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Understanding Metabolic Resistance

*This content was previously published by Corteva Agriscience.

When a weed scientist says a novel weed resistance issue is not well understood, it’s a little concerning.

Most farmers understand the need to apply multiple herbicide groups and rotate them to reduce the number of herbicide-resistant weeds going to seed. This practice reduces target-site weed resistance when a weed alters its genetic code so the chemical no longer fits the protein it was designed to attack.

However, some weeds are evolving to deploy suites of enzymes that work together to metabolize (detoxify) a chemical before it can kill a weed — known as non-target or metabolic resistance.

 

How big is this problem?

“Ten or 15 years ago, we weren’t seeing much metabolic resistance in waterhemp, as it was all target-site resistance,” says Pat Tranel, Professor and Associate Head of the Department of Crop Sciences in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

“Today, I’d estimate more than half of our waterhemp in Illinois has glyphosate resistance [target-site], and 50% have atrazine resistance [metabolic/non-target]. Approximately 10% of the waterhemp population has HPPD resistance which is all metabolic,” Tranel says. He suspects there’s more metabolic resistance than we realize in preemergence Group 15 herbicides because reduced residual control by a few weeks makes it difficult to pinpoint whether it’s resistance or weather-related.

At a molecular level, scientists can easily determine target-site resistance because they know the protein and can look directly at the genetic code of waterhemp to determine the responsible mutation. But for non-target metabolic resistance, it’s still a guessing game. Researchers can sometimes identify an enzyme class that detoxifies
a chemical but know little about which genes code for those enzymes.

Tranel and his colleagues have determined that waterhemp has evolved resistance to seven different herbicide groups, and all have some metabolic resistance. “Our research focuses on what enzymes or genes are involved, what is selecting for those enzymes, and why the same mechanism can confer resistance to other herbicide groups. Until
we understand all this, we’re at a loss to make herbicide recommendations for metabolic resistance,” he says.

 

Defining the resistance

Tranel uses Enlist® crops to explain metabolic resistance. The same gene used to confer 2,4-D resistance in Enlist corn or soybeans can also metabolize the Group 1
‘FOP’ herbicides like quizalofop. “The reason for this is an unpredictable cross-resistance that we talk about in weeds,” he says.

There’s some similarity around the chemicals of those herbicide molecules, allowing them to be recognized by the same metabolizing enzyme. This process is similar in weeds. “If a weed gets selected for an enzyme that can metabolize herbicide A that the farmer has used, it’s also possible that same enzyme can metabolize herbicide B,” Tranel says.

The metabolic resistance process gets further complicated over time. Weed scientists worry about weed populations that receive different herbicides over many seasons
will lead to numerous enzymes metabolizing numerous herbicide groups. In other words, the herbicides select for suites of enzymes that can collectively work together to metabolize different herbicides.

“It’s not an exaggeration that we are selecting weed populations that can metabolize herbicides that have not even been commercialized yet,” Tranel says.

Even when research narrows down the genes responsible for metabolic resistance, growers still need to worry about target-site resistance. Using multiple effective sites of action and rotating herbicides using a three-to-four-year plan is essential to manage target-site resistance.

“But just doing this alone will not prevent metabolic resistance,” stresses Tranel. “Farmers need to know they cannot beat weed resistance with herbicides. Non-chemical strategies are needed to manage weeds. The overriding goal should always be no weeds going to seed.”

Will farmers reach a point where mechanical weed seed destruction technology on combines becomes mainstream, like in Australia, where they’ve dealt with metabolic
weed resistance since the 1980s? Tranel thinks it’s certainly a possibility.

“Weed seed destruction technology has a fit, but with limitations as it works better in some crops than others,” he says. “Weeds will adapt, as I can predict waterhemp will start shattering seeds before combines roll. We preach diversity in strategies, as the more things you throw at weeds, it’s harder for them to adapt.”

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Fertility from a Manure Perspective

KEY POINTS

Introduction
Nitrogen (N), phosphorus (P), and potassium (K) are among the many nutrients that can be returned to the soil with a manure application. Manure can help nourish growing crops, rebuild soil nutrient levels, and gradually increase soil organic matter. This can be especially important in silage fields where nutrient removal is coupled with plant tissue removal. Silage production is often located close to livestock operations, where a manure source is available, so a manure application to a silage field after harvest is often a good option. Manure can be difficult to manage as a fertilizer because it can contain organic and inorganic material, be variable in nutrient concentrations from different and within animal species, vary from sample-to-sample, be in liquid or dry forms, and in some situations be low in nutrient concentrations, which can require large application volumes. Additionally, nutrients such as N and P within manure can be tied up until microorganisms release (mineralize) these nutrients from fibrous feed or bedding components and make them available for plant growth. Potassium in manure is readily available for crop uptake (Table 1).1 Nutrient content within manure can vary greatly because of animal species, manure moisture, diet, genetics and performance, bedding used, storage, handling, lagoon agitation, and other management factors (Table 2).2

Manure Attributes
Manure samples should be sent to qualified laboratories to determine the total N, P2O₅, and K₂O concentrations. Manure application rates are easier to calculate if the analysis is provided on an as-received or wet-basis in lb/ton or lb/1000 gal units. Conversion factors must be used if the analysis is not in these units. If manure applications are made prior to receiving the laboratory analysis, standard estimations for the manure source can be used (Table 2).2 The variation in nutrient concentrations should be noted between and within animal species. Knowing the analysis is also important for environmental reasons. Applying too much of a nutrient that can change and/or move by denitrification, volatilization, leaching, or erosion can result in ground and surface water contamination. When manure is not incorporated, N can be lost through volatilization and if applied in the fall, the opportunity for leaching increases. Phosphorus can be lost when flooding carries the manure off the target field and into creeks and other waterways.

