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Vaughn Reed, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.
A focal point of the Precision Nutrient Management team is the evaluation of fertilizer timing. Mr. Souza’s research shared in the blog post How Long Can You Wait has shown, with three years of data, that if fertilizer application is delayed until in-season, not only will optimum yield reached but the protein content will be increased. The study below which has just had one year of data will provide additional insight.
While the Sousa work focused on a single rate of nitrogen applied over 12 different application dates at on a few OSU research farms this study evaluated a range of N rates applied both pre-plant and in-season on farmer fields across the state. The rationale for a wide distribution was to achieve the primary goal of the study, which was to add regional specificity to the current sensor based nitrogen rate calculator (SBNRC www.nue.okstate.edu). More on that as the research matures. In order to achieve the range needed to reach the goal small plots were set up in numerous locations throughout the central/western portion of the state and hand harvested at maturity. In Figure 1 below, you can see the sites for the 2018-2019 growing season, as well as the prospective climate zones.
The trials were set up with four rates (25%, 50%, 75%, 100% of yield potential rate), two timings (pre-plant and in-season application), and a zero N check. Applications were applied using ammonia nitrate as the source, in order to minimize losses due to volatilization. Eight trials were harvested in six counties, and three different climatological zones.
The data from the first year of this trial confirmed the results seen in the Sousa study. In-season application of nitrogen was more efficient in terms of yield and quality than equivalent rates applied pre-plant. Out of the eight locations harvest, only two had a significant grain yield respond to the addition of N fertilizer. However, all eight locations the addition of N had significant positive impact on protein content. When looking at pre-plant versus in-season application, grain yield was not statistically significantly different from each other at any location. Protein content of in-season N was however significantly better than pre-plant application at 5 of the 8 locations.
Figure 2. below is the results from the Byron and Perkins location. At both sites all fertilizer application for this location responded above the check plot (0 N). At Byron we can see an increase in yield up till about 60 bu/ac in both the preplant and topdress application. The proteins increased with the rate of fertilizer applied. In both of the responsive locations while in-season N was never statistically greater than pre-plant N in all cases the in-season application had numerically higher yields and protein.
The next table below is from the Capron location. This location did not yield a significant increase in yield from the application of N across the board, including timings. But even though there was no impact on yield protein increased. In both of these locations the increase due to in-season N was statisically greater then the pre-plant. This response is replicated in three other locations in this trial that did not have yield respond.
This is one years data, across eight locations. The trials will be continued this fall (2019) for another growing season, and Mr. Souza is repeating his trial as well. Everything that has done thus far has shown that not only is grain yield not lost by not fertilizing at pre-plant but by delaying all fertilizer applications till in-season , grain yield is maintained if not increases and protein levels are consistently higher.
For question, comments, or request for on farm studies please contact.
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.
Update to the delayed nitrogen study.
Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.
Due to the surprising results seen from the delayed N study that was first reported below we repeated the the study for a third year at two locations, the Lake Carl Blackwell Research farm near Perry OK and the Ballagh Research Farm near Newkirk OK. Due to the excessive rain fall the wheat was planted and trials established later than normal and a cool winter and spring and winter the crop green up (end of dormancy) was delayed compared with the two first cropping seasons. For this season we started applications before visual symptom difference between the N-rich Strip (pre-plant) and the rest of the field actually occurred. This can be seen with the pre-plant dates of late Oct-Early Nov and the notation of visual difference above the yield bars. Just as the other two previously crop years, the timing of the application did impact wheat yield and protein. In this season at LCB we see a increase in yield with application of N during the first part of March compared to the preplant with yields dropping off below the preplant when N was applied in mid April. At the Ballagh farm there is no yield benefit from delaying N after preplant but there was steady increase in protein, again at this location yield is lost when N was delayed past mid April. In both of these locations mid April was after the growth stage of Feekes 7. After three cropping seasons with some extremely different weather patterns we saw that in this work, pre-plant N was never better than in-season N applied prior to mid April, Feekes 7. In most cases N applied in-season yields and protein values were greater than that of the pre-plant treatment. My take home message from this project is multi fold; First, pre-plant may be cheaper and easier but it often falls short of in-season applications, Second that there should be no reason to rush putting top-dress nitrogen on. The application window is much wider than most ever expected and the closer we get to peak demand the better the yield and quality will likely be. And third, and final make the application of nitrogen when the conditions are the most conducive to getting the N in the ground and limiting losses.
