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Using soil moisture trend values from moisture sensors for irrigation decisions
Sumit Sharma, Extension Specialist for High Plains Irrigation and Water Management
Kevin Wagner, Director, Oklahoma Water Resources Center
Sumon Datta, Irrigation Engineer, BAE.
Sensor based and data driven irrigation scheduling has gained interest in irrigated agriculture around the world, especially in semi-arid areas because of the easy availability of commercial irrigation scheduler technology such as soil moisture sensors and crop models. Moisture sensing has particularly gained interest among the agriculture community due to ease of availability of the sensors to the producers, affordable costs, and easy to use graphical user interface. Economic potential of sensors in saving irrigation costs, data interpretation training through extension education programs, and policy initiatives have also helped with adoption of the sensors, especially in the United States. However, sensor adoption and efficient use can still be challenging due to poor data interpretation, steep learning curves, overly high expectations and subscription costs. This blog briefly discusses scenarios where sensors can be helpful in irrigated agriculture. For moisture sensor types, functioning and installation, readers are referred to BAE-1543 OSU extension factsheet.
Irrigation Scheduling
Irrigation scheduling with soil moisture sensors follows traditional principles of field capacity (FC), plant available water, maximum allowable depletion (MAD), and permanent wilting point (PWP). Figure 1 shows the transition of soil moisture level from field capacity to MAD, and to permanent wilting point in a typical soil. The maximum amount of water that a soil can hold after draining the excess moisture is called field capacity. At this point, all the water in soil is available to the plants. As the moisture content in the soil declines, it becomes more difficult for the plants to extract moisture from the soil. The soil moisture level below which the available moisture in soil cannot meet the plant’s water requirement is called the MAD. The water stress that occurs once moisture level goes below this moisture level can cause yield reductions in crops. Therefore, irrigation should be triggered as soon as the soil moisture level approaches this point (MAD) to avoid any yield losses (for detailed information on MAD, its value for different soils and crops, and irrigation scheduling, readers are referred to BAE-1537). Modern soil moisture sensors can come self-calibrated and are equipped with water stress threshold levels for different crops to avoid water stress or overwatering (Figure 2). These decisions are useful in furrow and drip irrigation systems where irrigation triggers can be synchronized with MAD values.
Figure 2: Screenshots of graphic user interface of three sensors a) GroGuru b) Sentek c) Aquaspy (Top to bottom) with threshold levels for soil moisture conditions. Aquspy and Sentek credits: Sumit Sharma. GroGuru image credits: groguru.com
Soil Moisture Trends and Irrigation Depths
Soil moisture sensors can help make data-informed decisions about scheduling irrigation. Previous studies have shown that the moisture values may vary from one sensor to the other and may not represent the exact moisture levels in soil. However, all soil moisture sensors exhibit trends in recharge and decline in soil moisture conditions. These real time soil moisture trends can be used to make informed decisions to adjust irrigation and improve water use efficiency. In high ET demand environments of Oklahoma, pivots are usually not turned off during the peak growing season, yet sensors can help in making decisions for early as well as late growing periods.
One of the easiest adjustments that could be made using soil moisture sensor data is the adjustment of irrigation depth. In an ideal situation, every irrigation event should recharge the soil profile to field capacity; however, this is often limited by the crops’ water demand and the well/irrigation capacity to replenish soil moisture levels. Each peak in soil moisture detected by sensors shows irrigation or rain, which ideally should be bringing moisture to same level after irrigation. However, reduction in moisture peaks in the soil moisture profile with every irrigation often indicates greater crop water demand than what is replenished with irrigation. In such scenarios, as allowed by capacity and infiltration rates, the irrigation depth can be increased. These trend values are particularly useful for center pivot irrigation systems, where triggering irrigation based on MAD might lag due to time and space bound rotations of the pivots in Oklahoma weather conditions.
Figure 3: A screenshot from Aquaspy agspy moisture sensor showing moisture at 8” (blue) and 28” (red) with each irrigation event. Data and image credit: Sumit Sharma
Last irrigation can be a tricky decision to end the cropping season. For summer crops, this is the time when crop ET demand is declining due to decline in green biomass and cooler weather patterns. Similar moisture trends can be used to make decisions for the last irrigation events, which can be skipped or reduced if the profile moisture is good, or can be provided if profile moisture is low. This is important because in an ideal situation, one would want to end the season with a relatively drier profile to capture and store off-season rains. Additionally, saving water on last irrigation can save operational cost and potentially cover the cost of moisture sensor subscriptions.
These decisions can be illustrated with Figure 3, which shows the trends of declining and recharging in a soil profile under corn at 8- and 28-inch depth. This field was irrigated with a center pivot irrigation system which was putting 1-1.25 inches of water with each irrigation event; however, the peak water recharge rate at both depths was declining with each irrigation. This coincided with peak growth period indicating rising ET demand of the crop than what was replenished by the irrigation. Later, two rain events, in addition to irrigation, replenished soil moisture in both layers. As the pivot was already running at a slow speed, slowing it further was not an option without triggering runoff for this soil type and this well capacity. Further in the season, when the crop started to senesce and ET demand declined, each irrigation event added to the moisture level of the soil. This allowed the producer to shut down the pivot between 70% starch line and physiological maturity for the crop to sustain at a relatively wet soil profile and leave the soil in relatively drier profile for the off-season.
