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osunpk

osunpk

Since 2008 I have served as the Precision Nutrient Management Extension Specialist for Oklahoma State University. I work in Wheat, Corn, Sorghum, Cotton, Soybean, Canola, Sweet Sorghum, Sesame, Pasture/Hay. My work focuses on providing information and tools to producers that will lead to improved nutrient management practices and increased profitability of Oklahoma production agriculture

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The Easy Button for Nitrogen…….

Brian Arnall, Precision Nutrient Management Extension Specialist.

The basics for nitrogen (N) fertilizer rate determination can be described in a mechanistic approach by the Stanford Equation NFert = ( NCrop – NSoil ) / Neff. This equations states that the N fertilizer rate is equal to the amount of nitrogen taken up by the crop minus the amount of nitrogen supply by the soil, divided by the efficiency of the nitrogen fertilizer used. I outline the importance of this equation in the blog “Components of a variable rate nitrogen recommendations“.

There are nitrogen “Easy Buttons” which utilizes averages collected over diverse environments to create accurate N rate recommendations. The best example of this is the yield goal rules of thumb such as wheats 2.0 lbs N per yield goal bushel minus soil test nitrate. Yield goals are generally calculated as the average of the best 3 out of 5 years, or the 5-year average times 20%. Also, the 2.0 lbs of N is more than what is in a bushel as it also adds in an efficiency factor or a 0.5 lbs per bushel cushion. This method and others like it provide an accurate N rate with slight probability of yield loss. However, the rec is often highly imprecise. Meaning that if I apply the method to 100 fields the average will be spot on, however if I look at the performance of the recommendation on a single field, I will likely be disappointed.

Illustration of accuracy versus precision.
Figure 1. Illustration of accuracy versus precision.

When it comes to nitrogen recommendations the Easy button method will use components which help ensure that the rate prescribed will maximize yield 90-95% of the time. For example, take the data presented in Figure 2. Over fifteen years of the long-term winter wheat fertility study near Lahoma, Oklahoma the average pounds of N per bushel to reach economic optimum nitrogen rate (EONR) was 1.6, however if 2.0 of N was applied per bushel yield would have been maximized 13 out of the 15 years. While 2.0 lbs. of N per bushel would have been quite accurate for maximizing yield, it would be highly imprecise as over the 15 years optimum pounds of N per bushel ranged from 0.0 to 3.2.

Figure 2. Grain yield (bushels per acre), economical optimal N rate (EONR), and pounds of nitrogen per bushel producer at the EONR, from 15 years of data from the long-term fertility trials located near Lahoma, Ok.

The trick to improving your N rate recommendation closer to a precise and accurate system is to obtain representative site-specific values for the Stanford Equation NFert = (NCrop – NSoil) / Neff.

Looking at the 15-year long-term data above the yields range from a low of 27 to a high of 88 bushels. Of those 15 years, I personally planted multiple years, usually sometime in October, and many of those years while sowing I could have guessed a range of 55-60 bushel, which just happened to be just above the 15-year average.   It was not until February and March when the yield potential really started to express itself. Why, well there is a lot of weather between Oct to March, a lot of environmental positive and negative impacts on that final grain yield. This is the best timing to go out with approaches, models, or techniques to estimate yield potential for N rate recs.

While I am a big fan of soil testing, pre-plant soil samples for N are just a snap shot in time. But the While I am a big fan of soil testing, pre-plant soil samples for N are just a snapshot in time, but the nitrogen cycle Figure 3, will roar on after the soil sample is collected. Organic matter (OM) is the central component of this cycle and drives availability of NH4 and NO3 in the system. For each 1% OM in the top 6″ of the soil there is approximately 1000 lbs of organically bound N. The amount of N going into and out of OM pool is driven by C:N ratio of residues, soil temperature and soil moisture. While we very well what the mechanisms of the cycle are and can model the reactions quite well. Our inability to predict long term weather patterns is the greatest factor limiting our ability to predict future availability of NSoil.

Figure 3. Complete Nitrogen Cycle. http://psssoil4234.okstate.edu/lecture

This is where the reader should be asking “how can we get better site specific data” and I begin the discussion on why I have been promoting the of the Sensor Based Nitrogen Rate Calculator (SBNRC) and N-Rich strip method.

Lets talk about how the approach follows Stanford’s mechanistic approach to N management. First the Yield Potential component of the SBNRC which is related to NCrop. In effect researchers have built models over the past two decades that can correlate the NDVI collected from a sensor, such as the GreenSeeker, with the crops biomass and chlorophyll content. If given the number of days the crop has been growing it is possible to use the NDVI collected from the crop as a tool to predict final grain yield. The closer the wheat gets to hollow stem, or the corn gets to tassel, the better the prediction. One reason is that we have allowed more “environmental influence” to happen. Dr. Bill Raun, a founder of the SBNRC concept kept great discussion and data sets on his NUE.OKSTATE.edu website. On the “NUE Website on YP” he provides information on how yield prediction work while on the “NUE Website YP Library” he has not listed every algorithm created, and the math behind them, but also a recipe book for how anyone can create their own algorithm. While there are a lot post sensing stresses that can bring down final grain yield, the models that have been built and continually improved, do quite a good job on predicting final grain yield in-season. Resulting a much more site specific value for NCrop. The blog”Sensing the N-Rich Strip and Using the SBNRC” goes into a further discussion of using the online SBNRC.

That now leaves NSoil, which I will argue is at least as important as NCrop. As weather so greatly influences the nitrogen cycle it would be nice to have a weather station on every field paired with a 0-4 ft soil description which could be incorporated into a model. Given those might be out of reach we have found the the use of a reference strip, high N or low N, really provides an site specific estimate the of nitrogen the crop has access to. If the high N reference (N-Rich) strip is showing up that means the remainder of the field is N deficient. This may be due to losses or lack of mineralization, either way more N is needed. If the N-Rich strip is not evident then the crop is finding enough N outside of the reference strip to support its current growth. This could be that residual N or mineralization is high, or it could mean that crop growth and therefore N demand is low. Having the N check strip in each field allows for a season long evaluation. We can use NDVI to characterize how big or little of a response we have to N. We call this the Response Index (RI). An RI of 1.8 means that we could increase yield by 80% if we add adequate N, if the RI is 1.05 then we are looking at a potential increase of 5%. I have a previous blog which goes into the application of the reference strip. “Nitrogen Rich Strips, a Reminder

Finally we combine the two, YP and RI. By predicting the yield of the area out side the N-Rich strip we can determine environmental yield potential, YP0. Basically what can the field yield if nothing is added. We multiple YP0 by the RI to get the yield potential with added N, YPN. Then its as simple as N rate = (YPN – YP0 ) x N needed per bushel. So for example if YP0 is 40 bushel RI =2, then YPN is 80 bushel. I need to fertilize the additional 40 bushels of wheat and I can use the 2.0 N per bushel can come up with a top-dress rate of 80 lbs N per acre. We are now incorporating site specific in-season NCrop and NSoil data.

And just a reminder for those of you new to my blog, I have a lot of research documenting that it is not only OK, but often best if we wait on N application in wheat and other crops. Value of In-Season N blog.

Every step we take towards the easy button is often a step towards site specific imprecision due to the use of generalized terms or models. Depending on your goals this very well could be acceptable for your operation, but with nitrogen prices as volatile as they are, should we not be considering pushing the easy button to the side, for now. Let’s add a bit of site-specific data so that we can take advantage of the N the system may be giving us, or the yield we did not expect. Let the N-Rich Strip be that first step.

Relevant Peer Review Publications.