Note: This trial used ammonium nitrate as its N source to evaluate the plants response and remove potential fertilizer efficiency problems. However while these trials were being conducted mirror studies using Urea as the N source were also being conducted. Those results are currently being compiled right now and we hope to share the results soon.
Questions for comments feel free to contact me via email at firstname.lastname@example.org
Original Post made Oct 1, 2018
How long can wheat wait for Nitrogen?
Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.
The N-rich strip method allows wheat producers a greater window of decision making regarding the application of nitrogen (N) fertilizers. Besides having greater accuracy in N rates than standard methods (based on the SBNRC – OSU) also helps to reduce costs in the production system and to preserve the environment avoiding over N applications.
With the experiments performed in the last two crop seasons (2016/18 and 2017/18), we can now be even more accurate with regard to the best application time to increase the N use efficiency by the crop. The objective of our study was to determine the impact of prolonged nitrogen deficiency on winter wheat grain yield and protein. Eight studies were conducted with 11 N application timings in no-till dryland conditions. A pre-plant treatment of 90 lbs ac-1 of N was broadcast applied as ammonium nitrate (AN). We used AN as our source because we wanted to measure the crops ability to recover and eliminate the impact of source efficiencies. When visual symptom differentiation (VSD) was documented between the pre-plant and the non-fertilized check, i.e the N-Rich Strip showed up, top-dress applications were performed every seven growth days (GDD> 0) (https://www.mesonet.org/index.php) until 63 growth days after VSD at all sites. The only N the treatments received where applied according to treatment structure. No preplant N was applied other than trt 1, and all locations had residual N under 15 lbs 0-6” sample.
The first visual response to fertilizer N ranged from November 11 to February 5 (Table 1). The soil can have residual N from the previous season which can supply the subsequent crop in the beginning of the development what makes the wheat not demonstrate any sign of stress in the early season. For example LCB2017 a and b which were located 100 yards apart but under a different point in the crop rotation (LCBa was wheat after wheat and LCBb wheat after canola) had a 30 day difference in date of first N response. This range in first and last dates allowed us to evaluate N application over a wide range of dates and determine whether the first sign of stress is actually the best indicator of top dress application timing.
As shown in the Tables 2 and 3 below only three of the 78 comparisons made back to the pre-plant application were significantly less in terms of grain yield. All three of these comparisons where from when N application was delayed until late March or April. When the delayed applications were compared to 0DAVD yields only two of the 68 comparisons showed a significant decrease on yield. One was the pre-plant application for LCB2017a while the other were the 63DAVD application for LCB2017b. In most locations applications made in March yields were at the highest point, however when delayed till April yield trends on the downward trend. The 2017 crop reached hollow stem (Feekes 6) around Feb 20th while the 2018 crop reached hollow stem around March 10th.
Grain protein concentration was decreased only once when compared to both the pre-plant and 0DAVD treatments. This one timing, LCB2018b 64DAVD, was the only application made in May. During this time the crop was in the early stages of grain-fill. In all locations delaying N application until February/March increased grain protein content above the check, and in most cases above the 0DAVD trt.
All the data was combined and plotted by cumulative GDD’s>0 from planting (GDDFP) across all locations to determine a general “best” timing. Using the pre-plant application yield as a base there was no yield loss if the applications was made prior to the 143 GDDFP. When the results were normalized by 0DAVD N there was no yield loss if the applications were made prior to 130 GDDFP. The quadratic model created provides the opportunity to identify the point of highest grain yield, which was approximately 94 GDDFP. In terms of the relationship between the application of N based on GDDFP and % of protein content on the grain, a linear response of N delay application observed for grain protein concentration. Our results suggest that the later the application, the higher the protein % in the grains.
We have concurrent work looking at similar approaches with other sources of N such as Urea and UAN. While all of these studies are being continued the past two years of work have presented some easy take homes.
First: Timing of N application does matter, but yellow wheat does not necessarily mean yield loss.
Second: Two years in a row ALL Nitrogen could be delayed until hollow stem without yield Loss, in fact yields of trts with N applied at this time typically better than that of the pre-plant.
