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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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Phosphorus decisions, Is it worth cutting P?

With the current conditions and input cost many wheat producers are considering cutting back on inputs. I can’t disagree with the plan, but I would caution against what you cut. If you have read any of my past blogs, or seen me speak, you should know I’m all for cutting back on pre-plant nitrogen (N). Based on some recent trials I would not argue cutting the potassium (K) side, but phosphorus (P) that’s another story that we will walk through in this blog.

First and foremost, soil testing is the key to P management. If your soil test is below the critical threshold for the test you use, 32.5 for Mehlich 3 (M3P), then you need to add phos. We have enough work that shows current recommendations work for P in wheat. Reeds paper Evaluation of incorporated phosphorus fertilizer recommendations on no-till managed winter wheat Link to Paper goes over soil test recommendations in no-till and the recent double crop soybean project Double Crop P and K Blog highlights the importance of P fertility, regardless of yield level. Also if your soil test is below a 5.5 and you haven’t limed (Liming is the best solution, Band-aids not so cheap Blog ), then the next best option is adding additional P to alleviate the aluminum toxicity Band-aids for low pH Blog. In-short if the fields soil test P and or pH is below optimum you should not forgo P application.

But the primary reason I am writing this blog is for those looking at fields with composite soil test that is right around the critical thresholds, and they are trying to make the call on to apply P or not to apply P. Even on fields with soil test values in the good level, I am usually in favor of banding in-furrow fertilizer wheat, but not because of the same reasons I am for corn. With corn you are planting in cool soils and the availability of nutrients like P is lower in cool wet soils. For wheat cold soil isn’t the concern until we reach the end of the planting window. It will serve as a bit of a “pop-up” as the crop comes out of dormancy in the spring. I have also seen little to no value of N applied in furrow. I see same response to DAP (18-46-0), MAP (11-52-0), and TSP (0-46-0) when all applied at same rate of P. Meaning it was the P not N making the difference.

For me the reason I still recommend getting a little phosphate out even when the soil test comes back is that the great majority of fields have a large range of variability. Looking at a set of 650 grid sampled fields across Oklahoma and Kansas it showed on average soil pH 6.0 and M3P was 34 ppm. Both pH and P are at adequate/optimum levels. However, the average is usually somewhere between the low and high point and in this data set and the range of soil pH was 1.8 units and the range in M3P was 67 ppm. That meant on average of the 648 field with pH values the average difference between low pH and high pH was 1.8 units and the difference between low P and high P was 64 ppm.

Summary of grid soil sample data from fields in Oklahoma and Kansas. Data shared by participating farmers and consultants. Data presented is the number of fields in summarized for each variable, the Average value is what we expect as the average composited field value, the Range is the average difference between the min and the max of all fields.

The field below is from Kingfisher county and was sampled at a resolution of 10 acres per sample. This is a fairly course resolution for grid sampling but provides a great view of how variable our soils can be. The field average pH is 5.3, which is below optimum but our aluminum tolerant wheats would be able to handle fairly well. For the P the average is 22 ppm which needs about 18 lbs of P2O5 to max yields. If the farmer applied a flat rate of 20 lbs there would be significant forage loss on about 65% of the field, for grain only about 45% of the field due to underapplication of P. Note that low P and low pH are not correlated well, meaning the areas low in pH are not always low in P.

Example of a grid soil sampled field from west central Oklahoma. Field sampled at a 10 ac resolution. Even at such a course sampling; soil pH averaged 5.3 with range of 4.7 to 6.8, Soil test P average 20 ppm with a range of 7 to 40 ppm.

Banding P makes it more efficient because it slows the rate of tie. However, we have plenty data that says broadcast applied P is still a great option, even after planting. So what are my take homes from this blog?

First: If you are grazing wheat get down 40-50 lbs of N pre. But I have plenty of data the pre-plant N on grain only wheat is not needed. I have the same amount of data that shows the only value of in-furrow N for grain only is that it forces you to plant more seeds, because it just lowers stand.

Second: When it comes to wheat pay attention to Phosphorus and soil pH. Even our acid tolerant wheats preform better in neutral soil pHs, especially forage wise.

Third: A composite soil sample is an AVERAGE of the field. If your average is right at the ok level (pH of 5.6ish and M3P of 30 ppm), then half of your field is below optimum and will benefit from P.

