Fertilizer « Down and Dirty with NPK

Grain Sorghum, 2023 edition

May 4, 2023 4:07 pm / 2 Comments on Grain Sorghum, 2023 edition

As I sit in my office writing this I am seeing the chances for Stillwater to get a good rain today slowly dwindle away. Last night we had a 75% chance of 0.56. Its now 3pm we have received 0.01 and have a 60% chance of getting an additional 0.10. And as this is how 2023 has gone, but we are still better off than so many west and north of us.

No some of the zeroed out wheat ground and winter fallow ground has seen its first moisture in 100+ days. Planters and drilling are rolling and or ready to roll. So I wanted to throw out a few thoughts and re-share an older blog.

In August of last year I was talking about how the extended drought was impacting organic matter and nitrogen cycling “Nitrogen cycle hiccups and a lot of drying“. Wish I could say things have changed since then but we all now otherwise. While we have moisture to plant and germ our H₂O fuel tank is far from full. Its going to take significant rainfall to rebuild the soil profile, not to mention the ponds. And I can not forget how last year we had great rains in May and were going pineapple by the end of July. I had N response studies all over the state in sorghum, at every trial nitrogen was not a limiting factor.

By this point if you know me or have every read anything I have written in the past you should know what is coming. My recommendation for pre-plant N is 0.0 lbs. Go ahead and put a starter down where you have low P or pH that’s out of range, and Fe and/or Zn in the calcareous soils where needed, but that’s it. We are continually adding to the research data base that says sorghum responds exceptionally well to in-season nitrogen applications in some cases nearly all the way to boot stage. I believe we are close to determining/explaining why the crop does so well but not ready to share that work just yet.

I just do not have the trust in the what rains may come to spend money on a fertilization pass that has been proven to be less valuable. Get the seed in the ground and crop up, put out some N-Rich strips. Let the weather play out for a month or so and see 1) Do I have soil moisture to get me through harvest or am I living day by day on a hope and a prayer? 2) is my N-Rich strip showing?

For Question 1) if your living day to day is further investment in the crop warranted? If you have soil moisture and rain in the forecast, its time to rock and roll. For question 2) which I hope you take my advice on doing. If the N-Rich is showing up 30 days into the you can use some rough yield goal estimations and apply 1 lb N per bushel or go get access to a GreenSeeker sensor (available through OSU extension offices) and use OSU’s online calculator SBNRC. If the strips not showing up then you need to consider that a month into the crops growth the soil has supplied 100% of the crops N need. Depending on if you want to push yield or save N adjust your rec accordingly. I would say reducing planned N rate by 40-50 lbs would a legitimate option. There are more and more agronomist utilizing N strips in wheat and sorghum so you could check around.

Final thoughts.
The more I do research on N timing and N management the more I am finding that there are some great benefits to limiting early N availability to the crop. To the point were I am finding and increasing value of an early season N stress on crop performance and grain yield.

Now for rehashed research. Much like wheat, sorghum can and probably should wait for N.

Can Grain Sorghum Wait on Nitrogen? One more year of data.

Original Posting 4.7.2022

Michaela Smith, Ph.D. candidate under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist

The impressive ability of sorghum to recover from significant N stress with late applied nitrogen was originally reported in the blog “Can grain sorghum wait on nitrogen”. This projected was replicated again in 2021 and these are the results. During the 2021 growing season, frequency of rainfall events and amounts were similar to the 2020 growing season. Figure 1. shows the application dates and rainfall events.

Planting date and date of Preplant N was April 27, 2022. Graph downloaded from the Oklahoma Mesonet.

Table 1. Planting information for the 2021 delayed nitrogen trial. Dekalb 3307 is labeled as a 61 day to mid-bloom cultivar.

Statistically there was no significant difference in grain yield from the pre-plant (0) and any application up to the 56 day application. This data matches up quite well the yield results from 2020.

Figure 2. Grain sorghum yield results for the 2021 delayed nitrogen study.

Looking and the current soil moisture conditions (Figure 3.) and fertilizer price I think this data supports the recommendation to get the seed in the ground and see how the situation plays out. If there are decent rains at and shortly after planting then there is time to apply nitrogen with little risk of yield loss. If fact the weather during late May and early June provide some of the best chances to getting the fertilizer rained in (Figure 4) . If the weather doesn’t cooperate and provide us the much needed rains, then by waiting to apply we are not left with a lot of Expensive nitrogen setting out in the field of a failed crop.

