ASK THE AGRONOMIST BLOG

During harvest, nutrients that are necessary to the vitality of a crop are removed from the soil. We’re all familiar with potassium, nitrogen and phosphorous and how they’re essential ingredients for crops to flourish. However, they aren’t the only valuable nutrients that contribute to soil fertility. Let’s talk a bit about the unsung heroes of soil fertility — sulfur and zinc.

Sulfur
Sulfur is considered the fourth major nutrient in crop production and is necessary for protein synthesis in a plant. Protein synthesis, when supported by sulfur, promotes plant vitality and development, including pollen development. Most sulfur in the soil is located in the organic matter and cannot be taken up by the plant until mineralization, which is when sulfur is converted to sulfate, or SO4-2, by bacteria in the soil. Sulfate is mobile and, in many cases, acts like nitrogen, which is why it’s recommended to apply sulfate at the same time as nitrogen. Sulfur deficiency even mimics nitrogen deficiency, resulting in yellowing of leaves.

Sulfur deficiency is generally a result of a few events.

Harvest: It is estimated that harvest removes approximately .1 of 1 pound of sulfur per bushel of corn and .17 of 1 pound per bushel  of soybeans.

Deposition: Reduced greenhouse gas emissions in the atmosphere means less sulfur dioxide is deposited back into the soil. This situation is largely in part because of the increased restrictions on these emissions.

Soil matter: Soil makeup may affect the availability of sulfur. Mineralization, the conversion of sulfur to sulfate, occurs only when organic material in the soil exists — organic material decomposes and encourages mineralization. If mineralization does not occur because of lack of organic material in the soil, then sulfur becomes immobile, resulting in sulfur deficiency.

Zinc
Zinc plays a critical role in plant growth. In fact, without zinc, the enzymes that are responsible for plant development would not be able to complete their metabolic reactions in the plant, which would stop the growing process. Zinc is responsible for transporting calcium through the plant and is necessary for the production of chlorophyll and carbohydrate metabolism. When there’s a lack of zinc in the soil, leaves begin to yellow and eventually turn a bronze color.

Zinc deficiency is usually caused by one of a few different factors.  

Harvest: Whether it was simply used up by last year’s crop, removed from the top soil during combining or compacted in the soil by heavy equipment, harvest can play a factor in diminishing zinc from soil. We recommend soil sampling in fall to detect for nutrient deficiencies, including zinc, especially in areas that generated high crop yields in 2018.  

Soil type: The type of soil can also affect zinc prevalence. Because zinc is a natural element that emits from rocks, areas where there are sodic or calcareous soils may already be equipped with the proper amounts of zinc. Sandy soils or soils containing low organic matter may benefit greatly from increased zinc applications. High pH levels in the soil may also inhibit the presence of zinc, and cold soils in the spring limit uptake of the nutrient. The more you know about the levels of zinc in your soil, the better off you’ll be come spring.

Previous nutrient applications: Other nutrient applications can affect the production of zinc. According to the University of Minnesota Extension, there is a direct relationship between phosphorus and zinc, where large levels of phosphate can antagonize the micronutrient, resulting in zinc deficiency and, eventually, yield loss.

Application Recommendations
Both of these critical nutrients can be deficient within a plant because of unavailability within the soil biosphere. We recommend .10 pounds of sulfur per bushel of corn and .17 for soybeans. For example, for 200 bushel per acre corn, this would require about 200 plus pounds of nitrogen and 20 pounds of sulfur per bushel. Zinc should be added with a pre-plant fertilizer according to soil tests and crop removal rates. The key to any proper fertility plan is balance.

If one nutrient level is too high, another nutrient in comparison will be too low. Make sure you have a well-rounded fertility program in place that understands the unique characteristics of your individual soil’s composition and how to best manage both its strengths and weaknesses.

Additional Resources

https://www.agry.purdue.edu/ext/corn/news/timeless/sulfurdeficiency.pdf

https://www.sulphurinstitute.org/fertilizer/

https://extension.umn.edu/micro-and-secondary-macronutrients/zinc-crop-production

https://www.cropnutrition.com/efu-secondary-nutrients

With the exciting news regarding the availability of Stine^® LibertyLink^® GT27^™ brand soybeans for the 2019 growing season, there have been questions about how growers can maximize the technology. One question I keep hearing is, “can I spray both products on the beans at the same time?” Before answering that, growers must first understand certain characteristics regarding each of these chemistries to maximize their efficacy and prolong their usage with LibertyLink GT27 technology.