Third: Protein content increased as N applications was delayed.
Fourth: The conclusions of this and other studies support that N-Rich Strip concept does not increase risk of lost yield.
Fifth: Applying the majority of the N at or just after hollow stem maximized grain yield and protein with a single shot.
Sixth and Final: Be more concerned about applying N in an environment conducive to increased utilization and less about applying at the first sign of N stress. Take a look at the wheat N uptake curve by K-State.The crop really doesnt get going in terms of N-uptake until jointing i.e. hollow Stem.
Questions for comments feel free to contact me via email at email@example.com
Vaughn Reed, PhD. Student Precision Nutrient Management
Brain Arnall Precision Nutrient Management Extension Specialist.
Data presented below are the results of Mr. Reeds Masters research project.
On farm research trials are important, because they give us the ability to see responses over a larger geographic area, and even more importantly, evaluate our recommendations on fields that are managed by producers, not researchers. They also allow us to look at current production practices and see if there are any missed opportunities. Several years ago, we looked at whether producers were leaving yield on the table by not applying enough nitrogen (N), phosphorus (P), potassium(K), and sulfur (S) to winter wheat. We did this by applying strips of N, P, K, and S fertilizer on farmers’ fields with the instructions to not change their fertilizer management strategies. If one or more of the strips resulted in higher yields then it could be assumed that either the nutrient was under-applied by the producer, or in the case of N, lost. That study concluded that at 75% of the locations, yield was maximized by the producer with [their respective] NPKS management system, however the greatest responses came from the addition of P and that Oklahoma State University’s soil testing and analysis was adequate for nutrient recommendations. That studies results were published in 2017 and is open access, so available for anyone to read. https://dl.sciencesocieties.org/publications/cftm/abstracts/3/1/cftm2017.02.0014
There are many producers around the state that follow winter wheat with double crops (DC). Often, this practice is done with limited inputs to reduce economic risk. Oklahoma State does not make different recommendations for DC or full season crops, with the exception that yield potentials can differ. In 2016 and 2017 we duplicated the Wheat NPKS study across 3 double crops (soybean, grain sorghum, sunflower) following winter wheat and canola. With a recent climb in DC yields we wanted to investigate if producers were applying enough nutrients to maximize grain yield. Additionally it would allow us evaluate the accuracy of OSU’s soil test based fertilizer recommendations in a double crop. Over the two years, 61 on-farm sites ranging from central to NE Oklahoma had 200 lb/ac of product per nutrient applied in strips 6ft wide by 150 ft long. Urea (46-0-0), triple super phosphate (0-46-0), muriate of potash (0-0-60), and gypsum (0-0-0-19) were used for sources N, P, K, and S, respectively (92 lbs N, 92 lbs P, 120 lbs K, 38 lbs S). In most cases the fertilizer was applied post planting and post-emergence to ensure strips were applied an areas with good stand.
Much like with the wheat-NPKS study 75% of the locations did not respond to additional fertilizer. Twenty treatment comparisons of the 244 made across all 61 locations (50 soybean, 7 grain sorghum, 4 sunflower) yielded a statistically significant change in yield due to the addition of N-P-K-or S. For this report, a comparison was the yield of each nutrient versus the non-treated check, therefore there were four comparisons made per location. Seventeen of the twenty positive responses were found in soybean, three with grain sorghum, and no responses were found in sunflower plots. Lack of response from grain sorghum and sunflower locations is contributed to small amount of grain sorghum and sunflower fields in the study.
Nitrogen rates, for non-legumous crops, are yield driven, meaning the higher yielding a crop, the higher amount of N required. Both grain sorghum and sunflower crops, due to neither being legumes, were expected to see N response, especially to those locations that applied little to no N to begin with. A yield response from the addition of N was found in one grain sorghum location, where the producer application was not enough to maximize yield, and the additional N pushed the yields. As expected, there were no soybean locations that responded to the addition of N.