Fourth: If you can band P great, but if you cant broadcast is still a viable option. Do Not Skip P when soil test says there is a need.

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

Top-dress Wheat with P and K ??

Brian Arnall, Precision Nutrient Management Extension Specialist
Hunter Lovewell, Past PNM MS student.

Original Blog Name: Managing P and K in a wheat Double-crop Soybean System.
I planned to wait until the soybean yields came in to share the data from this project, but the wheat results are just too interesting this year.

So the trial posed the question, when is the best time to apply the phosphorus (P) and potassium (K) for the soybean crop in a wheat double crop soybean system, if any is needed above what is applied for the wheat crop. We applied the wheat’s P&K at establishment, but the soybeans P&K was applied either at wheat establishment, top-dress wheat timing, or post wheat harvest pre soybean planting. We used the sources of granular triple super phosphate (0-46-0) and potash (0-0-60) for all applications. We hypothesized the wheat crop would not benefit from the soybeans portion of P&K and that the top-dress application timing for the soybeans P&K would result in the greatest soybean yields.

The trials consisted of thirteen treatments replicated four times. Phosphorus and K rates were determined using Oklahoma State University (OSU) recommendations based on pre-plant soil test, Mehlich 3 P. Treatments with a “+” to the right of a letter represent adding the recommended double-crop fertility to the recommended rate needed for the wheat crop of that same nutrient.

So far, we have six site years with completed cycles with locations at the Eastern Research Station (ERS) near Haskell, Oklahoma, Ballagh Family Research Farm (BF) near Newkirk, Oklahoma, Skagg Family Farm (SF) near Lamont, Oklahoma, and Lake Carl Blackwell Research Farm (LCB) near Perry, Oklahoma. The research was conducted during the 2019-2020 growing season and the 2020-2021 growing season. For the 2021-2022 cycle we added two more locations one again on the Skagg Family farm and the second on a new cooperator, O’Neil Farms (OF) near Ponca City.  For all locations no P or K was applied by the farmers at any point, but they did manage IPM. See location descriptions below.

Location names, years, soil series name, texture classification and soil test pH, P, and K results. For P and K rates based upon soil test results see the OSU Factsheet PSS-2225 https://extension.okstate.edu/fact-sheets/osu-soil-test-interpretations.html

The first two years of work is written up in Mr. Hunter Lovewell’s thesis titled “EFFECTS OF PHOSPHOROUS AND POTASSIUM APPLICATION TIMING ON A WHEAT DOUBLE-CROP SOYBEAN SYSTEM” which I can share with those interested. To be honest, Hunter had a couple tough seasons. Basically where wheat did well, beans typically failed and where you had good beans the previous wheat had failed. All the same he had some interesting results. What follows is pulled from his conclusions.

“While a significant response to the application of P and K was limited, the results show that there are environments in which the wheat crop can benefit from additional P and K fertilizer applied for the soybean crop. In the case of the soil (SF-SH) with low M3P and an acidic soil pH, the additional P applied during the winter wheat growing season, intended for soybeans, alleviated the aluminum toxicity issues with acidic pH, increasing wheat yields. Beyond the single location with low soil test P and pH no other significant response was found to the addition of and P. This may be explained in that most locations were only marginally deficient P and the majority of the varieties used in the study were considered to have acid soil tolerance. Penn and Arnall (2015) found that cultivars with aluminum tolerance had increased P use efficiency. The BF location showed a significant wheat grain yield response to the K fertilization, but the additional K applied for the soybean crop showed no benefit for the wheat crop. While there was no significant increase in soybean grain yield to the additional K fertilizer observations suggest that the application of K fertilizer for soybeans may be of benefit. As was mentioned before the double-crop system is susceptible to yield-limiting conditions, heat, and moisture, due to the maturity of the crop during the peak summer months. The soybean grain yields achieved in this study were all below the previous five-year yield average for all the locations. The low achieved yields and crop stress may have limited this study’s ability to identify a significant response to the application of fertilizer. “

So, one of the most interesting finding from the first six sites was that topdressing P increased yield of the wheat crop on the soil that had low pH and P. And since the P recs applied were only considering STP values and not soil pH, we had underapplied P for the wheat.

