Crop rotations for weed management? At first glance, it doesn’t seem possible. We know, however that in our previous videos, Dr. Anderson showed us how (1) no-till reduces weed prevalence and (2) how he verified this idea experimentally. In this third video, Dr. Anderson discusses why rotating cool season crops into our warm season rotations are so beneficial to weed control. Dr. Anderson demonstrates how through the synergistic effects of no-till combined with diverse rotations, one can reduce weed pressure by a factor of eight before the first drop of herbicide is used. We recommend you view the first two videos (“Fate of the Weed Seed in Conventional and No-Till Soil” and “Seedling Emergence in Conventional and No-Till Fields” with Dr. Anderson.
Anyone who has kept up with us at Merit or Myth knows that there is a growing list of benefits that are associated with cover crops. From reducing runoff and erosion to increasing organic matter and suppressing weed emergence, it seems more research comes out every year proving the merit of this practice.
As with all tools, however, cover crops are only one piece of the puzzle, not the whole picture. This is because the fields in which we grow our crops are all dynamic ecosystems that are influenced by everything with which they come in contact. Given that we’re in the middle of a three-part series on weeds, it’s important to understand how the implementation of cover crops effects weed management, specifically when it comes to herbicide usage.
THE INTERSECTION OF HERBICIDES AND COVER CROPS
For better or for worse, the practice of spraying herbicide has conventionally been an accepted reality of farming. It makes sense: in simplest terms, a producer looking to grow plant A is going to encounter some problems when mother nature wants him to grow plants B, C, and D along with it. The quickest way to subdue mother nature? Spray chemicals, ask questions later.
We’ll leave the long-term effects of spraying herbicide for another time (if you would like a bit more information on this, check out our own Dr. Buz Kloot’s take in his video, “Weeds: A Chemical or An Ecological Problem?”). The bottom line for now is that, regardless of what it does to the environment in the long-term, when it comes to herbicide, very few of us have a thorough grasp on the subject. Extension agent at the University of Wisconsin Dan Smith has seen this firsthand when it comes to the crossroads of herbicide and cover crops. His advice? Make sure you read the label.
“Most herbicide labels contain information for forage crops,” Smith says, “but they don’t contain information for cover crops. It’s important to dig into that label to make sure you don’t have any restrictions on that herbicide, things that would prevent you from legally feeding that to your livestock or selling it to a livestock farm.”
Easier said than done, we know. Reading herbicide labels isn’t exactly like flipping through your favorite Dr. Seuss book. These labels are routinely long and include terms and chemicals of which not every farmer holds a comprehensive knowledge. However, it’s more important than ever for us to understand what these labels have to say.
HERBICIDE: TIMING IS EVERYTHING
While the benefits of cover crops are extensive they don’t exactly happen overnight. This reality has lead farmers to seek more readily available ways to utilize cover crops in the short-term, such as using them as a forage crop. We must be aware, though, if we’re to use cover crops as forage that some herbicides carry significant risk for animal consumption. In this regard, timing is everything. This is why Smith says that a good place to start when it comes to reading herbicide labels is the rotational crop section.
“The rotation data is a legal requirement from the time of herbicide application to the time that we’re going to harvest or graze that cover crop that turns into a forage crop,” Smith says. “That could be a diet for cover crop establishment, but remember that you can grow a cover crop following any herbicide application as long as you never harvest that cover crop.”
Of course, individual herbicide types and brands have extensive variation and herbicide carryover can be effected by a variety of conditions, from organic matter content to soil pH to rainfall and soil type. This is yet more evidence that the greatest teacher when it comes to farming is below our feet. Read your herbicide labels and find out how they affect your soil firsthand. It may be a little more work in the short-term, but once the benefits of cover crops are realized, you’ll be thankful that you did.
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In our previous video, Dr. Randy Anderson walked us through the various fates of the weed seed in conventional and no-till fields. In this video, the theory comes alive as he discusses the results of a three year study he did in comparing conventional and no-till weed seedling emergence.
There are many issues facing the modern-day farmer, though most of them are nothing that new. After all, nature has always kept us on our toes in the form of drought, flood, and other extreme events. You would think that with technological advances and increased agricultural acumen, however, we would have taken steps towards reducing the negative effects of nature…. or at least be part of the solution, not the problem. Unfortunately, when it comes to erosion, it would appear that we ourselves are the ones to blame for digging us into a deeper ditch.
Now certainly, erosion has always been in existence. It is not necessarily a man-made problem, but unlike many other agricultural issues, it has come to the forefront largely because of human activity. Nowhere is this more apparent than in the Midwestern United States. Here, soil erosion has grown so extreme that Jerry Hatfield, director of the USDA-ARS National Laboratory for Ag and the Environment, believes that we’re losing, on average, 5 tons of soil per acre per year due to erosion (with higher-end areas losing closer to 100 tons per acre per year).
These numbers by themselves can be a bit staggering, but they become even more alarming when we consider soil replacement rates. Essentially, many believe we’re losing soil faster than soil can be restored , thus, if nothing changes, the situation will only become direr.
SOIL EROSION: DIGGING DEEPER
Let’s get to the heart of the issue:
“(Erosion rates are) all rainfall driven,” says Hatfield. This reality may seem to contradict the above statement that increased erosion is a man-made problem. As seems to always be the case when it comes to agriculture, a closer look into things reveals the greater truth.