In-Season Prediction of Yield Potential Using Wheat Canopy Reflectance,  Agron. J. 93:131-138

Nitrogen Fertilization Optimization Algorithm Based on In-Season Estimates of Yield and Plant Nitrogen Uptake
  J. Plant Nutr. 24:885-898

Real-Time Sensing and N Fertilization with a Field Scale GreenSeeker Applicator

Identifying an In-Season Response Index and the Potential to Increase Wheat Yield with Nitrogen (pdf)

Nitrogen Response Index as a Guide to Fertilizer Management
 

Evaluation of Green, Red, and Near Infrared Bands for Predicting Winter Wheat Biomass, Nitrogen Uptake and Final Grain Yield 

Full List of NUE Publications

If you have any questions please feel free to contact me @ b.arnall@okstate.edu

Nitrogen Source: What’s “cheap” now may be lost later

Raedan Sharry, Ph.D. Student, Precision Nutrient Management
Brian Arnall, Extension Specialist, Precision Nutrient Management

Note, this blog is focused on grain only winter wheat production.

Crop producers looking to increase profits often consider how to reduce costs without sacrificing yield and/or quality. This applies to essentially all production functions including nitrogen application. Winter wheat growers in the southern Great Plains have a wide number of options available to them when considering nitrogen source and application technique. At the time of writing (08/27/2021) fertilizer prices obtained from the Two Rivers Farmers Cooperative are as follows ($/unit): UAN (28-0-0) $0.62, NH3 (82-0-0) $0.45, and Urea (46-0-0) $0.62. These price levels equate to approximately a 57% increase in urea cost, 65% increase in UAN28, and a 65% increase in NH

Application Timing

Winter wheat producers in the southern plains have historically applied nitrogen (N) fertilizer prior to planting, often utilizing anhydrous ammonia for application due to its generally lower price point per unit of N relative to other sources. However, research at Oklahoma State shows that if the total N application is delayed until approximately feekes 5 to feekes 7 stages (jointing) yields were increased 23% of the time while grain protein was increased 68% of the time. By delaying N application to later in the growing season N is more likely to be available when the crop requires by avoiding conditions conducive to losses. Further reading on delaying nitrogen application can be found here (https://osunpk.com/2020/09/10/value-of-in-season-application-for-grain-only-wheat-production/)

A study located a Perkins, OK observing yield and protein response provides an example of an expected response to delayed N. In this study 3 N fertilizer rates (180, 90 and 45/45 split) across 5 different timings (Pre, 30, 60, 90, and 120 days after planting) where investigated. Grain yield was maximized by the 180 lb. rate applied 60 days after planting, while protein was maximized at the 120 days after planting timing. This same trend continues across all N rate levels as the later N applications whether at 60 or 90 increased yield relative to the pre while the 120 days after planting application maximized protein level regardless of rate level. However, maturity of the 120 day application treatment was severely delayed. This experiment shows the ability to sustain yield while decreasing N rate if N application is pushed to later in the season to avoid conditions that lead to N losses as displayed by the 90 lbs. at 90 days after planting treatment compared to the 180 lb. pre-plant rate.

Winter Wheat grain yield (bushels per acre) and grain protein (%) results from a study looking at application of nitrogen. Zero, is zero N check, 180 and 90 treatments were all of the 180 or 90 lbs N per acre was applied at pre-plant, 30, 60, 60, or 120 GDD>0 after planting. The 45s refers to split application were 45 lbs N was applied at pre-plant and an additional 45 lbs N was applied at 30, 60, 60, or 120 GDD>0 after planting. All N applied at NH4NO3. Pre (4.11.20), 30 (8.12.20), 60 (2.23.21), 90 (3.19.21), 120 (5.2.21). Blue bars are grain yield, orange dots protein.

Application Cost

Application costs are directly related to choice of source utilized. For instance; anhydrous ammonia application is predicated on the use of a pulled implement such as a low disturbance applicator for in-season application or a tillage implement for pre-season application. This is compared to other sources such as urea or ammonium nitrate which may be broadcast, or UAN that can be applied using a sprayer. The relationship between source and cost of application is inherently related to the application efficiency of the equipment used. Table 2 below provides a rough idea of cost associated with different application methods. (Information Retrieved from Iowa State). Fuel cost assumed at $2.60/gal. Labor cost assumed to be $15.00/hr.

ImplementOperating EfficiencyFuel cost/acLabor Cost/acOperating cost/ac
90’ SP Sprayer~78 ac/hr$0.34$0.19$0.53
60’ Dry Spreader~30 ac/hr$0.39$0.50$0.89
35’ Sweep Plow~21 ac/hr$1.43$0.71$2.14

In many operations across the southern plains efficiency has become a key factor in decisions such as input selection and equipment purchases. This has come in response to the need to cover more acres with less labor. With that in mind and looking back to table 2 it is easy to see that a self-propelled sprayer is likely able to cover more acres than other equipment options. This most likely should be considered when considering options for N management in the wheat crop.

Summary

With wheat sowing quickly approaching for many and field preparation nearing completion it is important to consider your nitrogen management options. Delayed N application allows for flexibility in management plan and depending on source utilized may increase application efficiency over pre-plant applications requiring a tillage implement. As fertilizer prices continue to remain high it is also important to consider the likely increase in N use efficiency due to applying N closer to when N requirement is peaking. Controlling cost while continuing to maximize output is imperative to sustainable profitability in crop production.

Any Question or Comments please feel free to reach out me.
Brian Arnall b.arnall@okstate.edu

Can Grain Sorghum Wait on Nitrogen?

Michaela Smith, Masters student under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist

            Grain sorghum producers in Oklahoma are challenged greatly by their environment and sporadic rainfall patterns, which diminish as the season progresses. These uncontrollable variables influence timing of nitrogen (N) application and nitrogen use efficiency. Using rainfall events as an incorporation method forces producers to apply before the event regardless of its intensity or delay application until field conditions are acceptable while anxiously waiting for another rainfall event. When deciding to delay N application it’s important to know the effects on physiological development and grain yield.

Figure 1. Field trial at Perkins, showing visual heading differences among nitrogen application timings. Timing from left to right were made 49 DAP, CHECK, 63 DAP.

Trial structure and breakdown

            This study was conducted over the 2020 growing season consisting four locations, including one double cropping system following wheat. Ten in-season applications were made using ammonium nitrate (AN) as the N source at a rate of 90 lbs. ac. Using AN as the N source reduced the risk of nitrogen loss through the process of volatilization as the goal of the research was to test the plant not the fertilizer. A pre-plant treatment served as the standard check, while in-season applications were initiated at 21 Days After Planting (DAP) and applications made sequentially at 7-day intervals. A non-fertilized check was included to the study to confirm locations were responsive to N fertilized applications Hybrid, plant date, and seeding rate can be found in Table 1.

Table 1. Planting information or the delayed nitrogen sorghum trials.

Physiological Response to Application Timing

            Two of the four locations demonstrated an effect to physiological development and maturity with the delay of nitrogen application. A delay in heading by a one to two-week period was observed at Perkins and Lahoma for applications made after May 21st (Table 2.). This delay in heading contributed to similar delay in maturity and potential harvest date. At Perkins decreased plant height was observed in the pre-plant plot and was associated with the onset of late season nitrogen deficiency (Figure 2). While this response was unexpected, the impact of nitrogen deficiency experienced early in the crop growth on the root and shoot growth has been well documented in many species. As a plant experiences nitrogen limitations growth changes from above ground to the below ground parts (roots) in an attempt to alleviate nitrogen stress. This increase in root growth could contribute to a more efficient uptake of nitrogen and decrease loss. In contrast to Figure 2, pre-plant application is shorter than compared to later season applications, this could be a result of inadequate N uptake thus leading to N loss by leaching, whereas later applications had increased root growth for efficient N interception and uptake.

Table 2. Delay in Heading for the Perkins (gray) and Lahoma (green). Letters indicate the start and finish of heading. S represent the start of heading while F indicants the finish of heading, SF denote treatments the started heading and finished within the same week.
Figure 2. Visual maturity differences between nitrogen application timings. Timing of applications are listed within the figure.