Now moving on to the 2021-22 season. Well as most of the famers know, this season has been a doozy. That said, we were not able to establish the treatments until February 1st. Therefor in the case of the 2021-22 wheat season the first application of P&K was made at top-dress timing and then the second application was made post wheat harvest. So, we are unable to say how a preplant wheat P&K application would have performed. But the wheat grain yield response to P&K was better than I could have ever imagined.

Rainfall totals for January-June for the Medford (Skaggs, SF-Nfld) and Burbank (O’Neil, OS) mesonet locations. http://www.mesonet.org

The rain post application (Feb 1st) was marginal but better than other areas in the central/southern Plains. There was about 1” of precipitation in February, almost 3” in March and under 0.2” in April. May rains for the OF site near Burbank aided in allowing the yields to climb, maxed out at 82 bushels per acre, while the SF-Nfld missed out on many of the late rains and yields topped out at 39 bushels.

Winter wheat grain yields from the Skaggs SF-Nfld and O’Neil ON fields. Phosphorus and potassium treatments applied on February 1st at rates based upon soil test and OSU recommendations.

At both sites there is a clear and distinct response to P fertilizer. Note the N and NK treatments significantly lower than all other treatments. The last column on each figure title NPK is the average of all other treatments that only received the wheats P&K rate and had yet had the soybeans P&K applications.

We were able to statistically analyze the locations together by calculating a relative yield for each location. This is done by dividing the yield of each plot by the yield of the N only treatment, we did this for each replication. We then ran a t-test to look at significant treatment difference, so below any treatments that has the letters above the columns, such as an ab and b, are not statistically different at a 95% level.  

Relative grain yield (Trt yld / N trt yld) for both of the 2021-22 locations. Treatments with same letters over column not significant based on, t-Test LSD ran at alpha = 0.05. Black column represent additional treatments which were fertilized with additional P&K after winter wheat grain harvest.

The relative yield data was able to confirm that across both locations an application of P in February significantly increased yields at a consistent level of 30-50%.  It is interesting that while the NP+K+ treatment almost sorts out as being statistically the highest.

While I am not even close to suggesting that you should delay application of P fertilizer in wheat production, I am a big fan of in-furrow applications, this work does point to opportunities. Such as the ability to return to the field after the wheat is up and apply broadcast P if perhaps you could not at planting. But specifically, the potential for in-season Variable Rate phosphorus based upon crop response, maybe a P-Rich strip. What I can tell you this means is that I have more work to do. First, I need a better understand of when and where this is possible. Then it is time to figure out how to use this to our advantage to more efficiently use P fertilizer.
I do want to reiterate, I am not suggesting to move away from Preplant P nor in-furrow.

Keep an eye out for the soybean data because hopefully we catch a few good rains and find out if the timing of P&K will impact the double crop yields.

I want to send a big Thank you to all the cooperators who have put up with me and my time over years to get this data and the Oklahoma Soybean Board for their continued support of this project.

Feel free to send any questions for comments my way at b.arnall@okstate.edu

Utilizing N fixing biologicals.

In the past couple years significant efforts have been made to produce N fixing microorganisms that can be utilized in an agriculture system. The atmosphere is 78% N2 and prokaryotic microorganisms such as the bacteria species Azotobacter, Bacillus, Clostridium, and Klebsiella take that N2 gas and turn it into plant available NH4. These organisms have been around providing nitrogen for plants, for as long as there has been plants. In agriculture we have heavily utilized their relationship with legumes however have struggled bringing them into other realms of production. Naturally they tend to be found in areas that are very low levels of nitrogen. For example, prokaryotes were found in the un-fertilized check of the 130-year-old Magruder Plots but are not found any other treatment that receives fertilizer organic or commercial.

 Nitrogen-fixing nodules on soybean roots. Image credit: Bo Ren, Purdue University

Now there are several products marketed as containing N fixing microorganisms suited for use in today’s corn, sorghum, and wheat production. While I have an active research program evaluating the use of such materials in Oklahoma, this blog will not address what works or how well. This blog will touch upon my thoughts on how to utilize a technology such as this if you pull the trigger to implement.

So there is one key to getting a ROI on products that create plant available nitrogen, and it’s a really simple key.
Under Apply Nitrogen
If you apply enough or more N than the crops needs, then there is ZERO value in a product that creates more N. For example, applying one of these products in your 250-bushel yield goal corn after you’ve already laid down 300 lbs of N preplant. Unless you lose it all to leaching, your probability of seeing a ROI on your biological investment is pretty poor. I have a hard time understanding the thought process behind paying for a N fixing product and not lowering your fertilizer rate. I can see one of two reasons. 1) You believe you historically under apply N and are losing yield because of such 2) Are in an environment which has a high potential of late season N losses, and you are unable to make recovery applications.

