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The Mechanics of Soil Fertility: Use of Sugar in Field Crops
Jolee Derrick, Precision Nutrient Management Ph. D. Student
Grace Williams, Soil Microbiology Ph. D. Candidate
Brian Arnall, Precision Nutrient Management Specialist
Recently, there has been increased interest in adding sugar to spray tank mixes, whether for post-emergence weed control or foliar nutrient applications. While there is limited work on impact of sugar inclusion in herbicide applications, some papers have posed potential enhancement (Devine and Hall, 1990). But since this is coming from a soil science group, we will only focus on soil impact. Following up the last blog, unlike humic substances, which represent more complex and relatively stable carbon forms, sugar is a highly labile carbon source. This rapid utilization of simple carbon sources is well documented to stimulate microbial activity and growth (Kuzyakov and Blagodatskaya, 2015). The general idea of utilizing sugar applications is that sugar has the capacity to improve spray performance, stimulate biological activity, increase organic matter mineralization, and ultimately result in improved yields.
Sugar additions can influence soil processes differently depending on system conditions. In systems with higher residual nitrogen and organic matter, responses may differ from those observed in Oklahoma production environments, where soils are typically lower in organic matter and microbial activity can occur for much of the year. Understanding how sugar functions in these systems requires a basic discussion of carbon dynamics. Sugar itself is almost entirely carbon and is readily consumed by microbes. It’s a simple molecule, which allows it to dissolve easily in water and be quickly utilized in the soil system. Crop residues, like wheat straw, are also carbon-rich but much more complex. They contain cellulose, hemicellulose, and lignin which are long carbon chains that take time to break down because microbes need specialized enzymes to access them.
For the sake of simplicity, we can group carbon into two key pools: labile carbon and particulate organic matter (POM). Labile carbon includes easily decomposed materials, which include the previously mentioned simple sugars that microbes can metabolize rapidly. These pools differ in turnover time and microbial accessibility, with labile carbon driving short-term microbial responses (Cotrufo et al. 2013). POM breaks down more slowly and serves as a longer-term nitrogen source through residue breakdown.
Soil microorganisms require both carbon and nitrogen to grow and maintain biomass, typically at a ratio of approximately 24 parts carbon to 1 part nitrogen. When readily available carbon is abundant, but nitrogen is limited, microbes increase their nitrogen demand and begin scavenging nitrogen from the surrounding soil. This process, better known as nitrogen immobilization, temporarily reduces nitrogen availability to crops. Additions of readily available carbon sources have consistently been shown to increase microbial nitrogen immobilization in soil systems (Recous et al. 1990).
In systems where sufficient nitrogen is present, microbial populations can expand rapidly. Fast-growing microbial species may dominate, continuing to immobilize nitrogen within their biomass. Eventually, when nitrogen becomes limiting, microbial populations decline to levels the system can support. This boom-and-bust cycle can disrupt nitrogen availability during critical stages of crop growth. These rapid shifts in microbial population and activity following carbon inputs are commonly observed in soil systems receiving easily decomposable substrates (Blagodatskaya and Kuzyakov, 2008).
This dynamic becomes especially relevant when considering residue management practices common in Oklahoma. Under no-till or limited-tillage systems, the crop residues have wide carbon-to-nitrogen (C:N) ratios, creating conditions where nitrogen immobilization can occur during the growing season.
Table 1 provides approximate C:N ratios for several crops commonly grown in Oklahoma. When additional carbon is introduced into these systems without accompanying nitrogen, the likelihood of microbial immobilization increases. While immobilization is not bad, it does create a question mark as Oklahoma’s variable climate means the following release of nutrients will be unpredictable.
Table 1. Table depicting the range of C:N ratios for residues of commonly utilized crops in Oklahoma. Ratios were obtained from Brady, N. C., & Weil, R. R. (2017). The Nature and Properties of Soils (15th ed.)
Now consider conventional tillage systems. In Oklahoma, no-till systems typically contain 2 to 3 percent organic matter, which is relatively high given our climate and extended periods of microbial activity. Conventional tillage systems often fall between 0.75 and 2.25 percent organic matter. Because soil organic matter is approximately 58 percent carbon, this represents a substantial difference in the soil carbon pool.
Tillage can temporarily enhance microbial access to both previously mentioned carbon pools. When tillage exposes previously protected carbon, microbial activity increases rapidly. This initial flush can temporarily increase nitrogen mineralization as organic nitrogen is converted to plant-available forms. However, this phase is short-lived. As microbial populations expand, nitrogen demand increases, leading to immobilization and reduced nitrogen availability.
Hypothetically, increased microbial growth and activity would rapidly mineralize organic matter, trigger a surge in NO₃⁻, deplete soil organic matter, and as resources become limiting and the environment can no longer sustain elevated microbial populations, this boom would be followed by a population crash. This relationship is ultimately driven by the soil C:N ratio, which introduces an interesting additional complexity of residue. Different residues bring very different carbon-to-nitrogen balances into the system, and microbes respond accordingly. High carbon residues give microbes plenty of energy but very little nitrogen, so they pull N out of the soil to meet their needs. Residues with lower C:N ratios (soybean, alfalfa, etc.) do opposite, releasing nitrogen as they break down. Now the real question becomes where the critical point sits, and when does management push the system from the threshold of immobilization and mineralization.
These hypotheses form the foundation for new research currently underway through the Precision Nutrient Management Program. Initial proof-of-concept work has already been completed, providing a necessary steppingstone to address these questions.
Figure 1. Graph depicting the different concentrations of nitrate leached corresponding to applied treatments in the proof-of-concept work
The preliminary work (Figure 1) evaluated different sugar sources applied alongside a high-nitrogen product to assess the extent of nitrogen immobilization. Although these studies were conducted using potting soils, clear trends were apparent. Treatments containing sugar consistently showed greater nitrogen immobilization compared to treatments without sugar. This response is consistent with studies showing that additions of simple carbon substrates stimulate microbial growth and increase nitrogen immobilization (Dendooven et al. 2006). Building on this work, an active field-based research project is underway to evaluate how sugar additions influence nitrogen availability and microbial dynamics under real-world Oklahoma production conditions.
From an agronomic standpoint, sugar functions primarily as a readily available carbon source that stimulates microbial growth. In nitrogen-limited systems, this response increases the likelihood that nitrogen will be incorporated into microbial biomass rather than remaining immediately available for crop uptake.
Finally, we conclude with a conceptual consideration. If increased OM mineralization leads to greater plant biomass, this process may partially offset losses of OM. Greater biomass production could return more residues to the soil, contributing to the OM pool in the upper soil profile. Therefore, the system may compensate for OM mineralization through the rebuilding of organic matter via plant inputs. However, the stabilization of this carbon depends on microbial processing and physical protection within the soil matrix (Cotrufo et al. 2015)
However, while the underlying logic is sound, this concept has not been extensively studied within Oklahoma cropping systems. This blog does not address the impact of sugar applications on residue breakdown, and the potential impact of such. Future research through the Precision Nutrient Management Program will further investigate the mineralization process to better understand carbon dynamics within these systems.
Take Home:
- Oklahoma production systems generally have lower residual N and high carbon residues, creating conditions conducive to N immobilization
- Adding sugar increases microbial growth, creating population booms that will momentarily increase mineralization, but then immediately immobilize residual nitrogen.
- Tillage can amplify the negative effects of sugar by exposing more carbon and reducing soil organic matter
- Proof-of-concept work shows sugar triggered a net nitrogen immobilization in a carbon heavy environment
- Proof-of-concept work also suggests that when additional nitrogen is present, sugar additions may shift the system toward net mineralization rather than immobilization.
Work Cited:
Blagodatskaya, E., & Kuzyakov, Y. (2008). Mechanisms of real and apparent priming effects. Biology and Fertility of Soils, 45, 115–131.
Brady, N. C., and R. R. Weil. “The Nature and Properties of Soils, 15th Edn (eBook).” (2017).
Cotrufo, M. F., Wallenstein, M. D., Boot, C. M., Denef, K., & Paul, E. (2013). The Microbial Efficiency-Matrix Stabilization (MEMS) framework. Global Change Biology, 19, 988–995.
Cotrufo, M. F., Soong, J. L., Horton, A. J., Campbell, E. E., Haddix, M. L., Wall, D. H., & Parton, W. J. (2015). Formation of soil organic matter via biochemical and physical pathways of litter mass loss. Nature Geoscience, 8(10), 776–779.
Dendooven, L., Verhulst, N., Luna-Guido, M., & Ceballos-Ramírez, J. M. (2006). Dynamics of inorganic nitrogen in nitrate- and glucose-amended alkaline–saline soil. Plant and Soil, 283(1–2), 321–333.