Phosphorus and potassium are both sufficiency based, not yield driven. This means that if the soil is at 100% sufficiency, the crop will produce at its highest rate achievable, based on that nutrient. 100% sufficiency for P and K are approximately 65 STP and 250 STK, respectively. Phosphorus and potassium strips yielded the most results, especially in soybean locations. Of 20 responses, five responses were due to P, ten due to K, and four due to S. Locations that responded to the addition to P were locations that either had low levels of STP (approx. 80% sufficiency or less), or had low pH, which leads to less availability of P (pH>5.0).
Potassium yielded the most positive results, with ten responsive locations, as well as the most interesting results, with only three sites falling below 100% sufficiency. The other responses were attributed to having low Cl levels (Cl, as in Chloride, which while responses are rare, is a necessary nutrient, and sometimes can lead to losses in yield, especially in sandy environments), as well as drought stress conditions. Potassium has been shown to have a vital role in nutrient uptake and water retention, as it is found to be critical for root growth, and these are displayed highest in crops found in drought like conditions. One hypothesis for the K response is related to root growth. The later planted DC will spend less resources in root development before going reproductive. Soybean is a heavy user of K, combine smaller roots, typically hot drier soils, and high K demand it is not surprising to find this occurrence.
Sulfur, while not wide-spread reported in Oklahoma, has recommendations by OSU built on a yield driven scale. There were four responsive locations found in this project. While one location had low soil test S values there were located areas that received high rainfall events during the growing season, and therefore the response was attributed to leaching of S.
So, after all that, what is the bottom line? Here is our observations:
- Producers maximized yield 75% of the time, with 25% of locations responding to any additional nutrient.
- The 20 responses to additional nutrients occurred across 15 locations, four locations had responses to more than one nutrient
- By nutrient: Note for P and K, due to site variability it was not expected to observe statistic yield increase due to P or K unless soil test was below 70% sufficiency, of which no location had soil test P or K below 70%.
- 38 locations were below 100% sufficiency of phosphorus, with five observed responses
- Seven locations were below 100% sufficiency of potassium, two observed responses. An additional eight locations responded that were not predicted by soil test
- Based on pre-plant soil test there were no sites expected to respond to the addition of Sulfur, 4 locations did respond.
- Soil test results were adequate in correctly identifying locations that would not respond to the addition of nutrients (93.5% accurate), while not as accurate at predicting sites that would respond.
- For K, soil testing was less accurate, as eight of the ten responsive locations had soil test values above 250 soil test K (125 ppm or 100% sufficiency). For this reason, we are currently doing work evaluating K recommendations for soybeans.
This work confirms that of the fields we evaluated, the majority was not yield limited by N, P, K or S. However, as with anything, we have more work to do in order to further refine our recommendations, and always looking to learn more about how to aid producers.
If you read my blog very often you know I spend a lot of my time talking about and thinking about nitrogen (N) management. And a great aspect of a blog is the ability to share ideas and theories, and this idea has been rattling around for awhile. What follows is not my recommendation for how to manage N but my assessment of challenge that comes with adopting a new N management strategy.
My wife, years ago, introduced me to the Pick 2 concept also known as the triple constraint theory of project management. I have thought of it and used it often when I am trying to get a project completed. This concept suggest that if you are able to get something of high quality, and have it done quickly but you will have to pay for it, aka it will not be cheap. While you can get something produced cheap and quickly, but it will not be of quality. And of course you may be able to get something of quality produced cheaply, however it will not be done quickly.
Some time back, while contemplating my reply to a tweet about N management by Dr. Josh McGrath @NPK_Professor, it hit me that it was quite similar to triple constraint theory. I have been researching and speaking on improved N management strategies for a decade now. While I have seen some change in practice and improved efficiencies, overall movement is slow. I have for awhile known the challenge I was up against but never able to communicate it well. I believe that at least in concept the 2 Pick diagram begins to make the point.
Lets talk the 3 components
Almost theoretical in concept itself. My definition of efficiency is being as close a zero net addition of N as possible. The goal being if we add 150 pounds of N as fertilizer we remove 150 pounds of N in grain, feed, or fiber. In other words 1 lb in and 1 lb out. My blog Nitrogen Management Report Card takes a look at nitrogen use efficiency.
This one is not too hard to explain. The strategy has to be economically viable. You can go even further and say that the new N management approach should produce an economic return that is equal to or better than the currently implemented strategy.