So what to do if using a N Fixer? I do not have the confidence yet to say, “Apply X product, it will produce Y lbs of N, so cut your rate by Y lbs”. That uncertainty is one of the greatest challenges, not knowing will I get 10 lbs or 40 lbs? If I did, then I would just subtract that off my planned rate. Side note, as someone who has been doing on farm N rate studies for a decade plus, I would have to add that most were likely over applying by that much and could cut back anyways. For me the use of the N Fixers should force your hand into utilizing in-season N applications, regardless the crop. So that you can better predict or determine impact of the product.

This is where the use of a refence strip (N-Rich or Zero N) is the golden ticket. We need a way to quickly evaluate the amount of N the crop has access to. The N-Rich method works best when preplant N is drawn way back. I would add that reduced pre-plant is a great scenario for N Fixers. The N-Rich in comparison to the rest of the field will provide you guidance towards your in-season goals. If the N-Fixers are doing a great job the N-Rich will not be showing up any time soon and you can make your N rate adjustments accordingly. If you are a Pre-plant or die kind of farmer, then I say you need to pull back the reins on the preplant rate but give the N Fixers some room to add value and add in your Zero N strips. These will again let you observe what is happening in the soil apart from your fertilizer. If it is getting on the late side of in-season N and you cannot find your zero, might be a good time to walk away and hang up the fertilizer applicator keys. I have lots of blogs and pubs on the use of reference strip so send me a note if you want to dive further into these approaches.

Nitrogen Rich Strips being applied in winter wheat. Photo credit: Zack Rendel, Rendel Farms Miami Oklahoma.

Feel free to reach out with questions or comments. B.arnall@okstate.edu

Related Blogs

Its dry and nitrogen cost a lot, what now?

The title says a lot about the primary question I am receiving right now. And the latest long range “forecast” does not make me feel any better about the current situation. But it is what it is and many great plains wheat farmers are having to make a decision.

The current situation in the wheat belt is that we are dry to depth, when the 32 inch PAW is on short supply and this comes from a combination of no rain and above average temperatures.

Average 32-inch Plant Available Water. Graph retrieved from Mesonet on January 20th, 2022.
120-Day rainfall accumulation across Oklahoma. Graph retrieved from Mesonet on January 20th, 2022. Start data of this time frame is September 22, 2021
The daily average temperature departure from the 15 year mean temperature for the Lahoma Research Station. The Mesonet long-term averages utilize 15 years of daily data (e.g. daily average, daily maximum/minimum, or daily total) for every current and past Oklahoma Mesonet station.

Fertilizer prices are holding fairly strong, at expensive, and the wheat crop currently seems to be going in reverse. So what is a wheat farmer to do? If we are looking on the bright side the lack of moisture in the surface will help reducing any potential losses through urea volatilization. It does not make the potential for loss zero though. If I am bound and determined to fertilize now, I would be very selective of the source and method of application. The biggest driver, tillage and residue amounts.

  • Conventional Till / No residue (plenty of bare soil showing) and small wheat-
    • UAN via Streamer nozzles
      • Why: With UAN (urea ammonium nitrate) you have a liquid N source that will get onto and into the soil and readily available nitrate. Streaming on will help concentrate the fertilizer and potential reduce any urea volatilization if any dews were to occur. Urea would sit until dissolved and lead to potential losses if the first moisture was heavy dew and not a incorporating rainfall.
  • No-till / high residue (no bare soil showing)-
    • Dry Urea
      • Why: If Our residue is dry when the urea is spread the wind will help push it below the residue surface providing protection until a good rain. If UAN is applied to this dry or even slightly damp residue and not washed off with a rainfall in a week or so the amount of N tied up in that residue will likely be significant.
  • The big wheat (very little bare soil, lots of wheat tissue.
    • Urea or UAN Streamer
      • Why not Flat fan. At least with the current status the wheat is not growing and bigger wheat has increasing levels of tip die back. So while UAN sprayed on actively growing wheat can be absorbed foliarly, stressed wheat can not do it as well. Plus the UAN that hits dead or damaged tissue will not make it into the plant. The UAN applied via flat fan will need incorporation via rain in a couple days.