Yield Response to Application Timing

Response of N was observed at all locations (Figure 3), while the delay of nitrogen varied in its effects across all locations. Grain yield from each N application was compared back to the pre-plant application to evaluate the effects of timing. All four locations responded positively to N fertilizer.  At both LCB and Lahoma grain yield was maintained with applications made as late as 42 to 63 DAP respectively before any negative trend in grain yield was observed. Perkins was the only locations to have a statistically significant increase in grain yield due to delayed N applications. At this site, which is a sandy loam, waiting until 42 DAP resulted in a 15 bushel increase over the pre-plant plot. Now Alva which was double crop showed that rainfall is key.  At this site, none of the in-season treatments made it up the level of the pre-plant. The reason for this will be discussed further below.

Figure 3. Grain sorghum yield results from the nitrogen timing studies conducted at four locations in Oklahoma.

Influence of Rainfall

            The loss in grain yield at Perkins in the pre-plant application could likely be reflective of nitrogen loss due to leaching. Pre-plant applications have been well documented in the aspect loss as a result of crop requirement and early physiological development. Long term mesonet rainfall data depicts a decline in the probability of rainfall with the progression of the growing season across all locations. In early season the probability of 0.5 inches of rainfall ranges from 8 to 10% respectively for LCB, Lahoma, and Perkins, and dramatically decline to percentages at low as 5% in mid-July during grain filling period. For Alva rainfall probability is substantially lower as its season was initiated during the drier months, which depicted a probability of 6% for 0.5 inches of rainfall, and 4.5% for 1 inch for early season rainfall crucial for pre-plant incorporation and crop establishment. These probabilities drop considerably compared to regular season as the months progress onward, mid to late August probability for 0.5 inches ranges from 0.8 to 11.5%, while for a 1 inch is 0 to 6.9%. Past weather data provided by the mesonet illustrates how later in the season rainfall and its amount is variable, suggesting that in a double crop scenario delayed application is not recommended while it is in regular season crop due to the increased chance of rainfall probability. 

Summary

            The purpose of this study was to evaluate the impacts of delayed nitrogen application in grain sorghum. In order to develop an accurate conclusion additional site years are required, although current data could suggest delaying nitrogen application for full season grain sorghum is possible without a detrimental loss in grain yield. This means producers have time to evaluate the crop and market to determine if more inputs are needed and economical, while allowing implementation of technologies such as the N-Rich Strip and SBNRC.

If you have any questions for comments please reach out.
Brian Arnall
b.arnall@okstate.edu
405.744.1722

Acknowledgement of LSB Industries for support of this project.

Nitrogen timing in a winter wheat forage system

Bronc Finch Ph.D. student under the leadership of D.B. Arnall
Brian Arnall, Precision Nutrient Management Specialist.

The recent weather conditions have caused a delay in the ability to top-dress winter wheat in some parts of Oklahoma. Despite this delay, conditions have still been good for growth, which means a steady increase towards the hollow stem and jointing stages. As these stages approach, or have passed, many concerns have been raised about the decision to apply nitrogen to increase spring forage production of winter wheat. A study conducted over the past two years at Oklahoma State University, in cooperation with Noble Research Institute has had the opportunity to evaluate how a nitrogen application at or just after hollow stem impacts the forage production of winter wheat. This study was set up with three fertilizer treatments of a 60 lb N pre-plant only, 120 lb N pre-plant only, and a 60 lb pre-plant and 60 lb top-dress applications. In the first season of the trial, 2018-2019, the fertilizer application was applied shortly after the wheat achieved the Feekes 6 stage (hollow-stem) due to rain and other conditions preventing a timely top-dress. In the 2019-2020 season of the trial the treatments were applied at a more ideal time, near the end of February and beginning of March before hollow stem. For this study the first cutting was targeted for just prior to hollow stem and the second cutting conducted at early boot stage. 

In 2018-2019 the additional 60 lb N applied in the 120 lb N pre-plant increased the dry biomass production in the second harvest by 0.4 and 0.9 tons per acre above the 60 lbs treatment at Chickasha and Lake Carl Blackwell, respectively (Figure 1). The delay of the additional 60 lbs of N increased the yield by an additional 0.7 and 1.7 tons per acre, respectively. The 2019-2020 season showed similar results at the Lake Carl Blackwell location in the second harvest, where the additional 60 lbs N at pre-plant increased biomass yield by 0.6 tons, with the delaying of the additional 60 lbs increasing biomass yield by 0.6 more as compared to the same rate when applied at pre-plant. But that additional yield gained with the split application came at cost as the 120 pre-plant resulted in 0.6 tons more in the first harvest. These results suggest that more N was needed in the pre-plant and top-dress application. The 2019-2020 Chickasha trial showed little difference in rate, more than likely 60 lbs N was enough maximize forage yield.

Figure 1. Dry matter harvest results for each of the harvest dates from the forage wheat trials from Chickasha (left) and Lake Carl Blackwell (right) in 2018-2019 (top) and 2019-2020 (Bottom). Three fertilizer treatments 60: 60 lbs Nitrogen applied at pre-plant, 120: 120 lbs of Nitrogen applied at pre-plant, and 60/60: 60 lbs of Nitrogen applied at pre-plant and an addition 60 lbs of Nitrogen applied at top-dress.

 Total biomass production for 2018-19 winter wheat forage (Figure 2) showed to have a greater increase in total biomass production when the N was split applied with the second application being made shortly after hollow stem. The split application increased total biomass production by as much as 1.3 tons per acre more than the same rate applied as all pre-plant. The 2019-2020 year total biomass production shows to be about the same whether the N was applied all pre or split and applied in February.

Figure 2. Total dry matter harvest results for forage wheat trials from Chickasha and Lake Carl Blackwell in 2018-2019 (Left) and 2019-2020 (Right) Three fertilizer treatments 60: 60 lbs Nitrogen applied at pre-plant, 120: 120 lbs of Nitrogen applied at pre-plant, and 60/60: 60 lbs of Nitrogen applied at pre-plant and an addition 60 lbs of Nitrogen applied at top-dress.

Figure 3 documents N uptake of winter wheat biomass for both years continues the same trend as total biomass. Nitrogen uptake can be directly related to protein as the calculation for protein is %N * 6.25. In all cases uptake was greater than applied. In 2018-2019 split application increased over all nitrogen uptake. Much like the yield of 2019-2020 the N uptake was not significantly impacted by the timing of the N application.

Figure 3. Total nitrogen uptake results for forage wheat trials from Chickasha and Lake Carl Blackwell in 2018-2019 (Left) and 2019-2020 (Right) Three fertilizer treatments 60: 60 lbs Nitrogen applied at pre-plant, 120: 120 lbs of Nitrogen applied at pre-plant, and 60/60: 60 lbs of Nitrogen applied at pre-plant and an addition 60 lbs of Nitrogen applied at top-dress.

Although the assessment of N application made at or after hollow stem in a winter wheat forage system was not an objective of this study, the circumstances have given a unique opportunity to evaluate the outcome. In the 2018-2019 trials when top-dress application was applied at or just following the hollow stem, yield and nitrogen uptake were both increased over the equivalent pre-plant application. For the 2019-2020 season where N was applied at the planned time yields and N uptake were equivalent to the pre-plant. While this data is not conclusive it does indicate the producers can apply N fertilizer to winter wheat forage at or after hollow stem and successfully increase both forage yield and nitrogen uptake.

For questions or comments please feel free to reach out.
Brian Arnall
b.arnall@okstate.edu
405.744.1722

Acknowledgement of LSB Industries for support of these projects.

Value of in-season application for grain only wheat production.

Data used in this blog is summarized from work by
Joao Souza, under the leadership of D.B. Arnall
Lawrence Aula, under the leadership of W.R. Raun

Key Points

  • Wheat is highly resilient and can endure nitrogen stress for a significant period of time and fully recover.
  • Delaying all nitrogen until the Feekes 5 to Feekes 7 time frame resulted in improved yields over the pre-plant 32% of the time and a loss of yield 5%. However, grain protein was improved 82% of the time with delayed nitrogen.
  • It is better to delay nitrogen application to avoid conditions conducive to N loss. 