The third component is the one that is more challenging to quantify, and in my opinion one of the greatest drivers in N management adoption. Risk, you know all the of the What Ifs. I can not think of a time when I gave a talk on increasing N use efficiency when I did not have at least one producer approach me with a What If question/statement. What if its to wet, what if its too dry, what if I lose to much, what if I under apply? The what ifs outline those things a producer or agronomist see as potential risk. I use the words perceived or real not to say the concerns are unfounded, shoot in Ag we all know not only can everything go wrong but at some point it probably will. Its that sometimes the level of concern may be greater than the actual risk. And to be honest N has been one of the few things producers could manage to reduce risk, i.e. loss of yield. What I mean is a producer can not control the weather or market but they could make darn sure they had enough nitrogen in the ground to produce every pound possible.
Lets talk about our Pick 2 options:
Economic and Low Risk:
This one for me is really easy to describe, whether it is winter wheat or corn. This pairing is 100% Pre-Plant Anhydrous Ammonia.
And even though there is a greater inherent risk of losing N due to high rainfall or over applying N because in season environment limited yield potential, there is only 1 application of a low cost N source and the perceived risk of yield loss due to not having enough N is much less. For Oklahoma wheat producers 100 lbs of N as anhydrous is easy and considered risk adverse, however it is not efficient in terms of nutrient use. If fact in a good year this method typically only gets close to the 33% NUE that Dr. Raun and Dr. Johnson discussed in their 1999 Agronomy Journal paper titled “Improving Nitrogen Use Efficiency for Cereal Production” Link.
Efficient and Low Risk:
To be absolutely efficient in a perfect world we provide the N when the plant needs it not before or after. Many refer to this as spoon feeding, which while is absolutely economical in a drip irrigation system it is not in dry land environments. In this scenario uptake rate can be determined using on site weather stations and growth models. N losses could be determined using the same onsite weather data and some soil and N cycle modeling. But with spoon feeding the number of applications is potentially quite high and is often limited by the overall cost of application. Therefore making this option not economical.
Economic and Efficient:
This involves reduced to no pre-plant and application(s) made in-season after enough time, and environment, has passed to collected the data/information needed to determine yield potential, activity of the N-Cycle and losses. This is the method that utilizes precision ag, this is where I place the use of N-Rich Strip and Sensor Based Nitrogen Rate Calculator. Previous blogs Nitrogen Rich Strips Re-Post: Sensing the N-Rich Strip and Using the SBNRC . Even though we have plenty of data, on farm and small plot, that spans almost two decades of environments and dozens of states adoption is slow. But as I look out over the entire N management landscape adoption of most N management strategies are slow.
First I acknowledge there are a dozen other aspects to why technology is not adopted, and this is just one of many theories. But as I see it, it is the Risk component that can be the hinge for the changing of a N management strategy. We can not change the math on Efficiency or Economics, but we can change how we not only perceive risk but how we manage around risk. How and what a producer views as a risk often influences management. If I am a wheat producer in Oklahoma and my greatest concern is yield, then it makes since to leverage N inputs early to ensure crop never stresses. If losses occur then I can top it off. However on the flip side if I see being over leverages with inputs early as a risk, then I will delay N application and see what my crop and environment is going to provide in the given cropping season. And yield stability, how consistent are the yields year after year, will likely be the driver of where I see my risk being.
In conclusion this is not a recommendation, not a review of current science or an opinion of what is right or wrong. This blog was a way to convey what I have interpreted from the past 15 years of observation.
Please feel free to contact me with comments or questions.