Devine, M. D., & Hall, L. M. (1990). Implications of sucrose transport mechanisms for the translocation of herbicides. Weed Science, 38(3), 299–304.
Kuzyakov, Y., & Blagodatskaya, E. (2015). Microbial hotspots and hot moments in soil: Concept & review. Soil Biology and Biochemistry, 83, 184–199.
Recous, S., Mary, B., & Faurie, G. (1990). Microbial immobilization of ammonium and nitrate in cultivated soils. Soil Biology and Biochemistry, 22, 913–922.
Mechanics of Soil Fertility: Understanding Humic and Fulvic Acids
Brian Arnall, Oklahoma State University, Precision Nutrient Management Extension Specialist
Oliver Li, Oklahoma State University, Soil Chemistry
Interest in humic and fulvic acid products has increased substantially in agricultural production systems during the past two decades. These materials are frequently promoted as tools for improving soil biology, increasing nutrient availability, enhancing fertilizer efficiency, and stimulating plant growth. Because humic substances are known to be important components of soil organic matter, it is reasonable to ask whether adding humic or fulvic products to soil can meaningfully influence soil fertility.
As with many soil fertility questions, the answer depends on understanding two key factors: the mechanism involved and the magnitude of that mechanism relative to the soil system. Soil processes operate within large natural pools of organic matter, nutrients, and microbial activity. Therefore, evaluating the potential effects of humic products requires examining both how these compounds function chemically and biologically and how their application rates compare with the soils organic matter.
What Are Humic and Fulvic Acids?
Humic substances are heterogeneous organic compounds formed during the decomposition and transformation of plant and microbial residues. Historically, soil scientists have divided these materials into three operational fractions based on their solubility behavior: humic acid, fulvic acid, and humin (Stevenson, 1994; Tan, 2014). Humic acids are relatively large molecules that are insoluble under acidic conditions but dissolve in alkaline solutions. Fulvic acids are smaller molecules that remain soluble across the entire pH range, which allows them to move more freely in soil solution.
Both humic and fulvic acids contain numerous functional groups, particularly carboxyl and phenolic groups, which carry negative charge. These functional groups allow humic substances to interact with metal ions and nutrient cations and contribute to several important soil properties, including cation exchange capacity, buffering capacity, and metal complexation (Stevenson, 1994; Lehmann and Kleber, 2015). Because these materials originate from decomposed organic residues, they represent one portion of the complex mixture that collectively makes up soil organic matter. The distribution of the soil organic matter fractions varies among soil types and land uses, but fulvic acids and humic acids are each typically estimated to comprise approximately 10–35% of total soil organic matter (Guimarães et al., 2013).
Nutrient Retention and the Role of Cation Exchange
One of the most commonly cited mechanisms associated with humic substances is their ability to retain nutrients through cation exchange. The negatively charged functional groups present on humic molecules attract positively charged ions in soil solution. Through this electrostatic attraction, humic materials can retain several plant nutrients, including ammonium, potassium, calcium, magnesium, and certain micronutrients such as zinc and copper (Stevenson, 1994; Tan, 2014). This mechanism functions in the same manner as cation exchange on clay minerals. Of course, negatively charged surfaces do not retain negatively charged ions. As a result, nutrients such as nitrate are not held by humic substances and remain mobile in soil solution.
Laboratory measurements indicate that humic materials may possess relatively high cation exchange capacity on a mass basis. Reported values commonly range from approximately 300 to 600 cmolc kg⁻¹ depending on the source material and extraction method (Stevenson, 1994; Tan, 2014). These values demonstrate that humic substances can retain a large amount of cationic nutrients. A question that can be posed, however, is how this capacity compares with the nutrient retention already provided by soil organic matter.
Understanding the magnitude of humic additions requires comparing product application rates with the organic matter already present in soil. Calculations based on typical cation exchange values suggest that one pound of humic material with a CEC of 300–600 cmolc kg⁻¹ could theoretically retain approximately 0.04 to 0.08 pounds of ammonium-nitrogen. When viewed in isolation this number may appear meaningful. However, agricultural soils already contain large quantities of organic matter. An acre furrow slice, representing approximately the upper six inches of soil, weighs roughly two million pounds. Soil containing one percent organic matter therefore contains about 20,000 pounds of organic material per acre (Brady and Weil, 2016). Humified organic matter typically has cation exchange capacities ranging between 150 and 300 cmolc kg⁻¹ (Stevenson, 1994), meaning that the exchange capacity associated with native soil organic matter is already substantial. To put this into perspective, one pound of humic material can retain roughly 0.04 to 0.08 pounds of cation charge. Ammonium and potassium carry a single positive charge, while calcium carries two, meaning two ammoniums can be held for every two calcium. To provide contrast to the application of a humic substance, increasing soil organic matter by just 0.1% equivalent to about 2,000 pounds of additional organic material per acre can provide the capacity to retain approximately 40 to 80 pounds of cation charge or 40 to 80 pounds of ammonium.
The key point is not that humic materials cannot retain nutrients. They clearly can. Rather, the scale of material already present in soil is extremely large compared with the few ounces or pounds of humic products typically applied in agricultural systems. Consequently, the nutrient retention capacity associated with soil organic matter overwhelmingly dominates the soil system.
Micronutrient Complexation
Humic and fulvic substances are also known to interact with micronutrients through metal complexation reactions (also known as ‘chelation’). Carboxyl and phenolic functional groups can coordinate with metal ions such as iron, zinc, copper, and manganese to form organic complexes (Stevenson, 1994; Tan, 2014). These complexes can influence micronutrient mobility and availability in soils.
Fulvic acids are particularly effective at forming soluble complexes because they remain dissolved across the full range of soil pH. In some cases, these complexes may increase micronutrient mobility and transport within the soil solution. This mechanism has been well documented in soil chemistry research and may explain some responses observed in systems where micronutrient availability is limited.
Effects on Plant Physiology
In addition to soil chemical interactions, humic substances may influence plant growth through physiological mechanisms occurring in the rhizosphere. Several studies have shown that humic substances can stimulate root development, including increases in root elongation, lateral root formation, and root hair production (Nardi et al., 2002; Canellas and Olivares, 2014).
Research suggests that these responses may involve interactions with plant hormonal pathways and membrane transport processes. Humic substances have been shown to activate plasma membrane H⁺-ATPase enzymes, which are involved in proton pumping and nutrient uptake across root membranes (Canellas et al., 2002; Trevisan et al., 2010). Activation of these transport systems can enhance nutrient absorption and influence root architecture.
These physiological effects appear to occur primarily at the root–soil interface, where dissolved organic molecules interact directly with plant tissues. As a result, the responses observed in plant growth experiments are often attributed to rhizosphere signaling processes rather than large changes in bulk soil fertility.
Microbial Responses to Humic and Fulvic Compounds
Soil microorganisms respond strongly to carbon availability, and different carbon sources can produce very different microbial responses. Simple carbohydrates such as glucose and sucrose are readily metabolized by soil microbes and therefore produce rapid increases in microbial respiration and biomass. Humic substances, in contrast, consist of chemically complex and partially oxidized organic compounds that decompose much more slowly (Lehmann and Kleber, 2015).
Experimental studies comparing carbon sources consistently show that microbial respiration increases dramatically when simple sugars are added to soil, whereas humic substances produce smaller responses (Blagodatskaya and Kuzyakov, 2008). This difference reflects the relative degradability of these compounds as microbial energy sources.
Carbon Inputs from Humic Products Compared with Natural Soil Carbon
Soil microbial activity is largely driven by carbon supplied from plants through root exudation, residue decomposition, and organic matter turnover. The carbon pools already present in soil are therefore important for understanding the potential influence of humic product additions. A soil containing one percent organic matter holds approximately 11,600 pounds of carbon per acre (Brady and Weil, 2016).
Research on plant–soil carbon cycling indicates that living roots release significant quantities of organic carbon into soil each growing season through root exudation and rhizodeposition (Kuzyakov and Domanski, 2000). These plant-derived carbon inputs commonly amount to hundreds of pounds of carbon per acre and serve as a major energy source for soil microbial communities. Viewed in this context, humic product applications represent extremely small additions to the soil carbon pool. Consequently, microbial stimulation in agricultural soils is dominated by carbon inputs from plant residues and root exudates rather than by small additions of humic materials.
