Crops

Know your soil's biological history

Written by Jason Worthington on .

If the topic of fungi, bacteria or other microbes comes up regarding crop production, we tend to think of them as something that might harm a crop. We think of pathogens, challenges to plant health and lower grain yield. That’s a natural thought process. From fungicides to varietal resistance and cultural practices, disease management is a top priority. On the flip side, we seldom think about how to impact our beneficial bacteria—but it appears that awareness is growing. And that’s a good evolution.

In 2015, Missouri had over 1.5 million acres of prevented planting. If much thought was given to how 2015 fallow acres impacted the 2016 crop, it was generally centered on keeping weeds under control. Another consideration was how to adjust soil fertility. But there wasn’t a great amount of consideration on what might have happened to beneficial microbe populations. In 2016 we were reminded just how important the beneficial microbes in our soil are, and prevented planting acres from 2015 may still impact cropping decisions in 2017.

There is a common term used by plant pathologists to describe the necessary components for a disease to exist. It’s called the disease triangle. The three sides of the triangle are: 1) the infectious agent; 2) a host plant; and 3) favorable conditions. Without any of the three sides, the triangle is incomplete, and a disease does not advance. The same goes for beneficial microbes. They are infectious agents requiring a host plant and favorable environment. The only difference is they provide benefit to the host rather than harm. In 2015, on prevented planting acres, the host plant was removed. The result, in many cases, was that beneficial microbe populations plummeted. One possible result of reduced microbe populations is a condition called fallow corn syndrome.

Fallow corn syndrome received a lot of attention in 2016. While there is little doubt that fallow corn syndrome existed, to what extent is debatable. Fallow corn syndrome can easily be confused with nutrient deficiencies in the soil, herbicide injuries and common conditions associated with cool, wet weather. Fallow corn syndrome is a phosphorous and zinc deficiency in corn growing in soil that has adequate levels of those nutrients. The plant is deficient of these nutrients due to an inability to retrieve phosphorous and zinc. This failure results from a significantly reduced population of mycorrhizae.

Mycorrhizae microbes work as an extension of the corn’s root system helping to reach and solubilize nutrients that are highly immobile in the soil. Mycorrhizae have the ability to colonize many different plant species and do not necessarily need corn as a host to maintain populations. Planting cover crops in fields that would otherwise lay fallow is one prevention measure, and weeds are a host that can support populations. The most likely locations where fallow corn syndrome may have existed fit some specific parameters. They were non-planted fields where growers actually did a good job of controlling weeds, didn’t plant a cover crop, and planted corn in 2016. The actual impact of fallow corn syndrome depends on how quickly mycorrhizae populations recover. Biological products like Quickroots or Cue (designed to either inoculate seed with mycorrhizae or stimulate growth and reproduction of beneficial microbes) may speed mycorrhizae population recovery.

An issue that may be more common in 2017 than 2016 is reduced soybean nodulation in fields that were fallow in 2015. Like mycorrhizae, rhizobia bacteria, which fixate N for soybean plants, form a symbiotic relationship with the crop. Unlike mycorrhizae, different rhizobia species are require specific plants to survive. Rhizobia japonicum, the species associated with soybeans, will not maintain adequate populations to provide significant nodulation when soybean plants are not present. While inoculating soybean seed annually is an excellent practice, it becomes increasingly important during extended absences of soybeans. Because crop rotations were disrupted with non-planted acres, there are fields this year that may be planted to soybeans for the first time since 2014.

As time pushes on, we tend to forget about the impact some weather deliver and how they can continue to affect our soil. Past cropping practices don’t just have longterm effects on things like the weed seed bank, or soil compaction. They also affect the biological activity of soil. As always we need to remember the needs of this crop year. However, it pays to remember what fields have endured past years and what we expect of them into the future.

New technology and new technique

Written by Dr. Jason Weirich on .

Back in April, I wrote about the use of new weed control technologies. We had just received approval from China for the Xtend trait. Just a few days after the election, we finally received federal registration for the use of XtendiMax with VaporGrip. With all of the media and publicity around off-target dicamba applications in the past season, these announcements could not have come fast enough. 

Proper stewardship of the new technology is a must—not only from a weed-resistance management or environmental perspective, but from a neighborly perspective. 