In high ET demanding conditions of Western Oklahoma, crops often rely on moisture stored in deep soil profiles during the peak ET period when well capacities can’t keep up with crop water demand. In the high ET demanding environments of Oklahoma, irrigated agriculture depends heavily on profile moisture storage. Declining soil profile moisture is common during peak ET periods in high water demanding crops such as corn. These observations are useful if one starts the season with considerable moisture in the soil profile, however such trends may be absent if the season is started with a dry soil profile. Dry soil profiles can be recharged early in the season with pre-irrigation or deeper early irrigations (if allowed by the infiltration rate of the soil), when crop ET demand is low, to build the soil moisture profile. As such, sensors can be used in reducing the irrigation depth or skipping irrigation in early cropping systems if one starts with a full profile. This usually allows root growth through the profile to chase the moisture in deeper layers. It should be noted that the roots will grow and chase moisture only if there is a wet profile, and not through a dry soil profile.
Sensor installation and calibration are important for efficient use of these devices in irrigation decision making. Poor installation can often lead to poor data and wrong decision making. Although modern sensors are self/factory calibrated, some do provide the option to adjust threshold levels manually based on field observations. Early installation of sensors can be useful in making informed decisions as soon as the season starts. For a more detailed analysis of proper sensor installation, refer to BAE-1543. Producers are encouraged to integrate other means of irrigation planning with soil moisture sensing, such as a push rob to probe the soil profile or OSU Mesonet’s irrigation planner to further validate the sensor data. Further, the cliente should consider their irrigation capacities before investing in soil moisture sensors, as sensors may always show a deficit in low well capacities which cannot meet crop’s water demand.
References:
Taghvaeian, S., D. Porter, J. Aguilar. 20221. Soil moisture-sensing systems for improving irrigation scheduling. BAE-1543. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/soil-moisture-sensing-systems-for-improving-irrigation-scheduling.html
Datta, S., S. Taghvaeian, J. Stivers. Understanding soil water content and thresholds for irrigation management. BAE-1537. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/understanding-soil-water-content-and-thresholds-for-irrigation-management.html
For more information please contact Sumit Sharma sumit.sharma@okstate.edu
Toto, I’ve a feeling we’re not in Kansas anymore. Double Cropping, Orange edition
It has been pointed out that the blog https://osunpk.com/2025/06/09/double-crop-options-after-wheat-ksu-edition/ had a significant Purple Haze. And I should have added the Oklahoma caveat. So Dr. Lofton has provided his take on DC corn in Oklahoma.
Double-crop Corn: An Oklahoma Perspective.
Dr. Josh Lofton, Cropping Systems Specialist.
Several weeks ago, a blog was published discussing double-crop options with a specific focus on Kansas. I wanted to address one part of that blog with a greater focus on Oklahoma, and that section would be the viability of double-crop corn as an option.
Double-crop farming is considered a high-risk, high-reward system to try. Establishing a crop during the hottest and often driest parts of summer can present challenges that need to be overcome. Double-crop corn faces these same challenges and, in some seasons, even more. However, it is definitely a system that can work in Oklahoma, especially farther south. If you look at that original blog post, one of the main challenges discussed is having enough heat units before the first frost. When examining historic data, like those below from NOAA, the first potential frost date for Northcentral and Northwest Oklahoma may be as early as the first 15 days of October but more often will be in the last 15 days of October. In Southwest and Central Oklahoma, this date shifts even later to the first 15 days of November. This is later than Kansas, especially northern Kansas, which has a much higher chance of experiencing an early October freeze. I do not want to downplay this risk; however, it is one of the biggest risks growers face with this system, and a later fall freeze would greatly benefit it. We have been conducting trials near Stillwater for the past five years on double-crop corn and have only failed the crop once due to an early freeze event. But in that year, both double-crop soybean and sorghum also did not perform well.
The main advantage of double-crop corn is that if you miss the early season window, it offers the best chance for the crop to reach pollination and early grain fill without the stress of the hottest and driest part of the year. Therefore, careful management is crucial to ensure this benefit isn’t lost. In Oklahoma, we have two systems that can support double-crop corn. In more central and southwest Oklahoma, especially under irrigation, farmers can plant corn soon after wheat harvest, similar to other double-crop systems. This planting window helps minimize the impact of Southern Rust, which can significantly reduce yields in some years, and may reduce the need for extensive management. This earlier planting window is often supported by irrigation, enabling the crop to endure the hotter, drier late July and early August periods. Conversely, in northern Oklahoma, planting often occurs in July to allow pollination and grain fill (usually 30-45 days after emergence) to happen in late August and early September. During this period, the chances of rainfall and cooler nighttime temperatures increase, both of which are critical for successful corn production.
Other management considerations include maturity. Based on initial testing in Oklahoma, particularly in the northern areas, we prefer to plant longer-maturity corn. Early corn varieties have a better chance of maturing before a potential early freeze but also carry a higher risk of undergoing critical reproduction stages (pollination and early grain fill) during hot, dry periods in late summer. Testing indicates that corn with a maturity of over 110 days often works well for this. However, this does not mean growers cannot plant shorter-season corn, especially if the season has generally been cooler, though the risk still exists depending on how quickly the crop can grow. Based on testing within the state, the dryland double-crop corn system typically does not require adjustments to other management practices, such as seeding rates or nitrogen application. Because of the need to coordinate leaf architecture and manage limited water resources, higher seeding rates are not recommended. Maintaining current nitrogen levels allows the crop to develop a full canopy.