You may have caught in the paragraph above I said, “If I was bound and determined”. If I had the option I am not pulling the trigger until after I have received some good moisture. I fully expect and have already seen rigs running before every decent chance of rain. Unfortunately many of those chances have not panned out and that will remain my concern moving forward. I want to make sure we have some water in the tank before investing in the system.

But now we increase the risk/fear by waiting and the question I get is what if we don’t get good rains or don’t get good incorporating rains. The short answer is, if we don’t get rains the N application is the least of our concerns. If we approach March 15th and we have not had the rains needed to put a little water in the tank and incorporate the N then we are not likely looking at a bumper crop which will need N. What survives in that scenario will be living off deep soil water, and where there is deep soil water there is a good chance of deep N. The shallow soils will be so stressed that nutrient demand will be very little.

Now lets talk waiting and applying N. How late before we just say we are done. To answer I am going to draw from a data set I talk about a lot, the delayed N work by Dr. Souza. 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.

With this data we can answer two questions, first at what point did we lose yield compared to pre-plant and second how late could we apply and still increase yield above the check. So comparing to the pre lets us know how long could we wait with losing yield. Across the trials we lost yield three times by waiting too long, at LCB2017b that was 4/19, Lahoma18 it was around 3/30, and then Newkirk2020 we lost yield by waiting until 4/6. This data is why I am pretty comfortable waiting until mid March when and if needed. Now if we look at the check, that will tell us if things start improving late can we get still get a yield bump with added N. Newkirk 2020 was the only time and place we could increase yield above the zero after the 4/14 additions.

Table 1. Date of nitrogen application. Each month is color coded.
Table 2. Evaluation of winter wheat grain yield and protein results compared to the Pre-plant Nitrogen treatment. Red boxes means the treatment yielded statistically lower results, Yellow is no difference, Green means the treatment has increased grain yield or protein. Perkins2018, LSC2018b, and LCB2019, did not have a grain yield respond to N (no red box in Zero check) and therefore will not be discussed.

Take Home Message

My recommendation is that if you are not required to take delivery or needing to cover a lot of acres, i.e. time limited, I would not get in a hurry to apply N on this wheat crop. I think if we combine weather by market this a good time to wait and see. Once we get a rain and have some soil moisture it will be time to run the rigs. The crop currently does not need a lot of N so why spend the $. If things don’t improve by mid to late march, consider the wheat a cover and look towards a summer crop with the hopes of rains in April. If you need to take the crop to yield, then you can wait a while longer and still get a return on the N, with hopes the price could come down a bit.

Finally, While I don’t suggest running fertilizer in front of the first chance of rain, I would make sure I had an N-Rich strip on each and every single field. Strips can go out well past green up and serve a great purpose. The N-Rich strip will help you determine if the crop is able to mine any soil N or if the N tank is dry.

Feel free to reach out with questions or comments.
Brian Arnall Precision Nutrient Management Specialist.
b.arnall@okstate.edu

Special thanks to EDC Ag Products Co LLC for suppling NH4NO3 used in the delayed N project.

Relevant past blogs for your reading enjoyment.

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

Banding P as a band-aid for soil acidity, not so cheap now.

Whoi Cho, PhD student Ag Economics advised by Dr. Wade Brorsen
Raedan Sharry, PhD Student Soil Science advised by Dr. Brian Arnall
Brian Arnall, Precision Nutrient Management Extension.

In 2014 I wrote the blog Banding P as a Band-Aid for low-pH soils. Banding phosphate to alleviate soil acidity has been a long practiced approach in the southern Great Plains. The blog that follows is a summary of a recent publication that re-evaluated this practices economic viability.

Many Oklahoma wheat fields are impacted by soil acidity and the associated aluminum (Al) toxicity that comes with the low soil pH. The increased availability of the toxic AL3+ leads to reduced grain and forage yields by impacting the ability of the plant to reach important nutrients and moisture by inhibiting root growth. Aluminum can also tie up phosphorus in the soil, further intensifying the negative effects of soil acidity. More on the causes and implication of soil acidity can be found in factsheet PSS-2239 or here (https://extension.okstate.edu/fact-sheets/cause-and-effects-of-soil-acidity.html). The acidification of many of Oklahoma’s fields has left producers with important choices on how to best manage their fields to maximize profit.