Precision Nutrient Management Specialist
Oklahoma State University
As I write this on May 5, 2019, the wheat is at or nearing flowering and Stillwater just received another 2.22 inches last night helping the 30 day rain total to be just shy of 9 inches. Its wet, cool, and the wheat has truly gone from rags to riches (the crop not the market). I have been regularly fielding calls on late season N and protein. I thought it would be a good time to repost my previous protein blog and add some thoughts and updates. Since the original post we have more data on nitrogen (N) timing work and one year of data from a trial we call “Protein Progression”. First if you are interested in the timing study the full blog summarizing 2 years of work can be seen here How long can wheat wait for Nitrogen? . But the short short version was that two years in a row delaying the application of ANY nitrogen until very late in the season, past hollow stem, resulted in the best combination of yield and protein. Meaning even when wheat was yellow and stunted yields and quality recovered when N was applied at or shortly after hollowstem. This work is being continued and expanded this year. I have only shared the Protein Progression results in a few presentations, because they do not tell a consistent story. For a few years now I have been giving this advice when asked about late season nitrogen. Based upon the work I have done, this year is my 11th wheat crop in this position and I have always had at least 1 study with late N, that when nitrogen was applied at flag leaf the probability of a positive return on investment was below 50% and closer to 33%. Very seldom did I see the flag leaf applications of nitrogen provide much benefit. At the flag leaf stage when there was a positive benefit it could be yield, protein or both. When it came to anthesis (flowering) applications the probably increased to closer to a 66%-75% chance of positive impacts (Understand these percentages are drawn from my experiential learning across many environments, I have not yet run the data to determine exact values). Late applications in the right environment could increase protein by up to 2% and in the wrong environment, devastate yield due to burn. The weather needs to be cooler and humid to reduce the potential of burn and the rate of nitrogen must high enough to actually impact protein levels. Per each 1% of protein concentration of wheat grain there is 0.1 lbs N per bushel. So to increase to increase the protein content of a 60 bushel wheat crop by 1%, 6 lbs much be converted from fertilizer to protein. To get this amount of nitrogen on the crop without burning it up I have been using UAN (28-0-0) and water at a ratio of 1:1 putting on 20 total gpa. When applied this way I have not seen burn, I do however avoid spraying when its hot, windy with low humidity.
Below are last years results of the Protein Progression study. In this I wanted to look at N application timing pre vs post, the addition of sulfur (many sources state added sulfur increases yield), flag and anthesis application. Last year we had locations near Stillwater (LCB) and Chickasha. Both yielded in the 60 bushel range which was OK but well below the five year average of both sites. At the LCB we saw a great response to N fertilizer. The more it was delayed the better off yields were. We saw a consistent negative impact of S at top-dress, which is a result I can not explain, there was no crop damage due to application. The flag leaf N application significantly increased yields, at flag leaf there was evidence of N deficiency. And the anthesis application of N had no impact on protein. At Chickasha where the none fertilized check yielded 53 bushels, the response to N was reduced. Sulfur had no impact on yield or protein, flag lead N and anthesis N increased protein by about 1%.
What did I learn from those studies, I confirmed the response to late N is not very predictable. The low protein site (LCB average protein of 11.75) did not respond to late N but the high protein location (Chickasha’s average protein content was 15%) did. I was able to see N at flag leaf did impact yield when N deficiency was noted. It also confirmed this study will be continued for multiple years. The more environments we can get data from the better we can predict response/non response.
If you have any questions feel free to send me an email at firstname.lastname@example.org.
Original Post Sept 27, 2017
A result of the 2016-17 winter wheat crop was a significant amount of discussion focused on protein levels. For two years running now, the protein levels have been low across the board. Low protein brings in a challenge to sell, could impact local basis, and even more concerning is that low protein is an indicator that nitrogen was limiting during grain fill. Therefore, the field maximum yield potential was not achieved. In this blog, we talk about what protein is, what can be done to maintain a good protein level, and what can be done to increase protein if desired.
First, the definition of protein is any of a class of nitrogenous organic compounds that consist of large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms, especially as structural components of body tissues such as muscle, hair, collagen, etc., and as enzymes and antibodies. Protein is also one of the many attributes that determines end-use quality and marketability of winter wheat. Sunup TV met with Dr. Carver in the baking and milling lab to create a great video discussing wheat quality impact on baking and milling.
We determine protein by measuring the percent of nitrogen in the grain and multiplying by a factor of 5.7. So if the grain has N % of 2.5, the protein content is 14.25. The amount of N in the grain is affected by many variables such as weather during grain fill, yield level, and N availability during grain fill. If weather is conducive to good grain fill and test weight is high, we will often see protein values dip. On the other hand when grain fill conditions are hot and dry and we have light test weight, wheat protein will be higher. Research has shown (Figures 1 and 2) that generally as yields increase protein levels decrease. Of course if N is limited during grain fill, the N available for the grain is reduced, and the plant is forced to get all grain N from re-immobilizing N in the leaf tissue.