Methods for Manure Application
Broadcast, injection, and irrigation are the most often used methods for manure application. Benefits of broadcast applications include speed of delivery and wider application widths, when compared to injection. Broadcasting may reach widths of 50 feet while injection systems are much narrower and requires more time to apply. However, without immediate incorporation, broadcast manure can be subject to loss of N through volatilization, loss of P through surface runoff, and complaints by neighbors from odor. If wintertime broadcast (Figure 1) manure application is unavoidable:

 


Figure 1. Wintertime broadcast manure application on a field with less than 15% slope and far from waterways.

Injection and irrigation of liquid manure can help control application variability, provide a better method of matching application timing to the nutrient need of the crop, and help mitigate
potential environmental issues.

The injection method allows for application to growing crops such as alfalfa, grass, cover crops, and used as a sidedress in corn. Injection systems are compatible with no-till management. However, labor and equipment costs for injectable systems can be high; therefore, several factors should be considered before investing in injection equipment:

Liquid and solid manure (when possible) should be placed (injected) three to six inches below the soil surface. The five primary application tools for injection that disturb soil the least, are disk injection, chisel injection, high-pressure injection, aeration, and surface banding for shallow injection in standing forages.4 Aeration systems create holes in the soil that allows later surface applied manure to seep into the soil. Regardless of the potential benefits of injection systems, many still prefer broadcasting manure because of the speed of application. If the manure injection equipment is too expensive for an individual livestock producer, consider custom applicator options for that application.

There are many different types of irrigation systems used for liquid manure application. Hand-move, stationary big gun, traveling big gun, wheel lines and center pivot irrigation are some of the most popular systems used for liquid manure application. Each has its advantages and disadvantages depending on the amount of manure that will be applied by a system, the amount of screening and solid separation needed to keep each type of system free from plugging during application, and the labor requirement needed for operation. Benefits of using irrigation systems to distribute liquid manure include:

Health concerns regarding small particulate drift have been expressed when irrigation is used to apply liquid manure. Concerns include toxins, pathogens, odor spikes, air quality, and surface and groundwater contamination.5 Additionally, application sites are typically limited to fields that are located near lagoons due to the expense to pipe liquid manure to the irrigation systems. It is very important to screen out the solids that have the potential to plug the sprinkler nozzles used to apply the liquid manure. The nutrient concentration (NH3) and salt concentration levels of liquid manure should be closely monitored because manure with an electrical conductivity (EC) greater than 6 mmho/cm can damage corn and soybeans if applied before the eight-leaf growth stage for corn and the V3 growth stage for soybeans. Extremely high EC ratings manure, above 12 mmho/cm, can kill small and emerging plants.

This concern can be managed if the liquid manure is diluted with fresh water to keep the EC below 6 mmho/cm.6 These issues and others should be evaluated for the local area before irrigation equipment is purchased for the sole benefit of manure distribution or retrofitting existing irrigation systems for this type of manure application. Always follow local regulations to determine the equipment needed to comply with the use of irrigation equipment for a liquid manure application.

Dry Manure Composting
Benefits of composting dry animal manure:

Many of the challenges for a dry manure application can be mitigated through composting. The composting process takes time, an area dedicated to the composting process, management, equipment, and labor. Composting a mixture of organic residues like manure and bedding and even animal carcasses can result in a uniform, nutrient dense, low odor source of fertilizer for crops. Composting is more than just piling the manure and waiting to apply it later. Composting requires routine mixing that adds oxygen to the manure which stimulates aerobic microorganisms. Under dry conditions it may be necessary to add water or liquid manure to keep the microorganisms active. The mixing process is necessary to keep the compost pile at a temperature of 113 to 160 °F which pushes the composting process forward. The time needed for composting to reduce the viability of weed seeds varies by weed species, but 42 days has shown to reduce the viability of most weed species.7

Manure Management Plan (MMP)
With any manure production or application to a field-crop or pasture, there is a concern for the potential risk of environmental impact and contamination from manure storage, application, or spill if it is not managed properly. This is why all farms, facilities, or properties that apply manure to crop fields and pastures or that have manure-producing animals must have a written MMP. A written MMP is needed for any farming operations that has an Animal Concentration Area (ACA) or pasture.

In addition, all farming operations that land-apply manure or agricultural process wastewater, whether they generate the manure or import it from another operation, must also have a written MMP.8 This plan can be written by the livestock farmer, farmer, or by a certified nutrient management specialist but must be kept on the farmstead and available upon request. Different sized animal operations will have different designations and different regulations and requirements that will need to be followed. Larger animal feeding operations (AFOs) are defined as an agricultural business or operations where the animals are raised in confined situations for at least 45 days per year. Concentrated Animal Feeding Operations (CAFOs) are defined as an intensive animal feeding operation in which over 1,000 animal units are confined for over 45 days a year. An animal unit is the equivalent of 1,000 pounds of “live” animal weight. Any size AFO that discharges any manure or wastewater into a ditch, stream, or any other waterway regardless of size is considered a CAFO. Concentrated Animal Operations (CAOs) are defined as an agricultural operation where the animal density of all livestock on the farm exceeds eight or more animal equivalent units (AEUs) with an animal density of two AEU per acre on an annualized basis.9 An AEU is one thousand pounds live weight of livestock or poultry animals, on an annualized basis, regardless of the actual number of individual animals comprising the unit. CAFOs and CAOs must have a more detailed written manure plan known as a Nutrient Management Plan (NMP), which focuses on nutrient management and will need to be prepared by Certified Nutrient Management Specialists.

These NMPs are submitted to local county conservation districts for review and approval. The NMP offers guidance for:

The components of an MMP include:

While many of the components for a MMP are consistent from state-to-state there are different state specific regulations. The National Pollutant Discharge Elimination System (NPDES) program provides the federal foundation for the MMPs, but there are many local differences due to climate and soil changes that can impact manure nutrient management. These differences include state specific programs, policies, and tools to help comply with state differences. Along with these different programs are specialized tools and training to help manage state specific regulations and permitting. Consult your local state land grant university for regulations concerning an MMP specific for your area.