The final question often comes as; how does it yield? This will depend greatly. Corn looks very good this year across that state, especially what was able to be planted earlier in the spring. However, in recent years, delaying even a couple of weeks beyond traditional planting windows has lowered yields enough that double-crop yields are often similar. We have often harvested between 50-120 bushels per acre in our plots around Stillwater with double-crop systems. So, the yield potential is still there.
In the end, Oklahoma growers know that double-crop is a risk regardless of the crop chosen. There are additional risks for double-crop corn, such as Southern Rust in the south and freeze dates in the north. This risk is increased by the presence of Corn Leaf Aphid and Corn Stunt last season, and it is not clear if these will be ongoing problems. Therefore, growers need to be careful not to expect too much or to invest too heavily in inputs that may not be recoverable if there is a loss. One silver lining is that if double-crop corn doesn’t succeed in any given year, growers can still use it as forage and recover at least some of their costs.
Any questions or concerns reach out to Dr. Lofton: josh.lofton@okstate.edu
Meet the Aster Leafhopper and Learn How to Distinguish it from the Corn Leafhopper
Ashleigh M. Faris: Extension Cropping Systems Entomologist, IPM Coordinator
Release Date June 3 2025
Last year’s corn stunt disease outbreak, caused by the corn leafhopper transmitting pathogens associated with corn stunt disease, has been on everyone’s minds. Over the past few weeks, I’ve received several calls from growers, crop consultants, and industry partners concerned about leafhoppers in corn. Fortunately, none have been corn leafhoppers, the vast majority have instead been aster leafhoppers. So far, no corn leafhoppers have been reported north of central Texas. Oklahoma did not have any reports of overwintering corn leafhoppers so if we have the insect this year it will need to migrate northward from where it currently resides. For a refresher on the corn leafhopper and corn stunt disease, check out these two previously posted OSU Pest e-Alerts: EPP-25-3and EPP-23-17.
Leafhoppers in general are insects that we have had for many years in our row and field crops. But we likely did not pay attention to them or notice them until this past year due to our heightened awareness of their existence thanks to the corn leafhopper and corn stunt disease. Below is guidance on how to distinguish between the corn leafhopper and aster leafhopper. Remember, if the corn leafhopper is detected in the state, OSU Extension will notify growers, consultants, and industry partners through Pest e-Alerts and our social media channels.
Aster Leafhopper Overview
The aster leafhopper (aka six spotted leafhopper), Macrosteles quadrilineatus, is native to North America and can be found in every U.S. state, as well as Canada. This polyphagous insect feeds on over 300 host plant species including weeds, vegetables, and cereals. Like many other leafhoppers, the aster leafhopper can be a vector of pathogens that cause disease, but corn stunt is not one of them. Instead, aster leafhoppers cause problems in traditional vegetable growing operations, as well as floral production. There is currently no concern for this insect being a vector of disease in row or field crops, including corn. Check out the OSU Pest a-Alert EPP-23-1to learn more about this insect and aster yellows disease.
Aster Leafhopper versus Corn Leafhopper
The corn leafhopper (Photo 1A) and the aster leafhopper, as well as many other leafhopper species have two black dots located between the eyes of the insect (Photo 1). Aster leafhopper adults are 0.125 inches (3 mm) long, with transparent wings that bear strong veins, and darkly colored abdomens (Photo 1B). Their dark abdomen can cause the aster leafhopper to appear grey when you see them in the field. Their long wings can also make the insect appear to have a similar appearance to the corn leafhopper (Dalbulus maidis) (Photo 1).
Characteristics that differentiate the corn leafhopper from the aster leafhopper are as follows. When viewed from above (dorsally): 1) the corn leafhopper’s dots between the eyes have a white halo around them and the aster leafhopper’s dots between eyes lack the white halo and 2) the corn leafhopper has lighter/finer wing veination than the aster leafhopper (Photo 1). When when viewed from their underside (ventrally) 3) the corn leafhopper lacks markings on their face whereas the aster leafhopper has lines/spot on the face and 4) the abdomen of the corn leafhopper lacks the dark coloration of the aster leafhopper (Photo 2).
Confirming Corn Leafhopper Identification
It is important to note that many insects will have their cuticle darken as they age. This, along with there being light and dark morphs of many insects can lend to additional confusion when distinguishing one species from another. If you believe that you have a corn leafhopper then you need to collect the insect and send it to a trained entomologist that can verify the identity of the insect under the microscope. Leafhoppers in general are fast moving insects but they can be collected in an insect net or using a handheld vacuum (see EPP-25-3). You can submit samples to the OSU Plant Disease and Insect Diagnostic Lab.
Please feel free to reach out to OSU Cropping Systems Extension Entomologist Dr. Ashleigh Faris with any questions or concerns. @ ashleigh.faris@okstate.edu
PRE-EMERGENT RESIDUAL HERBICIDE ACTIVITY ON SOYBEANS, 2025
Liberty Galvin, Weed Science Specialist
Karina Beneton, Weed Science Graduate Student.
Objective
Determine the duration of residual weed control in soybean systems following the application of Preemergent (PRE) herbicides when applied alone and in tank-mix combination.