Xtend or Enlist will be tools that allow you to use a mode of action that hasn’t been used in soybeans or cotton in the past. And, it will show you if you have any off-target movement within a few hours or days. These new formulations are labeled for over-the-top or preplant applications to Xtend soybeans, but it’s not the same old dicamba formulations from the past—Banvel, Clarity, Detonate. Monsanto’s XtendiMax with VaporGrip, and BASF’s Engenia are two formulations that have considerably reduced the volatility of dicamba. 

These traits will provide you with new flexibility to control weeds, especially some of the difficult-to-manage herbicide-resistant weeds that have become prevalent in the MFA trade territory. 

But using the technology won’t be as simple as mixing herbicides in the past. This new trait will come with some new procedures as well. You will now be required to visit a website listed on the label to find out what products can go in the tank. Each manufacture or retailer has submitted a list of proposed tank mixes. These have been sent to an approved lab. This lab looks at several characteristics of the tank mix volatility, driftable fines, and compatibility to name a few.

Ken Carmack, adjuvant specialist for MFA, has been working with the top adjuvant manufacturers to develop MFA’s Crop Advantage lineup. This lineup is second-to-none. Rest assured when you see the approved Crop Advantage adjuvants on the list, they have been tested by our experienced field team. 

Drilling down in the specific requirements of this list, you will see that nothing is supposed to go in the tank unless it is listed on these websites. Some of the questions that I have received over the past few weeks are about the use of foliar nutritional products that may have gone in the tank in the past. Again, you want to make an application with any of the new cropping systems, Enlist of Xtend, you will need to follow the label and look at the website seven days before application. I would look at this as a living document. I believe the companies will add and remove different herbicides at any given time, albeit hopefully adding more than removing. You must check within seven days before application. 

I write this not to scare you from using these great tools, but to inform you about application requirements.

I am sure you will have plenty of opportunities to learn about this system, during the winter grower meetings that you attend. Please reach out to your local MFA for more information on MorSoy RXT soybeans and approved herbicides.

If you would like to hear about a specific topic or agronomy issue, please send me an email at This email address is being protected from spambots. You need JavaScript enabled to view it..

Variable yields call for variable rates

Written by Dr. Jason Weirich on .

What a year. From a drought to what seemed like we had moved to the rain forest, Midwest weather never seems to be consistent. Maybe that’s the new norm.

And like the weather, crops were variable. In the combine seat this fall, more than likely you watched the yield monitor read-out dramatically rise and fall as you worked across the field. While I hope the overall yield was good, the acre-by-acre results probably looked like the picture at right.

With variable yields like we saw over much of MFA’s trade territory this year, the amount of nutrient removal will be variable, too. It’s all based where you are in the field and what yield you made there.

This variability can cause problems for growers as you think about how to replace the phosphorus and potassium your crop removed. The old standby of flat-rating fertilizer like my grandpa did hasn’t proved itself as the best use of your fertilizer dollar. Variable-rate technology allows you to replace and build your soil test levels in each field. You can target the optimal nutrient levels and make your fertilizer dollar go further. MFA’s Nutri-Track program is focused on putting nutrients where they are needed and avoiding over-application in areas that won’t perform.

While on the topic of nutrient management, and as we head into another application season, you need to take a step back and think about what practices you adopted on your farm.

The 4Rs promote the best management practices to achieve your yield goals while reducing nutrient loss and increasing nutrient use efficacy. So what are the 4Rs? Right source, right rate, right time, right place.

It’s important as a producer to pay attention to all the above. Not only from an expense standpoint, but from an environment standpoint.

Applying fertilizer while paying attention to the 4Rs will help growers produce more with less land. It will also help you retain nutrients where you intend for them to be—in the field instead of heading downstream.

There are increasing regulatory pressures zeroing in on your farm. Nutrient stewardship is just one of them. Out East, EPA has assigned 44 percent of the nitrogen and phosphorus loads to the Chesapeake Bay to agriculture. If that seems distant enough for comfort, look to the Des Moines Water Works issue. There is legal battling there over field runoff as I write this. Then there is Gulf hypoxia. These issues won’t just go away.

While you may be most interested in the 4Rs as a way to get the most efficient use of inputs, it is also important as a way to demonstrate our commitment to soil stewardship, proper fertilization practices and the economic benefit of using proper fertilization techniques.

