Crops

Supplement with sulfur for plant growth, health

Higher yields, earlier planting and successful clean air policies have increased the need for sulfur fertilizer and put a much-deserved spotlight on this often-overlooked nutrient. New research is being conducted at the university level and by MFA to determine the best management practices for sulfur on your farm.

Sulfur is a vital contributor to nitrogen efficiency, protein produc­tion and chlorophyll formation. In fact, sulfur is ranked only behind nitrogen (N), phosphorus (P) and potassium (K) in importance to crop production. Plants low in sulfur are often pale and yellow, symptoms that may be confused with nitrogen deficiency. Sulfur in the sulfate form does share sever­al characteristics with the nitrate form of nitrogen. It is mobile in the soil and subject to leaching, especially in soils with lower cation exchange capacity. It is also difficult to determine sulfur need through soil testing because of spatial and temporal variability.

However, unlike nitrogen, sulfur is generally immobile within plants. We recognize “firing” on the lower leaves of a corn plant as a sign of either N or K deficiency. This is because these nutrients are mobile in the plant and can be moved from old growth to new growth. Sulfur deficiency shows up on the young­est growth first and must be supple­mented from outside the plant.

Clean air policies have done an excellent job removing sulfur from the atmosphere, resulting in much less “acid rain” than in the past. As a grade-schooler in the 1980s, I was regularly taught about acid rain and its negative impact on the environment as well as the damage it inflicted on man-made objects such as machinery, buildings and other structures. Acid rain is rarely discussed today. There is still some sulfur in rainfall due to pollution and the natural activity of volca­noes, but it is much less compared to previous years. This is obvious­ly a positive, but the free 15-20 pounds of sulfur that Midwest fields received in the past have been reduced to 5 pounds or less and must be replaced with fertilizer.

Sulfur fertility is delivered in three main forms: elemental sulfur (90%, dry), ammonium sulfate (21-0-0-24S, dry) and ammonium thiosulfate (12-0-0-26S, liquid). Ammonium sulfate and ammonium thiosulfate are readily available to crops. Elemental sulfur must be ox­idized or “broken down” before it is available, so for a quick response in front of or over a crop, ammonium sulfate or ammonium thiosulfate should be used. That is why these products are our primary sources for wheat top-dress.

Another source of sulfur utilized by growers is Croplex, which has an analysis of 12-40-0-10S-1Zn- 0.3B. The sulfur in Croplex is a combination of elemental and ammonium sulfate. This “best of both worlds” approach helps assure there is plenty of sulfur throughout the growing season.

Sulfur is often associated with wheat top-dress and for good reason. Wheat needs sulfur when it breaks dormancy and begins to green up. Much of our sulfur comes from the soil’s organic matter through the mineralization process, and the cold soils of late winter/ early spring are not conducive to this activity. However, wheat is not the only crop that uses and needs sulfur. In fact, it is not the crop that needs it most. Producing 80-bushel wheat takes a total of 18 pounds of sulfur, but 180-bushel corn will use 29. Soybeans will use 27 pounds of sulfur to make 60-bushel yields, while 5-ton alfalfa uses 25 pounds.

Recognition of the need for increased sulfur has prompted recent research into the nutrient. Purdue University in Indiana has several years of plot data that shows response to sulfur, not only in corn but also in soybeans. Sulfur applied near planting (from planting to V2-V3) to early-planted soybeans resulted in significant gains. More surprisingly, this occurred on soils with higher-testing (greater than 3.5%) organic matter. The cool, wet soils that early-planted soybeans encounter seem to be the catalyst for these gains.

Magazine articles discussing this research last year generated interest and questions in MFA’s trade terri­tory, so MFA added soybean sulfur studies to our field trials in 2021. We did not have early-planted soy­beans in our trials last spring so we were unable to do that research, but we will look at it in the future.

If you are planting soybeans early this year, I would encourage you to consider an at-planting or early postemergence application of sulfur to evaluate this practice in your own fields. I would also encourage you to make sulfur a part of your overall fertility program, giving special attention to crops that are planted earlier into cool soils and to fields with lower organic matter values.

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Crop protection plans can’t be an afterthought

The 2022 growing season is just around the corner, and herbicide planning is more important than ever this year. In the previous issue of Today’s Farmer, MFA Director of Agronomy Doug Spaunhorst touched on potential supply chain challenges with some common herbicide products. In particular, supply looks to be tight for widely used products such as glyphosate, glufosinate and 2,4-D. There will likely be situations where we need to carefully look at a field’s weed spectrum to identify the need for these products and find alternative herbicides.