Building Organic Matter in the Central Plains
Increasing soil OM in the central Great Plains is achievable, but the magnitude of change is governed primarily by carbon inputs and water availability rather than any single management practice. Systems that combine no-till, increased residue return, diversified crop rotations, and where feasible cover crops or manure inputs are the most effective because they simultaneously increase carbon inputs and reduce decomposition losses (Lyon et al., 2007; Mikha et al., 2013; Nielsen et al., 2016). In semi-arid systems, realistic rates of OM increase are modest: over a 5-year period, changes are often small, approximately +0.05 to 0.1% OM, but significant in relation to the system which is often at total OM levels between 0.7 and 1.25 prior to establishment of conservation practices. The increase is confined to the top inch of the soil surface (Mikha et al., 2013; Saha et al., 2024). Mechanistically, these gains occur through greater residue and root-derived carbon inputs, reduced soil disturbance which slows microbial oxidation, and improved aggregation that physically protects organic matter from decomposition (Six et al., 2002; Lehmann and Kleber, 2015). However, as emphasized throughout this discussion, the scale of change is small relative to the large existing organic matter pool, and meaningful increases require long-term, system-level management focused on maximizing biomass production rather than relying on small external carbon additions such as commercial products.
Take-Home Points
- Humic and fulvic acids can retain cations, chelate micronutrients, and influence plant and microbial processes.
- Typical application rates are small relative to existing soil organic matter, so whole-soil impacts are limited.
- Most observed effects are localized in the rhizosphere, not broad changes in soil fertility.
- Evaluating both mechanism and scale is key to understanding their role in nutrient management.
References
Blagodatskaya, E., & Kuzyakov, Y. (2008). Mechanisms of real and apparent priming effects and their dependence on soil microbial biomass and community structure. Biology and Fertility of Soils, 45(2), 115–131.
Brady, N. C., & Weil, R. R. (2016). The nature and properties of soils (15th ed.). Pearson.
Canellas, L. P., Olivares, F. L., Okorokova-Façanha, A. L., & Façanha, A. R. (2002). Humic acids isolated from earthworm compost enhance root elongation and lateral root emergence in maize. Plant Physiology, 130(4), 1951–1957.
Canellas, L. P., & Olivares, F. L. (2014). Physiological responses to humic substances as plant growth promoters. Chemical and Biological Technologies in Agriculture, 1, 3.
Guimarães, D. V., Gonzaga, M. I. S., Silva, T. O., Silva, T. L., Dias, N. S., & Matias, M. I. S. (2013). Soil organic matter pools and carbon fractions in soil under different land uses. Soil and Tillage Research, 126, 177–182.
Kuzyakov, Y., & Domanski, G. (2000). Carbon input by plants into the soil: Review. Journal of Plant Nutrition and Soil Science, 163(4), 421–431.
Lehmann, J., & Kleber, M. (2015). The contentious nature of soil organic matter. Nature, 528(7580), 60–68.
Lovley, D. R., Coates, J. D., Blunt-Harris, E. L., Phillips, E. J. P., & Woodward, J. C. (1996). Humic substances as electron acceptors for microbial respiration. Nature, 382, 445–448.
Lyon, D. J., Stroup, W. W., & Brown, R. E. (2007). Crop production and soil water storage in long-term winter wheat–fallow tillage experiments. Soil and Tillage Research, 94(2), 387–397.
Mikha, M. M., Vigil, M. F., Benjamin, J. G., & Sauer, T. J. (2013). Cropping system influences on soil carbon and nitrogen stocks in the Central Great Plains. Soil Science Society of America Journal, 77(2), 702–710.
Nardi, S., Pizzeghello, D., Muscolo, A., & Vianello, A. (2002). Physiological effects of humic substances on higher plants. Soil Biology and Biochemistry, 34(11), 1527–1536.
Nielsen, D. C., Lyon, D. J., Hergert, G. W., Higgins, R. K., Calderón, F. J., & Vigil, M. F. (2016). Cover crop mixtures do not use water differently than single-species plantings. Agronomy Journal, 108(3), 1025–1038.
Saha, D., Kukal, S. S., & Bawa, S. S. (2024). Long-term impacts of conservation agriculture practices on soil organic carbon and aggregation. Soil Science Society of America Journal.
Six, J., Conant, R. T., Paul, E. A., & Paustian, K. (2002). Stabilization mechanisms of soil organic matter: Implications for C saturation of soils. Plant and Soil, 241(2), 155–176.
Stevenson, F. J. (1994). Humus chemistry: Genesis, composition, reactions (2nd ed.). Wiley.
Tan, K. H. (2014). Humic matter in soil and the environment. CRC Press.
Trevisan, S., Francioso, O., Quaggiotti, S., & Nardi, S. (2010). Humic substances biological activity at the plant–soil interface. Plant Signaling & Behavior, 5(6), 635–643.
For any questions or commments please feel free to reach out to Brian Anrall, b.arnall@okstate.edu
Small Pest, Big Problems: Wheat Curl Mites and Wheat Streak Mosaic Virus Detected in Oklahoma
Ashleigh Faris, Cropping Systems Entomologist, IPM Coordinator
Meriem Aoun, Wheat Pathologist
Department of Entomology & Plant Pathology,
Oklahoma State University
Wheat Curl Mite (WCM) activity has been confirmed in Washita County, located in western Oklahoma. While the mites themselves are difficult to see, they can have a considerable impact on wheat health, primarily due to their role as vectors for several viral diseases such as wheat streak mosaic virus (WSMV). The Plant Disease and Insect Diagnostic Laboratory (PDIDL) has confirmed WSMV in the sample where WCM were detected in Washita County. This week, the PDIDL has also confirmed infection by WSMV in Blaine County (Canton, OK), McCurtain County (Garvin, OK), and Cleveland County (Noble, OK).
Identification
The Wheat Curl Mite is nearly invisible to the naked eye. At approximately 1/100 of an inch long, these pests require a 10x – 20x hand lens for proper identification.
- Appearance: They are white or cream-colored, cigar-shaped (cylindrical), and possess only four legs located near the head (Figure 1).
- Behavior: They are typically found in the protected areas of the plant, such as developing, youngest leaves or the furrows of the leaf surface. As the leaf unfurls, the mites migrate to the next emerging leaf.
Figure 1. Wheat curl mites and eggs on a wheat leaf (A, B), and mites on a maturing wheat kernel (C). Images courtesy G. Bauchan and R. Ochoa, USDA-ARS.
Biology and Life Cycle
Understanding the WCM life cycle is critical for preventative management:
- Rapid Reproduction: Under optimal temperatures (75° – 85°F), a WCM can complete its life cycle in 7 to 10 days. This allows populations to explode rapidly during warm autumns or springs.
- Dispersal: WCMs cannot fly; they rely entirely on wind currents to move from plant to plant or field to field. They crawl to the tips of leaves and hitchhike on the wind.
- Survival (The Green Bridge): WCMs are obligate parasites, meaning they require living green tissue to survive and reproduce. They persist through the summer on volunteer wheat and various perennial or annual grasses. This is known as the green bridge. If this bridge is not broken, mites move into the newly planted crop in the fall.
Damage and Virus Transmission
WCMs cause two types of damage:
- Direct Feeding: Mites suck sap from the leaf cells. This causes the edges of the leaf to roll inward (the curl part of WCM) (Figure 2). This curling provides a protected microclimate for the mites to reproduce. Heavy infestations can cause stunting and a slowed appearance in growth.
- Viral Vector (Primary Concern): The WCM is the sole vector for Wheat Streak Mosaic Virus (WSMV), High Plains Wheat Mosaic Virus (HPWMoV), and Triticum Mosaic Virus (TriMV).
- Symptoms: Infected plants show yellowing, mottled or streaked leaves, and severe stunting (Figures 3 & 4).
- Impact: If infection occurs in the fall, yield loss can be up to 100%. Spring infections are generally less damaging.
Scouting Techniques
Because the mites are so small, scouting focuses on leaf symptoms and having a hand lens:
- Check your Fields: Examine the youngest leaves of the wheat plant. Look for the characteristic inward rolling of the leaf edges (Figure 2).
- Use Magnification: Slowly unroll a suspect leaf and use a hand lens to look for tiny, white, slow-moving specks in the leaf furrows.
- Pattern of Infestation: Wind-dispersed mite infestations often start at the edge of a field (particularly edges adjacent to volunteer wheat or CRP land) and move inward in the direction of prevailing winds. Areas with infestations may show signs of yellowing and appear as patches distributed at random across the field (Figure 4).
Figure 2. Infestation of wheat curl mites on wheat results in tightly curled leaves and entrapment of subsequent leaves within the curl (A). After full leaf emergence, a tight curl at the leaf edge remains (B). Images courtesy of UNL Extension.
Figure 3. Wheat streak mosaic virus (WSMV) symptoms includeyellowing, mottled or streaked leaves. Image courtesy of Meriem Aoun, Oklahoma State University.
Figure 4. Plants at field margins, neighboring a wheat curl mite source, are the first to become infected with viruses of the Wheat Streak Mosaic Virus (WSMV) complex and develop symptoms, such as yellowing and streaking. Notice the gradient in color from the field edge (left) toward the center of the wheat field. Image courtesy of UNL Extension.
