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.