 

Following the 4Rs of nutrient stewardship has been proven to increase the sustainability and profitability of an agricultural operation. As described by The Fertilizer Institute (https://nutrientstewardship.org/4rs/) the 4R Nutrient Stewardship provides a framework to achieve cropping system goals, such as increased production, increased farmer profitability, enhanced environmental protection and improved sustainability. To achieve those goals, the 4R concept incorporates the: Right fertilizer source at the Right rate, at the Right time and in the Right place.

Historically winter wheat producers have utilized pre-plant nitrogen (N) fertilizer application due to efficiency of time and the lower cost of the primary N source, anhydrous ammonia. However, as the growing cycle of winter wheat is approximately 9 months long with only 80% of the total N accumulation reached by flowering.  Research as shown that N applied prior to planting is more likely to be lost due to leaching or denitrification. Researchers at Oklahoma State University have invested significant efforts in evaluating N management strategies. This blog will present the data from multiple trials which allowed for the comparison of nitrogen applied pre-plant versus in-season. The trials were conducted over a four-year period at multiple locations across central Oklahoma.

Figure 1: Nitrogen uptake of winter wheat from planting to harvest. Adapted from Silva et al.2019. Kansas State University dissertation.

Delayed Nitrogen – NH4NO3
This study was started in the fall of 2016 and concluded with the 2020 wheat harvest. In all, twelve trials were established and achieved maturity. This study was designed to evaluate the recovery of winter wheat grain yield and protein after the crop was N stressed. Treatments included an untreated check, pre-plant application and ten in-season treatments. The application of in-season treatments was initiated when N deficiency was confirmed and treatments were applied in progressive order every seven growing days to the point of 63 growing days after visual deficiency (DAVD). A growing degree days is any day that the average daily temperature is at or above 40⁰ F.  Ammonium nitrate (NH4NO3) was applied at a rate of 90 lbs N ac-1 for all treatments.

Nitrogen response was observed at eleven of the twelve locations, and those sites will be the focus of this review. Nitrogen applications were started ranging from Nov. 10th to Mar. 7th for 0 DAVD and, concluded with 63 DAVD occurring between mid-February and early-May. The analysis of the data evaluated the yield and protein of the in-season applications compared to both the pre-plant application and the application made at the first sign of N deficiency, 0DAVD.

Across the eleven responsive years, the pre-plant application never outperformed the 0DAVD in terms of grain yield or protein. In fact, across all location if the in-season application was made prior to the end of March, the yield and protein was equal to or better than pre-plant applications. Four out of elevens sites, yield was significantly improved with in-season applications, and protein was improved in ten out of eleven locations. For the ten site/years that had applications in March, the mid-March application of 90 lbs of N, which is about the stage of hollow stem (Feekes 6), statistically increased yield four times and protein nine times compared to the pre-plant treatment.

The studies objective was to evaluate how long the crop could be deficient and fully recover. There was no relation between when the crop became deficient and when the crop could no longer recover. Yield as maintained as long as the N was applied by late March, or just before the flag leaf is visible (Feekes 8), grain yield was the same as if applied on the first day of deficiency. However, if the N was delayed to March protein was increased six out of the eleven locations.

Figure 2: Image of the delayed nitrogen study with treatments identified.

 

Delayed Nitrogen – Urea

A mirror study to the Delayed Nitrogen – NH4NO3 was established in the fall of 2018 and concluded with the 2020 harvest. This study was placed next to the NH4NO3 and treatments applied on the same days using the same rate (90 lbs N ac-1) applied as urea to evaluate efficiency of urea applications over a range of dates.
Three of the four locations produced a positive response to N fertilizer and documented similar results as the NH4NO3 project. Across these three sites in-season N was always equal to the pre-plant rate if applied before the flag leaf is visible. In addition, if the urea was applied just after hollow stem, not only was yield maintained but protein was significantly increased compared to both the pre-plant and 0DAVD treatments at all three responsive sites.

Split Rate Nitrogen – NH4NO3

This study looked at multiple rates and times of N application but for this factsheet we will focus on a small set of treatments. Performed over two years and four total sites this project looked at split application of N versus a one-time application, 45/45 split or 90 lbs of N. Application timing was 0, 30, 60, 90, 120 growing days (GDD>0), trying to have applications at planting in December, February, March and April. In three of the four sites the 90 day application produced the greatest yield and protein for both 45/45 and 90 treatments. In this study the one-time application of 90 lbs N ac-1 out yielded the 45/45 split in two of the four years and was equal the other two. The 90 day application of 90 lbs N ac-1  produced a higher protein concentration at all sites compared to the 45/45 split applied on the same date.

Nitrogen Rate by Time – Urea Source

This study evaluated four rates of N (0, 40, 80, 120 lbs N) applied at three times (30 days pre-plant, pre-plant, and Feekes 5) using urea. Feekes 5 is the growth stage prior to hollow stem when the wheats leaf sheaths are becoming strongly erect. This project was completed over two locations for two years, however of the four site/years only three statistically responded to N fertilizer. In those three responsive trials the Feekes 5 application grain yield was equal to pre-plant once, greater than pre-plant once, and less than pre-plant once. The grain protein was only statistically different between the pre-plant and Feekes 5 once, with an increase in protein with late N. The one location with yield loss can be likely attributed to N loss from urea volatilization. The urea was applied on no-till immediately after a heavy rainfall with no substantial precipitation occurring for a week after application.

Summary

This factsheet summarizes four separate research projects which can contribute data from 24 trials to evaluate the application of in-season N compared to pre-plant N, see Table 1. Of these 24 site/years we can draw conclusions from the 22 that responded to N fertilizer applications. Across these trials applying all N pre-plant resulted in the highest grain yield once, applying all N in-season near or after hollow stem resulted in an increase in grain yield above that of the pre-plant seven times. However, the delaying of N application until hollow stem resulted in a significant increase in grain protein concentration at 18 of the 22 trials. 

These results are significant for the winter wheat growers of the southern Great Plains as this research documented not only the ability but the necessity to move away from pre-plant and fall N applications for winter wheat grain production. The window for N application is likely much greater than most wheat producers would have considered. This work showed that not only could N be delayed and yield not sacrificed but, when delayed; yield will be maintained and protein concentration increased.

The final conclusion is that the timing of N application should not be based upon the presence of N deficiency or calendar date. Rather the timing should be based upon the weather and enviroment during application. While many of the projects used NH4NO3 as the N source to limit the impact of N loss via volatilization, the primary source for in-season nitrogen in the region are dry urea and urea ammonium nitrate (UAN) solution. Both of these sources have well documented loss due volatilization. The location from the Nitrogen Rate by Time trial which Feekes 5 applications were statisically below the pre-plant application supports this. This data set provides signifiant evidence that the optimum application window is quite wide and allowing producers more flexiabltiy to avoid those environments which will likely lead to N losses.

Table 1: Summary of all trial locations and years. The X represents statistical significance, alpha = 0.05. In-season application represents all treatments applied at least 30 growing degree days after planting. Majority of the treatments in the studies were applied after spring green up.

Nitrogen rate and timing for a forage wheat crop. Year 1 Results.

Written by
Mr. Bronc Finch, PhD. Student, Precision Nutrient Management. 
Dr. Brian Arnall, Precision Nutrient Management Extension Specialist. 
In cooperation with Dr. James Rogers, Noble Research Institute. 