Management Recommendations
Currently, there are no effective rescue chemical treatments for WCM once symptoms appear in the field. Miticides generally do not reach the mites hidden inside the curled leaves. Management must be proactive:
- Manage volunteer wheat and grassy weeds: This is the most effective management tool to break the green bridge. Ensure all volunteer wheat and grassy weeds are completely dead (via tillage or herbicide) at least two weeks prior to planting the new crop. WCMs will starve within days without a living host.
- Delayed Planting: Planting wheat later in the fall reduces the window of time that mites must migrate into the crop and slows their reproduction rate as temperatures drop.
- Variety Selection: Some wheat varieties offer resistance or tolerance to WCM or WSMV. Consult the latest OSU variety trial data to select adapted varieties for north-central Oklahoma that carry these traits. Currently, Breakthrough is the most resistant OSU variety, which carries the WSMV resistance gene, Wsm1.
Corn Hybrids’ Yield Response to Limited Well Capacities in the Central High Plains
Macie McPeak: M.S in Irrigation and Water Management
Sumit Sharma : Extension Specialist for High Plains Irrigation and Water Management
Background
The Central High Plains, which include the Oklahoma Panhandle, Southwest Kansas, Southeast Colorado, and Northern Texas Panhandle, is a heavily farmed semi-arid region that depends on the Ogallala Aquifer for irrigation to ensure stable crop yields. However, the continuous decline of the Ogallala Aquifer has resulted in increased need for irrigation strategies that conserve water while maintaining crop profitability. Corn remains the most water consuming crop with highest productivity per unit of irrigation applied, and strong economic returns in the Central High Plains region. However, corn is also the most sensitive to water stress among all the existing cropping systems (including sorghum, cotton, and sunflower, soybeans and wheat). Declining water table has reduced the well capacities in many areas in the region, which cannot meet crop water demand, making it a growing challenge for corn production. Therefore, there is a need for research in irrigation strategies and agronomic choices such as drought tolerant hybrids, seeding rate, planting date, and hybrid maturity for sustainable and profitable corn production with reduced well capacities in the region. This blog discusses the yield response of different corn hybrids to limited well capacities in the Oklahoma Panhandle area of the Central High Plains.
Limited well capacities only meet partial crop water demand, which in general leads to yield declines especially in high water demanding crops such as corn. Several previous studies suggest that crop productivity does not significantly decrease as long as irrigation is maintained at approximately 75–80% of full evapotranspiration (ET) replacement (Su et al., 2022; Klocke et al., 2007; Zhao et al., 2019). However, when irrigation levels are more restricted, such as under reduced well capacities, there can be substantial yield losses and diminished economic returns. The magnitude of yield reduction varies with region, hybrids, and growth stage at which water stress occurred. For example, in the Central High Plains the corn ET demand is highest in Texas Panhandle and decreases as we move north towards Nebraska. Zhao et al. (2019) found that applying 75% ET in the Texas Panhandle produced corn yields equivalent to full irrigation, whereas reducing irrigation to 50% caused significant yield reductions. Similarly, Klocke et al. (2007) reported that limited irrigation at roughly 50% of full ET replacement in Nebraska achieved 80–90% of fully irrigated yields across multiple crop rotations. Therefore, the irrigation strategies which work in one region may not work the same way in other regions with different crop water demand and must be tested for the region-specific climatic conditions.
The current study was conducted in 2025 at the Oklahoma Panhandle Research and Extension Center in Goodwell, OK. Four Pioneer brand corn hybrids including P13777 (113 day maturity), P10625 (110 day maturity), P05810 (105 day maturity), and P14346 (114 days maturity) were planted at 22,000 and 28,000 seeds per acre. The hybrids were irrigated with a center pivot fitted with variable rate irrigation system at 200, 300, 400, and 500 GPM well capacities. The well capacities were simulated by adjusting the frequency of irrigation events.
Results & Discussion
The crop received 12.1 inches of rain from planting until physiological maturity, while total rainfall from April till September was over 15 inches. Manual probing of the field showed near 4 feet soil profile at the time of planting which can hold up to 2 inches of plant available water per foot. The well capacities 200, 300, 400, and 500 GPM treatments received 7.4, 8.9, 10.8, and 12.0 inches of irrigation, respectively. The data showed no significant effect of population on corn yield across hybrids for any well capacity. However, the hybrids showed significant interaction with well capacities, which indicated that hybrid yield response varied at different capacities (Figure 1). In general, the average yield declined from longest maturity to shortest maturity hybrids irrespective of the well capacity, but was only statistically significant at for 200 GPM (Figure1). At this irrigation level, the shortest maturity hybrid P05081 yielded significantly lower yield than longest maturity hybrid P14364, while P13777 and P10625 were not different from either of these two hybrids.
Although there was no statistical difference among the hybrids at 500, 400, and 300 GPM, when compared across well capacities, yield reductions were most pronounced at the 200 and 300 GPM irrigation levels for each individual hybrid, indicating that irrigation capacity was the primary yield limiting factor under restricted water availability (Figure 2). While the exact causes of this abrupt decline are not yet understood, as mentioned in the beginning of this blog, previous literature has suggested that severe yield decline in corn can be expected when irrigation is reduced to 60% ET replacement in the study region. Both 300 and 200 GPM well capacities met 60 and 65% crop ET demand, while 400 and 500 GPM met 71 and75% crop ET demand, respectively. More data will be needed to ascertain these threshold levels of well capacities for corn production in this region.
All the hybrids showed a positive yield response to Irrigation+Rain with different yield gains per inch of water applied (Figure 3). Hybrid P10625 registered highest yield gain of 14.1 bushel per inch of water applied, followed by P13777 (12.0 bu), P05081 (11.9 bu), and P14364 (11.6 bu). The stronger coefficient of regression (>80%) for two short maturity varieties indicated that irrigation was stronger yield limitation factor for these hybrids, in comparison to 114 and 113-day maturity hybrids for irrigation explained on 67 and 69% variability, respectively. This suggests that besides irrigation there might be other factors which could contribute to filling the yield gaps for given irrigation levels in longer maturity hybrids.
Planting population did not significantly affect grain yield across irrigation capacities. When pooled across the hybrids for individual planting populations, 28,000 seeding rates resulted in gain of 0.1, 2.6, 5, and 12 bushels per acre for 200, 300, 400, and 500 GPM, respectively. This indicates that higher planting populations at well capacities of 400 or above should be considered, while reducing population at 300 GPM or lower might be more cost-effective option.
Take Home
- Irrigation capacity remains the primary determinant of yield potential under limited well capacities in the Central High Plains.
- Pre-irrigation and recharging the soil profiles will be critical to support crop water demand for limited well capacities.
- Short maturity hybrids appeared to have consistently lower average yield and more vulnerable for yield losses at limited irrigation. However, one must consider that the growing conditions were more conducive for corn production in 2025 which generally favor long maturity hybrids. Therefore, long-term data will be required to assess the performance of short maturity hybrids during inclement growing seasons.
- Even though population didn’t significantly influence the grain yield. The 28,000 seeding rates overall had higher average yield at 400 and 500 GPM. Therefore, producers should consider the higher population at these well capacities or more.
- Overall, irrigation is the most important factor for yields, but there is a need for long-term agronomic data on hybrid maturity and population along with economic analysis to ascertain these findings.
Thoughts from an Agronomist- 1 Management of the Primordia
Josh Lofton, Cropping Systems Specialist
Many crop management recommendations emphasize actions that must be taken well before a crop reaches what we often call “critical growth stages.” Management this early can seem counterintuitive when the crop still looks small, healthy, or unchanged aboveground. However, much of a crop’s yield potential is determined early in the season at a level we cannot see in the field. Long before flowers, tassels, or heads (or any reproductive structure) appear, the plant is already making developmental decisions that shape its final yield potential. Understanding this “behind the scenes” process helps explain why timely, early-season management is often more effective than trying to correct problems later.
At the center of this process is the shoot apical meristem, commonly referred to as the growing point. This tissue produces leaf and reproductive primordia, which are the earliest developmental stages of future everything in the plant. These primordia form well before the corresponding plant parts are visible. Once these structures initiate—or if they fail to begin due to stress—the outcome is permanent. The plant cannot later in the season go back and recreate leaf number, leaf size, or reproductive capacity. As a result, early environmental conditions and management decisions play a disproportionate role in determining yield potential.