Why we are doing the research
PRE herbicides offer an effective means of suppressing early-season weed emergence, thereby minimizing competition during the critical early growth stage. However, evolving herbicide resistance and the need for longer-lasting weed suppression underscore the importance of evaluating multiple modes of action and their residual properties alone and tank-mixed.
Field application experimental design and methods
Field experiments were conducted in 2022, 2023, and 2024 growing seasons in Bixby, Lane, and Ft. Cobb FRSU Research Stations across Oklahoma. Each herbicide (listed in Table 1) was tested individually, in 2-way combinations, 3-way mixtures, and finally as 4-way combinations that included all active ingredients listed at the label rate.
Soybeans were planted at rates between 116,000 and 139,000 seeds/acre from late May to early June, depending on the year and location. The variety used belongs to the indeterminate mid- maturity group IV, with traits conferring tolerance to glyphosate (group 9 mode of action), glufosinate (group 10), and dicamba (group 4). Not all soybean varieties have metribuzin tolerance. Please read the herbicide label and consult your seed dealer for acquiring tolerant varieties. Row spacing was 76 cm at Bixby and Lane, and 91 cm at Fort Cobb. PRE treatments were applied immediately after planting at each experimental location.
POST applications consisted of a tank-mix of dicamba (XtendiMax VG® – 22 floz/acre), glyphosate (Roundup PowerMax 3®- 30 floz/acre), S-metolachlor (Dual II Magnum® – 16 floz/acre), and potassium carbonate (Sentris® – 18 floz/acre). Applications were made on different dates, mostly after the first 3 weeks following PRE treatments. These timings were based on visual weed control ratings, particularly for herbicides applied alone or in 2-way combinations, which showed less than 80% control at those early evaluation dates. The need for POST applications also depended on the species present at each site, with most fields being dominated by pigweed, as illustrated in the figure below.
Results
Tank-mixed PRE herbicide combinations generally provided superior residual control compared to a single mode of action application (Shown in Figure 1). Timely post-emergent (POST) herbicide applications helped sustain high levels of weed suppression, particularly as the effectiveness of residual PRE declined.
Residual control of tank-mixed PRE
Some herbicides applied alone or in simple 2-way mixes, such as sulfentrazone + chloransulam- methyl and pyroxasulfone + chloransulam-methyl required POST applications within 20 to 29 days after PRE, indicating moderate residual control.
In contrast, 2-way combinations containing metribuzin, such as sulfentrazone + metribuzin and pyroxasulfone + metribuzin, extended control up to 50 days after PRE in some cases, highlighting metribuzin’s importance even in less complex formulations.
Furthermore, 3-way and 4-way combinations including metribuzin provided the longest-lasting control, delaying POST applications up to 51–55 days after PRE.
Injury of specific weeds
Palmer amaranth (Amaranthus palmeri) control in Bixby was consistently high (≥90%) at 2 weeks after PRE in 2022 and 2024 across all treatments. At 4 WAPRE, treatments containing metribuzin alone or in combination maintained strong control (90% or greater).
Texas millet (i.e., panicum; Urochloa texana) and large crabgrass (Digitaria sanguinalis) were effectively managed with most treatments delivering over 90% control early in the season and maintaining performance throughout. In 2024, control remained generally effective, though pyroxasulfone alone showed a temporary lack of control for Texas millet, and single applications declined in effectiveness against large crabgrass later in the season. These reductions were likely due to continuous emergence and the natural decline in residual herbicide activity due to weather. The most consistent late-season control for both species came from 3- and 4-way herbicide combinations.
Morningglory (Ipomoea purpurea) control reached full effectiveness (100%) only when POST herbicides were applied, across all years and locations. Their late emergence beyond the residual window of PRE herbicides reinforces the importance of sequential herbicide applications for season-long control.
Take home messages:
- Incorporating PRE and POST herbicides slows the rate of herbicide resistance
- Tank mixing with *different modes of action* ensures greater weed control by having activity on multiple metabolic pathways within the plant.
- Tank mixing with PRE herbicides could reduce the number of POST applications required, and
- Provides POST application flexibility due to residual of PRE application
For additional information, please contact Liberty Galvin at 405-334-7676 | LBGALVIN@OKSTATE.EDU or your Area Agronomist extension specialist.
Laboratory evaluation of Liquid Calcium
Liquid calcium products have been around for a long time. The vast majority of these products are either a calcium chloride or chelated calcium base which is now commonly found with the addition of a humic acid, microbial, or micronutrient. Many of these make promises such as “raises your soil pH with natural, regenerative, liquid calcium fertilizers that correct soil pH quickly, efficiently, and affordably!”. From a soil chemistry aspect the promise of adding 3 to 5 gallons of a Ca solution, which is approximately 10% Ca, will raise the soil pH is impossible on a mass balance approach. In this I mean that to increase the pH of an acid soil {soil pH is the ratio of hydrogen (H) and hydroxide (OH) in the soil, and having an acid soil means the concentration of H is greater than that of OH} requires a significant portion of the H+ that is in solution and on soil particle to be converted to OH, or removed from the system entirely.