With the amount of wheat acreage in Oklahoma being utilized for grazing cattle, and much of that land grazed completely instead of harvested for grain, many questions have arose regarding the management of grazed cropland. A major question in the management of a graze-out wheat crop pertains to fertilizer management strategies. A study developed in co-operation with the Noble Research Institute is attempting to answer these questions among others. In 2019 the trial was established at three locations: near Lake Carl Blackwell in Stillwater, OSU South Central Research Station in Chickasha, and Noble Research Dupy farm in Gene Aurty, Oklahoma. Each of these three sites were setup with three nitrogen (N) treatments in Gallagher winter wheat, with 2 pre-plant applications of 60 and 120 pounds per acre, and a 60 pound pre-plant and 60 pound top-dress application. Grazing simulation harvests were taken at two times with the top-dress N being applied after regrowth was noticed following the winter season. The Dupy location was planted late and therefore only had a single harvest at the end of the season. Rising plate meter measurement were collected at feekes 7.5 and represented in the graphs below as Mid-season. The Chickasha location revealed unexpectedly high residual soil N levels, which resulted in no differences in dry matter biomass for the first harvest, which was delayed until early march due to excessive rains. The second harvest at Chickasha did show treatment differences with a 0.4 ton difference between the 60 and 120 lbs preplant N rates and increase of 0.8 ton increase over the 120 lb pre-plant when the additional 60 lbs of N was delayed. LCB had a timely first harvest in December resulting in the 120 lb N application outperforming the 60lb N applications by ≥0.33 tons. The second harvest further showed how the split application of N proves beneficial for biomass production. As the split application increased yields by 1.7 and 2.6 tons over the 120 lb and 60 lb preplant applications, respectively. The Dupy location revealed no significant difference in dry matter biomass yield between N treatments at the time of the rising plate meter measurements or for the final cutting.

Figure 1. Dry matter harvest results for each of the harvest dates from the graze out wheat trials from the Chickasha, Lake Carl Blackwell, and Dupy locations for three fertilizer treatments. 60: 60 lbs of nitrogen applied preplant, 120: 120 lbs of nitrogen applied preplant, 60/60: Split application 60 lbs of nitrogen preplant and 60 lbs applied top-dress. Dupy only had one harvest date, the Mid-season yield is estimated via rise-plate measurements taken at Feekes 7.5.

 

The Chickasha and Lake Carl Blackwell (LCB) locations produced an increase in total yield with both the increase of applied N and the split application of N. The 60 lb increase in applied N at preplant, 60 lbs vs 120 lbs, produced a 0.7 and 1.2 ton increase in total dry matter harvested at Chickasha and LCB, respectively. As expected an increase in N increased the yield of wheat biomass for grazing production. The top-dress application, which was made as a late season post Feekes 6 (hollow stem), produced more biomass for graze-out wheat production. The split application of 60 lbs of N preplant and 60 lbs of N top-dress increased dry matter by .8 and 1.3 tons over 120 lbs applied preplant at Chickasha and LCB, respectively. Chickasha yielded higher biomass production than the LCB location due to increased residual N.

Figure 2. Total dry matter harvest results for the graze out wheat trials from the Chickasha, Lake Carl Blackwell (LCB), and Dupy locations for three fertilizer treatments. 60: 60 lbs of nitrogen applied preplant, 120: 120 lbs of nitrogen applied preplant, 60/60: Split application 60 lbs of nitrogen preplant and 60 lbs applied top-dress.

For the following discussion remember that protein is determined by N concentration, so that a increase in N uptake is the same as an increase in protein. Evaluation of the N uptake (% N in the biomass x amount of biomass harvested) over the season revealed treatment effects at all locations, which was not seen from biomass yield. Chickasha and LCB revealed a 20% or greater increase in N uptake with the 120 lb application over the 60 lb application of N at pre-plant. The late season top-dress application yielded a 3, 27, and 27 percent increase in uptake for Chickasha, LCB, and Dupy locations, respectively, over the 120 lb pre-plant application. Although, these results are expected from these results, there are a few things we did not expect. The 120 lb N application did not increase the N uptake above that of the 60 lb application. However, the split application of N resulted in an additional >40 lbs uptake, aka increased protein.

Figure 3. Total nitrogen uptake results for the graze out wheat trials from the Chickasha, Lake Carl Blackwell, and Dupy locations for three fertilizer treatments. 60: 60 lbs of nitrogen applied preplant, 120: 120 lbs of nitrogen applied preplant, 60/60: Split application 60 lbs of nitrogen preplant and 60 lbs applied top-dress.

This study also includes summer forages with and without additional fertilizer. The study will be continued for multiple years on the same locations to evaluate the impact of management on production and soil characteristics.  But one surprising note has already been made, in all three locations a greatly delay top-dress still increased N-uptake. In two location it significantly increase yield and protein. This data is falling in line with the grain only data (How late can you wait) showing that an application of N at Feekes 6 (Hollow stem) and even shortly after can provide positive return on investments.

 

For any questions for comments please contact
Brian Arnall
b.arnall@okstate.edu
405-744-1722

 

Watch Forage Nitrate Closely on Certain Crops

Nitrate is one of the major nitrogen (N) forms utilized by plants. Excessive nitrate accumulation can occur when the uptake of nitrate exceeds its utilization in plants for protein synthesis due to factors such as over N fertilization and stressful weather conditions. It can be toxic to livestock when too much nitrate is accumulated in the forage crops. Sorghum and millet have been noted as having a high potential for accumulating nitrate. Producers should watch their forage nitrate closely to avoid cattle fatality and to better manage their hay crop since we have seen many high nitrate forage samples every year. Normally, drought stress, cloudy weather and other climatic conditions will enhance nitrate accumulation in the plant. In addition, forage planted in failed wheat fields with high soil residual nitrogen unused by wheat can result in high forage nitrate problem too.

Figure 1. Summary of our laboratory nitrate test results in the past on two major warm season forage crops.

It is considered potentially toxic for all cattle when nitrate in the forage is greater than 10,000 ppm. Producers should avoid grazing or feeding with high nitrate hays. More detailed interpretation can be found from OSU Extension Fact PSS-2903 Nitrate Toxicity in Livestock. The most reliable way to find out nitrate in the hay is to collect a representative sample and have it tested by a laboratory. OSU Extension Fact PSS-2589 Collecting Forage Samples for Analysis highlights the proper techniques to collect forage samples. Samples can be submitted for nitrate and other forage quality analyses to the Soil, Water and Forage Analytical Laboratory in Stillwater through the local county extension office. We normally have the results ready within 24 hours form the time when sample is received by the lab. However, many samples we receive at the lab were not sampled properly. More attention should be paid on sampling standing forage, such as a haygrazer by following the right procedures:

Clip at least 20 representative plants at grazing or harvesting height from the suspected area. Cut the whole plants (include leaves and heads) into 2-3” long pieces, combine and mix well in a bucket.

Fill the cut sample into a forage bag. Use quartering to reduce the amount if there is too much sample to send to a lab.

Put the forage bag into a plastic bag will give you more accurate moisture content, but never put plastic bags inside our forage bags.

There is also a quick screening test using diphenylamine at your county extension office. This video shows how to properly use the test kit: https://www.youtube.com/watch?v=vArUP6KFQFI&feature=youtu.be

 

Hailin Zhang

Department of Plant and Soil Sciences

Hailin.zhang@okstate.edu

DAP in short supply? Revisiting, DAP vs MAP, Source may matter!