Corn is a good example of how early development influences final yield. By the time corn reaches the V4 growth stage, the plant only has four visible leaves with collars, yet internally it is far more advanced. Most of the total leaf primordia that will eventually form the full canopy have already begun, and the potential size of the ear is starting to be established. During this stage, the growing point is still below the soil surface and somewhat protected from some stressors but highly susceptible to others. Nitrogen deficiency, cold temperatures, moisture stress, compaction, or herbicide injury at or before V4 can reduce leaf number and limit leaf expansion. Even if growing conditions improve later, the plant cannot replace leaf primordia that were never formed, which reduces its ability to intercept sunlight and support high yields.
As corn approaches tasseling (VT), the crop enters a stage that is visually and physiologically important. Pollination, fertilization, and early kernel development occur at this time, and stress can have a critical impact on kernel set. However, by VT, the plant has already completed leaf formation, and much of the ear size potential has already been determined several growth stages earlier. Management at VT is therefore focused on protecting yield rather than creating it. Late-season nutrient applications may improve plant appearance or maintain green leaf area, but they cannot increase leaf number or rebuild ear potential lost due to early-season stress. This distinction helps explain why some late inputs show limited yield response even when the crop looks responsive.
Grain sorghum provides another clear example of why early management is emphasized. Although sorghum often grows slowly early in the season and may appear unimportant during the first few weeks after emergence, the first 30 days are among the most critical periods in its development. During this time, the growing point is actively producing leaf primordia and transitioning from vegetative growth toward reproductive development. Head size potential is primarily established during this early window, and the plant’s capacity to support tillers is influenced by early nutrient availability and moisture conditions. Stress from nitrogen deficiency, drought, weed competition, or restricted rooting during the first 30 days can reduce head size and kernel number long before visible symptoms appear.
Once sorghum reaches later vegetative and reproductive stages, much like corn at VT, management shifts from building yield potential to protecting what has already been determined. Improving conditions later in the season can help maintain plant health and grain fill, but it cannot fully compensate for early limitations imposed at the primordial level. This is why early fertility placement, timely weed control, and moisture conservation are consistently emphasized in sorghum production systems.
Across crops, a typical pattern emerges: the growth stages we observe in the field often reflect decisions the plant made weeks earlier. When agronomists stress early-season management, they are responding to plant biology rather than simply following tradition. By the time visible “critical stages” arrive, the plant has already established many of the components that define yield potential.
The key takeaway is that effective crop management must be proactive rather than reactive. Early-season decisions support the crop while it is still determining how many leaves it can produce, how large its reproductive structures can become, and how much yield it can ultimately support. Waiting until stress becomes visible often means responding after the plant has already adjusted its potential downward. Recognizing what is happening at the primordial level helps explain why management ahead of critical stages consistently delivers the greatest return, even when the crop appears small and unaffected aboveground.
For questions or comments reach out to Dr. Josh Lofton
josh.lofton@okstate.edu
Double Crop Options After Wheat (KSU Edition)
Stolen from the KSU e-Update June 5th 2025.
Double cropping after wheat harvest can be a high-risk venture for grain crops. The remaining growing season is relatively short. Hot and/or dry conditions in July and August may cause problems with germination, emergence, seed set, or grain fill. Ample soil moisture this year can aid in establishing a successful crop after wheat harvest. Double-cropping forages after wheat works well even in drier regions of the state.
The most common double crop grain options are soybean, sorghum, and sunflower. Other possibilities include summer annual forages and specialized crops such as proso millet or other short-season summer crops, even corn. Cover crops are also an option for planting after wheat (see the companion eUpdate article “Cover crops grown post-wheat for forage”).
Be aware of herbicide carryover potential
One major planting consideration after wheat is the potential for herbicide carryover. Many herbicides applied to wheat are Group 2 herbicides in the sulfonylurea family with the potential to remain in the soil after harvest. If a herbicide such as chlorsulfuron (Glean, Finesse, others) or metsulfuron (Ally) has been used, then the most tolerant double crop will be sulfonylurea-resistant varieties of soybean (STS, SR, Bolt) or other crops. When choosing to use herbicide-resistant varieties, be sure to match the resistance trait with the specific herbicide (not only the herbicide group) that you used. This is especially true when looking at sunflowers as a double crop. There are sunflowers with the Clearfield trait, which allows Beyond herbicide applications, and ExpressSun sunflowers, which allow an application of Express herbicide. While both of these herbicides are Group 2 (ALS-inhibiting herbicides), the Clearfield trait and ExpressSun are not interchangeable, and plant damage can result from other Group 2 herbicides.
Less information is available regarding the herbicide carryover potential of wheat herbicides to cover crops. There is little or no mention of rotational restrictions for specific cover crops on the labels of most herbicides. However, this does not mean there are no restrictions. Generally, there will be a statement that indicates “no other crops” should be planted for a specified amount of time, or that a bioassay must be conducted prior to planting the crop.
Burndown of summer annual weeds present at planting is essential for successful double-cropping. Assuming glyphosate-resistant kochia and pigweeds are present, combinations of glyphosate with products such as saflufenacil (Sharpen) or tiafenacil (Reviton), or alternative treatments such as paraquat may be required. Dicamba or 2,4-D may also be considered if the soybean varieties with appropriate herbicide resistance traits are planted. In addition, residual herbicides for the double crop should be applied at this time.
Management, production costs, and yield outlooks for double crop options are discussed below.
Soybeans
Soybeans are likely the most commonly used crop for double cropping, especially in central and eastern Kansas (Figure 1). With glyphosate-resistant varieties, often the only production cost for planting double crop soybeans was the seed, an application of glyphosate, and the fuel and equipment costs associated with planting, spraying, and harvesting. However, the spread of herbicide-resistant weeds means additional herbicides will be required to achieve acceptable control and minimize the risk of further development of resistant weeds.
Weed control. The weed control cost cannot really be counted against the soybeans, since that cost should occur whether or not a soybean crop is present. In fact, having soybeans on the field may reduce herbicide costs compared to leaving the field fallow. Still, it is recommended to apply a pre-emergence residual herbicide before or at planting time. Later in the summer, a healthy soybean canopy may suppress weeds enough that a late-summer post-emergence application may not be needed.
Variety selection for double cropping is important. Soybeans flower in response to a combination of temperature and day length, so shifting to an earlier-maturing variety when planting late in a double crop situation will result in very short plants with pods that are close to the ground. Planting a variety with the same or perhaps even slightly later maturity rating (compared to soybeans planted at a typical planting date) will allow the plant to develop a larger canopy before flowering. Planting a variety that is too much later in maturity, however, increases the risk that the beans may not mature before frost, especially if long periods of drought slow growth. The goal is to maximize the length of the growing season of the crop, so prompt planting after wheat harvest time is critical. The earlier you can plant, the higher the yield potential of the crop if moisture is not a limiting factor.
Fertilizer considerations. Adding some nitrogen (N) to double-crop soybeans may be beneficial if the previous wheat yield was high and the soil N was depleted. A soil test before wheat harvest for N levels is recommended. Use no more than 30 lbs/acre of N. It would be ideal to knife-in the fertilizer. If that is not possible, banding it on the soil surface would be acceptable. Do not apply N in the furrow with soybean seed as severe stand loss can occur.
Seeding rates and row spacing. Seeding rate can be slightly increased if soybeans are planted too late in order to increase canopy development. Narrow row spacing (15-inch or less) has often resulted in a yield advantage compared to 30-inch rows in late plantings. Soybeans planted in narrow rows will canopy over more quickly than in wide rows, which is important when the length of the growing season is shortened. Narrow rows also offer the benefits of increasing early-season light capture, suppressing weeds, and reducing erosion. On the other hand, the advantage of planting in wide rows is that the bottom pods will usually be slightly higher off the soil surface to aid harvest. The other consideration is planting equipment. Often, no-till planters will handle wheat residue better and place seeds more precisely than drills, although the difference has narrowed in recent years.
What are typical yield expectations for double-crop soybeans? It varies considerably depending on moisture and temperature, but yields are usually several bushels less than full-season soybeans. A long-term average of 20 bushels per acre is often mentioned when discussing double-crop soybeans in central and northeast Kansas. Rainfall amount and distribution can cause a wide variation in yields from year to year. Double-crop soybean yields typically are much better as you move farther southeast in Kansas, often ranging from 20 to 40 bushels per acre.
A recent publication explores the potential yield of double-crop soybeans relative to full-season yield (Figure 2) and the most limiting factors affecting the yields for double-crop soybeans. The link to this article is: https://bookstore.ksre.ksu.edu/pubs/MF3461.pdf.
Grain Sorghum
Grain sorghum is another double crop option. Unlike soybeans, sorghum hybrids for double cropping should be earlier maturing hybrids. Sorghum development is primarily driven by the accumulation of heat units, and the double crop growing season is too short to allow medium-late or late hybrids to mature before the first frost in most of Kansas.