Final Thoughts Heading into the 2021 Sorghum Planting Season.
– Make sure you have a soil sample, knowing P and K will be critical.
– No need to front load N fertilizer, especially if soil moisture is short.
– Utilize in-furrow P if soil pH and or soil test P is low.
– If you skip pre-plant N APPLY N-RICH STRIPS!!!!
– If you apply pre-plant N consider applying 50% of the expected N or less.
– If you are applying any level of pre-plant N, Create Zero-N Strips.

Figure 3. 32-inch plant available water downloaded from the Oklahoma Mesonet on April 6, 2022.

Figure 4. Probably of rainfall for the Breckinridge Mesonet location for the grain sorghum growing season.

For more information or questions contact
Brian Arnall b.arnall@okstate.edu 405.744.1722

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

Original Post March 22, 2022.
Data for this post available in thesis Impact of delayed nitrogen application in grain sorghum
Smith, Michaela Lynn (2021-05). Available at https://shareok.org/discover

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

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

Trial structure and breakdown

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

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

Physiological Response to Application Timing

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

Table 2. Delay in Heading for the Perkins (gray) and Lahoma (green). Letters indicate the start and finish of heading. S represent the start of heading while F indicants the finish of heading, SF denote treatments the started heading and finished within the same week.

Figure 2. Visual maturity differences between nitrogen application timings. Timing of applications are listed within the figure.

Yield Response to Application Timing

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

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

Influence of Rainfall

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

Summary

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

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

Acknowledgement of EDC Ag Products Co LLC for support of this project.

Did in-furrow starter products increase yields?

September 28, 2022 10:19 am / Leave a comment

Bronc Finch, Precision Nutrient Management Post-Doctorial Scientist.
Brian Arnall, Precision Nutrient Management Specialist.

As winter wheat planting time approaches this question arises often when fertilizer decisions are being made. There are several products that have been marketed to wheat producers that contain combinations of nitrogen (N), phosphorus (P), and potassium (K) as well as some plant essential micro-nutrients. These products are designed to be placed with the seed as an in-furrow application at planting and provide nutrients earlier in the season than traditional dry spreading methods. While the state of Oklahoma macro-nutrient deficiencies are often corrected with traditional fertilizing methods and micro-nutrient deficiencies are not commonly witnessed in winter wheat; these products are often sold with the expectation yield increases can still occur. This has led to the question can these fertilizer products improve winter wheat yield production regardless of soil analysis results? To answer this Oklahoma State University developed a study evaluating eleven different starter fertilizer options available to producers (Table 1). Of these eleven fertilizer options three are commonly available fertilizers, and eight of them are products available through specific companies. The study was carried out at three locations a year for two years.

Table 1. Winter wheat starter fertilizer treatment structure, guaranteed analysis in percent of nutrient, rate of product and nutrients applied in lb/ac unless otherwise noted.

To compare the ability of these products to increase yield beyond the recommendation of soil test results, pre-plant soil samples were collected to a 6-inch depth at each of these research sites. Soil analysis of the five-site years used in this evaluation (Table 2) reported no deficiency at the Lake Carl Blackwell research farm. Deficient concentrations of P (< 32.5 ppm) was recorded at the North 40 research site and Perkins research station, along with a low pH (4.8) at the Perkins research station. Acidic soils are of concern for crop production having many detrimental impacts to root production, however there is also influence on nutrient availability. Aluminum concentrations are often higher in low pH soils which will result in root pruning and the binding of applied P, increasing the concerns when soil analysis P concentrations are already deficient.

Table 2. Pre-plant soil test analysis results for all site years, taken as 0-6 inch composites

Evaluation of these commercially available products at non-nutrient deficient sites show no influence of any in-furrow placed fertilizer product on winter wheat grain yield compared to an unfertilized check, yielding an average of 52 bu ac^-1 in 2014-2015, and 93 bu ac^-1 in 2015-2016 (Figure 1). Figure 1, along with the following figures, show the mean and variability of winter wheat grain yield of each of the commercially available starter fertilizer product treatments, as well as the check treatment which received no fertilizer application. The column for each treatment represents the grain yield in bu ac^-1 which is the average of three replications the variability of grain yield at an individual treatment can be observed by the error bars which depict the range of grain yields within a specific treatment. The larger the error bar the less consistent the yield and the harder it is to separate out statistical differences in yield.