The blog below walks through the full chemical process of liming a soil but in essence to reduce the H+ concentration we add a cation (positively charged ion) such as Ca or magnesium (Mg) which will kick the H+ of the soil particle and a oxygen (O) donator such as CO2 with ag lime or (OH)2 which is in hydrated lime. Each of these O’s will react with two H’s to make water. And with that the pH increases.
However regardless of the chemistry, there is always a lot of discussion around the use of liquid calcium Therefore we decided to dig into the question with both field and laboratory testing. This blog will walk through the lab portion.
This was a laboratory incubation study. The objective was to evaluation the impact of the liquid Ca product (LiqCa**) on the soil pH, buffer capacity, Ca content and CEC of two acidic soils. LiqCa was applied at three rates to 500 g of soil. The three rates were equivalent to 2, 4, and 6 gallon per acre applied on a 6” acre furrow slice of soil. One none treated check and two comparative products were also applied. HydrateLime (CaO) as applied at rate of Ca equivalent to the amount of Ca applied via LiqCa, which was approximately 1.19 pounds of Ca per acre. Also AgLime (CaCO3) was applied at rates equivalent to 1, 2, and 4 ton effective calcium carbonate equivalency (ECCE). The Ag lime used in the study had a measured ECCE of 92%. The two soils selected for both acidic but had differing soil textures and buffering capacities. The first LCB, had an initial soil pH (1:1 H2O) of 5.3 and a texture of silty clay loam and Perkins had a initial pH of 5.8 and is a sandy loam texture. Both soils had been previously collected, dried, ground, and homogenized. In total 10 treatments were tested across two soils with four replications per treatment and soil.
Project protocol, which has been used to determined site specific liming and acidification rates, was to apply the treatments to 500 grams of soil. Then for a period of eight weeks this soil wetted and mixed to a point of 50% field capacity once a week then allowed to airdry and be mixed again. At the initiation and every two weeks after soil pH was recorded from each treatment. The expectation is that soil pH levels will change as the liming products are impacting the system and at some point, the pH reaches equilibrium and no longer changes. In this soil that point was week six however the trail was continued to week eight for confirmation. See Figures 1 and 2.
ANOVA Main effect analysis showed that Soil was not a significant effect so therefore both soils were combined for further analysis. Figure 3 shows the final soil pH of the treatments with letters above bars representing significance between treatments. In this study all treatments were significantly greater than the check with exception of LiqCal 2 and CaO 6. Neither LiqCal or CaO treatments reached the pH level of Aglime, regardless of rate.
Summary
The incubation study showed that application of LiqCal at a rate of 4 and 6 gallons per acre did significantly increase the soil pH by 0.1 pH units and 6 gallons per acre increased the Buffer index above the check by 0.03 units. Showing the application of LiqCal did impact the soil. However the application of 1 ton of Ag lime resulted in significantly great increase in soil pH, 1.0 units by 8 weeks and a buffer index change of 0.2 units. The Aglime 1 was statistically greatly than all LiqCal treatments. Ag lime 2 and 4 were both statistically greater than Ag lime 1 with increasing N rate with increasing lime rate. Given the active ingredient listed in LiqCal is CaCl, this result is not unexpected. Ag lime changes pH by the function of CO3 reacting H+ in large quantities. In a unsupported effort a titration was performed on LiqCal, which show the solution was buffered against pH change. However it was estimated that a application of approximately 500 gallons per acre would be needed to sufficiently change the soil pH within a 0-6” zone of soil.
Results of the field study.
https://osunpk.com/2025/06/02/field-evaluation-of-lime-and-calcium-sources-impact-on-acidity/
Take Home
The application of a liquid calcium will add both calcium and chloride which are plant essential nutrients and can be deficient. In a soil or environment suffering from Cl deficiency specifically I would expect an agronomic response. However this study suggest there is no benefit to soil acidity or CEC with the application rates utilized (2, 4, and 6 gallon per acre).
** LiqCal The product evaluated was derived from calcium chloride. It should be noted that since the completion of the study this specific product used has changed its formulation to a calcium chelate. This change however would not be expected to change the results as the experiment did include a equivalent calcium rate of calcium oxide.
Other articles of Interest
https://extension.psu.edu/beware-of-liquid-calcium-products
https://foragefax.tamu.edu/liquid-calcium-a-substitute-for-what/
Any questions or comments feel free to contact me. b.arnall@okstate.edu
Field evaluation of lime and calcium sources impact on Acidity.
At the same time we initiated a lab study looking at the application of LiqCal https://osunpk.com/?p=2096 , we also initiated a field trial to look at the multi-year application of LiqCal, Pelletized Lime and Ag-Lime.
A field study was implemented on a bermudagrass hay meadow near Stillwater in the summer of 2019. The study looked to evaluate the impact of multiple liming / calcium sources impact on forage yield and soil properties. This report will focus on the impact of treatments on soil properties while a later report will discuss the forage results.