Wheat Trial, Cimarron Valley Research Station

Two specific management strategies are widely utilized in Oklahoma to counter the negative impacts of soil acidification: Lime application and banding phosphorus (P) fertilizer with seed. While banding P with seed ties up Al allowing the crop to grow, this effect is only temporary, and application will be required every year. The effects of liming are longer lasting and corrects soil acidity instead of just relieving Al toxicity. Historically banding P has been a popular alternative to liming largely due to the much lower initial cost of application. However, as P fertilizers continue to increase in cost the choice between banding P and liming needed to be reconsidered.

A recent study by Cho et al.,2020 compared the profitability of liming versus banding P in a continuous wheat system considering the impacts that lime cost, wheat price and yield goal has on the comparison. This work compared the net present value (NPV) of lime and banded P.  The study considered yield goal level (40 and 60 bu/ac) as well as the price of P2O5 fertilizer and Ag Lime. The price of P2O5 used in this study was $0.43 lb-1 while lime price was dictated by distance from quarry, close to quarry being approximately $43 ton-1  and far being $81 ton-1. For all intents and purposes these lime values are equivalent to total lime cost including application. Wheat prices utilized in the study were $5.10 bu-1  and $7.91 bu-1. It is important to note that baseline yield level was not considered sustainable under banded P management in this analysis. This resulted in a decrease in yield of approximately 3.2 bu ac-1  per year. This is attributable to the expected continued decline in pH when banding P is the management technique of choice.

The analysis in this work showed that lime application is cost prohibitive in the short term (1 year) when compared with banding P regardless of lime cost, yield goal level, and wheat value (within the scope of this study). This same result can be seen over a two-year span when yield is at the lower level (40 bu ac-1). While in the short-term banding P was shown to be a viable alternative to liming, as producers are able to control ground longer lime application becomes the more appealing option, especially when producers can plan for more than 3 years of future production. In fact, under no set of circumstances did banding P provide greater economic return than liming regardless of crop value, yield, or liming cost when more than 3 years of production were considered and only under one scenario did banded P provide a higher NPV in a 3-year planning horizon.

While historically banding P was a profitable alternative to lime application for many wheat producers the situation has likely drastically changed. At the time of writing this blog (09/17/2021) Diammonium Phosphate (DAP) at the Two Rivers Cooperative was priced at $0.78 lb-1. of P2O5. This is a drastic increase in P cost over the last year or so since Cho et al. was published in 2020. With P fertilizer prices remaining high it will be important for producers to continue to consider the value of liming compared to banded P. This is particularly crucial for those producers who can make plans over a longer time frame, especially those more than 3 years.

Addendum: As fertilizer prices have continued to rise a quick analysis utilizing the $0.78 lb-1 of P2O5was completed to consider the higher P fertilizer cost. Under this analysis an estimated decrease in NPV of approximately $38 an acre for P banding occurred. When considering this change in NPV, lime application becomes the more profitable option for alleviation of soil acidity symptoms even in the short term (assuming lime price values are equivalent to the previous analysis). This underlines the fact that it is imperative to consider the impact on profitability of the liming vs. banding P decision in the current economic climate for agricultural inputs.

Link to the Open Access Peer Reviewed publication “Banding of phosphorus as an alternative to lime for wheat in acid soil” https://doi.org/10.1002/agg2.20071

In-furrow fertilizers for wheat

From Guest Author, Dr. Dorivar Ruiz Diaz, Nutrient Management Specialist, Kansas State University

Wheat is considered a highly responsive crop to band-applied fertilizers, particularly phosphorus (P). Application of P as starter fertilizer can be an effective method for part or all the P needs. Wheat plants typically show a significant increase in fall tillers (Figure 1) and better root development with the use of starter fertilizer (P and N). Winterkill can also be reduced with the use of starter fertilizers, particularly in low P testing soils.

Figure 1. Effects on wheat tillering and early growth with in-furrow P fertilizer on soil testing low in P. Photo taken in 2020 in Manhattan, KS. Photo by Chris Weber, K-State Research and Extension.

In-furrow fertilizer application

Phosphorus fertilizer application can be done through the drill with the seed. In-furrow fertilizer can be applied, depending on the soil test and recommended application rate, either in addition to or instead of, any pre-plant P applications. The use of dry fertilizer sources with air seeders is a very popular and practical option. However, other P sources (including liquid) are agronomically equivalent and decisions should be based on cost and adaptability for each operation.