While glyphosate and glufosinate are used to control susceptible weeds that are already emerged, in 2022 it will be critical to prevent weed emergence from occurring in the first place. In addition to using these types of herbicides in our first pass, it will be equally important to use residual chemistry in our second pass for continued weed prevention. If we have successfully prevented new weed emergence and have a clean field three weeks after the first pass, we can apply the next round of residual herbicides and eliminate the need for herbi­cides that only control emerged weeds.

To determine the correct herbi­cides that will be required, thorough and timely scouting is essential ahead of both the burndown pass and the in-crop application. Many products used for the first herbicide application ahead of corn already contain active ingredients that have excellent activity on broadleaf weeds, including those that are difficult to control.

However, this is not necessarily the case for grass weeds. On the bright side, many common grass weeds can be controlled with a low­er rate of glyphosate than needed for broadleaf weed control.

For instance, giant foxtail up to 20 inches tall can be controlled at a 75% rate of most glyphosate products when compared to rates needed to control many broadleaf weeds. While MFA will never rec­ommend reducing rates required by label, this is an example that would reduce glyphosate usage while still using a full labeled rate to control a target weed.

Newer soybean herbicide traits offer additional opportunities to re­duce the use of herbicides that are likely to be in tight supply. While older formulations of 2,4-D may be hard to come by, availability of Enlist products looks favorable. In addition, there is no waiting period between Enlist applications and planting of Enlist-tolerant soybeans as there is with older 2,4-D for­mulations. In soybeans with Xtend or XtendFlex traits, Xtendimax or Engenia herbicides also provide excellent broadleaf weed activity.

Regardless of herbicide-tolerance traits, there are other options for grass control in soybeans. Herbi­cides commonly used in soybeans to control glyphosate-tolerant vol­unteer corn also control most grass weeds. These products are known as FOPs and DIMs due to the active ingredient names and can be used as a glyphosate alternative strictly for grass control in soybeans. In addition, corn hybrids with the Enlist trait will be tolerant to the FOP family of herbicides. Products such as Assure II may be used for in-crop grass weed control in corn with this trait.

By the time we enter the next growing season, there will likely be several more challenges related to crop protection supplies. Growers should have a cropping plan that includes residual herbicides to provide protection from weeds that have a history of showing up in each field. Pair that with frequent and thorough scouting to identify emerged weed species.

By following these practices, we can develop recommendations to provide proper weed control and prevention while helping to avoid potential supply issues. Your MFA manager, key account managers and local agronomists are here to help develop these plans and deliver weed-control solutions for your farm.

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Stay ahead of weeds with fall applications

It’s hard to believe harvest season is nearly over and timing for fall herbicide application is now front and center. I was hoping the supply chain issues we faced earlier this year would be resolved and product orders and anticipated arrival dates would have reverted to “normal,” although who knows what the definition of “normal” is anymore? Unfortunately, several indicators have signaled to us that acquiring products in 2022 may be equally or more difficult than what we expe­rienced in 2021. That’s why I want to emphasize the importance of having a couple of crop protection plans in place. Products you used in the past may either price you out of the market or require you to call an audible before spraying due to tight or empty inventory.

Successful audibles in the game of football, called at the line of scrimmage, have been planned and rehearsed with all players focused on the routes ahead and which op­ponents to block. The outcome of a well-planned and rehearsed audible called in the field is often no dif­ferent at the farm level. I say “often no different” because we all know how unforgiving and unpredictable Mother Nature and government decisions can be at times.

So what can we expect for 2021 fall herbicide supply? We know products that contain glyphosate and 2,4-D will be in tighter supply. It’s fair to encourage folks to order what they need for this growing season and not what they may need for the next two or three years. No one wants a repeat of the toilet paper debacle we faced during the beginning of the pandemic in 2020.

Herbicide applications in the fall are a great way to stay ahead of the game and control winter annual weeds that emerge during and after harvest. A couple things to keep in mind when deciding on fall chem­ical products. Historically, glypho­sate and 2,4-D have been econom­ical and effective options for many difficult-to-control winter annual weed species. These products have been applied across a large portion of acres in our trade territory in the past. If you have access to glypho­sate and 2,4-D, I would direct use of this mixture towards fields with heavy weed populations first. Most growers know which fields on their farm are typically weedier than others. Start there.