Table 1. has the management of the six treatments we evaluated, all plots had 30 gallons of 28-0-0 streamed on each spring in May. Treatment 1 was the un-treated check. Treatment 2, was meant to be a 2 ton ECCE (Effective Calcium Carbonate Equivalency) Ag Lime application when we first implemented the plots in 2019, but we could not source any in time so we applied 2.0 ton ECCE hydrated lime (CaO) the next spring. The spring 2023 soil samples showed the pH to have fallen below 5.8 so and Ag lime was sourced from a local quarry and 1.0 ton ECCE was applied May 2024. Treatment 3, was meant to complement Treatment 2 as an additional lime source of hydrated lime, it was applied June 2019. My project has used hydrated lime as a source for many years as it is fast acting and works great for research. Treatment 4 had 100 lbs. of pelletized lime applied each spring. The 100 lbs. rate was based upon recommendation from a local group that sells Pell lime. Treatments 5 and 6 were two liquid calcium products *Liq Cal * and **Lig Cal+ from the same company. The difference based upon information shared by the company was the addition of humic acid in the Liq Cal+ product. Both LiqCal and LiqCal+ where applied at a rate of 3 gallons per acre per year, with 17 gallons per acre of water as a carrier. Table 1, also shows total application over the six years of the study.
After six years of applications and harvest it was decided to terminate the study. The forage results were intriguing however little differences where seen in total harvest over the six years, highlighting a scenario I have encountered in the past on older stands of bermuda. That data will be shared in a separate blog.
The soils data however showed exceptionally consistent results.
In February of 2025 soil samples were collected from each plot at depths of 0-3 inch’s and 0-6 inches (Table 2.). It was our interest to see if the soil was being impacted below the zone we would expect lime and calcium to move without tillage, which if 0-3″. Figure 1. below shows the soil pH of the treatments at each depth. In the surface (blue) the Ag Lime and Hydrated lime treatments both significantly increased from 4.78 to 6.13 and 5.7 respectively. While the Pel lime, LiqCal and LiqCal+ had statistically similar pH’s as the check at 4.8, 4.65, and 4.65. It is important to note that the Ag Lime applied in May of 2024 resulted in a significant increase in pH from the 2019 application of Treatment 3. The Spring of 2024 soil samples showed that the two treatments ( 2 and 3 ) were equivalent. So within one year of application the Ag lime significantly raised soil pH.
As expected the impact on the 3-6″ soil pH was less than the surface. However, the Ag Lime and Hydrated lime treatments significantly increased the pH by approximately 0.50 pH units. This is important data as the majority of the literature suggestion limited impact of lime on the soil below the 3″ depth.
The buffer pH of a soil is used to determine the amount of lime needed to change the soils pH. In Figure 2. while numeric differences can be seen, no treatment statistically impacted the buffer pH at any soil depth.
The soil calcium level was also measured. As with 0-3″ pH and Buffer pH the Ag Lime and Hydrated lime had the greatest change from the check. These treatments were not statistically greater than the Pell Lime but where higher than the LiqCal and LiqCal+.
Each value is the average of four replicates.
Take Homes
In terms of changing the soils pH or calcium concentration, as explained in the blog https://osunpk.com/2023/01/24/mechanics-of-soil-fertility-the-hows-and-whys-of-the-things/, it takes a significant addition of cations and oxygens to have an impact. This data shows that after six years of continued application of pelletized lime and two liquid calcium products the soil pH did not change. While the application of 2 ton ECCE hydrate lime did.
Also within one year of application Ag lime the soil pH significantly increased.
* LiqCal The product evaluated was derived from calcium chloride. It should be noted that since the completion of the study this specific product used has changed its formulation to a calcium chelate. This change however would not be expected to change the results as the experiment did include a equivalent calcium rate of calcium oxide.
** LiqCal+ The product evaluated was derived from calcium chloride. It should be noted that since the completion of the study this specific product used has changed its formulation. The base was changed from calcium chloride to a calcium chelate. Neither existing label showed Humic Acid as a additive, however the new label has a a list of nutrients at or below 0.02% (Mg, Zn, S, Mn, Cu, B, Fe) and Na at .032% and is advertised as having microbial enhancements.
Any questions or comments feel free to contact me. b.arnall@okstate.edu
Sorghum Nitrogen Timing
Contributors:
Josh Lofton, Cropping Systems Specialist
Brian Arnall, Precision Nutrient Specialist
This blog will bring in a three recent sorghum projects which will tie directly into past work highlighted the blogs https://osunpk.com/2022/04/07/can-grain-sorghum-wait-on-nitrogen-one-more-year-of-data/ and https://osunpk.com/2022/04/08/in-season-n-application-methods-for-sorghum/
Sorghum N management can be challenging. This is especially true as growers evaluate the input cost and associated return on investment expected for every input. Recent work at Oklahoma State University has highlighted that N applications in grain sorghum can be delayed by up to 30 days following emergence without significant yield declines. While this information is highly valuable, trials can only be run on certain environmental conditions. Changes in these conditions could alter the results enough to impact the effect delay N could have on the crop. Therefore, evaluating the physiological and phenotypic response of these delayed applications, especially with varied other agronomic management would be warranted.
One of the biggest agronomic management sorghum growers face yearly is planting rate. Growers typically increase the seeding rate in systems where specific resources, especially water, will not limit yield. At the same time, dryland growers across Oklahoma often decrease seeding rates by a large margin if adverse conditions are expected. If seeding rates are lowered in these conditions and resources are plentiful, sorghum often will develop tillers to overcome lower populations. However, if N is delayed, there is a potential that not enough resources will be available to develop these tillers, which could decrease yields.
A recent set of trials, summarized below, shows that as N is delayed, the number of tillers significantly decreases over time. Furthermore, the plant cannot overcompensate for the lower number of productive heads with significantly greater head size or grain weight.
