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November 2011 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

Will AMS Be There in the Spring If I Apply It Now?

Nov 28, 2011

Question: Will sulfur applied in the fall as AMS be there in the spring, or will it leach out? 

Answer: This is a lengthy answer, but I hope it helps. As with nitrogen, organic sulfur, contained in the soil and in crop residue, is mineralized by microbes into the inorganic form that plants can use. But other microbes are also at work, converting inorganic sulfur into the organic form. This process is called immobilization.
Mineralization and immobilization go on all the time. Sometimes we have net mineralization, and other times we have net immobilization.
Often, when soil warms up in the spring and soil microbes increase, there is a period of net immobilization. That creates a shortage of sulfur available to young corn plants. I call this situation the "carbon penalty" because the supply of carbon in old-crop residue causes increased microbial activity. Sulfur levels will drop like a rock.
If nitrogen is temporarily immobilized, plants can take it up later, when it becomes available. But, because sulfur is not mobile inside plants, they must take up a large portion of their supply in the spring.
So failing to apply sulfur to help pay the carbon penalty can have season-long effects in continuous corn.
If a field is flooded and the oxygen is removed, anaerobic microbes convert sulfate, the available form of sulfur, into the unavailable form. If the field stays waterlogged for a week or more, the microbes can convert sulfur to a gas, and it can be lost.
You can tell when sulfur is volatilizing out of a field by the odor. If a field has been wet for a long time, you sometimes detect a septic smell. That smell is sulfur, leaving the field as a gas.
When soil is flooded, the first microbes to activate are denitrifying bacteria. The microbes that convert sulfur to a gas become active later. If you smell that septic odor, your nitrate nitrogen is already gone--although nitrogen in the ammonium form may still be present.
Sulfur also can be lost through soil erosion, and it can be leached away by water. But it never travels alone.
Sulfate ions cling to base cations (calcium, magnesium and potassium) like a cocklebur. So if you put on too much sulfur and then get a lot of rain, you can lose all three.
The first cation it typically takes is potassium. If you overapply sulfate to light sand or a silt loam soil and use ammonium sulfate as your total nitrogen source, you risk losing potassium. That is especially likely to occur on a sandy soil with irrigation.
Sulfur can become unavailable by fixing to clay particles in certain types of soil. A kaolinite clay, which is often found in the South, has negative charges on only one side of the clay lattice, and positive charges on the other side. Negative-charged sulfur ions fix to those positive sites. Such soils require more applied sulfur to get the same response. A montmorillonite clay, on the other hand, has negative charges on both sides, so sulfur ions do not attach.
Acid soils will also tie up sulfur. Because sulfur availability is controlled by microbial activity, balanced pH is essential. Acid soils reduce microbial activity, and that reduces sulfur availability.
When pH gets above 7.5, calcium and sulfur ions form gypsum, so you may have a lot of sulfur, but it can’t get into the plant because it is bonded with calcium.
Sulfates are not acidic (although elemental sulfur is). But if you apply ammonium sulfate, it takes twice as much limestone to neutralize the soil as it would if you applied the same amount of nitrogen as anhydrous ammonia, UAN (urea-ammonium nitrate) or urea. That’s because ammonium is twice as acidic as ammonia.
For every pound of ammonium nitrogen applied, it takes 8 lb. of limestone to neutralize the acidity. Remember to account for acidity in your sulfur sources.
In highly leachable soils, apply elemental sulfur in the fall, rather than sulfate, to prevent loss. In spring, use the sulfate form. Elemental sulfur may not become available quickly enough when applied in the spring.
High phosphate levels cause poor sulfur uptake. Corn roots load up with phosphate, which precipitates to the root lining. Negatively charged phosphate ions repel sulfur, reducing sulfur absorption, as well as zinc and manganese.
In high-phosphorus soils, carry a high sulfur load by applying some of your nitrogen as ammonium sulfate. Your goal is to pull the excess phosphorus out of the soil with your crop, while sticking sulfur back in.
Maintain the proper ratio between nitrogen and sulfur. Tissue testing gives an indication of the ratio of sulfur to nitrogen in the plant. Corn needs about 1 lb. of available sulfur per 14 lb. of available nitrogen.
Pay special attention to sulfur in soils that have less than 3% organic matter. Organic matter is your main supplier of sulfur. With more than 3% organic matter, sulfur probably will take care of itself.
There are different sulfur extraction processes and reporting methods. Don’t compare results from one lab to another unless you know the same process was used. One lab might consider a reading of 8 ppm to 12 ppm to be medium, while another lab’s idea of medium might be 25 ppm.