Seeding rates and row spacing. Late-planted sorghum likely will not tiller as much as early plantings and can benefit from slightly higher seeding rates than would be used for sorghum planted at an earlier date. Narrow row spacing is advised, especially if the outlook for rainfall is good.
Fertilizer considerations. A key component for the estimation of N application rates is the yield potential. This will largely determine the N needs. It is also important to consider potential residual N from the wheat crop. This can be particularly important when wheat yields are lower than expected. In that situation, additional available N may be present in the soil. Assess the amount of profile N by taking soil samples at a depth of 24 inches and submitting them for analysis at a soil testing laboratory.
Double crop sorghum planted into average or greater-than-average amounts of wheat residue can result in a challenging amount of residue to deal with when planting next year’s crop. Nitrogen fertilizer can be tied up by wheat residue, so use application methods to minimize tie-up, such as knifing into the soil below the residue.
Weed control. Weed control can be important in double-crop sorghum. Warm-season annual grasses, such as crabgrass, can reduce double-crop sorghum yields. Using a chloroacetamide-and-atrazine pre-emergence product may be key to successful double-crop sorghum production. Herbicide-resistant grain sorghum varieties will allow the use of imazamox (Imiflex in igrowth sorghums) or quizalofop (FirstAct in DoubleTeam grain sorghum) that can control summer annual grasses.
No-till studies at Hesston documented 4-year average double crop sorghum yields of 75 bushels per acre compared to about 90 bushels per acre for full-season sorghum. A different 10-year study that did not have double crop planting but did compare early- and late-planting dates averaged 73 bushels per acre for May planting vs. 68 bushels per acre for June planting.
Sunflowers
Sunflowers can be a successful double crop option anywhere in the state, provided there is enough moisture at planting time to get a stand. Sunflowers need more moisture than any other crop to germinate and emerge because of the large seed. Therefore, stand establishment is important. Planting immediately after wheat harvest on a limited irrigation field can be a good fit to help with stand establishment.
Seeding rates and hybrid selection. When double-cropping sunflowers, producers should use similar seeding rates to what is typical for the area for full-season sunflowers. While full-season sunflowers can be successful in double-crop production, utilizing shorter-season hybrids can increase the likelihood of the sunflowers blooming and maturing before a killing frost.
Weed control. First, it is important to check the herbicide applications on the wheat. The rotation restriction to sunflowers after several commonly used wheat herbicides is 22-24 months.
Weed control can be an issue with double-crop sunflowers since herbicide options are limited, especially post-emergence. Thus, controlling weeds prior to sunflower planting is critical and may be complicated pre-plant restrictions for some herbicides. Planting Clearfield or ExpressSun sunflowers will provide additional post-emergence herbicide options, but ALS-resistant kochia and pigweeds still won’t be controlled. Imazamox (Beyond in Clearfield sunflower) has activity on small annual grasses as well as many broadleaf weeds, if they are not ALS-resistant.
Summer annual forages
With mid-July plantings, and where herbicide carryover issues are not a concern, summer annual sorghum-type forages are also a good double crop option. A study planted July 21, 2008 near Holton, when summer rainfall was very favorable, provided yields of 2.5 to 3 tons dry matter/acre for hybrid pearl millet and sudangrass at the low end to 4 to 5 tons dry matter/acre for forage sorghum, BMR forage sorghum, photoperiod sensitive forage sorghum, and sorghum x sudangrass hybrids. Earlier plantings may produce even more tonnage, as long as there is adequate August rainfall.
One challenge with late-planted summer annual forages is getting them to dry down when harvest is delayed until mid- to late-September. Wrapping bales or bagging to make silage are good ways to deal with the higher moisture forage this late in the year.
Corn
Is double-crop corn a viable option? Corn is typically not recommended for late June or July plantings because yield is usually substantially less than when planted earlier.
Typically, mid-July planted corn struggles during pollination and seldom receives sufficient heat units to fill grain before frost. Very short-season corn hybrids (80 to 95 RM) have the greatest chance of maturing before frost in double crop plantings, but generally have less yield potential when compared to hybrids of 100 RM or more used for full-season plantings. Short-season hybrids often set the ear fairly close to the ground, increasing the harvest difficulty. Glyphosate-resistant hybrids will make weed control easier with double crop corn, but problems remain present with late-emerging summer weeds such as pigweeds, velvetleaf, and large crabgrass. Keep in mind, corn is very susceptible to carryover of most residual ALS herbicides used in wheat.
Considerations for altering seeding rates and variety/hybrid maturity for the crops discussed above are summarized in Table 1.
Table 1. Seeding rate and variety/hybrid relative maturity considerations for double crops compared to full-season.
| Crop | Seeding rate | Relative maturity |
| ???????? Difference between double crop and full-season ???????? | ||
| Soybean | Increase | No change or longer |
| Sorghum | Increase | Shorter |
| Sunflower | No change | Shorter |
| Corn | No change | Shorter |
Volunteer wheat control
One of the issues with double cropping that is often overlooked by producers is the potential for volunteer wheat in the crop following wheat. If volunteer wheat emerges and goes uncontrolled, it can cause serious problems for nearby wheat fields in the fall as a host for the wheat streak mosaic complex of viruses [wheat streak mosaic (WSMV), High Plains disease (HPD), and triticum mosaic (TriMV)] that are transmitted by the wheat curl mite (WCM).
Volunteer wheat can generally be controlled fairly well with glyphosate or Group 1 herbicides such as quizalofop (Assure II, others), clethodim (Select Max, others), or sethodydim (Poast Plus, others), but control is reduced during times of drought stress. Atrazine can provide control of volunteer wheat in double-crop corn or sorghum, but control can be erratic depending on rainfall patterns.
For more detailed information about herbicides, see the “2025 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide available online at https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf or check with your local K-State Research and Extension office for a paper copy. The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
To Subscribe to the KSU Agronomy E-Updates follow this link
https://eupdate.agronomy.ksu.edu/index_new_prep.php
Authors contributing to the post
Sarah Lancaster, Weed Management Specialist
slancaster@ksu.edu
John Holman, Cropping Systems Agronomist
jholman@ksu.edu
Logan Simon, Southwest Area Agronomist
lsimon@ksu.edu
Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu
Jeanne Falk Jones, Multi-County Agronomist
jfalkjones@ksu.edu
Nitrogen and Sulfur in Wheat
Brian Arnall, Precision Nutrient Management Specialist
Samson Abiola, PNM Ph.D. Student.
Nitrogen timing in wheat production is not a new topic on this blog, in-fact its the majority. But not often do we dive into the application of sulfur. And as it is top-dressing season I thought it would be a great opportunity to look at summary of a project I have been running since the fall of 2017 which the team has call the Protein Progression Study. The objective was to evaluate the impact of N and S application timings on winter wheat grain yield and protein. With a goal of looking at the ratio of the N split along with the addition of S and late season N and S, in such a way that we could determine BMP for maximizing grain yield and protein.
My work in the past has shown two things consistently, that spring N is better on the average and S responses have been limited to deep sandy soils in wet years. Way back when (2013) on farm response strips showed high residual N at depth and no response to S. https://osunpk.com/2013/06/28/response-to-npks-strips-across-oklahoma/. But there has been a lot of grain grown since that time expectations are that we should/are seeing an increase in S response. In fact Kansas State is seeing more S response, especially in the well drained soils in east half of the state.
Some KSU Sulfur works.
https://www.ksre.k-state.edu/news/stories/2022/04/video-sulfur-deficiency-in-wheat.html
https://eupdate.agronomy.ksu.edu/article/sulfur-deficiency-in-wheat-364-1
Click to access sulphur-in-kansas-plant-soil-and-fertilizer-considerations_MF2264.pdf
So the Protein Progression Project was established in 2017 and where ever we had space we would drop in the study. So in the end across six seasons we had 13 trials spread over five locations. Site-years varied by location: Chickasha (2018-2022), Lake Carl Blackwell (2018-2023), Ballagh (2020), Perkins (2021), and Caldwell (2021).
First lets just dive into the the N application were we looked at 100% pre vs 50-50 split and 25-75 split (Table 2.) Based upon the wealth of previous work https://osunpk.com/2022/08/26/impact-of-nitrogen-timing-2021-22-version/, its not much of a surprise that split application out preformed preplant and that having the majority applied in-season tended to better grain yields and protein values.
This next table is were things get to be un-expected. While the data below is presented by location, we did run each site year by itself. In no one site year did S statistically, or numerically increase yield. As you can see in Table 2 below, the only statistical response was a negative yield response to S. And you can not ignore the trend that numerically, adding S had consistently lower yields. Even more surprising was the same trend was seen in Protein.
