the process. In addition, most corn acres are still not using no-till or conservation tillage, so it is possible that further adoption could make matters even worse.

A lesson in all of this is that reductionist approaches to ecological issues that narrowly focus on solving one problem, such as soil erosion, without understanding the entire agricultural ecosystem are vulnerable to missing harmful unintended consequences. No-till is a valuable practice in some respects, but as used in industrial agriculture, it depends on heavy use of herbicides, which cause their own harm to agroecosystems, such as loss of habitat for monarch butterflies, bees, and other helpful organisms.

It is also important to remember that other agroecologically-based practices like cover crops can accomplish the benefits of no-till and much more. Not only that, but organic no-till can also be practiced without the use of herbicides.

But it is no coincidence that industrial no-till has been such a popular practice and rhetorical tool among the industrial ag community. It fits into the highly simplified and unsustainable system that the big ag industry wants to maintain. It is one of the few practices that big ag can promote that has some environmental benefits. And unlike agroecology, it depends on expensive purchased products. That’s good for the industry’s bottom line, but not so good for the rest of us.

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About the author: Doug Gurian-Sherman is a widely-cited expert on biotechnology and sustainable agriculture. He holds a Ph.D. in plant pathology. See Doug's full bio.

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  • A. Tasistro

    Currently, development work is being placed on Conservation Agriculture (, rather than Conservation Tillage or just No-Till.

    Conservation Agriculture has a broader scope because it is based on three components: 1) elimination of tillage, 2) maintenance of ground cover with residues, and 3) crop rotations, which include cover crops. As it brings about an increase in soil organic matter contents, Conservation Agriculture also contributes to carbon sequestration.

  • Mark P. Ludwig

    So many problems with this blog! First no till is easily the most positive development in big ag in the last 40 years. The changes a continuous no till soil undergoes reduce runoff considerably. While there is indeed a problem of stratification of nutrients, the increased stability of the soil due to glomulin (natural glues from micro organisms) and natural pore structure development hold that P in place. P also bonds tightly to soils, so if the soil stays put so does most of the P. P pollution is much more tied to over application of manure due to livestock farming. Better management of that resource is much more effective than worrying about pure crop operations, which generally keep P at a fraction of what a livestock farm has in their soils. Cover crops are swell, and no till guys are leading the way in adoption. CC and NT are highly compatible, framing this as an either or is total nonsense. I suggest you send some of your folks to the national no till conference next year and gain some actual understanding of the system, the culture of no till and the magnificent suite of tools we have today to get the job done. Lastly the implication that “big industrial farming” is to blame for all the nutrient issues is just plain wrong. I have seen tiny organic farms that were total disasters; leaky manure piles, self cleaning barnyards pouring crap into the streams, sloppy chemical handling (yes, they do spray pesticides on organic farms too). I also have seen massive farms doing a fantastic job; good residue coverage, substantial buffers around waterways, state of the art nutrient management. It’s management that makes the difference not size, and in my experience bigger farms have better management and the financial resources to implement BMPs. Lastly unless you have a source for an extra half a million qualified farmers to implement your organic no till model nation wide you might better spend your time working with the current staff to tweek their system and quit running down your natural allies in the no till camp. When they marched a bunch of amateurs into the country side in Cambodian and Zimbabwe to build a peoples agriculture it really didn’t go that well. FYI – I raise grass fed beef on my farm and work in ag conservation for my day job.

    • Doug Gurian-Sherman

      Mark (and David), Thanks for the thoughtful comments.

      I agree with several of them. I acknowledged that no-till has some real benefits. In fact the whole second and third paragraphs of the post mentions them….the same ones you mention. But while valuable for the reasons that you (and I) mention, I also believe that no-till has been oversold. It is great for some purposes, but not for others. And while some farmers using no-till are also using cover crops, and are leading the way to them, only a small fraction of those using no-till also use cover crops, although the numbers may be increasing. For example, probably close to 40 percent of soybean farmers use no-till, and about 25 or 30 percent of corn farmers, but probably considerably less than 10 percent use cover crops regularly.

      Over-application of manure, especially from CAFOs is a huge problem, and we have looked at this at length ( ). It is not clear how much of the phosphorus runoff problem is coming from manure or superphosphate applications. You seem to have missed the linked research. It does not really matter what the source of the phosphorus is, but rather that it builds up over time to the point where, because it remains mostly at the surface with no-till, substantial amounts of it dissolve in water and end up in stream and lakes.

      Phosphorus application levels could be much better managed, as you suggest, and that could be part of the solution (and should be). Or, as I suggest, occasional tillage might solve the problem, although we do not have enough data to know that. My discussions with mid-west commodity crop growers is that many are actually moving from no-till to various forms of conservation tillage, such as rotational tilling (yes, we do talk with farmers of all kinds. For example, I was just at the University of Illinois talking with farmers, scientists, and extension. I would love to visit your farm some time when I am back in Michigan).

      The problem with your solution is that, especially with high crop prices, there is incentive to push yields by applying a lot of fertilizer, so what you are suggesting is probably pushing against farm economics. Unless phosphorus prices get higher (which may happen eventually), over-application combined with no-till may remain problem.

      Organic or small farmers can indeed cause problems, and you are right that management is extremely important. I did not say that big ag is solely responsible for nutrient pollution issues, as you suggest. But the fact is that big ag farms the large majority of acres in the U.S. (organic is just a couple of percent). We know for a fact that the large majority of nitrogen pollution that causes the dead zone in the Gulf of Mexico, for example, comes from tile-drained industrial corn and soybeans in the upper Mississippi River basin. And while there have been some increases in efficiency, the dead zone is as big as ever.

      Better management is exactly what we are after. But ultimately that means not only conservation tillage, but also longer crop rotations (you will not reduce pest pressure, and pesticide use, in monocultures. The biology is simply stacked against it), cover crops, better integration of livestock with crops, and so on. The problem is, that farm policy, incentives and research are mostly pushing in the wrong directions. And big ag, or the organizations and companies that support it, are trying to keep it that way.

      We look at the entire farm and farm landscape, and from that perspective, we have a long way to go to become the kind of sustainable farming system we need. No-till or conservation tillage need to be integrated into agroecologically sound farming systems and landscapes to really be sustainable.

  • David Buland

    This article again No-Till has been picked up by the Ag. Press to down grade the’science’ in UCS.
    Also why does the blog talk about No-till OR Cover Crops. Most cover crop farmers also use No Till; the two technologies are used together, not separately as the article infers. This particular blog undercuts my respect for the ‘science’ use in UCS.

  • Susan Hopkins

    Perhaps it would be fairer to say that the practice of industrial, agricultural monoculture is the core reason for the eutrophication of lakes. No-till has so many advantages that it is a shame to dismiss it out of hand.

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