How Quickly Does Tile Pay For Itself?

Nov 22, 2011


Question: I’m trying to decide whether to tile some acreage yet this year. How quickly does tile usually pay for itself, and how late in the year can I put it in?
Answer: We estimate that drainage tile typically pays for itself through increased yields within about five years of installation in farmland with drainage issues. You can put tile in just about any time weather permits. If you’re seriously considering putting some tile in yet this fall, I’d encourage you to do so in order to take advantage of an opportunity Congress is providing through December 31, 2011. Farmers who put in new tile by then will be allowed to completely deduct the entire tile cost using a100% bonus depreciation. This deduction is not contingent on any income levels or phase-outs for purchasing too much. Some exceptions do exist, so see your local tax specialist for more information on the potential benefits. Also check out the links below for more information.

Deductions Still Available for Tiling

Does Gypsum Provide Any Real Benefit to Soils?

Nov 18, 2011

Question: Does gypsum offer any real benefit to soil?

Answer: Farmers use the naturally occurring mineral to improve soil tilth, water infiltration and nitrogen uptake in their fields. According to the American Coal Ash Association, a utility industry group, farmers used 279,000 tons of gypsum in 2008. That’s more than three times the amount they used in 2002. With gypsum, the soil structure becomes more sponge-like, so even tight clay soils readily absorb water and move it down through the soil profile, rather than allowing it to pond or run off, according to Ron Chamberlain, director of gypsum programs for Beneficial Reuse Management. The company sells a synthetic gypsum product, Gypsoil, for agricultural use. Synthetic gypsum is a byproduct of fossil-fueled power plants that work to remove sulfur dioxide from flue gases in an effort to curb pollution and comply with clean air regulations. In recent years, synthetic gypsum has gained ground with farmers because of its availability and lower price. Purdue University research indicates that gypsum also offsets the impact of aluminum toxicity in low pH soils, helps curb phosphorus runoff and increases iron uptake by reducing the effects of bicarbonates. Some seed companies are conducting field research to determine whether the soil benefits from gypsum also support increased crop yields. To date, the data shows mixed results.

What Do You Think About Sidedressing With Urea?

Nov 15, 2011

Question: What is your opinion about sidedressing with urea? Also, when is the best time or at what height of the corn is best?

Answer: When we talk sidedressing with urea that’s typically done with a buggy or with an airplane. It’s rare to see someone knifing urea in as a sidedress application. I’m not saying it can’t be done but that it’s rare. Because you’re surface applying the urea you have to protect it from loss through volatility, meaning you need to either use a coated urea or you need to put a urease inhibitor down with the urea. As for timing of application, I would recommend applying two-thirds of my nitrogen upfront either pre-plant or at planting and the rest as late as the sidedressing equipment will allow. That’s probably around V6 with a tractor and fertilizer buggy or one or two leaves pre-tassel with an airplane, Your goal is to not see any nitrogen deficiency during the vegetative or reproductive stages. Also, for sidedress applications, farmers have a choice in what nitrogen product to apply. Many are asking if there is an agronomic difference between 28% and anhydrous ammonia. At sidedress, as far as the plant’s uptake of the nitrogen, these products will both convert to ammonium and nitrates for uptake. The difference between these two is their timing of availability. If you had yellow corn, and you were to sidedress the corn to make it green, 28% has ammonium and nitrate, and that turns corn back green. So you’ll see a quicker response to 28%. Anhydrous ammonia is different. With anhydrous, you create a core and it could be 14 days before nitrogen would be released from that core. If you’ve applied enough nitrogen upfront to keep the corn green through the vegetative stages, and you’re sidedressing N for ear fill, there most likely will be no difference between anhydrous and 28%.