Aside from glyphosate and 2,4-D, there are other fall herbicide options to consider in fields where corn will be planted the following year. Many of these products have residual activity where glyphosate does not and 2,4-D is limited. These fall herbicides include Basis/ Resolve Q, Resolve SG and Princep.

In fields where soybeans will be planted the following spring, several herbicides that contain Authority can be applied in the fall. Other products such as Canopy/ Canopy EX, Classic, Envive, Fierce XLT, Pursuit, Sharpen and Synchro­ny XP are also labeled in the fall for spring-planted soybeans.

Some of the previously listed herbicides are, or have, active ingre­dients that inhibit acetolactate syn­thase (ALS) and can persist longer in soils where the pH is greater than 7. Be cautious of the maximum annual use rate on ALS chemistries in the spring if you have fields with pH values in the mid to upper 7s.

If you are unsure if you will be planting corn or soybeans next spring, there are still many op­tions that can be applied in the fall. Anthem Flex, Authority MTZ, Autumn Super, Elevore, Express, Fierce MTZ, Gramoxone, Harmony, Kyber, Quelex, Volunteer, Metribuz­in and Valor EZ can be used in the fall where either corn or soybeans will be planted the following spring. Some products may need to be tank-mixed for optimal weed control. Most of these products, if they have much grass activity, will need to be applied to weeds smaller than the 4- to 8-inch-tall grasses we have controlled with glyphosate in the past.

Generally speaking, fields with heavy winter weed pressure are better candidates for fall herbicide applications than fields with low weed pressure. Adding residual herbicides in the fall generally translates into a cleaner seedbed but should not replace a spring residual application. By springtime, the concentration of herbicide in the soil solution will unlikely be at concentrations lethal to prob­lematic emerging species such as waterhemp, Palmer amaranth and horseweed.

With all the uncertainty in the crop protection market, I cannot stress enough the importance of having a cropping plan for the 2021-2022 season. I can assure you MFA’s crop protection team is diligently working to meet the needs of our customers, and our agronomy team is equipped and ready to service our locations and member-owners as crop protection needs continue to evolve.

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Shortages of P and K can limit production of your crop

What is your P and K fertilizer program? If you’re basing your rate on what you have always done, have you ever questioned why you apply what you do? It’s pretty easy to get stuck in a rut and use the same fertility program year after year without looking at it more closely, as long as yields keep increasing.

If this sounds familiar, we should talk.

The basics of soil fertility haven’t changed much over the years, but that doesn’t mean we should take it for granted. Our plants are factories that need a certain amount of nutri­ents to operate at peak capacity, just like an automotive manufacturing plant. When something is in short supply—whether that is phospho­rus or a computer chip—both types of plants are going to throttle back production until they can get all the materials they need. How do we avoid this shutdown? In simple terms, it’s just a matter of under­standing supply and demand.

Let’s start with supply. The vast majority of nutrients are supplied to the plant from the soil solution. While the soil can store significantly more nutrients than our plants will demand in a single season, those nutrients are not all readily avail­able for uptake. Many nutrients are bound tightly with other com­pounds in the soil. They are essen­tially in long-term storage, which means that it takes a significant amount of time for them to arrive in soil solution for the plant to use. As the plant takes nutrients from the soil solution, replacement nu­trients are transferred from “storage” to restock the system. The processes that facilitate that movement are not instant.

Soil testing can help us manage and understand this process. Many diverse and complicated factors control how much of the total quantity of nutrients contained in the soil are available for plant uptake, making it nearly impossible to estimate what is readily available for a plant to use. Soil testing ap­proaches this problem in a different way. Chemicals are used to flush nutrients out of the soil sample, and then the nutrients that are re­leased are measured. The chemicals and methods are designed to closely mimic how a root would extract nutrients from the soil. By compar­ing how yield responds with the addition of readily plant available fertilizers versus the known soil test value, we can determine where the soil is providing enough nutrients for complete plant growth.

Again, a soil test is not necessarily an inventory of all the nutrients contained in the soil, it’s more like the amount of nutrients that are in soil solution ready for plant uptake. To relate it to the factory model, it tells us how many computer chips are actually sitting in the factory that we can use to build pickup trucks today.