Figure 1. Winter wheat grain yield (Bu ac-1) at 12.5% grain moisture at the Lake Carl Blackwell location for 2014 – 2015 (top) and 2015 – 2016 (bottom). Error bars depict one standard error of the mean, and the dashed line represents the mean of the check to which all treatments were compared.

When the soil test P level was below 32.5 ppm, some P containing starter fertilizers where able to increase winter wheat grain yield in 2014-2015 growing season at North 40. Products containing 40 – 52% P; MAP, DAP + Awaken and MES-Z, improved grain yield by up to 14 bu ac^-1 compared to the check. At the North 40 locations APP did not show the same increase in yields as DAP and MAP. The addition of micro-nutrients by Awaken combined with DAP yielded a 20 bu ac^-1 increase over Awaken used alone, but no increase compared to DAP or MAP used alone. Similarly, the addition of Zinc by MES-Z yielded similar to the base product, MAP.

Figure 2. Winter wheat grain yield (Bu ac-1) at 12.5% grain moisture at the North 40 location for 2014 – 2015 (top) and 2015 – 2016 (bottom). Error bars depict one standard error of the mean and the dashed line represents the mean of the check to which all treatments were compared to

When P deficiency was compounded by a low pH such as observed at Perkins there was response to more in-furrow products. Compared to the check, increases up to 32 bu ac^-1 in winter wheat grain yield was found by DAP, MES-10, MES-Z, Nachurs + CornGrow, and DAP + Awaken. Further investigation revealed the source of P fertilizer (DAP, MAP, and APP) reported no difference in yield averaging 55 bu ac^-1. The addition of S and K by Nachurs was not different from APP, which is a similar liquid fertilizer, averaging 52 bu ac^-1. Micro-nutrient additions by Awaken combined with DAP (56 bu ac^-1), and by CornGrow combined with Nachurs (56 bu ac^-1) did not increase winter wheat grain yield compared to each other or their respective base products of DAP (59 bu ac^-1) and Nachurs (53 bu ac^-1). Similarly, additions of S by MES-10 and S and Zn by MES-Z yielded similar to one another with 65 and 72 bu ac^-1respectively but produced 14 bu ac^-1 more yield on average than the base product MAP. At Perkins, which is a well-drained sandy loam soil, we often see a yield response to S when yield levels so seeing a response to the products that added 7 lbs of S, was not un-expected.

Figure 3. Winter wheat grain yield (Bu ac-1) at 12.5% grain moisture at the Perkins location for 2015 – 2016. Error bars depict one standard error of the mean and the dashed line represents the mean of the control to which all treatments were compared

With these results in mind and the current cost of fertilizers, the addition of fertilizer products on non-limiting soils is not expected to result in an increase in winter wheat grain yield. Also, many of these products contain micro-nutrients that are rarely found to be at deficient levels for much of the winter wheat production region in Oklahoma. Therefore, the use of these products on non-nutrient limiting soils would unnecessarily increase the cost of production and decrease the return on investment. However, that is not to say these products should be avoided completely, in the event of a nutrient limiting soils some products show potential benefit for correct soil deficiencies. As observed some P containing products were able to provide adequate P concentrations for increasing yields and overcoming low pH conditions. This work along with previous work evaluating efficient fertilizer management suggest the correction of a nutrient deficient soil to be more important than the source of the nutrients and supports the need for soil testing and following recommendations.

This blog is a summation of Mr. Jonathon Williams thesis which was published in the Journal of Agricultural Sciences. Impact of in-furrow fertilizer on winter wheat grain yield and mineral concentration https://doi.org/10.1017/S0021859622000557

SIDEBAR

So we do small plot research to me in control of as many variables as possible. But all farmers and consultants know that fields are are variable and the results of small plots do not always translate well. I get that 100%, but for me as a scientist I need to understand the little things so that I can apply the knowledge on a large scale. Just last month I wrote a blog about cutting phosphorus rates BLOG. The third major take home of the blog was:
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.“
That applies to what we learned from the above study. We found if soil test said nutrient was adequate we did not see a response of adding more. However if we combine the two blogs, if your composite soil test comes back just at the optimum level, there is a good chance at least 45% of field is below optimum and may respond.