Maintaining Protein, and yield.
Managing nitrogen to maintaining protein and maximizing yield comes down to making sure that N is available at critical growth periods. With wheat, the critical uptake stage is typically the time frame between hollow stem and soft dough. The two graphs below show nitrogen uptake in wheat and barley. If the same graph was made for dual purpose wheat, the upward swing would start sooner but would follow the same general trend.
When it comes to making sure N is available during this time of peak need, the only way we can do that is apply just before it is needed. This means split application. While putting all the nitrogen out pre-plant as anhydrous ammonia is the cheapest method, it is also the method that provides the lowest nitrogen use efficiency and is most likely to show deficiencies late in the season. One of the challenges with 100% preplant N application is that years with good yield potential coincide with years with good/high high rainfall, which means more nitrogen loss. Some interesting results from studies implemented in the 2016-17 cropping season showed the importance of nitrogen application timing. The study is determining how long nitrogen application can be delayed after the N-Rich strip becomes visible (https://osunpk.com/2013/09/19/nitrogen-rich-strips/). For the study, 90 lbs of N was applied on one of the treatments at planting When that plot became visibly greener or bigger than the rest, N application was triggered. After the 0 DAVD (Days after visual difference where the day had growing degree days >0), another treatment was applied every 7 growing days for 63 growing days. Each plot, excluding the zero N check, received 90 lbs as NH4NO3 (we use this to take the variable of volatilization out of the data). In all cases, 90 lbs applied in late January to early February was better than 90 lbs pre-plant. Keep in mind there was 0 N applied at planting for each DAVD application timing; yet, we still hit 50-80 bushel wheat with nothing but in-season N. This is the result of supplying the N when the plant needs it. I should add this is just one year of data, and every year is different. The study is being replicated again this year and will be highlighted at the Lahoma field day.
For dual-purpose wheat, the total amount of N expected for the forage production needs to be applied pre-plant. Oklahoma State recommends 30 lbs N for every 1,000 lbs of forage expected For grain-only wheat, there needs to be only 20 to 40 lbs of N available to the crop when planted (this includes residual N). The remaining N should be applied at green up or early spring. The only way to ensure that N is applied when the crop needs it is to utilize the N-Rich Strip method. Having a N-Rich strip in your field lets you know when the wheat needs more nitrogen and when it does not.
Two years testing the N-Rich Strip and Sensor based nitrogen rate calculator (SBNRC) from the Texas boarder to the Kansas boarder showed that the SBNRC on average reduced N but maintained yield and protein when compared to standard farmer practice (Table 1).
Some producers may plan to market high protein for a premium if available. Fortunately, there are opportunities to increase protein via management. While most of the strategies for increasing protein happen later in the growing season, some of the early decisions can be a significant contributing factor. Variety selection and keeping the plant healthy and free of competition (i.e., pest management) throughout the growing season are going to increase the opportunity to produce high protein wheat. After that, the equation goes back to Figures 3 and 4 and making sure the crop has access to nitrogen during peak periods, including grain fill. If you will note, the bottom two graphs of Figure 5 both show significant increases in protein on the later applications. For both locations, this was when N (90 lbs N ac-1) was applied after full flag leaf emergence. There has been a significant amount of work at OSU looking at late application of N stretching back into the 1990s http://nue.okstate.edu/Index_Publications/Foliar_N_Curt.pdf. The focus has been looking at timing, source, and rate. The take home of decades of work can be summarized as such. Yes, protein can be increased with late season application, but not always. Applying N at or after flowering has a significantly greater probability of increasing protein than a application at flag-leaf. Source of N has had little impact if managed properly (UAN, 28-0-0, has to be watered down so that it does not burn the plant). The rate of N does matter quite a bit. Most of the work suggests that for every pound of N applied, the percent grain protein could increase by .05%. So to increase protein from a 12.5% to 13.5%, it would require approximately 20 lbs of N per acre. My work has shown the same trend that a 20 lbs application at post-flowering had more consistent increases in protein than lower rates at the same time or similar rates applied at flag leaf.
This wheat season we are looking to improve our knowledge of management on protein content through multiple studies by continuing the evaluation of varieties and management practices.
If you have any questions for comments please feel free to contact me.