When applying fertilizer with the seed, rates should be limited to avoid potential toxicity to the seedling. When placing fertilizer in direct contact with wheat seed, producers should use the guidelines in Table 1.

Table 1. Suggested maximum rates of fertilizer to apply directly with the wheat seed

 Pounds N + K2O (No urea containing fertilizers)
Row spacing
(inches)
Medium-to-fine
soil textures
Course textures or dry soils
 
151611
102417
6-83021

Air seeders that place the starter fertilizer and seed in a 1- to 2-inch band, rather than a narrow seed slot, provide some margin of safety because the concentration of the fertilizer and seed is lower in these diffuse bands. In this scenario, adding a little extra N fertilizer to the starter is less likely to injure the seed – but it is still a risk.

What about blending dry 18-46-0 (DAP) or 11-52-0 (MAP) directly with the seed in the hopper? Will the N in these products hurt the seed?

The N in these fertilizer products is in the ammonium-N form (NH4+), not the urea-N form, and is much less likely to injure the wheat seed, even though it is in direct seed contact. As for rates, guidelines provided in the table above should be used. If DAP or MAP is mixed with the seed, the mixture can safely be left in the seed hopper overnight without injuring the seed or gumming up the works.  However, it is important to keep the wheat mixed with MAP or DAP in a lower relative humidity.  A humidity greater than 70% will result in the fertilizer taking up moisture and will cause gumming or caking within the mixture.  

How long can you allow this mixture of seed and fertilizer to set together without seeing any negative effects to crop establishment and yield?

The effects of leaving DAP fertilizer left mixed with wheat seed for various amounts of time is shown in Figure 2. Little to no negative effect was observed (up to 12 days in the K-State study).

Figure 2. Effects on wheat yield from mixing P fertilizer with the seed. Study conducted in 2019 and 2020 at four sites. Graph by Chris Weber, K-State Research and Extension.

Although the wheat response to these in-furrow fertilizer products is primarily from the P, the small amount of N that is present in DAP, MAP, or 10-34-0 may also be important in some cases. If no pre-plant N was applied, and the soil has little or no carryover N from the previous crop, the N from these fertilizer products could benefit the wheat.

Dorivar Ruiz Diaz, Nutrient Management Specialist
ruizdiaz@ksu.edu

Chris Weber, former Graduate Research Assistant, Soil Fertility

Nitrogen Rich Strips, a Reminder

With the recent increase in fertilizer prices just prior to winter wheat planting season I felt it was a good opportunity to bring this older post back up and give it an update. Since the blog was originally written in 2013 there has been a lot of work done both to better understand the nitrogen fertilizer need / timing of winter wheat and efforts to updated and improve the algorithms behind the Sensor Based Nitrogen Rate Calculator.

The Nitrogen Rich Strip, or N-Rich Strip, is a technique/tool/process that I spend a great deal of time working with and talking about.  It is one of the most simplistic forms of precision agriculture a producer can adopt.  The concept of the N-Rich strip is to have an area in the field that has more nitrogen (N) than the rest.  In recent years we have been utilizing Zero-N strips in corn. The approach to some may be new but at one point most producers have had N-Rich Strips in their fields, albeit accidentally.  Before the days of auto-steer it was not uncommon, and honestly still is not, to see a area in the field that the fertilizer applicator either doubled up on or skipped.  In our pastures and dual purpose/graze out wheat every spring we can see the tell-tale signs of livestock deposits.  When over laps or “Cow Pox” become visible we can assume the rest of the field is behind in nitrogen.  The goal of an N-Rich Strip is to let the field tell you when it needs more N. Research has shown wheat can be yellow and recover completely and it may even be a benefit. See the link for the Value of In-season Nitrogen at the end of this blog.