Balancing Crop Nutrient Removal and Availability
Practicing good soil fertility stewardship is the premise of the 4Rs of nutrient management–applying the right fertilizer source, at the right rate, at the right time, and in the right place.10 The first step in determining the correct manure application rate is to measure the current nutrient levels of a manure targeted field through assays of comprehensive and representative soil samples. It is also important to know the field history of any manure applications over the previous couple of years. This is important because there can be N credits from the organic N in the manure that can be released from previous applications. Nitrogen credits vary and lower each year until that credit reaches zero after the third year. The desired manure application rate for each field is based on the projected crop yield, the nutrient removal for a specific crop, and the current fertility in the soil as determined by soil analysis. The available N content is calculated as 60% of the organic-N and 80%
of the NH4+ (depending on the manure source), for the first year after manure application if the manure is incorporated immediately. If the manure is not immediately incorporated, then the NH4 + component should be reduced by 15% per day for each day the manure is not incorporated.11 Any NH₄ that is applied and incorporated into the soil, before the soil temperature has dropped to 50 °F, can be converted by the soil into NO₃-, which is at risk for loss by leaching before the crop can take it up. The NH₄+ is very stable in the soil and is resistant to leaching, while NO₃- is easily leachable by water movement through the soil, especially in light or sandy soil types. This is why it is advantageous to apply manure after the soil has cooled to below 50 °F. In many situations, additional fertilizer may need to be added to the field to compensate for nutrients that are lacking in the manure. In addition, any potential nutrient loss when manure is applied to the soil surface must be accounted for.

Manure application timing and placement can impact the rate. Fall and surface-applied manure applications have greater opportunities for loss. Applying manure during drought conditions has advantages and disadvantages. Applying manure during a drought can allow for an earlier application window in the fall, with less potential for any manure N to be converted to nitrate (NO₃-) or leached away. However, injecting manure during a drought can make it more difficult to run an injection chisel knife through the soil, which can require a higher horsepower tractor to run the same size application equipment, increasing the cost per acre for that application operation. Spring applications can be challenging due to the potential for extended wet weather causing delays or volatilization. Additionally, the workload during the spring is already busy with preparing fields for planting. Summer manure applications can be limited to crop rotations that allow for the crop to be harvested during the summer months prior to an application and to irrigation applied liquid manure that allows for application while there is a crop growing in the field.

Article Link

Sources:
1 Sawyer, J.E., and Mallarino, A.P. 2016. Using manure nutrients for crop production. PMR 1003. Iowa State University. Extension and Outreach.
https://store.extension.iastate.edu/product/Using-Manure-Nutrients-for-Crop-Production.
2 Shapiro, C.A., Johnson, L., Millmier Schmidt, A., Richard, K.K., and Iqbal, J. 2021. Determining crop available nutrients from manure. University of Nebraska Lincoln. Nebraska Extension G1335
https://extensionpublications.unl.edu/assets/html/g1335/build/g1335.htm.
3 White, C. and Meinen, R. 2022. The do’s and don’ts of winter manure spreading. Pennsylvania State University. PennState Extension. https://extension.psu.edu/the-dos-and-donts-of-winter-manure-spreading.
4 Maguire, R., Beegle, D., McGrath, J., and Ketterongs, Q.M. 2023. Manure injection in no-till and pasture systems. Virginia Tech and Virginia State University. Virginia Cooperative Extension. Publication CSES-22P. https://digitalpubs.ext.vt.edu/vcedigitalpubs/5983297597286735/MobilePagedReplica. action?pm=1&folio=1#pg1.
5 Austin, J., Yost, M., Miller, R., Allen, N., Larsen, R., Creech, E., and Cardon, G. 2021. Manure application through pressurized irrigation systems. Utah State University. Utah State University Extension Crops. https://extension.usu.edu/crops/research/manure-application-through-pressurized-irrigation-systems.
6 Kranz, W.L., Koelsch, R.K., and, Shapiro, C.A. 2007. Application of liquid animal manure using center pivot irrigation systems. University of Nebraska Lincoln. Nebraska Extension Publications EC778. https://extensionpubs.unl.edu/publication/9000016364607/application-of-liquid-animal-manures-using-center-pivot-irrigation-systems/.
7 Keena, M.A. 2022. Composting animal manures: A guide to the process and management of animal manure compost. North Dakota State University. Ag Home, Extension, publication.
https://www.ndsu.edu/agriculture/extension/publications/composting-animal-manures-guide-process-and-management-animal-manure-compost.
8 2022. The basics of manure management requirements. Pennsylvania State University. Penn State Extension. https://extension.psu.edu/programs/nutrient-management/manure/overview-of-deps-manure-management-manual/the-basics-of-manure-management-requirements#:~:text=Manure%20Management%20Plans%20 identify%20manure,and%20requirements%20for%20winter%20application.
9 Environmental health: Concentrated animal feeding operations (CAFOs). Wisconsin Department of Health Services. https://www.dhs.wisconsin.gov/environmental/cafo.htm#:~:text=Concentrated%20Animal%20 Feeding%20Operations%20(CAFOs)%20are%20agricultural%20meat%2C%20dairy,lands%2C%20 animals%20are%20given%20food.
10 What are the 4Rs. The Fertilizer Institute. 4 Rs nutrient stewardship. https://nutrientstewardship.org/4rs/.
11 Camberato, J.J. 1996. Land application of animal manure. Clemson University. Clemson Extension. EC 673. https://www.mssoy.org/uploads/files/clemson-analysis.PDF.
Legal Statements
Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be considered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions.
Bayer and Bayer Crops are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. 2023 Bayer Group. All rights reserved

