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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.
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.
- UAN via Streamer nozzles
- 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.
- Dry Urea
- 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.
- Urea or UAN Streamer
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.
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.
Special thanks to EDC Ag Products Co LLC for suppling NH4NO3 used in the delayed N project.
Relevant past blogs for your reading enjoyment.
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.
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.
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.
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.
If you have any questions please feel free to contact me @ firstname.lastname@example.org
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.
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
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.
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.
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.
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
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
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.
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.
|Implement||Operating Efficiency||Fuel cost/ac||Labor Cost/ac||Operating 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.
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 email@example.com
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.
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 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.
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.
Acknowledgement of LSB Industries for support of these projects.
I have been trying to write this blog addressing the yellow wheat for about two weeks now. But with finally finding a dry”ish” day or two and a lot of calls and emails about yellow wheat, I am just now getting to it.
So the short story is there is a lot of wheat out there in the state that is show signs of chlorosis, or yellowing. I wish I could say I have all the answers for you in this article, but I will have to lay heavily upon the agronomist best answer, “Well it Depends.”.
First we will start with the things I know least about and then move on to things that are more in my wheelhouse. In the last two weeks I have been on multiple email strings trying to chase down the cause of chlorosis in fields all over the state. One of these included Dr. Bob Hunger and the Plant Disease & Insect Diag Lab (PDIDL) and in one field his final thought was “So, my best guess is cold and wet soils along with fungi colonizing the older leaves that are starting to senesce.” At the same time I am finding regular occurrence of Tan Spot and Leaf Rust increase. All these pathogen cause some level of chlorosis and if you do not get down and pull some samples you will never know the cause.
A new for me this year is what I am calling the herbicide ding. I was able to get over a lot of my wheat that first week of March with a shot of herbicide, everything was almost to hollowstem. The wheat really got dinged. Very visual yellowing and stunting of the plants. Talking with Dr Manucheri, she had seen the same thing in her plots in Tipton. I have also visited several farmer fields with the same symptoms. Dr. Manucheri shared with me the Finesse label. Directly from the label “Temporary discolorations and/or crop injury may occur if herbicide is applied when the crop is stressed by severe weather conditions (such as heavy rainfall, prolonged cold weather, or wide fluctuations in day/night temps), disease or insect damage, low fertility, applications to course soils, or when applied in combination with surfactant and high rates of liquid fertilizer solutions.” This can be found on page 5, http://www.cdms.net/ldat/ldFSL002.pdf . You can just about mark off every weather and application condition mentions, on the same field.
Now to the yellow wheat I can comfortably talk about. There is nitrogen deficiencies out there. That should not come as a shock with the amount of rain we have received over the last couple months. I also believe that a fair amount of the wheat crop out there is a bit lacking on roots department.
The overarching wet cools soils that we have more than likely have led to reduced root exploration in some areas. And if you combine short roots with a nitrate leaching then the probability of N being out of the reach of the crop is high. Then the question is “Is there still time to do anything?”. The trip I look over the weekend (3/28, 3/29) that encompassed a great deal of the North Central Ok wheat belt showed me that the majority of the wheat had really progressed physiologically in the last two weeks. At this point, a positive return on N investment hinges on the stage the wheat is at.
Our delayed N work over the past several years show that we have maintained the yield on our trials even when fertilizer was delayed into the first week of April. https://osunpk.com/2019/08/14/how-long-can-wheat-wait-for-nitrogen-one-more-year-of-data/
This table shows the application dates of the 10 site years of the delayed nitrogen study. The first column is the location, to the right of the location is two rows the top is grain yield and the bottom is grain protein. Each of the following columns corresponds to an application date. Applications began at each study when the The colors are related to whether that application was statistically (Alpha=0.05) worse than, equal too, or better than applying nitrogen at the first sign of deficiency (0DAVD). For this comparison it is important to know that at no location did preplant have significantly greater yield than 0DAVD.In the majority of those years that first week of April corresponded with the growth stage Feekes 8, last leaf just visible. As the crop moves beyond that point, catching up did not happen. Currently there is wheat out there in the state that has not hit hollow stem (Feekes 6) and there is wheat at Flag leaf (Feekes 9).
The high rainfall totals we have could have also led to another deficiency sulfur. In the past S deficiency is fairly hard to find in Oklahoma. Our long history of low S using winter wheat and high sub-soil S levels have kept the response to Sulfur low, but not uncommon. Sulfur is a mobile nutrient and will also be lost via leaching especially in sandy soils in the northern part of the state. Sulfur deficient is different from N in that it shows in the newer growth as a general yellowing of crop. Kansas State has a lot of great resources on sulfur management in wheat. https://webapp.agron.ksu.edu/agr_social/m_eu_article.throck?article_id=2132
If your wheat is yellow and before you call the fertilizer applicator, first confirm it is nitrogen and or sulfur and not something else. A key point to nitrogen deficiency is that the cholorsis will be worst on the oldest leafs while new growth is green. If N deficiency is confirmed then figure out how far along your wheat is. If the crop is around hollow stem to Feekes 8, if you can get the N on soon there is a good chance to get your money back plus. Keep in mind with air temps above 60 degrees UAN will burn the tissue so it is best to use streamer nozzles, which will still burn but the tissue damage is lessened. If you do not have access to streamers you can dilute the UAN with water and use flat fan nozzles. Cutting the UAN with water reduce the impact of leaf burn, I typically recommend at least 2 part UAN to 1 part water, but a 1 to 1 is the safest.
If you have any questions or concerns please feel free to email any questions you may have.
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.
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.
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.
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.