Lessons From the Field

January 24, 2014 08:51 PM

Agronomists reply to inquiries about sulfur, tillage and volunteer beans


Find answers to a variety of crop pro­duc­tion questions on Farm Journal’s "Ask an Agronomist" blog. The Farm Journal agronomists and experts respond to questions sent to testplots@farmjournal.com based on their inde­pendent experience and in-the-field insight. Past questions and answers can be found at www.FarmJournal.com/ask_an_agronomist. Here are three recent questions and answers from the blog.

Can the addition of sulfur in some amount, which will increase the "greenness" of corn, increase photosynthesis, which should increase the amount of sugars and in turn impact yield?

A  It can make a difference, depending on your sulfur loads in the field. A combination of tissue and soil testing can help you figure out where you stand. Traditionally, the more nitrogen you apply, the more sulfur is usually required. The lower the organic matter in the soil test, the more likely you’ll probably get a response.

As a rule of a thumb, the response to sulfur will be stronger in soil with 2.5% organic matter or less. As you move up from 2.5% organic matter, the response to sulfur will be lower because you get more sulfur naturally released from the soil. If you do have a deficit in sulfur, you will see a decrease in those things you mentioned—the greenness, photosynthesis and sugars.

The challenge is if you’re at 3.5% to 4% organic matter in the soil, meaning sulfur levels are adequate, because adding more sulfur isn’t going to improve your situation.

You need both tissue and soil tests to figure this out; the two together give you a more comprehensive reading on your fields. If the tissue tests and soil tests together are in the low range, you’ll get a response. When I look at our plots, if we’re in that zone where we need sulfur, usually we need to apply 15 lb. to 20 lb. of sulfur per acre. Also, a 50-lb. rate per acre of sulfur isn’t usually any better than 15 lb. to 20 lb., as a rule.

What kind of tool do I need for vertical tillage?

A  There is no single tool that works for vertical tillage. Vertical tillage is a system, not a one-season tillage pass or a single tool. It can take a couple of years to transition to a true vertical tillage system.

Before you buy any tool, think about what you’re trying to gain from using a vertical tillage system.

One of the best goals you can set is trying to achieve uniform soil density. That uniformity can help you develop a good-quality seedbed, which is crucial for uniform corn emergence and high ear counts.

Evaluate whether you have density layers or compaction problems in your soils. If so, at what depth? Your answer matters because it influences the type of tool you will use to correct those problems. At 4" deep, you can use a variety of tools to remove density layers. If it’s at 12" deep, though, you will need a more specific tool.

Consider your residue needs before purchasing vertical tillage equipment. For instance, if you’re in continuous corn, you need to select a tool to get rid of root balls and incorporate more residue. If you have deep density layers but don’t need the residue, you can use something like a disk ripper, which is designed to go deeper than a chisel plow. If you have shallow layers and don’t need a lot of residue, then you can run a chisel plow. If you have deep density layers but need a lot of residue, you can go with an inline ripper type of tool. On highly erodible soils, you need less aggressive tools.

Primary vertical tillage tools include chisel plows, disk rippers and inline rippers. Other tools better suited to leveling fields are harrows and coulters, which prepare the final seedbed.

Q  I had some volunteer soybeans in my corn in 2013 that I think affec­ted my yield outcome. This spring, I plan to take a wait-and-see approach to address them if the problem shows up again. Got any recommendations?

A  If volunteer soybeans show up in your corn next season, consider these postemergence control measures, outlined by Darrell Deneke, South Dakota State University (SDSU) Extension pest management coordinator. He says soybean plant size at the time of herbicide application will determine the degree of control you will get.

Small volunteer soybeans are easier to control than larger ones. Try to control any problem before volunteer soybeans exceed the V3 growth stage.

Using 2,4-D is one option, Deneke says, though SDSU research shows that soybeans are not as sensitive to 2,4-D as they are to other plant-growth regulator herbicides, such as dicamba or clopyralid. Plant-growth regulator herbicides such as Hornet contain clopyralid and should provide effective control to smaller soybeans.

Products containing dicamba, such as Status, Distinct and numerous gen­erics, will provide effective control in a wider range of volunteer soybean growth stages. Read all product labels for application directions and to ensure the herbicide you plan to spray is labeled for use in your state. 

To read more crop production questions and answers or to submit your own questions, go to www.FarmJournal.com/ask_an_agronomist

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