Spring is generally the wettest time of year. For the farmer who has, say, a corn and soybean rotation whose fields lay fallow in the spring, there’s no crop present to help transpire the water or protect the soil. Compounding this issue is the practice of conventional tillage which exposes soil, breaks down soil structure and thereby, decreases pore space and infiltration. The result? Runoff which leads to erosion. There are even some studies out there that suggest that erosion increases exponentially as runoff increases.
This information will be of no great surprise to those who have watched our three-part series on soil infiltration. In that series we learned the counter-intuitive reality that no-till soils perform better at infiltrating water than those under conventional tillage, be it moldboard plow or chisel plow.
Still, there is some hope. Seven million acres have already been enrolled in the ¹Conservation Stewardship Program (CSP) in South Dakota alone to reduce soil erosion and improve water quality as of 2017. The reality is, however, that while this is a needed step in the right direction, it’s more of a crawl than a leap. So what can we do? Once again, if our research is of any indication, it appears that the four principles of soil health are needed. This fact isn’t lost on Chad Watts, executive director of the Conservation Technology Information Center in Indiana.
“You protect land from erosion and reduce the amount of sediment you put into streams with these (types of soil health) practices,” Watts says, though he knows changing the hearts and minds of traditional farmers will take more convincing. That’s where Midwest native and soil health specialist Doug Peterson comes in.
“The practice of tillage is more ingrained in most people than their religion,” Peterson says.
The notion that conventional till decreases soil stability, soil function and enhances erosion and runoff is a tough pill to swallow for many. After all, most farmers were raised to believe that the very reason they should use conventional till is to help reduce such issues. Unfortunately, regardless of how strongly we adhere to our beliefs, that does not necessarily make them true. In this regard, Peterson doesn’t beat around the bush.
“There is no agronomic or economic reason for tillage to be justifiable anymore,” Peterson says. “It destroys everything that restores soil function.”
We saw strong evidence of this firsthand in South Dakota when the NRCS’ Jeff Hemenway walked us through an eye-opening slake test comparing infiltration in no-till versus conventional till soils.
“The tilled soil dissolves rapidly (in a slake test),” Peterson notes. “In the presence of rain, without the glues or [root] exudates, the soil particles in the aggregates break loose, and they are very susceptible to erosion.”
EROSION: NOT SIMPLY AN ISSUE OF CONVENTIONAL TILL
It’s become easy for advocates of no-till and regenerative farming to “bully” the idea of conventional till. Once again, however, a closer look at things makes it evident that converting to no-till is not a fix-all. If we must view it in such terms, tillage is not the enemy. If a farmer adopts the first principle of soil health (do not disturb), but neglects the other three, they’re only seeing a fraction of the picture. When it comes to erosion and enhancing infiltration, the second principle of soil health (keep the soil covered) is just as crucial. This is one of the many reasons why cover crops have seen a significant rise in recent years.
When you have a living canopy and live roots directly beneath the soil, you can reduce runoff head on. Instead of bombarding the soil, rain hits the canopy and slowly trickles down the plant into the roots. This slow-down effect on raindrop impact is one of the chief benefits of the third principle of soil health (keep a live root in the soil as many days as possible). The result is infiltration as opposed to runoff and erosion.
In this way, it seems rather evident that the solution to high erosion rates comes through the application of principles of soil health. Specifically, through the use of no-till, diverse rotations and cover crops (i.e., no fallow periods) which keep the soil covered and keep a live root in the ground year-round, we address the core issue that runoff and erosion are simply symptoms of: degraded soils.
“Your soil is more than just the medium in which you grow plants,” Watts says. “The downfall of many civilizations was when they degraded their soil to the point that it was no longer productive. When soil degrades to the point of no return, that’s when civilizations begin to fail. It behooves you to protect your soil.”
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¹ Conservation Stewardship Program (CSP): CSP helps farmers build on their existing conservation efforts while strengthening their operation. CSP is the largest conservation program in the United States with 70 million acres of productive agricultural and forest land enrolled.
To learn more about conservation practices, visit the NRCS’ Soil Health Page.
For more information about USDA NRCS programs, visit the pages below:
In a world where technology offers a quick fix to our weed problems, but inevitably leaves us with unintended consequences, the USDA Agricultural Research Service (ARS), Brookings, SD, Dr. Randy Anderson offers an approach to weed science that says “wait a minute”, what are we doing? In our systems to encourage or reduce weed proliferation before we consider which herbicide to use? To begin to grapple with this question, we have to understand the fate of the weed seed. Dr. Anderson considers weed seed when on the surface of the soil and when buried. Join us in this, the first of three discussions as Dr. Anderson shows us how we can use natural systems to reduce weed populations and save on herbicides.
As Dr. Anderson says, “A key point is when you leave the weed seeds on the soil surface you enhance these fates [predation, environmental exposure, natural death]. In other words, predation is much greater if insects can reach the seeds – if they are buried in the soil, the insects do not process the soil looking for weed seeds so therefore tillage actually protects seeds. Almost all studies with weeds seeds have shown that when you bury them in soil the weed seeds live longer and survive longer.”