Fall and Spring Anhydrous Ammonia Applications

Introduction

According to Emma Orchardson of CIMMYT (International Maize and Wheat Improvement Center) “Nitrogen is the most essential nutrient in crop production but also one of the most challenging to work with”.¹ This is why it is important to start with nitrogen (N) when considering a crop fertility program and consider more than the application rate. The 4 R’s of crop nutrition (the right source, the right rate, the right placement, and the right timing) should be considered for a crop nutrition program.² Anhydrous (contains no water) ammonia (NH3) is a widely used N fertilizer source for crop production. Due to its unique properties, there are important characteristics and safety precautions that should be understood and followed. Characteristics and precautions include:

While it is understood that NH₃ is a very hazardous substance, it can be a cost effective and easy to apply N source for crop production when handled and applied properly. Because of the chemical properties of NH₃, it is the preferred N source for a fall application and is also a viable N source for a spring application. Anhydrous ammonia, which is 82% N, is often the least expensive N source because most of the other N sources start with NH₃. It takes several chemical manufacturing processes to change NH₃ into other dry or liquid N fertilizer sources, all of which have a lower N concentration. The cost per pound of the lower N concentration products, delivered to the farm, over NH₃ often increases because of the additional chemical processes and the increased transportation cost per ton of N.

Chemical and Physical Properties of NH₃

Anhydrous ammonia, a pressurized liquid that turns immediately into a gaseous form when injected into the soil, quickly reacts with soil water to form ammonium (NH4+). This is why NH₃ is injected below the soil surface where it binds tightly to the soil. Once injected into the soil, NH₃ takes about a day to diffuse and expand into a 3- to 4-inch (7.6 to 10.2 cm) diameter cylinder around the injection point. This concentrated zone can be larger in sandy or in extremely dry soils. The rapid soil binding is due to the affinity NH₃ has for soil moisture where it picks up an additional hydrogen ion to convert it to NH4+. With the positive charge, NH4+ is attracted to negatively charged soil particles which keep it from moving with soil water. When NH4+ goes through nitrification, which is caused by bacteria in the soil, it is converted to nitrate (NO3-) and loses its positive charge. With the loss, NO3- becomes mobile or able to move with water through the soil profile and N can be lost as nitrate via leaching (movement of N below the roots with soil water) or by denitrification (the microbial process of reducing nitrate and nitrite into a gaseous N form in water saturated soils). These gaseous N forms can now be lost to the atmosphere and are not available for plant use. When compared to other N fertilizers, the rate of conversion of N to NO3- in the soil is slower with NH₃, helping to minimize the potential for N loss. Warm temperatures and wet soils can speed up the nitrification process.³

Fall Application

A fall NH₃ application is often appealing because it is usually lower in cost, there can be more time for application, and soil conditions are often better for injection (Figure 1). Fall applications can also help reduce soil compaction and spread out the workload for more timely spring planting. Success of fall applications can be increased by applying when soil temperatures drop below 50 °F (10 °C) at the 4-inch (10 cm) depth and with continuing cooler conditions forecasted. Including a nitrification inhibitor along with NH₃ and injecting it into fields with adequate drainage (do not remain wet or fields with excessively coarse or very sandy soil types) can also help reduce N loss.


Figure 1. Anhydrous ammonia application.

A nitrification inhibitor, which delays the process of NH₃ being converted to nitrate by the naturally occurring soil bacteria, works best when soils are at or below 50 °F. The NH4+ form of commercial N is the only form that is tightly bound to soil particles; therefore, maintaining the N in the NH4+ form as long as possible helps lessen the possibility of N loss via NO3- leaching or denitrification.

Splitting Fall and Spring Applications

If conditions are not ideal for a fall application (warm soil temperatures extending into late fall or wet soil conditions), the window for injection may be very small. Therefore, having an alternative plan that may include split N applications may be beneficial. A potential solution may be a fall application on the fields best suited for N retention and delaying the application until spring on fields where NH₃ is not well suited. Splitting applications in the fall and spring can help minimize many of the disadvantages associated with a single large fall or spring application by applying a lower rate in both the fall and spring. Applying some NH₃ in the fall can provide what the crop needs to get started in the spring. Applying the remainder in the spring, closer to when the plant needs the N, helps to increase efficiency, and reduce the potential for loss by leaching and denitrification.

Spring Application

Anhydrous ammonia can be and is often applied in the spring. Spring applications can help to limit N loss before it is needed by the crop. However, if the planting window opens soon after injection there are some factors that should be considered, as there can a be high concentration of NH4+ close to or in the seed slice that can potentially injure seeds and seedlings. Factors include:

Note. The different types of damage caused by the different causes can look very similar but the potential for seedling stunting or death are the same.


Figure 2. Anhydrous ammonia injury to a corn seedling.

Strip-till NH₃ Application

Injecting NH₃ via strip-till, which can be done as a fall or spring application, brings its own set of application concerns. As with most strip-till NH₃ applications, the seed is placed directly over the NH₃ injection point. While strip-tilling allows for the precision placement of a fertilizer band directly below the seed, which can increase the fertilizer use efficiency especially in low fertility soils, the concern is the germinating seed could be in a concentrated N fertilizer zone that can negatively affect germination and early growth (fertilizer burn).

There are no hard-set rules when to strip-till NH₃ in the spring or fall, but the injection point should be 7- to 8- inches (17.8 to 20.3 cm) deep with some situations that could require an application depth of up to 10 inches (25.4 cm). Injection timing should be at least three to four weeks before corn planting; however, depending on many variables, it could require more time before planting. The variability includes NH₃ rate, soil moisture, soil organic matter, soil condition, soil type, weather, and the amount of soil moved over the seed slice at planting, all of which can affect the N concentration in the seed germination zone at germination and during seedling growth.

The potential for seed or seedling injury can be huge if planting occurs soon after injection, if the soil is very sandy or dry at the time of a strip-till injection and the NH₃ rate is high. The one hard-set rule that should be adhered to is not reducing the depth of the strip-till injection point when the tractor horsepower is not adequate to pull the strip-till application rig at the desired depth due to tough or hard soil conditions. The reduced injection depth along with poor soil conditions can increase the potential for loss of germination and seedling injury that may require the crop to be replanted. Your local seed representative or agronomist should be consulted to assist with strip-till management strategies for your area.