One aspect of Protein Progression trials were that while 0-6″ soil test S tended to be low. We would often find pretty high levels of S when we sampled deeper, especially when there was a clay increase with depth. Sulfur tends to be held by the clay in our subsoil. We are also looking at better understanding the relationship between N and S. In fact a review article published in 2010 discussed that the N and S ratio can negative influence crop production when either one of the elements becomes un-balanced. For example we are seeing more often in corn that when N is over applied we can experience yield loss, unless we apply S. Meaning at 200 lbs of N we make 275 BPA, at 300 N lbs we make 250, but 300 N plus 20 S we can make 275 again. Part of the rationale is that excessive N limits S mineralization. On the flip side if S is applied while N is deficient and yield decrease could be experienced. Maybe that is what we are seeing in this date. Either way, this data is why the Precision Nutrient Management program is spending a fair amount of efforts in understanding the N x S relationship in wheat (which we are looking at milling quality also) and corn.
A quick dive into increasing protein with late N applications. At three of the five location GPC was significantly increased with Late N. In most cases the anthesis (flowering) application was the highest with exception of Caldwell. We will have another blog coming out in a month that digs into anthesis applied N at a much deeper level, looking at source, nozzle and droplet sizes.
Looking at this study in a vacuum we can say that it probably best to split apply your N and that in central and northern Ok the addition of S in rainfed wheat doesn’t offer great ROI. If I look at the whole picture of all my work and experience I would offer this. For grain only wheat, the majority if not all N should be applied in-season sometime between green up and two weeks after hollow stem. I have had positive yield responses to S applied top-dress, but it has always been deep sandy soils and wet seasons. I have not have much is any response to S in heavier soil, especially if there is a clay increase in the two feet of profile. So my general S recommendation is 10 lbs in sandy soils and if you show low soil test S in heavier ground and you are trying to push grain yields, then you could consider the addition of S as a potential insurance. That said, I haven’t seen much proof of it.
Take Homes
* Split application of nitrogen resulted in higher grain yields and protein concentrations when compared to 100% preplant.
* Putting on 75% of the total N in-season tended to result in higher grain yields and protein concentrations when compared to 50-50 split.
* Adding 10 lbs of S topdress did not result in any increase in grain yield or protein.
A big Thanks to the collaborators providing on-farm locations for this project. Ballagh Family Farms, Turek Family Farms and Tyler Knight.
Citation. Jamal, A.,*, Y. Moon, M. Abdin. 2010 Review article. Sulphur -a general overview and interaction with nitrogen. AJCS 4(7):523-529 (2010). ISSN:1835-2707.
Any questions or comments feel free to contact me. b.arnall@okstate.edu
Management of soybean inoculum
Josh Lofton, Cropping Systems Specialist
Brian Arnall, Precision Nutrient Management Specialist
Soybean, a legume, can form a symbiotic relationship with Bradyrhizobium japonicum (Kirchner, Buchanan) and create their N to supplement crop demands. However, this relationship depends upon these beneficial microorganisms’ presence and persistence in the soil. This specific strain of microorganisms is not native to Oklahoma and thus must be supplemented using inoculum as a seed treatment. However, the use of inoculums alone does not guarantee a successful relationship. Handling, storage, soil conditions, and other factors can impact the ability of these microorganisms to do their job.
Soybean nitrogen demand is high, with most reports indicating that soybeans need 4.5 to 5.0 pounds of nitrogen per bushel of grain yield. This means that a 30-bushel crop requires between 135 and 150 pounds of nitrogen per acre (in comparison, corn and wheat need only 0.8 or1.6 pounds, respectively). This relationship has been shown to supply an equivalent of 89 lbs of N to the soil. In the previous example, these bacteria could fulfill 50-90% of nitrogen demand, reducing input costs significantly.
However, the bacteria associated with soybean inoculum are living organisms. Therefore, the conditions they experience before being applied to the seed and after treatment (including both before and following planting) can significantly impact their relationship with the soybean plant and, thus, their ability to provide N to the plant. By introducing a high concentration of bacteria near the seed and emerging root, this symbiotic relationship is more likely to be established quickly.
The importance of using inoculum is often debated in Oklahoma, particularly given the fluctuating prices of commodities and inputs. A recent assessment of various soybean-producing areas throughout the state revealed that most fields experienced advantages from incorporating soybean inoculation (Figure 1).
These benefits can be seen when the inoculum maintains viability until it is planted. It is always recommended that the bacteria be stored in a cool, dark environment before application on the seed. These conditions help preserve the survival of these bacteria outside of the host relationship. An evaluation of soybean inoculant after being stored short-term in different conditions found that in as little as 14 days, viability can decrease when kept in non-climate-controlled conditions (Figure 2). Additionally, viability was further reduced at 21 days when stored at room temperature compared to a refrigerated system
However, conditions colder than this, such as the use of a freezer, can compromise survival as well. Storing inoculum in the freezer forms ice crystals within the living cells and damages the cell membranes, making the microorganisms less likely to be alive upon rethawing. Additional chemicals can be added to increase the viability of long-term storage and sub-freezing temperatures. From an application standpoint, a new product should be purchased if additional storage is needed beyond short-term storage.
An additional question frequently arises: “How often should I inoculate my soybean?” As mentioned, these bacteria are not native to Oklahoma. As a result, they are not well adapted to survive in our environment and must outcompete native populations in the soil. Additionally, periods of hot and dry conditions appear to reduce the bacteria’s ability to survive without a host, the soybean roots. These are conditions we often observe in Oklahoma systems. Therefore, inoculation should be applied with every soybean planting to ensure a sufficient population of these bacteria. These bacteria promote root nodulation and nitrogen fixation in the soil.
Other soil conditions, such as excessively dry or wet soils, high or low pH, and residual nutrients, can also impact the persistence of these microorganisms. Of these, soil pH has the biggest impact on the survival of these bacteria. High pH is less of a concern to Oklahoma production systems; however, soil with lower pH should be remediated. Like many bacterial systems, these bacteria optimally function at a pH range that closely resembles the ideal pH range for most crops. Lowering the soil pH below a critical threshold reduces the viability of the bacteria, hampers N-fixation processes, and diminishes the capacity of both the bacteria and soybean plants to form and maintain this relationship. While applying inoculum to soybean seeds in these adverse soil conditions can provide some advantages (Figure 3), but it often doesn’t increase yields. Therefore, inoculation with corresponding adjustments to soil pH represents the best approach.
While using inoculum is not a new concept, it is important to highlight the benefits it can provide when utilized correctly. The potential to reduce N input costs is attractive, but the effectiveness depends on proper handling, storage, and soil conditions until it can intercept the host. To maximize benefits, inoculum should be stored in a cool, dark environment and utilized in a timely manner. If there is doubt that there are not enough bacteria, an inoculum should be added. Oklahoma’s climate, particularly hot and dry conditions, can limit bacteria survival, reinforcing the need to treat the inoculum until it is in the ground carefully. Additionally, considering the soil environment is important to sustain the population of bacteria until it can inoculate its host. Emphasis on these small details can have a large impact on the plant’s ability to fix nitrogen and optimize productivity throughout the growing season.
TAKE HOMES
* Soybean requires more lbs of N per bushel than most grain crops.
* Soybeans symbiotic relationship with rhizobia can provide the majority of this nitrogen.
* Soybean rhizobia is not native to Oklahoma soils so should be added to first year soybean fields.
* Inoculum should be treated with care to insure proper nodulation.
* Due to Oklahoma’s climate and existing soil conditions rhizobia may not persist from year to year.
Any questions or comments feel free to contact Dr. Lofton or myself
josh.lofton@okstate.edu
b.arnall@okstate.edu
Appreciation of the Oklahoma Soybean Board for their support of this project.
Top-dress Wheat with P and K ??
Brian Arnall, Precision Nutrient Management Extension Specialist
Hunter Lovewell, Past PNM MS student.
Original Blog Name: Managing P and K in a wheat Double-crop Soybean System.
I planned to wait until the soybean yields came in to share the data from this project, but the wheat results are just too interesting this year.
So the trial posed the question, when is the best time to apply the phosphorus (P) and potassium (K) for the soybean crop in a wheat double crop soybean system, if any is needed above what is applied for the wheat crop. We applied the wheat’s P&K at establishment, but the soybeans P&K was applied either at wheat establishment, top-dress wheat timing, or post wheat harvest pre soybean planting. We used the sources of granular triple super phosphate (0-46-0) and potash (0-0-60) for all applications. We hypothesized the wheat crop would not benefit from the soybeans portion of P&K and that the top-dress application timing for the soybeans P&K would result in the greatest soybean yields.