From mid August through October, fertilizer applicators and grain drills are running across the southern great plains wheat ground. Di-ammonium Phosphate (DAP 18-46-0) is maybe the most popular form of phosphorous (P) utilized in wheat production today. DAP delivers a high content of nitrogen (N) while efficiently binding the toxic aluminum (Al) ions low pH soils. However due to the flooding that occurred throughout the spring the Ports have been closed and DAP could be in short supply. I have heard that many companies and Co-ops have already sourced Mono-ammonium phosphate (MAP 11-52-0) to supplement the lack of DAP for our early planted wheat crop. With this happening, I wanted to share some points about the two sources. In a broadcast incorporated scenario I do not have much preference for one over the other. It is when producers are applying the fertilizer in-furrow or applying to alleviate Al toxicity that source can matter. As described in the post below, in a soil with a neutral pH DAP and MAP perform equally well. So in this scenario I give MAP a slight edge over DAP if the price is the same. I say this as you can run less material per acre with MAP and refill a little less often. Many worry about the drop in N delivered with MAP versus DAP but in my work I see that is the P in the starter that gives us a good response and not the N, which can be delivered with pre-plant or top-dress. However, DAP wins out in soils with a pH below 5.5. The original blog below shows the results when DAP and MAP are banded in acidic soils using the same rate of P per acre.  The reason we see this happen is that when MAP dissolves it forms a slightly acidic solution (approx 4.0) while DAP will dissolve to form a slightly basic solution (approx 7.5). In our work BOTH DAP and MAP increased yield above the check in acidic soils, which goes to show MAP is an affect tool for short term remediation of aluminium toxicity (Band P for Al toxicity Blog). However it might require more MAP per acre to reach the equivalent results. Because of what we saw when comparing the two sources at equivalent rates of P, I would recommend increasing the rate of P2O5 from 30 lbs per acre to 35 or 40. This would be going from 65 lbs of DAP to 67-77 lbs of MAP per acre.

So the take home would be as this wheat season takes off and you find that DAP is hard to locate and you A) Have overall neutral (5.5+) pH levels do not hesitate using MAP. Run the normal amount of material getting a few extra lbs of P or apply less material to get the same amount of phosphate. B) Have a acidic situation and are banding to alleviate aluminum toxicity use the same amount of material or a little bit more.  Keep in mind in acidic soils with a low soil test P level you have to apply enough phosphate to take care of the Al and enough to take care of the P deficiency. Note the results of the NPKS wheat response strip (NPKS BLOG)

Original Post Published July 18, 2016
DAP vs MAP, Source may matter!

Historically the two primary sources of phosphorus have had different homes in Oklahoma. In general terms MAP (11-52-0) sales was focused in Panhandle and  south west, while DAP (18-46-0) dominated the central plains.  Now I see the availability of MAP is increasing in central Oklahoma. For many this is great, with MAP more P can be applied with less material. which can over all reduce the cost per acre. There is a significant amount of good research that documents that source of phosphorus seldom matters. However this said, there is a fairly large subset of the area that needs to watch what they buy and where they apply it.

If you are operating under optimum soil conditions the research shows time and time again source does not matter especially for a starter.  In a recent study just completed by OSU multiple sources (dry, liquid, ortho, poly ect ect) of P were evaluated.  Regardless of source there was no significant difference in yield.  With the exception of the low pH site. The reason DAP was so predominate in central Ok, soil acidity.  See an older blog on Banding P in acidic soils.

Picture1

Figure 1. The cover of an extension brochure distributed in Oklahoma during the 1980s.

When DAP is applied, the soil solution pH surrounding the granule will be alkaline with a pH of 7.8-8.2. This is a two fold win on soil acidity aka aluminum (Al) toxicity.  The increase in pH around the prill reduces Al content and extends the life of P, and as the pH comes back down the P ties up Al and allows the plant to keep going. However, the initial pH around the MAP granule ranges from an acid pH of 3.5-4.2.  There is short term  pH change in the opposite direction of DAP, however the the Al right around the prill becomes more available and in theory ties up P even faster.

Below is a table showing the yield, relative to untreated check, of in-furrow DAP and MAP treatments in winter wheat.  The N401 location had a ph 6.1  while Perk (green) has a pH of 4.8.  At Perkins in the low pH, both forms of P significantly increased yield, almost 20 bushel on the average.  DAP however was 5 bushel per acre better than MAP. At the N40 site the yield difference between the two sources was 1 bushel.

MAPvDAP2

Relative yield winter wheat grain yield MAP and DAP both applied at equal rates of P (32 lbs P2O5 ac) when compared to a untreated check.

In general it can be said that in acid soils DAP will out preform MAP while in calcareous high pH soils MAP can out preform DAP. So regarding the earlier statement about the traditional sales area of MAP or DAP if you look at the soil pH of samples went into the Oklahoma State University Soil, Water, and Forage Analytical lab the distribution makes since.

State pH

Average soil pH of samples sent into OSU soil water forage analytical lab by county.

In the end game price point and accessibility drives the system.  In soils with adequate soil pH levels, from about 5.7 to around 7.0, get the source which is cheapest per lbs of nutrient delivered and easiest to work with. But if you are banding phosphorus in row with your wheat crop because you have soil acidity, DAP should be your primary source.

How long can wheat wait for Nitrogen? One more year of data.

Update to the delayed nitrogen study.

Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.

Due to the surprising results seen from the delayed N study that was first reported below we repeated the the study for a third year at two locations, the Lake Carl Blackwell Research farm near Perry OK and the Ballagh Research Farm near Newkirk OK. Due to the excessive rain fall the wheat was planted and trials established later than normal and a cool winter and spring and winter the crop green up (end of dormancy) was delayed compared with the two first cropping seasons. For this season we started applications before visual symptom difference between the N-rich Strip (pre-plant) and the rest of the field actually occurred. This can be seen with the pre-plant dates of late Oct-Early Nov and the notation of visual difference above the yield bars. Just as the other two previously crop years, the timing of the application did impact wheat yield and protein. In this season at LCB we see a increase in yield with application of N during the first part of March compared to the preplant with yields dropping off below the preplant when N was applied in mid April. At the Ballagh farm there is no yield benefit from delaying N after preplant but there was steady increase in protein, again at this location yield is lost when N was delayed past mid April. In both of these locations mid April was after the growth stage of Feekes 7. After three cropping seasons with some extremely different weather patterns we saw that in this work, pre-plant N was never better than in-season N applied prior to mid April, Feekes 7. In most cases N applied in-season yields and protein values were greater than that of the pre-plant treatment. My take home message from this project is multi fold; First, pre-plant may be cheaper and easier but it often falls short of in-season applications, Second that there should be no reason to rush putting top-dress nitrogen on. The application window is much wider than most ever expected and the closer we get to peak demand the better the yield and quality will likely be. And third, and final make the application of nitrogen when the conditions are the most conducive to getting the N in the ground and limiting losses.

Note: This trial used ammonium nitrate as its N source to evaluate the plants response and remove potential fertilizer efficiency problems. However while these trials were being conducted mirror studies using Urea as the N source were also being conducted. Those results are currently being compiled right now and we hope to share the results soon.

Grain yield and protein results from the delayed nitrogen study preformed at the Lake Carl Blackwell near Perry in 2018-2019. 11/7/2018 was the pre-plant application date.

 

Grain yield and protein results from the delayed nitrogen study preformed at the Ballagh research farm near Newkirk in 2018-2019. 10/24/2018 was the pre-plant application date.

Questions for comments feel free to contact me via email at b.arnall@okstate.edu

Original Post made Oct 1, 2018

How long can wheat wait for Nitrogen?

Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.

The N-rich strip method allows wheat producers a greater window of decision making regarding the application of nitrogen (N) fertilizers. Besides having greater accuracy in N rates than standard methods (based on the SBNRC – OSU) also helps to reduce costs in the production system and to preserve the environment avoiding over N applications.

With the experiments performed in the last two crop seasons (2016/18 and 2017/18), we can now be even more accurate with regard to the best application time to increase the N use efficiency by the crop. The objective of our study was to determine the impact of prolonged nitrogen deficiency on winter wheat grain yield and protein. Eight studies were conducted with 11 N application timings in no-till dryland conditions. A pre-plant treatment of 90 lbs ac-1 of N was broadcast applied as ammonium nitrate (AN). We used AN as our source because we wanted to measure the crops ability to recover and eliminate the impact of source efficiencies. When visual symptom differentiation (VSD) was documented between the pre-plant and the non-fertilized check, i.e the N-Rich Strip showed up, top-dress applications were performed every seven growth days (GDD> 0) (https://www.mesonet.org/index.php) until 63 growth days after VSD at all sites. The only N the treatments received where applied according to treatment structure. No preplant N was applied other than trt 1, and all locations had residual N under 15 lbs 0-6” sample.