This information shows that delaying sorghum N applications can still be a viable strategy as growers evaluate their crop’s potential and possible returns. However, delayed N applications will often result in a lower number of tillers without compensating with increased primary head size or grain weight.
This date on yield components is really interesting when you then consider the grain yield data. The study, which is where the above yield component data came from, was looking at population by N timing. The Cropping Systems team planted 60K seeds per acre and hand thinned the stands down to 28 K (low) and 36K (high). The N was applied at planting, 21 days after emergence, and 42 days after emergence. The rate of N applied was 75 lbs N ac. It should be noted both locations were responsive to N fertilizer.
In the data you can without question see how the delayed N management is not a tool for any of members of the Low Pop Mafia. However those at what is closer to mid 30K+ there is no yield penalty and maybe a yield boost with delayed N. The extra yield is coming from the slightly heavier berries and getting more berries per head. Which is similar to what we are seeing in winter wheat. Delaying N in wheat is resulting in fewer tillers at harvest, but more berries per head with slightly heavier berries.
Now we can throw even more data into the pot from the Precision Nutrient Management Teams 2024 trials. The first trial below is a rate, time and source project where the primary source was urea applied in front of the planter for pre in range of rates from 0-180 in 30 lbs increments. Also applied pre was 90 lbs N as Super U. Then at 30 days after planted we applied 90 lbs N as urea, SuperU, UAN, and UAN + Anvol.
Pre-plant urea topped out at 150 lbs of Pre-plant (57 bushel), but it was statistically equal to 90 lbs N 51 bushel. The use of SuperU pre did not statistically increase yield but hit 56 bushel. The in-season shots of 90 lbs of UAN, statistically outperformed 90 pre and hit our highest yeilds of 63 and 62 bushel per acre. The dry sources in-season either equaled their in preplant counter parts.
The Burn Study at Perkins, showed that the N could be applied in-season through a range of methods, and still result good yields. In this study 90 lbs of N was used and applied in a range of methods. The treatments for this study was applied on a different day than the N source. Which you can see in this case the dry untreated urea did quite well when when applied over the top of sorghum. In this case we are able to get a rain in just two days. So we did get good tissue burn but quick incorporation with limited volatilization.
Take Home:
Unless working in low population scenarios. The data show that we should not be getting into any rush with sorghum and can wait until we know we have a good stand. We also have several options in terms of nitrogen sources and method of application.
Any questions or comments feel free to contact Dr. Lofton or myself
josh.lofton@okstate.edu
b.arnall@okstate.edu
Funding Provided by The Oklahoma Fertilizer Checkoff, The Oklahoma Sorghum Commission, and the National Sorghum Growers.
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.
A comparison of four nitrogen sources in No-till Wheat.
Jolee Derrick, Precision Nutrient Management Masters Student.
Brian Arnall, Precision Nutrient Management Specialist.
Nitrogen (N) fertilizer’s ability to be utilized by a production system is reliant upon the surrounding environment. The state of Oklahoma’s diverse climate presents unique challenges for producers aiming to apply fertilizers effectively and mitigate the adverse effects of unfavorable conditions on nitrogen fertilizers. To lessen the effect that unfavorable environments can have on N fertilizers, chemical additions have been introduced to base fertilizers to give the best possible chance at an impact. With that in mind, a study was conducted to investigate the impact of N sources and application timings on winter wheat grain yield and protein, aiming to identify both the agronomic effects of these sources and how variations in their timing may influence the crop. Included below is a figure of where and when the trials were conducted.
In each of the trials, four N sources (Urea, SuperU, UAN, and UAN + Anvol) were analyzed across a range of timings. The sources were categorized on two criteria: application type, distinguishing between dry and liquid sources, and the presence of additives versus non-additives. The two N sources were Urea and UAN. The other products in this study were SuperU and Anvol. SuperU is a N product that has Dicyandiamide (DCD) and N- (n-butyl) thiophosphoric triamide (NBPT) incorporated into a Urea base. Anvol is an additive product which contains NBPT and Duromide and can be incorporated with dry or liquid N sources.
For additional clarification, N- (n-butyl) thiophosphoric triamide is a urease inhibitor which prevents the conversion of urea to ammonia. Duromide is a molecule which is intended to slow the breakdown of NBPT. DCD is a nitrification inhibitor that slows the conversion of ammonium to nitrate.
Urea is a stable molecule which in the presence of moisture is quickly converted to stable ammonium (NH4), however it can be converted to ammonia gas (NH3) by the enzyme urease beforehand. Additionally, when urea is left on the soil surface and not incorporated via tillage or ½ inch of a precipitation event, the NH4 that was created from urea can be converted back to NH3 and gasses off. So, the use of urease inhibitors is implemented to allow more time for incorporation of the urea into the soil.
Ammonium in the soil is quickly converted to nitrate (NO3) by soil microbes when soil temperature is above 50F°. When N is in the NO3 form it is more susceptible to loss through leaching or denitrification. Therefore, nitrification inhibitors are applied to prevent the conversion of NH4 to NO3.