What can be done to minimize the possibility of anhydrous ammonia crop injury?

There is no specific amount of time in which fall, or spring applied NH₃ no longer has the potential to injure the crop. If planting needs to occur soon after application, recommendations to consider include:

 


Figure 3. Anhydrous ammonia sidedress application.

Article Link

Sources
¹Orchardson, E. 2020. Nitrogen in agriculture. CIMMYT. Nitrogen in agriculture. https://www.cimmyt.org/news/nitrogen-in-agriculture/
²Rogers, E. (Fronczak, S.) 2019. The 4R’s of nutrient management. Field Crops. Michigan State University Extension. https://www.canr.msu.edu/news/the-4r-s-of-nutrient-management
³Sawyer, J. 2019 Understanding anhydrous ammonia application in soil. ICM News. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/cropnews/2019/03/understanding-anhydrous-ammonia-application-soil
⁴Maharjan, B., Iqbal, J., Puntel, L., and Rees, J. 2023. Fertilizer-nitrogen injury to corn. CROPWATCH. University of Nebraska- Lincoln. https://cropwatch.unl.edu/2023/fertilizer-nitrogen-injury-corn Web sources verified 4/3/24.
Legal Statements
Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2024 Bayer Group. All rights reserved. 1213_103341

High pH and Salt Issues in Corn

Key Points

Salinity, sodicity, and high pH in soils can impact plant growth and yield potential. These issues are common in the western growing regions of the US, such as the Great Plains, and are primarily caused by the weathering or breakdown of soil parent material or by the use of poor-quality irrigation water.

High pH, Salinity, and Sodicity

Soil pH is a measure of the acidity (low pH) or alkalinity (high pH) of the soil. The pH value for good corn production is between 6.0 to 6.5. High pH problems are associated with a pH 7.8 or higher and are often accompanied by saline soils, sodic soils, or saline-sodic soils. Problems with soil pH (either too high or too low) can cause the following issues in plants:


Figure 1. The relationship between soil pH and nutrient availability. The wider the dark bar, the greater the nutrient availability. Image courtesy of Fernández, F.G. and Hoeft, R.G. Managing soil pH and crop nutrients. Chapter 8. Illinois Agronomy Handbook. University of Illinois.

Soil salinity is the content of soluble salts in the soil, which can readily dissolve in the soil water solution and be taken up by plants. These salt ions include sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), chloride (Cl- ), sulfate (SO42-), carbonate (CO32-), bicarbonate (HCO3- ), and nitrate (NO3-).

Soil sodicity is the concentration of exchangeable sodium ions in the soil. Sodic soils have high levels of sodium and low levels of other salts. Sodic soils can have structural issues because the sodium ions weaken soil aggregates, resulting in a collapse of the soil structure. This is especially common in sodic soils with high clay or silt content. Sodic soils often have a high pH, often greater than 8.4. Some soils may have both high saline and high sodium levels; these are termed saline-sodic soils. When salts build up in the soil, the following issues can occur in plants:

Identifying and Managing Salt and pH Issues:

A soil test is the best way to accurately diagnose problems with the soil. Most basic soil tests report the pH and electrical conductivity (EC), which measures salinity. General soil tests should be conducted every 4 years, but additional testing should be conducted if a problem is suspected. Soil cores should be taken from a 6- to 12-inch depth at several locations of the field, concentrating on the areas suspected to have issues. Keep track of where each sample was collected and keep them separate. For high pH soils, the sodium absorption ratio (SAR) or exchangeable sodium percentage (ESP) should also be calculated, as the two conditions are often linked. The SAR
and ESP are two different measurements of the concentration of sodium ions in the soil. Irrigation water samples should also be tested for salt levels where applicable.

Management options for high pH soils:

Note that it may be more difficult to lower the pH of high pH soils than to manage their soil nutrient availabilities. This is because high pH is often caused by the parent material of the soil, which will continue to break down over time and buffer any attempts to acidify the soil. Soils that contain free carbonates are the most difficult to alter in terms of pH, though the addition of thiosulfate to a 2 x 2 starter maybe helpful.

Management options for saline soils:

Management options for sodic soils:

Note that the practice of leaching the salts from the soil may also remove soil nutrients and pesticides, and will reduce irrigation efficiency. Consider the soil fertility level (fall may be the best time as nutrients have already been utilized by the plant), drainage, the quality of the irrigation water at the time of the leaching event, the availabilityof the irrigation water, and the type of irrigation system (to ensure the irrigation capacity is sufficient to apply enough water in a short enough of time to cause leaching).

Article Link

Sources Waskom, R.M., Bauder, T., Davis, J.G., and Andales, A.A. 2012. Diagnosing saline and sodic soil problems. Fact sheet 0.521. Colorado State University. https://extension.colostate.edu/docs/pubs/crops/00521.pdf Bauder, T.A., Davis, J.G., and Waskom, R.M. 2014. Managing saline soils. Fact sheet 0.503. Colorado State University. https://extension.colostate.edu/docs/pubs/crops/00503.pdf Davis, J.G., Waskom, R.M., and Bauder, T.A. 2012. Managing sodic soils. Fact sheet 0.504. Colorado State University. https://extension.colostate.edu/docs/pubs/crops/00504.pdf Farooq, M., Hussain, M., Wakeel, A., and Siddique, K.H.M. 2015. Salt stress in maize: effects, resistance mechanisms, and management. A review. Agronomy for Sustainable Development, 35(2):461–481.
https://doi.org/10.1007/s13593-015-0287-0 Fernández, F.G. and Hoeft, R.G. Managing soil pH and crop nutrients. Chapter 8. Illinois Agronomy Handbook. University of Illinois.

2 Key Findings from 2024 Nitrogen Trials

*This content was previously published by Corteva Agriscience.