The first visual response to fertilizer N ranged from November 11 to February 5 (Table 1). The soil can have residual N from the previous season which can supply the subsequent crop in the beginning of the development what makes the wheat not demonstrate any sign of stress in the early season. For example LCB2017 a and b which were located 100 yards apart but under a different point in the crop rotation (LCBa was wheat after wheat and LCBb wheat after canola) had a 30 day difference in date of first N response. This range in first and last dates allowed us to evaluate N application over a wide range of dates and determine whether the first sign of stress is actually the best indicator of top dress application timing.

Table 1 shows the planting date, date of first visual difference (0DAVD) and each of the application dates for all locations. Different colors represent individual months. Hollow stem occurred approximately Feb 20 in the 2017 crop and March 10th in the 18 crop.

 

Image of the 2016-17 Perkins location. Image collected March 21 2017.

As shown in the Tables 2 and 3 below only three of the 78 comparisons made back to the pre-plant application were significantly less in terms of grain yield. All three of these comparisons where from when N application was delayed until late March or April. When the delayed applications were compared to 0DAVD yields only two of the 68 comparisons showed a significant decrease on yield. One was the pre-plant application for LCB2017a while the other were the 63DAVD application for LCB2017b. In most locations applications made in March yields were at the highest point, however when delayed till April yield trends on the downward trend. The 2017 crop reached hollow stem (Feekes 6) around Feb 20th while the 2018 crop reached hollow stem around March 10th.

Grain protein concentration was decreased only once when compared to both the pre-plant and 0DAVD treatments. This one timing, LCB2018b 64DAVD, was the only application made in May. During this time the crop was in the early stages of grain-fill. In all locations delaying N application until February/March increased grain protein content above the check, and in most cases above the 0DAVD trt.

Tables 2-3 shows the winter wheat grain yield and protein concentration, respectively, of all treatments. The colors of the cells represent statistical difference from the Pre-plant treatment. Treatments with cells shaded yellow are equal to the pre-plant, Green is statistically greater than while red is statistically less than the pre-plant treatment.

 

2016-2017 Delayed nitrogen winter wheat grain yield and protein results. For the locations of Perkins and N40 the Dec-1 application has a higher yield due to a 2x application of N to equal 180 lbs.

 

2017-2018 Delayed nitrogen winter wheat grain yield and protein results. The Perkins location in 18 was the only location in the study which did not have a statistically significant response to added N.

All the data was combined and plotted by cumulative GDD’s>0 from planting (GDDFP) across all locations to determine a general “best” timing. Using the pre-plant application yield as a base there was no yield loss if the applications was made prior to the 143 GDDFP. When the results were normalized by 0DAVD N there was no yield loss if the applications were made prior to 130 GDDFP. The quadratic model created provides the opportunity to identify the point of highest grain yield, which was approximately 94 GDDFP. In terms of the relationship between the application of N based on GDDFP and % of protein content on the grain, a linear response of N delay application observed for grain protein concentration. Our results suggest that the later the application, the higher the protein % in the grains.

Growing degree days > 0 from planting and equivalent calendar days for all experimental sites (Lake Carl Blackwell, Perkins, Lahoma, Stillwater) utilized in the study evaluating the impact nitrogen fertilizer timing on winter wheat, conducted in north central Oklahoma over the 2016-2017 and 2017-2018 winter wheat growing seasons.

We have concurrent work looking at similar approaches with other sources of N such as Urea and UAN. While all of  these studies are being continued the past two years of work have presented some easy take homes.

First: Timing of N application does matter, but yellow wheat does not necessarily mean yield loss.
Second: Two years in a row ALL Nitrogen could be delayed until hollow stem without yield Loss, in fact yields of trts with N applied at this time typically better than that of the pre-plant.
Third: Protein content increased as N applications was delayed.
Fourth: The conclusions of this and other studies support that N-Rich Strip concept does not increase risk of lost yield.
Fifth: Applying the majority of the N at or just after hollow stem maximized grain yield and protein with a single shot.
Sixth and Final: Be more concerned about applying N in an environment conducive to increased utilization and less about applying at the first sign of N stress. Take a look at the wheat N uptake curve by K-State.The crop really doesnt get going in terms of N-uptake until jointing i.e. hollow Stem.

Wheat N-uptake. Figure adapted from Lollato et al.

Questions for comments feel free to contact me via email at b.arnall@okstate.edu

Managing Protein in Hard Red Winter Wheat_Repost and Update.

As I write this on May 5, 2019, the wheat is at or nearing flowering and Stillwater just received another 2.22 inches last night helping the 30 day rain total to be just shy of 9 inches. Its wet, cool, and the wheat has truly gone from rags to riches (the crop not the market). I have been regularly fielding calls on late season N and protein. I thought it would be a good time to repost my previous protein blog and add some thoughts and updates. Since the original post we have more data on nitrogen (N) timing work and one year of data from a trial we call “Protein Progression”.  First if you are interested in the timing study the full blog summarizing 2 years of work can be seen here How long can wheat wait for Nitrogen? . But the short short version was that two years in a row delaying the application of ANY nitrogen until very late in the season, past hollow stem, resulted in the best combination of yield and protein. Meaning even when wheat was yellow and stunted yields and quality recovered when N was applied at or shortly after hollowstem. This work is being continued and expanded this year. I have only shared the Protein Progression results in a few presentations, because they do not tell a consistent story. For a few years now I have been giving this advice when asked about late season nitrogen. Based upon the work I have done, this year is my 11th wheat crop in this position and I have always had at least 1 study with late N, that when nitrogen was applied at flag leaf the probability of a positive return on investment was below 50% and closer to 33%. Very seldom did I see the flag leaf applications of nitrogen provide much benefit. At the flag leaf stage when there was a positive benefit it could be yield, protein or both. When it came to anthesis (flowering) applications the probably increased to closer to a 66%-75% chance of positive impacts (Understand these percentages are drawn from my experiential learning across many environments, I have not yet run the data to determine exact values). Late applications in the right environment could increase protein by up to 2% and in the wrong environment, devastate yield due to burn. The weather needs to be cooler and humid to reduce the potential of burn and the rate of nitrogen must high enough to actually impact protein levels. Per each 1% of protein concentration of wheat grain there is 0.1 lbs N per bushel. So to increase to increase the protein content of a 60 bushel wheat crop by 1%, 6 lbs much be converted from fertilizer to protein.  To get this amount of nitrogen on the crop without burning it up I have been using UAN (28-0-0) and water at a ratio of 1:1 putting on 20 total gpa. When applied this way I have not seen burn, I do however avoid spraying when its hot, windy with low humidity.
Below are last years results of the Protein Progression study. In this I wanted to look at N application timing pre vs post, the addition of sulfur (many sources state added sulfur increases yield), flag and anthesis application. Last year we had locations near Stillwater (LCB) and Chickasha. Both yielded in the 60 bushel range which was OK but well below the five year average of both sites. At the LCB we saw a great response to N fertilizer. The more it was delayed the better off yields were. We saw a consistent negative impact of S at top-dress, which is a result I can not explain, there was no crop damage due to application. The flag leaf N application significantly increased yields, at flag leaf there was evidence of N deficiency. And the anthesis application of N had no impact on protein. At Chickasha where the none fertilized check yielded 53 bushels, the response to N was reduced. Sulfur had no impact on yield or protein, flag lead N and anthesis N increased protein by about 1%.