All treatments were applied at the same rate of 60 lbs of N ac-1, which is well below yield goal rate. A lower N rate was chosen to allow the efficacy of the products to express themselves more clearly, rather than a higher rate that may limit the ability to determine differences between product and rate applied. Furthermore, dry N sources were broadcasted by hand across the plots while liquid sources were applied by backpacking utilizing a handheld boom with streamer nozzles. Application timing dates were analyzed by identifying the growing degree days (GDD) associated with each timing which were correlated with the Feekes physiological growth chart displayed in Figure 3. Over the span of the study, N has been applied over six stages of growth. The range of application dates stems from the fact that it is difficult to get across all the ground exactly when you need to.
Over four years this study was replicated 11 times. Of those 11 site years, three did not show a response to N, so they were removed from further analysis. The graph above shows the average yield of each respective source (across all locations and timings). The data shows there is a statistical difference between SuperU and Urea vs. UAN, but no statistical difference between UAN treated Anvol and any other source. The data indicates that on average, a dry source resulted in a higher yield than when a liquid source was applied. This makes sense considering that in many cases, wheat was planted in heavy residue during cropping seasons that experienced prolonged drought conditions. Therefore, it is thought that a liquid source can get tied up in the residue. This was first reported in a previous blog posting, Its dry and nitrogen cost a lot, what now?, and years later, the same trends in new data indicate the same conclusion.
If we look at all timings and site years averaging together there is no statistical difference between a raw N source and its treated counterpart. This result is not surprising as we would expect that not all environments were conducive to loss pathways that the products prevented. Basically, we would not expect a return on investment in every single site year, and therefore you do not see broad sweeping recommendations. There was a 2-bushel difference between UAN and UAN Anvol. As this was a numerical difference, not a statistical one, I would say that while the yield advantage was not substantial there may be economic environments that would suggest general use.
While the evaluation of the four sources across all timings and locations showed some interesting results, this work was performed to see if there was a timing of application which would have a higher probability of a safened N returning better yields. As you look at the chart above it is good to remember the traditional trend for precipitation in Oklahoma, where we tend to start going dry in November and stay dry through mid-January. Rain fall probability and frequency starts to increase around mid-February, but moisture isn’t consistent until March. This project was performed during some of the dryest winters we have seen in Oklahoma. Also, just a note, since the graph above combines all the sites that have differing application dates the absolute yields are a bit deceiving. For example, the Nov and Feb timings include the locations with our highest yields 80+ bpa per acre, while January and February include our lowest. So, the way this data is represented we should not draw conclusions about best time for N app. For that go read the blogs Impact Nitrogen timing 2021-2022 Version and Is there still time for Nitrogen??
Figure 6a and b. A: The mesonet rainfall totals for Oct -Dec for the Lake Carl Blackwell research station for 2020-2023 A: The mesonet rainfall totals for Jan – April for the Lake Carl Blackwell research station for 2021-2024. The black line on both graphs is the 10 year average.
Now about the source by time. While it’s not always statistical you can see that the dry sources tend to outperform the liquid sources at most timings. Also, while there is never a statistical difference in the raw product and safened, there are trends. SuperU tended to have higher yields than urea when applied in Nov and Dec. It could be hypothesized that the addition of a nitrification inhibitor may have added value, however the UAN + Anvol in November also showed a positive response that would point to the value being derived from urease inhibition. As we move into the period of more consistent rainfall the differences between products start declining, which also makes sense.
The following figures illustrate rainfall events following N application, with the application dates indicated by arrows. Figure 7 corresponds to our trial conducted in 2020-2021, which revealed no statistical differences among the N sources for any timing. However you can see that for the first timing (orange bars) which received 0.7″ of rain two days after application that the yields are uniform than the grey bars with both safened products are numerically greater than the raw product, just makes since as a 0.1″ precipitation event happened 6 days application application and it wasn’t until day 9 that a good incorporating rainfall occurred.
Figure 8 has data the same location one year later, during which we observed statistically significant differences among the dry and liquid N sources. The environmental conditions during 2022 were drier, impacting the incorporation of N applications. The lack incorporating rainfall likely led to tie-up of the UAN on/in the residue, limiting access to plant available N.
It is essential to highlight the environmental conditions encountered throughout this project. From 2020 to 2023, moderate to extreme drought conditions were prevalent. During this period, the influence of a La Niña led to reduced moisture availability. For the first time in an extended period, the 2023-2024 wheat year began under a strong El Niño, which typically results in increased moisture accumulation compared to its La Niña counterpart. Currently, there are indications that a return to a La Niña system may occur by the end of the year, raising the expectation of a potential reversion to drought conditions. Consequently, this research may provide producers with options to consider regarding sources of N application in their production systems.
We plan to update this blog with a deeper analysis of the results seen at each location as soon as possible. But for now, we wanted to share the early look.
At this point the reason for the liquid yield gap is speculation. It could be increased loss via ammonia volatilization or it could be immobilization of the N by microbes. The next step of this process is to understand 1) is the UAN tied up in the residue via immobilization via microbes or is it lost to volatilization. 2) If tied up, what is the time frame between application and immobilization.
Take Home:
- It was observed that during low moisture conditions, dry N sources had significantly better results than liquid counterparts in no-till winter wheat production.
- On average, additive products had no significant impact on grain yield versus base fertilizers, however, when evaluated by location, differences could be found. Responses usually correlated with post-application weather conditions.
- When adequate precipitation was received shortly after application, N sources did not show differences.
Any questions or comments feel free to contact me. b.arnall@okstate.edu
Down and Dirty with NPK 