Variable yields call for variable rates

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 or stop by your local store for more information.

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Phosphorus trends down

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 ( 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

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

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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Northern rootworm is an unwelcome arrival

MFA’s Crop-Trak consultants have been finding an alarming number of northern corn rootworm (NCR) beetles in northwest Missouri and southwest Iowa. Kevin Moore with MFA’s Crop-Trak first noticed high numbers of adult northern corn rootworm in a cornfield rotated from soybean near Fairfax, Mo., in July 2016. In the weeks after that discovery, large populations of NCR beetles were discovered in multiple fields in Atchison, Nodaway, Holt, and Worth counties in Missouri as well as Page county, Iowa. The presence of a few rootworm beetles moving from corn-on-corn fields into later planted rotated cornfields is not uncommon because rootworm beetles feed on corn pollen and will seek out a food source. The alarm comes from the fact that such a high number of beetles are being found in areas where acres are dominated by corn/soybean rotations.

Rootworm species of economic importance include the northern corn rootworm first discovered in 1824 in the north central U.S. and the western corn rootworm (WCR) first discovered in western Kansas in 1868. In North America, corn rootworms are the most devastating insect pest to corn. Agronomists estimate that before the development and release of Bt corn traits to control corn rootworm larvae in 2003, 50 million acres were infested, accounting for over $1 billion in lost revenue. Before the adoption of Bt corn traits, the USDA estimated growers spent $200 million in control measures and suffered $800 million in lost yield. Yield loss and standability issues are a result of diminished root systems when rootworm larvae feeding is severe enough.

Most of Missouri’s corn is grown in a corn/soybean or corn/soybean/wheat rotation. While Missouri has populations of NCR and WCR, both species typically lay eggs in cornfields with the eggs hatching the following season. This makes corn-on-corn fields vulnerable to larvae feeding on corn roots. However, when fields are rotated to soybean, the newly hatched larvae starve without a host such as corn. Most Missouri growers have seen fewer rootworm problems than regions with more continuous corn or regions where rootworms have evolved new strains to survive.

In some areas of the Midwest, rootworm populations have adapted to crop rotation control measures. A “soybean variant” of WCR was discovered in Illinois in 1995. This strain will lay eggs in soybean in addition to corn, which makes crop rotation an ineffective method of control. Northern corn rootworm populations have also adapted to crop rotation by developing populations with an extended diapause. Extended-diapause rootworm beetles still lay eggs in cornfields, but the eggs can wait two seasons or more to hatch—allowing the larval pest to find corn roots to feed upon in a corn/soybean/corn rotation.

With high levels of northern corn rootworm beetles being documented in areas of northwest Missouri and southwest Iowa where corn on corn rotations are somewhat rare, the likelihood of extended diapause northern corn rootworm finally reaching Missouri is high. To confirm that beetles are emerging from rotated cornfields and not migrating into the fields, Crop-Trak consultants have searched for and found evidence of larval root feeding in rotated corn. Larvae and adults were also discovered by the float method in which corn roots are submerged in water causing underground larvae, pupae, or adults to float to the surface. Further confirmation of extended-diapause rootworm in Missouri is still needed. MFA’s Crop-Trak is working with the USDA, Kansas State University and the University of Minnesota for the necessary laboratory and field-testing needed to verify the cause of increased northern corn rootworm populations.

The possibility of extended-diapause northern corn rootworms in Missouri will greatly impact growers in Missouri. The two most effective methods of rootworm control, if crop rotation is not effective, is the use of Bt-rootworm hybrid traits such as SmartStax from Monsanto or Syngenta’s Duracade; or soil applied granular insecticides such as Aztec or Force. Discuss this issue with your MFA location or Crop-Trak consultant to assess rootworm threat levels and management strategies.

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Pastures tend to segregate nutrients

I remember helping sort cattle when I was growing up, and it always seemed to me the nature of a cow was to do the exact opposite of what I  was trying to get it to do. I think that is why I ended up focusing on equipment and plant nutrition in my studies at college. These things might not pay attention to me either but at least I didn’t feel like I was being deliberately disobeyed.

As precision agronomy manager for MFA, I see maps from a lot of pastures that have been grid sampled through our Nutri-Track program. I think grazing animals have the same mentality as those cattle I tried to sort when they “fertilize” a field; it’s anywhere but where you want it. Of all the fields I look at, without a doubt, pastures consistently have the most variable fertility. Near shade, water, or feeding areas nutrient levels are usually high—right off the charts. Meanwhile, areas have the best potential at forage production tend to be deficient in basic soil nutrients. For this reason, I think pasture ground may have the highest opportunity for return on investment for precision nutrient application.

There are several strategies we can use to help minimize uneven redistribution of nutrients in pastures. If you are not already, I would recommend implementing a rotational grazing program that will force your livestock to move more often and better distribute manure. During the winter, rotate supplemental feeding areas as often as possible. Both of these practices will lead to a more even grazing and “fertilizing” pattern. They also move livestock to parts of the pasture they wouldn’t otherwise visit and should help reduce plant damage from heavy traffic. It is also a good idea to drag your pastures annually to break up and distribute manure.

While these practices will help mitigate the problem of uneven nutrient distribution, we have an invaluable tool in the Nutri-Track program to help us manage pasture fertility effectively. By taking samples every 2.5 acres, we can identify the distribution of nutrients and fertilize accordingly.

As is the case with other fields in the Nutri-Track program, the first thing we want to do is correct the soil pH. The pH of the soil plays a critical role in availability of nutrients and overall performance of the forage crop. This is doubly true if your pasture has legumes or you are planning to seed legumes. In fact, the MU Extension guide G4651 “Renovating Grass Sods With Legumes” states that legumes should not be seeded into fields with a pH value that is less than 6. As a bonus, it has been shown time after time that the cost of the program is paid for through the savings in lime application versus a flat-rate program.

All too often, phosphorus and potassium fertility are an overlooked component of maintaining quality pastures. Nitrogen is important and does increase grass yield, but if phosphorous and potassium are ignored too long, you will see diminishing returns from nitrogen applications. If the soil is low in these nutrients, your pasture will never reach full yield potential regardless of how much nitrogen is applied.

Balanced fertility is also an important part of stand persistence. Healthy plants are better able to with stand traffic and tough conditions, whether due to a drought or a severe winter. Maintaining a healthy stand of forage also means less room for weed pressure which may help reduce chemical costs.

In more recent times I have seen many cattleman sort and move their cattle with apparent ease. I think it’s because they know their cows and what they want, that they are able to move them so effortlessly. Similarly, we can use the Nutri-Track program to identify and understand our herd’s nutrient placement strategy and rebalance the fertility throughout our pastures. The payoff for proper soil pH and nutrient levels is a healthy pasture. They’re good to look at, but more importantly, you’ll be providing higher quality and quantities of forage for your herd.

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