If the soil test tells us about nutrient supply, why does demand matter? Demand tells us how much fertility is hauled away in a grain truck or a bale of hay. We use that number to understand what we need to put it back into inventory for the next season. Demand is fair­ly easy to calculate. You just need the nutrient concentration in the crop and the yield. It may surprise you to know that nutrient concen­tration is actually easy information to find. Many of the crops we grow are used in livestock feed, and much work has gone into analyzing that feed for its nutrient concen­trations to create a balanced ration. For the most part, the nutrient con­centrations we use for crop removal estimates are based on long-term averages from feed information.

Yield can come from several different sources, whether it is your long-term yield average, yield goal or actual yield data. We can use any of those numbers along with the nutrient concentration to arrive at the total nutrient removal we can expect.

Admittedly, it’s easy to ignore your fertility program and just do what you’ve always done without think­ing about it. But like most decisions on the farm, it pays to understand how fertility is going to affect your plants in the field. If they face a shortage, it doesn’t matter what else you do. Those shortages are going to limit production.

As you build your fertility plan this year, I encourage you to figure out your supply and demand to ensure plant nutrition doesn’t limit your production. Reach out to your local MFA if we can help you in this process.

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Invest in P and K instead of Fe this fall

Supplies of toilet paper and hand sanitizer aren’t the only things negatively affected by COVID-19. Tractors, combines, farm equipment and pickup trucks are also hard to find these days. Many industries are facing a lack of labor and raw mate­rials, an issue projected to continue through at least 2022. Disruptions all along the supply chain have caused shortages of steel, plastics, microchips and tires, and many suppliers are facing a labor crunch because of the pandemic.

As a result, the tractor supply in North America is the tightest in 18 years, and precision equipment suppliers have been encouraging early orders to avoid delays and shortages of guidance systems and planter control systems. Some companies are so far behind that their dealers were taking orders for planters for the 2023 crop season in June of this year.

Not 2022. 2023.

This got me to thinking: At the end of the year, instead of invest­ing in iron (Fe) for your farming operation, why not invest in fertility (P and K)?

As a precision manager for MFA Districts 3 and 6 on the east side of Missouri, I help a team of precision specialists manage our Nutri-Track high-yielding fertility management system. We use 2.5-acre grid sam­ples to develop plant food recom­mendations that allow our growers to improve yield and be more efficient with their fertilizer dollar. Nutri-Track’s variable-rate fertility recommendations are developed specifically for each operation on an acre-by-acre basis.

Much of that work is done in the fall. Many soil samples are taken, and many variable-rate prescrip­tions are developed and applied, but we should—and could—be doing more.

Applying phosphorus and potas­sium in the fall between the end of harvest and the first freeze will re­plenish essential nutrients removed from the field and ensure they are in place for next year’s crop. We all know that compacted springs are beginning to feel like the rule instead of the exception. Widening the window for P and K application and moving acres to be fertilized from spring to fall can help lessen your stress in the busy season. Phosphorus and potassium applied in the fall, along with sulfur and zinc, will be ready to go to work for you in the spring.

It’s true that MFA’s extensive infrastructure gives us the ability to apply a lot of product in a short time during the spring rush. Plant foods are often delivered to the fer­tilizer plant, and then immediately loaded on to a truck and applied to a field within hours. That doesn’t mean, however, that bottlenecks don’t happen. Much of our dry fertilizer comes in on river barg­es. When rivers get out of shape due to spring floods (or a bridge in Memphis develops a crack and threatens to fall into the Mississippi, like we saw this past spring) getting phosphorus and potassium can be a challenge.

If you apply fertilizer in the fall, you won’t need to wait until the spring weather cooperates or worry about barge shipments being de­layed. There are many other reasons why fall applications are a good investment. Soil moisture is gener­ally lower in the fall, lessening the risk of soil compaction compared to wet spring soils. Equipment and applicators at your local MFA are usually more available in the fall. And fall fertilizer prices tend to be lower than spring prices.

While I’ve mostly focused on P and K here, fall application of an­hydrous ammonia is also common in much of our trade territory. This is a good practice, as long as you are also planning an in-season top-dress application and protect­ing that nitrogen with a product such as N-Serve or Centuro. These actually work to protect against N loss instead of just claiming to—but that’s a subject for a different day.

To me, it boils down to this: in most instances, on most soils, there is no good reason not to apply phosphorus and potassium in the fall. It can give you a leg up in the spring, provide some much-needed flexibility and allow you to alleviate some of the stress of having a lot to do in a short window.

New tractors, combines and planters may be hard to find right now, but fertility is one purchase you can always count on. So this fall, when you’re thinking about the investments to make in your farming operation, forget about the iron (Fe) and focus on the fertility (P and K).

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