I believe that the average non- farmer, the typical consumer, misunderstands the concept of fertilization in commercial agriculture. Hopefully, the 4R program can help dispel misconceptions by the general public. We know it can help you be more efficient.

For more information, please visit www.nutrientstewardship.org or stop by your local store for more information.

Phosphorus trends down

Written by Steve Fairchild on .

This summer when the International Plant Nutrition Institute released its latest soil sample survey, there was a new twist. For the first time, the organization did statistical analysis on long-term soil fertility trends. Looking at data from four million soil samples collected since 2001, IPNI was able to show that crop fields in parts of the Midwest are trending down in phosphorus. Missouri and Kansas were among the states leading in soil test phosphorus decline.

A look at input trends versus crop removal over that period, shows that in some areas cropland is being mined, a practice that will eventually reduce yield or require expensive fertility catch-up programs.

The trick with talking about soil nutrients in a sweeping fashion is that there is high variability in soil fertilities levels on different types of farms in the Midwest. The nearby map, shows the difference that separates Missouri and Kansas from Arkansas and Oklahoma. The kinds of crop grown have a significant effect on how much phosphorus is removed through harvest. Animal production and cycling nutrients back to the land through manure is a factor, too.

According to Dr. Tom Bruulsema, IPNI’s Phosphorous Program director, the soil sample survey revealed that “across North America, the fraction of soils testing below critical for phosphorus decreased from about 60 percent in the 1960s to a low of 40 percent in 2005, but has increased to 44 percent over the past ten years. In key states of the Corn Belt, the depletion trend continues from the mid-1980s. The 56 percent of soils currently above critical represent two levels of legacy.”

“Legacy” phosphorus refers to stores of phosphorus in soil profiles that may exist outside of cropping areas or remain unavailable to the crop. “While it is difficult to define the precise soil test level that separates “too much” from ‘optimum’ legacy, the tools of precision agriculture should equip growers to maintain soil test levels just a little above critical,” reported Bruulsema. “Variable rate technology—applying the ‘right rate’ of phosphorus in the ‘right place’ to match soil and crop need—enables the management of legacy to desirable levels.” He added, “Most soils retain most of any phosphorus applied. The little that leaks, however, can harm the environment. Acute risks of losses accompanying application of fertilizers or manures can be controlled through ‘right time’ and ‘right place.’ Timing applications to avoid periods when risks of runoff are high, and placing them into instead of on top of the soil can make large differences on the amount of phosphorus delivered to the edge of the field. Conservation practices that control soil erosion are also important in controlling losses of particulate forms of the legacy.”

As part of the organization’s continuing effort to educate growers, IPNI has developed an interactive website (http://soiltest.ipni.net) to share data from the soil test survey. This summary shows that soil tests do change over time in response to management. Regular soil sampling can pay its way

It is approved and proven and may be a thing of the past

Written by Dr. Jason Weirich on .

Atrazine has been in the news lately. Given that the chemistry, ap­proved long ago, is under regulatory review yet again, I think it’s worth going over just how it works and why it is important.

Let’s start off by taking a look at the mode of action of atrazine. Atrazine is a photosynthetic inhib­itor—more specifically a Photosys­tem II inhibitor. As many as half of available herbicides have a mode of action that involves interaction with some component in the energy transfer chain of Photosystem II. In early plant science classes we learned that the transfer of elec­trons from PSII to PSI is essential for the production of photosyn­thetic energy. By interrupting the photosynthetic pathway, the plant becomes unable to fix CO2, which results in its inability to produce the nutrients the plant needs to survive. The mode of action is unique and efficient.

You may wonder why I launched this column with a chemistry lesson. I did it as an insight into the specter of weed resistance. You are well aware of weed resistance and the struggles it can bring to your operation. In previous columns, you’ve seen me write about herbi­cide modes of action and the fact that effective modes of action make for effective weed control programs. In fact, you’ve probably grown tired of me writing about it. But, resis­tance is something to think about as we wait to see if atrazine stays on the market. If we lose atrazine, we will lose one of those effective modes of action—one of the critical tools in our tool box.