How Do I Place Starter Fertilizer Equipment on the Planter?

Nov 11, 2011

Question: I’m interested in adding starter fertilizer equipment to my clients’ planters but unsure what type of placement is best.  Is it better to use a coulter mounted application, in-furrow application, or a trail behind application?  I’m concerned about bringing up moist soil in my clients’ no-till fields that could disturb the planting depth.  I’m also concerned that the application method could change down pressure requirements in highly variable no-till soil conditions, leading to inconsistent planting depth. Do you have a review that answers my questions?

Answer: Our recommendation is if you’re going to attach anything to the planter that will bring up moist soil in front of the depth wheels you need to keep those depth wheels clean with some type of scraper. In variable no-till conditions, that moist soil is a common issue. As you thought, your fertilizer application methods can indeed change your down pressure requirements when you’re adding any attachments to the row unit. You may want to consider purchasing some monitoring equipment. There are tools you can purchase to help you with that from manufacturers including John Deere, Great Plains, Precision Planting among others. You will want to monitor smoothness of ride and depth control to make sure your starter attachment is not causing your planter wheel unit to come out of the ground. If you plan to put starter fertilizer in-furrow, our concerns are salt load and seed quality. You want to make sure your customers use a good quality seed, one that helps ensure you don’t have extreme pericarp damage that exceeds 6 percent. Seeds with large cracks in the pericarp will experience starter burn. When we put starter in-furrow, it’s very important to get good seed-to soil contact, closure and firming of the furrow.

What Do I Do About These Cornstalks?

Nov 07, 2011

Question: What do I do about these cornstalks in my no-till fields? They don’t want to break down, and I’m already concerned about planting next spring.

Answer: That’s definitely an issue that a lot of farmers are dealing with. Traits designed to protect cornstalks do such a good job, they don’t break down over winter like we’d like for them to. It’s good, especially in corn-on-corn rotations, to carefully think through the trash issue. When corn decomposes, it emits a toxin that can be troublesome the following spring in corn-on-corn situations. In no-till corn-on-corn, our studies show that the further you can plant corn away from the previous year’s crown root growth, the better your corn crop is likely to perform. That’s assuming you don’t have wheel track compaction from previous trips in the field. If you aren’t completely done with harvest this season, consider that your combine plays an important role in helping distribute residue evenly on fields which helps with decomposition. Shredders and spreaders that attach to the combine can even out distribution. However, in some cases, large headers on combines can create a trail of residue behind the machine. You can readily tell whether this is your situation by just observing what’s in your field. If it is a problem, then adjust your combine settings. One caution: shredding stalks in no-till operations comes with a risk that they'll blow away with high winds or that a flood will cause them to float away onto your neighbors’ fields. Another consideration is that residue management is part of a good fertility program. Residue decomposition is driven by soil microbes that are very sensitive to soil pH. Acid soils lead to poor decomposition, so it’s important to keep soil pH balanced.
Learn more about how to measure residue and mange it here.

What Is An Acceptable Loss At Harvest

Nov 03, 2011

Question: What do you consider to be acceptable loss in cornfields when harvesting?

Answer:  Farmers should aim to lose no more than 1 bushel per acre, as a general rule-of-thumb. What that translates to is you don’t want to see more than two corn kernels on the ground per square foot in your fields -- that amount equals a 1 bushel-per-acre loss. If you have losses greater than that, then it’s time to adjust your combine settings.
When you hit the fields for harvest, harvest every bushel you grew.
Harvest time can bring mixed feelings to farm families.
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