So far, we have six site years with completed cycles with locations at the Eastern Research Station (ERS) near Haskell, Oklahoma, Ballagh Family Research Farm (BF) near Newkirk, Oklahoma, Skagg Family Farm (SF) near Lamont, Oklahoma, and Lake Carl Blackwell Research Farm (LCB) near Perry, Oklahoma. The research was conducted during the 2019-2020 growing season and the 2020-2021 growing season. For the 2021-2022 cycle we added two more locations one again on the Skagg Family farm and the second on a new cooperator, O’Neil Farms (OF) near Ponca City. For all locations no P or K was applied by the farmers at any point, but they did manage IPM. See location descriptions below.
The first two years of work is written up in Mr. Hunter Lovewell’s thesis titled “EFFECTS OF PHOSPHOROUS AND POTASSIUM APPLICATION TIMING ON A WHEAT DOUBLE-CROP SOYBEAN SYSTEM” which I can share with those interested. To be honest, Hunter had a couple tough seasons. Basically where wheat did well, beans typically failed and where you had good beans the previous wheat had failed. All the same he had some interesting results. What follows is pulled from his conclusions.
“While a significant response to the application of P and K was limited, the results show that there are environments in which the wheat crop can benefit from additional P and K fertilizer applied for the soybean crop. In the case of the soil (SF-SH) with low M3P and an acidic soil pH, the additional P applied during the winter wheat growing season, intended for soybeans, alleviated the aluminum toxicity issues with acidic pH, increasing wheat yields. Beyond the single location with low soil test P and pH no other significant response was found to the addition of and P. This may be explained in that most locations were only marginally deficient P and the majority of the varieties used in the study were considered to have acid soil tolerance. Penn and Arnall (2015) found that cultivars with aluminum tolerance had increased P use efficiency. The BF location showed a significant wheat grain yield response to the K fertilization, but the additional K applied for the soybean crop showed no benefit for the wheat crop. While there was no significant increase in soybean grain yield to the additional K fertilizer observations suggest that the application of K fertilizer for soybeans may be of benefit. As was mentioned before the double-crop system is susceptible to yield-limiting conditions, heat, and moisture, due to the maturity of the crop during the peak summer months. The soybean grain yields achieved in this study were all below the previous five-year yield average for all the locations. The low achieved yields and crop stress may have limited this study’s ability to identify a significant response to the application of fertilizer. “
So, one of the most interesting finding from the first six sites was that topdressing P increased yield of the wheat crop on the soil that had low pH and P. And since the P recs applied were only considering STP values and not soil pH, we had underapplied P for the wheat.
Now moving on to the 2021-22 season. Well as most of the famers know, this season has been a doozy. That said, we were not able to establish the treatments until February 1st. Therefor in the case of the 2021-22 wheat season the first application of P&K was made at top-dress timing and then the second application was made post wheat harvest. So, we are unable to say how a preplant wheat P&K application would have performed. But the wheat grain yield response to P&K was better than I could have ever imagined.
The rain post application (Feb 1st) was marginal but better than other areas in the central/southern Plains. There was about 1” of precipitation in February, almost 3” in March and under 0.2” in April. May rains for the OF site near Burbank aided in allowing the yields to climb, maxed out at 82 bushels per acre, while the SF-Nfld missed out on many of the late rains and yields topped out at 39 bushels.
At both sites there is a clear and distinct response to P fertilizer. Note the N and NK treatments significantly lower than all other treatments. The last column on each figure title NPK is the average of all other treatments that only received the wheats P&K rate and had yet had the soybeans P&K applications.
We were able to statistically analyze the locations together by calculating a relative yield for each location. This is done by dividing the yield of each plot by the yield of the N only treatment, we did this for each replication. We then ran a t-test to look at significant treatment difference, so below any treatments that has the letters above the columns, such as an ab and b, are not statistically different at a 95% level.
The relative yield data was able to confirm that across both locations an application of P in February significantly increased yields at a consistent level of 30-50%. It is interesting that while the NP+K+ treatment almost sorts out as being statistically the highest.
While I am not even close to suggesting that you should delay application of P fertilizer in wheat production, I am a big fan of in-furrow applications, this work does point to opportunities. Such as the ability to return to the field after the wheat is up and apply broadcast P if perhaps you could not at planting. But specifically, the potential for in-season Variable Rate phosphorus based upon crop response, maybe a P-Rich strip. What I can tell you this means is that I have more work to do. First, I need a better understand of when and where this is possible. Then it is time to figure out how to use this to our advantage to more efficiently use P fertilizer.
I do want to reiterate, I am not suggesting to move away from Preplant P nor in-furrow.
Keep an eye out for the soybean data because hopefully we catch a few good rains and find out if the timing of P&K will impact the double crop yields.
I want to send a big Thank you to all the cooperators who have put up with me and my time over years to get this data and the Oklahoma Soybean Board for their continued support of this project.
Feel free to send any questions for comments my way at b.arnall@okstate.edu
In-season N application methods for Sorghum
Raedan Sharry, Ph.D. candidate under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist
The data about to be reported is from the study we have fondly named “Burn Baby Burn”, you will see why soon enough.
Grain Sorghum production continues to be an important component of many growers crop rotations in the Great Plains. However, for many growers who focus primarily on small grains production, equipment restraints may impose limits on in season nitrogen (N) management. When producers are able to delay the application until in-season it helps to ensure that N is available to the crop at the time of increased uptake during the reproductive stages of the crops life. Producers often have access to equipment and technologies that may be used to take advantage of improved N application timing, but may worry about the negative effects that nitrogen can have if the fertilizer is inadvertently applied to plant material. An experiment was initiated in Central Oklahoma to evaluate the yield response of grain sorghum to in-season nitrogen application methods.
Trials were placed at Lake Carl Blackwell near Stillwater, Perkins and Chickasha Oklahoma and included 9 in-season fertilization methods and a 0 nitrogen control. Treatments are listed in Table 1 below.
In total 120 lbs of N was applied to all treatments receiving in-season applications. 60 lbs was applied at planting to all treatments including the “Zero N Control”. The remaining 60 lbs. of N was applied according to application method in-season. The urea was applied by hand and the liquid treatments a push cart with adjustable boom height (Figure 1) was used to apply the UAN. Applications were made mid day at V8 growth stage. The temperature at the time of all applications was about 90 F and humidity below 75%. Nozzle position for 30″ and 60″ was set for between rows.
At two of the three locations (Stillwater and Perkins) the addition of 60 lbs. of N in-season increased yield above the control treatment. At the Stillwater (Lake Carl Blackwell) location there were no statistical differences (α=0.05) between in-season fertilized treatments except the T-Bar 20” treatment (Figure 2). The Perkins location (Figure 3) provided a similar result in which again there was no statistical difference between fertilized treatments, excluding the T-Bar 20” treatment.
The Chickasha location differed in that additional in-season nitrogen did not improve yield (Figure 4). While we want a response to applied N, in the case it allows use to solely evaluate the impact of burn associated with N application. The T-bar 20” treatment statistically negatively impacted grain yield and the FlatFan-20″ did at α=0.10, which means we are only 90% confident the yield lose was due to treatment. This response has been consistent across all three locations, on average decreasing yield approximately 21 bu/ac relative to the individual site grain yield average.
Even though it was mentioned for Chickasha, it is also important to note that while it was not statistically significant (α=0.05) the FF- 20” treatment (Flat Fan nozzles above canopy on 20” spacing) trended towards decreasing yields at all 3 locations and is likely detrimental to crop performance. At all locations substantial damage to leaf material was observed, similar to that pictured in Figure 5 below. Several of the treatments damaged leaf material on the plant through burn injury, but most were not negatively impactful on grain yield in the 2021 growing season. Grain sorghum yield did not benefit from moving the application point below the canopy using drop attachments, nor did adjusting nozzle spacing from 30 to 60”. Source was not a significant factor impacting grain yield regardless of it application method.
The observations from this study show that many of the in-season nitrogen application methods that are available to growers will not negatively impact yield. This however does not apply to tools such as the T-Bar. Similar tools that concentrate large amounts of N to leaf material are also likely to produce similar results. It is important to note that the T-bar was used on 20” spacings and not tested otherwise. Moving the spacing of the T-bar may lead to different results.
Growers who are looking to move N applications in their grain sorghum crop to in-season to capture the benefits associated will likely be able to with equipment that is already available to them. While leaf damage may be observed under sub-optimal application methods, damage is unlikely to contribute to significant yield loss. However, growers should keep in mind that environmental conditions may have a significant impact on the results seen from these types of application as growers should always look to limit stress to the plant when possible.
We of course will be putting out a second year of this study and will share the results when we can.
For more information or questions contact
Brian Arnall b.arnall@okstate.edu 405.744.1722
Down and Dirty with NPK 