The Corteva Agriscience nitrogen stabilizer sales team continues to collect and analyze on-farm data to help you and your customers make strategic, cost-effective nutrient management decisions. Although yield results are still to be determined, Chris Kluemke, nitrogen stabilizer market development specialist, Corteva Agriscience, says there are two trends worth noting as we head into the fall application season:

  1. Beneficial soil bacteria are not depleted by N-Serve® nitrogen stabilizer.

“We commonly hear concerns that our nitrogen stabilizers negatively affect non-target soil bacteria, but that’s simply not true,” says Kluemke, who oversees trials in Indiana and Illinois. “We worked with Trace Genomics to measure bacterial diversity across multiple sites, comparing treated, untreated and competitor-treated fields.”

The tests account for the number of species present as well as the relative abundance of each species. Both bacteria and archaea (another single-celled organism) are included. Generally, a higher diversity measurement means healthier soil.

The team sampled fall-applied fields in March and spring-applied fields in late May.

“The results show soil bacteria was consistent across the board, and all samples treated with N-Serve nitrogen stabilizer either met or exceeded the benchmark for healthy soil,” Kluemke says.

2. N-Serve nitrogen stabilizer outperforms other stabilizers in protecting nitrogen applications.


Samples depicted in data above were taken across 10 sites across Iowa and Illinois. Each dot represents the average across the 10 sites. The Nitrogen and Nitrogen Stabilizer applications occured in Fall 2023 prior to samples beginning to be taken.

In 6 months with higher-than-average rainfall across 10 trial locations, N-Serve nitrogen stabilizer maintained a higher amount of nitrogen in the ammonium form compared with competitors in similar conditions.

An average of 36% of Nitrogen was still available in the ammonium form in the second half of May in soils where fall-applied N was stabilized with N-Serve.

What’s next?
Kluemke says that the trials are ongoing and more data will be available later this year. With the weather conditions that growers across the Midwest have experienced this season, he expects a yield advantage for the fields treated with a Corteva nitrogen stabilizer. “With all the rain that we have gotten in several parts of the country this summer, there’s potential for nitrogen to be a limiting factor,” he says. “And the right choice of a stabilizer could pay big dividends.”

Article Link

® Trademarks of Corteva Agriscience and its affiliated companies. Do not fall-apply anhydrous ammonia south of Highway 16 in the state of Illinois. Always read and follow label directions. ©2024 Corteva. 022975 LC (09/24)

Performing a Corn Stalk Nitrate Test

Q. What is the corn stalk nitrate test?
The corn stalk nitrate test (CSNT) is conducted late in the season and can be a reliable end-of-season indicator of crop nitrogen (N) status. The test reflects N availability during the growing season and provides a tool to help growers determine if their N management practices were adequate. The CSNT provides an assessment of whether the crop had the right amount of N, too much N, or was N limited.

Q. When should you collect samples for the CSNT?
Sampling can be done anytime between ¼ milk line up to about 3 weeks after black layer formation, before grain harvest. If used for silage corn, sample at the time of harvest or within 24 hours after harvest, as long as there is no rainfall between the time of harvest and sampling. The stubble height needs to be at 14-inch (35.5 cm) for an accurate test.

Q. How should CSNT samples be taken?
• Starting at least 6 inches up to 14 inches (15 cm to 35.5 cm) above the soil line, cut an 8-inch (20 cm) long section of corn stalks, removing any leaf sheaths. Pruning shears can work well for taking samples.
• A sample should include 15 stalk sections from randomly selected representative plants throughout the field. Selected plants should be healthy, and stalks severely damaged by insects or disease should not be used. The sample should not represent more than 20 acres (8 hectares).
• If soil characteristics or past management practices vary across the field, separate samples should be collected for each area.

Q. How do you prepare the samples and what should you do with them?
• Cut stalk sections into 1- to 2-inch (2.5 to 5 cm) long segments or split the stalks to facilitate drying.
• Samples should be placed in paper bags (not plastic) and sent to a laboratory for analysis.
• Samples should be refrigerated (not frozen) if they are to be stored for more than one day before shipping.
• Most soil-testing laboratories will conduct the CSNT. Contact your laboratory to confirm that they will run the test and to find out about any procedures or paperwork they require.

Q. What will the lab results tell you?
The CSNT is based on the concentration of nitrate-N in the lower corn stalk when the plant is near or at maturity. Lab results will indicate the following:

• A low nitrate level reading indicates that not enough N was available for the plant to reach full yield potential.
• An optimal nitrate level reading indicates that the N was adequate for optimum economic yields in the field or sample area.
• An excessive nitrate level reading indicates that excess N was applied that could reduce profitability and result in N losses to the environment.

Q. What are the limitations of the CSNT?
The CSNT can be greatly influenced by weather, soil productivity, and management practices. The following factors can complicate interpretation of the test results:
• The test identifies optimal and excessive nitrate levels more accurately on medium yield potential soils compared to high yield potential soils.
• The test can incorrectly indicate excessive nitrate levels on fields with manure applications within the past two years and/or alfalfa in the rotation, particularly on high yield potential soils. The test should not be used for first-year corn following sod.
• Test levels can be high in extremely dry years and low in extremely wet years. Drought conditions can result in elevated nitrate levels in the lower stalk.

The test does not provide an indication of the amount of N that was over- or undersupplied. Test result readings of high concentrations (>2000 ppm nitrate) are more definitive and provide greater confidence that there is excess N available to the plant. Less confidence can be placed on low nitrate level interpretations or in specific N-rate adjustments.

Q. What can you learn and how can you use information from the CSNT?
The CSNT can be used as a long-term approach to evaluate your N management and to help guide future N applications toward economically optimal rates. The test will tell how you did, not what you need to do. The test will not tell you what management practices to change but instead provides information about how your N management is performing. Decisions can be made to adjust the fertility program for subsequent years based on the results of the CSNT.