What did I learn from those studies, I confirmed the response to late N is not very predictable. The low protein site (LCB average protein of 11.75) did not respond to late N but the high protein location (Chickasha’s average protein content was 15%) did. I was able to see N at flag leaf did impact yield when N deficiency was noted. It also confirmed this study will be continued for multiple years. The more environments we can get data from the better we can predict response/non response.

 

Results from the 2017-18 Protein Progression Study. The graphic on the left is from Lake Carl Blackwell near Stillwater, the center table is the treatment structure and the graphic on the right includes the yield and protein results from Chickasha. Nitrogen rate (pre + top) was 120 lbs N per acre, top-dress S rate was 10 lbs. The nitrogen rate at flag leaf and anthesis was 24 lbs N per acre, while the anthesis S rate was 10 lbs.  N source was UAN for all application and S source was ammonium thiosulfate. For flagleaf and athesis applications water was used as a carrier at a 1 to 1 ratio with the fertilizer.

If you have any questions feel free to send me an email at b.arnall@okstate.edu.

Brian

Original Post Sept 27, 2017

A result of the 2016-17 winter wheat crop was a significant amount of discussion focused on protein levels. For two years running now, the protein levels have been low across the board.  Low protein brings in a challenge to sell, could impact local basis, and even more concerning is that low protein is an indicator that nitrogen was limiting during grain fill. Therefore, the field maximum yield potential was not achieved. In this blog, we talk about what protein is, what can be done to maintain a good protein level, and what can be done to increase protein if desired.

First, the definition of protein is any of a class of nitrogenous organic compounds that consist of large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms, especially as structural components of body tissues such as muscle, hair, collagen, etc., and as enzymes and antibodies. Protein is also one of the many attributes that determines end-use quality and marketability of winter wheat. Sunup TV met with Dr. Carver in the baking and milling lab to create a great video discussing wheat quality impact on baking and milling.

 

We determine protein by measuring the percent of nitrogen in the grain and multiplying by a factor of 5.7. So if the grain has N % of 2.5, the protein content is 14.25.  The amount of N in the grain is affected by many variables such as weather during grain fill, yield level, and N availability during grain fill.  If weather is conducive to good grain fill and test weight is high, we will often see protein values dip. On the other hand when grain fill conditions are hot and dry and we have light test weight, wheat protein will be higher. Research has shown (Figures 1 and 2) that generally as yields increase protein levels decrease. Of course if N is limited during grain fill, the N available for the grain is reduced, and the plant is forced to get all grain N from re-immobilizing N in the leaf tissue.

Fig 1, Yield and protein averages from all of the OkState Long Term fertility trials. Data courtesy Dr. Bill Raun.

Fig 2, Grain protein and yield of from intensively managed wheat. Data Courtesy Dr. Romulo Lollato KSU.

 

Maintaining Protein, and yield.

Managing nitrogen to maintaining protein and maximizing yield comes down to making sure that N is available at critical growth periods. With wheat, the critical uptake stage is typically the time frame between hollow stem and soft dough.  The two graphs below show nitrogen uptake in wheat and barley.  If the same graph was made for dual purpose wheat, the upward swing would start sooner but would follow the same general trend.

Fig 3, Nutrient Uptake of Wheat found in “Agricultural and Biological Sciences » “Crop Production”, ISBN 978-953-51-1174-0, Chapter 5 By Juan Hirzel and Pablo Undurraga DOI: 10.5772/56095″

Fig 4, Nitrogen uptake in Barley at two nitrogen rates. http://apps.cdfa.ca.gov/frep/docs/N_Barley.html

When it comes to making sure N is available during this time of peak need, the only way we can do that is apply just before it is needed.  This means split application.  While putting all the nitrogen out pre-plant as anhydrous ammonia is the cheapest method, it is also the method that provides the lowest nitrogen use efficiency and is most likely to show deficiencies late in the season. One of the challenges with 100% preplant N application is that years with good yield potential coincide with years with good/high high rainfall, which means more nitrogen loss.  Some interesting results from studies implemented in the 2016-17 cropping season showed the importance of nitrogen application timing. The study is determining how long nitrogen application can be delayed after the N-Rich strip becomes visible (https://osunpk.com/2013/09/19/nitrogen-rich-strips/). For the study, 90 lbs of N was applied on one of the treatments at planting When that plot became visibly greener or bigger than the rest, N application was triggered. After the 0 DAVD (Days after visual difference where the day had growing degree days >0), another treatment was applied every 7 growing days for 63 growing days.  Each plot, excluding the zero N check, received 90 lbs as NH4NO3 (we use this to take the variable of volatilization out of the data). In all cases, 90 lbs applied in late January to early February was better than 90 lbs pre-plant. Keep in mind there was 0 N applied at planting for each DAVD application timing; yet, we still hit 50-80 bushel wheat with nothing but in-season N. This is the result of supplying the N when the plant needs it. I should add this is just one year of data, and every year is different. The study is being replicated again this year and will be highlighted at the Lahoma field day.

 

Fig 5, Results from the 2016-2017 delayed nitrogen study led by Mr. Joao Bigato Souza. The trials consisted of a preplant plot, unfertilized check plot, and then a series treatments in which N application was based on days from a visual difference between the pre-plant and check. All fertilized plots received 90 lbs N as NH4NO3. DAVD is days after visual difference. (Error in bottom left graph, the last date should be March 27 not April 4)

For dual-purpose wheat, the total amount of N expected for the forage production needs to be applied pre-plant. Oklahoma State recommends 30 lbs N for every 1,000 lbs of forage expected For grain-only wheat, there needs to be only 20 to 40 lbs of N available to the crop when planted (this includes residual N). The remaining N should be applied at green up or early spring.  The only way to ensure that N is applied when the crop needs it is to utilize the N-Rich Strip method. Having a N-Rich strip in your field lets you know when the wheat needs more nitrogen and when it does not.

Fig 6. Nitrogen Rich Strip (N-Rich) showing up in a No-till wheat field.

Two years testing the N-Rich Strip and Sensor based nitrogen rate calculator (SBNRC) from the Texas boarder to the Kansas boarder showed that the SBNRC on average reduced N but maintained yield and protein when compared to standard farmer practice (Table 1).

Table 1. Results from testing the Nitrogen Rick Strip and Sensor Based Calculator Method across Oklahoma wheat fields.

Increasing Protein

Some producers may plan to market high protein for a premium if available.  Fortunately, there are opportunities to increase protein via management. While most of the strategies for increasing protein happen later in the growing season, some of the early decisions can be a significant contributing factor. Variety selection and keeping the plant healthy and free of competition (i.e., pest management) throughout the growing season are going to increase the opportunity to produce high protein wheat.  After that, the equation goes back to Figures 3 and 4 and making sure the crop has access to nitrogen during peak periods, including grain fill.  If you will note, the bottom two graphs of Figure 5 both show significant increases in protein on the later applications. For both locations, this was when N (90 lbs N ac-1) was applied after full flag leaf emergence.  There has been a significant amount of work at OSU looking at late application of N stretching back into the 1990s http://nue.okstate.edu/Index_Publications/Foliar_N_Curt.pdf. The focus has been looking at timing, source, and rate. The take home of decades of work can be summarized as such.  Yes, protein can be increased with late season application, but not always. Applying N at or after flowering has a significantly greater probability of increasing protein than a application at flag-leaf. Source of N has had little impact if managed properly (UAN, 28-0-0, has to be watered down so that it does not burn the plant). The rate of N does matter quite a bit. Most of the work suggests that for every pound of N applied, the percent grain protein could increase by .05%. So to increase protein from a 12.5% to 13.5%, it would require approximately 20 lbs of N per acre.  My work has shown the same trend that a 20 lbs application at post-flowering had more consistent increases in protein than lower rates at the same time or similar rates applied at flag leaf.

This wheat season we are looking to improve our knowledge of management on protein content through multiple studies by continuing the evaluation of varieties and management practices.

If you have any questions for comments please feel free to contact me.
Brian A.
B.arnall@okstate.edu