Glyphosate is a Group 9 herbicide and is considered an organophosphorus compound.  Glyphosate is a systemic, translocating herbicide that inhibits the EPSP synthase pathway. The herbicide blocks essential amino acids necessary for the photosynthetic processes of the plant. It tends to work slowly, approximately 7–14 days, and is recommended to be sprayed with coarse to large-sized droplets in 5–10 gallons of water per acre. The typical rate for 41 percent solution is one quart per acre with a water conditioning agent (ammonium sulfate) at the rate of 8–17 pounds per 100 gallons of water and the use of a non-ionic surfactant for water droplet retention on leaves. This mix results in an active ingredient composition of 13.12 ounces per acre. The concentration of lethality at this rate is dependent on the water rate that is applied to the field, so as gallons per acre increase, so must the rate of glyphosate in the tank. It is recommended to spray glyphosate when weeds are actively growing and not under stress. In addition, precaution should be taken to avoid spraying during times of intense heat and moisture stress.

Glufosinate is a Group 10 herbicide and is also considered an organophosphorus compound. However, glufosinate is a contact, semi-translocating herbicide that inhibits glutamine synthetase. It mainly kills by inhibiting a plant’s ability to utilize nitrogen and causing ammonia within the plant to become toxic to the plant. The herbicide tends to work very quickly, within 24–72 hours, and is recommended to be sprayed with medium to coarse sized droplets in 15–20 gallons of water per acre. It is recommended at rates of 29–36 ounces per acre with a carrier of ammonium sulfate at the rate of 1.5–3 pounds per acre. It is not recommended to spray Liberty with FloodJet nozzles, controlled droplet application equipment or air-assisted spray equipment. It is recommended to spray glufosinate when weeds are actively growing and not under stress. In addition, it is helpful to spray during daylight hours, in adequate temperatures (86 degrees Fahrenheit and above) with higher relative humidity.

Based on these differences, the following recommendations should be observed:

1. It is best to utilize these products in a sequential-combined application. Use glyphosate in burndown combinations with other effective modes of action and residual herbicides. For post-emergent applications, combine glyphosate and glufosinate with additional effective modes of action and residual herbicides. This provides the best chance of overcoming nature’s ability to adapt and combat herbicide resistance. For additional effective modes of herbicide action, contact your local extension weed specialist or Stine regional agronomist.

2. For optimum weed control and long-term effectiveness of the trait system, it is recommended to utilize three effective site-of-action herbicides per application with one of those being a soil-applied residual herbicide.
3. Always utilize the “most restrictive” label for guidelines. In this case, that would be glufosinate (Liberty).
4. Spray volume should be applied in the 15–20 gallons per acre window.
5. 1.5–3 pounds of ammonium sulfate should be used per acre.
6. Target medium to coarse droplets. A good rule of thumb is volume per acre plus pressure should equal 60. For example, if you are spraying 15 gallons, then pressure should equal 45 psi.
7. DO NOT use the addition of non-ionic surfactants.
8. DO NOT apply during periods of heavy dew or fog. If relative humidity is low, increase droplet size to coarse droplets to counteract evaporative loss. DO NOT apply after two hours before sunset.
9. Anti-foam agents may help prevent excessive foaming.
10. DO NOT apply after R1 growth stage.
11. Rainfast = 4 hours

For more information about herbicide applications with LibertyLink GT27 brand soybeans, contact your local Stine sales agronomist.

Drought. Extreme heat. Insect pressure. These elements are just a few affecting the U.S. corn crop this growing season. We’re hearing reports of post-pollination kernel abortion and silking issues across the Corn Belt, from as far south as Kansas to as far east as Indiana. And, according to the most recent report from the U.S. Department of Agriculture’s National Agricultural Statistics Service, 32 percent of the U.S. corn crop is listed in fair condition or below (poor or very poor). In Missouri alone, 44 percent of the corn crop is listed in poor to very poor condition.

Extreme drought is affecting crops in areas of the southern Corn Belt, including parts of southern Nebraska, southern Illinois, southern Indiana, Kansas and Missouri. In Iowa, there are a few reports of post pollination kernel abortion due to recent hot, dry conditions. Kernel abortion takes place when certain conditions disrupt the photosynthesis process of the plant and prevent the ear from silking properly. This makes it more difficult to pollinate and, in some cases, the plant is simply unable to support all of the kernels. This issue may have a significant impact on growers’ yields come harvest. And, unfortunately, there’s nothing you can really do this season if this situation occurs.

In addition to the drought, Indiana, Illinois and Missouri are also facing extreme heat conditions, causing corn silks to dry out prematurely which leads to incomplete pollination. This tends to affect the basal portion, or the butt end, of the ear.

To add to the corn issues, there have also been several reports of Japanese Beetle pressure. These little pests feed off silks and the pollen. This leads to clipped silks and decreased pollination, which ultimately affects grain fill. For growers who experienced increased pressure this year, I recommended applications of a Lorsban-type insecticide over the canopy. This typically helps ward off further damage to the plant by the pest, and helps control the population. Since Japanese beetles can survive in your soil through the winter months, there are also certain measures that can be taken to prevent them from coming back again next year.

Although there’s no way growers can predict the weather and other elements that impact yield, they can talk to their local Stine sales agronomist about which corn and soybean numbers, seed treatments and chemical applications can help protect their acres. We’re here to help you make the best management decisions for your fields year-round.