CSNT results are most useful when evaluated over a period of several years on the same field. Basing future N rate decisions solely on one year’s CSNT values could result in poor management decisions. CSNT data collected over several years coupled with fertilizer and manure application history, growing season weather conditions, soil type and productivity, and general crop management history information can be used to determine if N fertilizer rates should be reduced to improve profitability.

The test is best suited to understanding when N applications are greater than the crop need. If the CSNT shows high nitrate levels for several seasons, then it becomes evident that N applications are too high and should be adjusted to more moderate rates. Continued monitoring of CSNT results will show if stalk nitrate levels decrease into the optimal range after adjusting N-application rates. Using the CSNT can result in greater N use efficiency and thus profitability, and helps to reduce the potential for negative environmental impacts from N that is not being utilized by the crop.

Article Link

Sources
Kaiser, D. and Fernandez, F. 2020. How to take and interpret the basal stalk nitrate test. University of Minnesota. https://blog-crop-news.extension.umn. edu/2020/09/how-to-take-and-interpret-basal-stalk. html
Laboski, C. 2016. Considerations when using the end-of-season corn stalk nitrate test. University of Wisconsin Integrated Pest and Crop Management. https://ipcm.wisc.edu/blog/2016/09/considerations-when-using-the-end-of-season-corn-stalk-nitrate-test/
Milander, J., Iqbal, J., Mamo, M., and Timmerman, A. 2022.-Using a Cornstalk Nitrate Test to Evaluate Nitrogen Management Decisions. University of Nebraska. https://cropwatch.unl.edu/2022/using-cornstalk-nitrate-test-evaluate-nitrogen-management-decisions
Zebarth, B.J., Drury, C.F., Tremblay, N., and Cambouris, A.N. 2009. Opportunities for improved fertilizer nitrogen management in production of arable crops in eastern Canada: A review. Canadian Journal of Soil Science. 89: 113-132. https://doi.org/10.4141/CJSS07102
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ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1213_134529

Tips for Summer Corn Scouting

*This content was previously published by Corteva Agriscience.

No matter when your customers were able to get into the field for planting this spring, regular scouting can help set the stage for a successful corn yield come harvest.

Getting into the field on a regular basis after planting will improve the timing on important crop protection decisions. Is there a new flush of weeds that needs to be managed? Will postemergence herbicides need to be applied sooner than anticipated? Are there any nutrient deficiencies? Are there any new insect or disease pressures? All these questions can be answered and addressed with regular scouting.

Scouting should occur multiple times throughout the growing season, but there are times when it’s more critical, says Joe Bolte, Market Development Specialist, Corteva Agriscience.

 

Pests to watch this year

With lengthy emergence periods, waterhemp and Palmer amaranth present an annual challenge — calling for a herbicide program approach that includes multiple modes of action for effective control. Bolte says, “Depending on your geography and planting date, waterhemp or Palmer amaranth may need to be controlled in every herbicide pass — not just the postemergence application.”

On the flip side, your customers in areas with heavy rainfall may not have had a chance to get their preemergence herbicides down in time. If this is the case, they may consider reallocating those preemergence herbicide dollars to create a more powerful postemergence pass.

Bolte also says that tar spot should be on everyone’s radar. Scouting the corn plant’s canopy will help determine if a fungicide application is warranted.

 

Scouting resources available

There are several free resources available to help customers with in-field corn scouting. “Many universities will put together scouting guides or calendars for common pests. Use these to determine when weeds, disease and insects are most likely to emerge in your geography,” Bolte says.

You also can contact your local Corteva Agriscience representative and download our Corn & Soybean Disease ID Guide and Corn Weed Scouting Checklist for more detailed information.

 

Key corn scouting timing

 


Corn & Soybean Disease ID Guide

 


Corn Weed Scouting Checklist

Article Link

™ ® Trademarks of Corteva Agriscience and its affiliated companies.
© 2024 Corteva. Groundwork – June 2024

Spray Timely and Early for More Effective Weed Control

*This content was previously published by Corteva Agriscience

When looking at a weed, its overall height can be deceptively short. How is that possible? Because, to a herbicide, the weed’s height is not a linear measurement from the ground to the top of the plant. When a herbicide is fighting a weed, that fight takes into account every inch of the weed. It includes every point of growth that is on the plant, coming out of the main stem.

Corteva Agriscience Herbicide Trait Specialist Steve Snyder illustrates this in a video on application practices. (Use the QR code to check it out.)

In the video, Snyder measures off a single 8” waterhemp weed and pulls it from the ground. He then breaks off each branch growing from the main stem of the plant and lays them end to end on the ground and measures the length of all the sections of the plant as a whole. The total length comes out to 33″. Snyder explains how, to the herbicide, this is a 33″ weed, not an 8″ weed. He says that this is one reason why it is so important to apply herbicide early and in a timely manner. The herbicide has a much greater chance of being effective when the plant is 6” tall or less, because the weed has far fewer growth points than a larger, more mature weed.

Snyder’s demonstration makes a good point. Weeds that are left to grow taller than 6” make the job of the herbicide just that much tougher. Catching weeds early is an important aspect of good weed control and helps ensure the treatment is as effective as possible.

Article Link

® Trademarks of Corteva Agriscience and its affiliated companies. © 2024 Corteva.

Soybean Growth and Development

Soybean growth stages begin with the emergence of cotyledons from the soil surface (VE). When the unifoliate leaves unfold, the plant has reached the VC stage. After the first trifoliate leaves are fully expanded, numbers are used to signify each vegetative (V) and reproductive (R) stage of growth. As the plant begins to set flowers, the growth stages become reproductive, and the plant progresses through pod development, seed development, and plant maturity. Vegetative growth stages begin to overlap with reproductive stages at about R1. A new growth stage is established when 50% or more of the plants meet the requirements of the growth stage.

 

Determining Growth Stages in Soybeans


Figure 1. Soybean growth stages.

 

Soybeans are largely either indeterminate or determinate in growth habit. For indeterminate products, vegetative growth continues after flowering, and the rate of development is directly related to temperature. Determinate products generally complete vertical growth by the time flowering is completed.