If EPA pulls the registration for atrazine, there will be significant agronomic ramifications. In the short term, you can expect to see an increase in the density of broadleaf weeds—not only in cornfields but subsequent soybeans as well. You know that weed density is greatly influenced by the previous year’s production practices. There is al­ways someone in the neighborhood with a persistent weed problem, right? It’s that grower who can’t quite get ahead of a growing weed population. The weed seed bank on his place just increases every year.

Another perspective is all those prevented-planting acres from the summer of 2015. The weeds that went uncontrolled will cause trouble for several years to come. The point is, the weed seed bank in your soil is something you have to manage with the tools available on the market. We’re deep into a period with no real new chemistries headed for the market. We can’t afford to lose any herbicide tools that we have.

In fact, we haven’t had a new mode of action introduced since the 1990s, and that release was HPPD herbicides. The HPPDs con­sist of herbicides such as Callisto, Balance, Impact/Armezon, and premixes such as Lexar, Corvus, Capreno and Resicore, just to name a few. Think about your weed con­trol program. Did it include any of these? Quite a few premixes on the market today contain atrazine. For example, Halex GT, BiCep II Mag, FulTime NXT, Keystone NXT and plenty of others. If the label allows, applications of atrazine tank mixed with HPPD herbicides deliver a couple of benefits. First, when atrazine is used in combination or rotation with other products that have different modes of action, it lowers the risk of weeds developing resistance to those products. For example, weed resistance has developed in 10 ALS inhibitor herbicides used in corn. On average, 65 percent of acres treated with these herbicides also receive atrazine either in a tank mix or sequentially. The atrazine is used to slow the spread weeds resistant to the ALS class of herbicides.

Atrazine is also a useful rotational mode of action to delay the spread­ing problem of glyphosate resis­tance. For particularly hard-to-con­trol weeds like common cocklebur, Palmer amaranth, waterhemp and wild sunflower already known to be resistant to other herbicides, atra­zine is the only product which can be applied either pre- or postemer­gence that provides effective control.

Second, atrazine in combina­tion with Callisto can significantly improve weed management and has demonstrated better efficacy when these herbicides are applied postemergence for control of water­hemp, lambsquarter, giant rag­weed and Palmer amaranth. With the combination of atrazine and Callisto, there is improved control of weeds resistant to Photosystem II and ALS-inhibiting herbicides. In Missouri and other parts of the MFA trade territory, there are a lot of weeds that fit into that category. In general HPPD herbicides alone do not have exceptional levels of efficacy on many agronomically im­portant weeds without the inclusion of atrazine.

With the recent reports about HPPD-resistant waterhemp from University of Missouri Weed Scientist Dr. Kevin Bradley, it seems inevitable that HPPD resistance will increase unless atrazine is available to mitigate resistant populations. Thus, atrazine is a must-have tank mix companion to HPPD herbicides, especially because a high percentage of corn acres in Missouri receive an HPPD herbicide.

Another implication comes to mind concerning the tools we need for weed control: no-till or conservation tillage. Without the herbicides that we have today, no-till wouldn’t be an option. Weed control technology affords us the ability to use herbicides instead of cultivation for many years. And that saves soil. Keeping soil in fields is important not only from an environmental standpoint but for long term yield— and to your bottom line. When you lose topsoil, you lose nutrients and productivity. Without atrazine, no-till operations will face immense challenges, and fewer acres will enter into no-till production.

Perhaps more sobering than the agronomic challenges that would arise if atrazine is removed from the market are the bottom-line ramifications for crop production. Recent studies show that the loss of atrazine could cost an average corn grower 6.4 to 7.7 bushels per acre. If corn is $3.84 per bushel, that would cost the grower $24.50 to $29.50 per acre. I think this is a conservative estimate—and it doesn’t include the additional costs to the grower for controlling escaped weeds through additional herbicides, additional applications or tillage passes.

You’ll need more of three things if atrazine is pulled from the mar­ket: management effort, money and time. Here is why. Over the past couple of years, I have encouraged the use of overlapping residuals. This management technique is im­portant in soybeans and becoming more important in corn produc­tion. I believe that this will be the only method for effective weed control going forward. I would love to tell you that a Silver Bullet is coming down the product pipeline, but that is not the case. Atrazine is a crucial tool for managing weeds. In fact, it is often the building block for a sound management plan against weed resistance. Losing it will be costly.

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