Cow Pox, Image courtesy Kaitlyn Nelson
Cow Pox, Image courtesy Kaitlyn Nelson

What I like most about the N-Rich Strip approach is its Simplicity.  The N-Rich Strip is applied and; Scenario 1. The N-Rich Strip becomes visible (Greener) you APPLY NITROGEN, Scenario 2.  The strip is not visible you Option A. DON’T APPLY NITROGEN Option B. Apply Nitrogen Anyways.  The conclusion to apply N or not is based on the reasoning that the only difference between the N-Rich Strip and the area 10 ft from it is nitrogen, so if the strip is greener the rest of the field needs nitrogen.  If there is no difference N is not limiting and our research shows N does not have to be applied.  However producers who decide to be risk adverse (in terms of yield) can apply N but it would be advised to do so at a reduce the rate.  Now is a good time to note that the N-Rich Strip alone provides a Yes or No, not rate recommendation.  At OSU we use the GreenSeeker optical sensor and Sensor Based Nitrogen Rate Calculator (SBNRC) to determine the rate, but that discussion will come later.  I equate the change from using yield goal N rate recs to the N-Rich Strip as to going from foam markers to light bars on a sprayer.   Not 100% accurate but a great improvement.

N-Rich Strip in no-till wheat near Hobart OK.
N-Rich Strip in no-till wheat near Hobart OK.
N-Rich Strips showing up on google earth image. You can see how the strip on the left is darker than the right suggested a greater need for nitrogen.

Now that we have covered the WHY, lets get down to the nuts and bolts HOW, WHEN, WHERE.

How the strip is applied has more to do with convenience and availability than anything else but there are a few criteria I suggest be met. The strip should be at least 10 ft wide and 300 ft long. The rate should be 40 to 50 lbs N (above the rest of the field) for grain only wheat and canola, 80 lbs N for dual purpose wheat. The normal recommendation is that when applying pre-plant either have a second, higher rate programmed into the applicator or make a second pass over an area already fertilized. Many will choose to rent a pull type spreader with urea for a day, hitting each field.


Also popular are applicators made or adapted for this specific use. ATV sprayers are the most common as they can be multi-purpose. In most cases a 20-25 gallon tank with a 1 gpm pump is placed on the ATV with an 8-10ft breakover boom. The third applicator is a ride away sprayer with a boom running along the rear of the trailer. In all cases when liquid is the source I recommend some form of streamer nozzle.
If this all sounds like to much then the easiest application method might just be a push spreader. No need for trailer or even a truck. In most cases I recommend whichever N source is the easiest, cheapest, and most convenient to apply.

Vincent N-Rich Strip Applicator, Ponca City OK
Vincent N-Rich Strip Applicator, Ponca City OK
Gard N-Rich Strip Applicator, Fairview Ok
Gard N-Rich Strip Applicator, Fairview Ok
Push spreader used by Oklahoma State Cooperative Extension service. Check with your local office. If they don’t have one, we can send one.

When the strip is applied in winter crops proper timing is regionally dependent. For the Central Great Plains, ideally the fertilizer should be applied pre-plant or soon after.  However,  in most cases as long as the fertilizer is down by December or even January everything works. Timing is more about how much the wheat is growing. If it is slow growing fall, timing can be delayed. When the N-Rich Strip approach is used on the Eastern Shore in Virginia and Maryland the strips have to be applied at green up. We have been trying this in Oklahoma and Kansas with good success.  It is always important to make the tools fit your specific regional needs and practices and not the other way around.

Where is actually the biggest unknown.  The basic answer is to place the N-Rich Strip in the area that best represents the field.  Many people question this as it doesn’t account for spatial variability in the field, and they are correct.  But my response is that in this case spatial variability is not the goal, temporal variability is.  Keeping in mind the goal is to take a field which has been receiving a flat yield goal recommendation for the last 30+ years and make a better flat rate recommendation.  My typically request is that on a field with significant variability either apply a strip long enough to cross the zones or apply smaller strips in each significant area.  This allows for in-season decisions.  I have seen some make the choice to ignore the variability in the field, made evident by the strip, and apply one rate and others choose the address the variability by applying two or more rates.  One key to the placement of N-Rich Strips is record keeping.  Either via notes or GPS, record the location of every strip.  This allows for the strips to be easily located at non-response sites.  It is also recommended to move the strip each year to avoid overloading the area with N.  

For more information on N-Rich Strips

Factsheets

https://extension.okstate.edu/fact-sheets/applying-nitrogen-rich-strips.html

https://extension.okstate.edu/fact-sheets/using-the-greenseeker-handheld-sensor-and-sensor-based-nitrogen-rate-calculator.html

https://extension.okstate.edu/fact-sheets/impact-of-sensor-based-nitrogen-management-on-yield-and-soil-quality.html

Related Blogs

YouTube Videos  

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

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.