 


Figure 2. Reproductive growth stages of soybeans.

 

Emergence (VE) Through First Trifoliate (V1)

After absorbing adequate moisture and depending on temperature, product, and planting depth, the primary root or radical emerges from a soybean seed. The hypocotyl pulls the cotyledons with it to the soil surface (VE, Figure 3). Cotyledons supply the plant’s nutrient needs for seven to 10 days after emergence. The loss of one cotyledon during this time has a limited effect on plant growth; however, if both cotyledons are removed at or soon after emergence, yield potential may be reduced by five to 10%.1,2 Soon after the cotyledons are fully exposed, unifoliate leaves emerge at the second node and begin creating energy through photosynthesis (the VC stage). Development and full extension of the first trifoliate leaflets (node 3) establishes the V1 stage of growth, and with each fully developed trifoliate on the main stem, another V stage is established.

 

Second Trifoliate (V2)

The V2 stage begins when the second trifoliate leaf is fully expanded. Root nodules begin to develop at this stage, and nitrogen (N) fixation in the nodules begins to occur when plants reach six to eight inches (15 to 20 cm) in height. As plants switch from soil-available N to fixed N, the plants may become yellowish. Lateral roots are developing rapidly in the top six inches (15 cm) of soil.

 

Third to Fifth Trifoliate (V3 to V5)

Axillary buds develop into flower clusters (racemes) in the top of the stem. Determinate varieties stop producing nodes on the main stem soon after the onset of flowering. For indeterminate varieties, the total number of nodes the plant can produce on the main stem is established at V5. Axillary buds that develop on an indeterminate soybean plant can help the plant recover from damage. This is typically the time that iron chlorosis deficiency symptoms become visible in impacted fields.

 


Figure 3. Emerging soybean (VE).

 

Sixth Trifoliate (V6)

Plants develop new growth stages about every three days, depending on environmental conditions. At this stage, lateral roots should overlap rows 30-inches wide or less. A 50% loss of leaves at this stage may reduce yield potential by about three percent.

 

Beginning Bloom (R1)

Flowering begins on the third to sixth node, continues up and down the main stem, and eventually moves to the branches. Nodes on the main stem usually have at least one flower. Vertical roots as well as secondary roots and root hairs continue to grow rapidly until R4 or R5.

 

Full Bloom (R2)

An open flower (Figure 4) develops at one of the top two nodes of the main stem. The plant has accumulated about 25% of its total dry weight and nutrients and about 50% of its mature height. Nitrogen fixation by root nodules is increasing rapidly. Loss of up to 50% of plant leaves from hail, insects, or disease at this stage may reduce yield potential by six percent.

 

Beginning Pod (R3)

A pod on at least one of the upper four nodes is 3/16-inch (5 mm) long or longer. Heat or moisture stress at this stage can reduce pod numbers, seed number per pod, or seed size, which may reduce yield potential. The ability of soybean plants to recover from temporary stress decreases from R1 to R5. Favorable growing conditions during this period may result in greater pod number and increased yield potential.

 

Full Pod (R4)

Pods are growing rapidly, and seeds are developing. At least one ¾-inch (19 mm) long pod has developed on at least one of the four upper-most nodes. Stress during this period (and through R6) can cause more reduction in yield potential than at any other growth stage. Timely rainfall or irrigation may help reduce the potential for yield loss.

 

Beginning Seed (R5)

At least one seed that is 1/8-inch (3 mm) long is present in a pod (Figure 5) at one of the four upper-most nodes. About half of the nutrients required for seed filling come from the plant’s vegetative parts and about half from N fixation and nutrient uptake by the roots. Nitrogen fixation peaks. Stress at this stage can reduce pod numbers, the number of seeds per pod, seed size, and yield potential. Plants attain maximum height, node number, and leaf area at this stage.

 

Full Seed (R6)

This “green bean” stage (Figure 6) marks the beginning of the full seed stage. At least one of the four upper nodes should have a pod with a green seed filling the pod cavity. The total pod weight peaks and leaves begin to yellow

 


Figure 4. A soybean plant flowering and forming pods.

 


Figure 5. Beginning seed (R5).

 


Figure 6. Green beans fill soybean pod.

 

Beginning Maturity (R7)

At least one normal pod on the main stem reaches its brown or tan mature color (Figure 8). Seed dry matter begins to peak. Seeds and pods begin to lose green color. Plants are safe from a killing frost. Yield potential may be reduced if pods are knocked from plants or if pods shatter, releasing seeds.

 

Full Maturity (R8)

When at least 95% of the pods on a plant have reached their mature color (Figure 9), the plant is fully mature. After the R8 stage has been reached typically five to 10 days of good drying weather are needed to obtain a harvest seed moisture content of less than 15%.

 


Figure 7. Soybeans at R7 growth stage.

 


Figure 8. Soybean pod and seeds changing to mature color (R7).

 


Figure 9. Fully mature soybean plant drying down.

 


Figure 10. Soybean pod and beans drying down.

 

Article Link

 

Sources:
Rees, J., Specht, J., Elmore, R., Nygren, A., and Mueller, N. 2019. Considerations after crusted soybean. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2019/considerations-after-crusted-soybean
Conley, S. 2018. A Visual Guide to Soybean Growth Stages. University of Wisconsin-Madison. https://ipcm. wisc.edu/blog/2018/05/a-visual-guide-to-soybean-growth-stages-2/
Purcell, L.C., Montserrat, S., and Ashlock, L. 2014. Soybean growth and development. Arkansas Soybean Production Handbook, Chapter 2.
Kandel, H. and Endres, G. 2023. Soybean production field guide for North Dakota. North Dakota State University. A1172. https://www.ndsu.edu/agriculture/ag-hub/publications/soybean-production-field-guide-north-dakota
Web sources verified 5/7/2024.
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Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. ©2024 Bayer Group. All rights reserved. 1314_12400.