So guess what my recommendation is. Soil SAMPLE, do it right (proper method and core numbers) and do it at the highest resolution you can afford, at least once.
Finally Do Not Skip on Nutrients when soil test says there is a need.
BA

Any questions or comments feel free to contact me. b.arnall@okstate.edu

Soil sample handling practices can affect soil nitrate test accuracy

September 10, 2022 6:55 am / Leave a comment

From Guest Authors,
Bryan Rutter, PhD student and Soil Testing Lab Manager, Kansas State University
Dr. Dorivar Ruiz Diaz, Soil Fertility Specialist, Kansas State University

The accuracy of a soil test is limited, in part, by the quality of the tested sample. For this reason, strong emphasis is placed on ensuring representative samples are collected in the field. However, these samples must also be handled properly after they have been collected.

Soils are home to a diverse population of microorganisms, many of which help decompose crop residue and cycle nutrients in soils. This nutrient cycling is crucial for crop production, but can skew soil test results if it continues in soil samples after they have been collected.

Microorganisms drive the soil nitrogen cycle

The nitrogen (N) cycle in soils is particularly complex and is strongly influenced by microbial activity and, therefore, temperature and soil moisture conditions. Bacteria and fungi consume organic material and use carbon as an energy source. During this process, N contained in the organic matter undergoes several transformations, ultimately converting it to ammonia. This conversion from organic-N to inorganic-N (NH₄⁺, ammonium) is called “mineralization.” Plants can then take up the ammonium (NH4+), or converted to nitrate (NO₃^–) by certain bacteria through a process known as “nitrification”.

The microbial activity requires moisture and heat, and the processes described above happen more quickly in warm, wet soils than in cold, dry soils. Microbial activity does not stop just because a sample has been collected and put in a bag. This activity continues as long as the environmental conditions are favorable. As a result, soil tests for plant-available N have the potential to change substantially if samples are not handled properly. This is an important consideration for growers because these soil test results are used to determine the profile-N credit and, ultimately, adjust N fertilizer recommendations.

Research study on soil sample storage

A recent study at the K-State Soil Testing Lab illustrates what can happen if sample submission is delayed. For this study, soil was collected from the Agronomy North Farm (Manhattan, KS) and thoroughly mixed/sieved to homogenize the material. This soil was then placed into sample bags, which were randomly assigned to different combinations of storage temperature and duration. One set of samples was kept in a refrigerator while the other set was kept in a cargo box in a truck bed. To monitor changes in soil test levels over time, three sample bags were removed from the refrigerator and truck box every two days (48 hours) and tested in the lab.

Figure 1. Change in soil test nitrogen parameters over a 14-day storage period. Samples stored in an unrefrigerated cargo box are indicated by purple points. Samples stored in a refrigerator (38F) are indicated by grey points. Graphs by Bryan Rutter, K-State Research and Extension.

Figure 2. Difference in the soil test nitrogen credits between refrigerated and unrefrigerated samples over a 14-day storage period. Profile-N credits assume a 24-inch profile soil sample depth, and are calculated as: *N ppm x 0.3 x 24 inches*. Graph by Bryan Rutter, K-State Research and Extension.

Take home points from the K-State Soil Testing Lab study:

Mineralization and nitrification led to more than a 3x increase in soil test nitrate in the undried and unrefrigerated “Truck Cargo Box” samples (purple points in Figure 1).
Soil test nitrogen did not change substantially in refrigerated samples.
Profile-N credits calculated from soil test N results were nearly 100 lbs of N/acre higher for the unrefrigerated samples (Figure 2).
Improper handling and storage of soil samples can dramatically reduce soil test accuracy and may lead to under or overfertilizing crops.

K-State Soil Testing Lab Recommendations

Submit soil samples to the lab as soon as possible, ideally on the same day they were collected.
If same-day submission is not possible, samples should be air-dried or placed in a refrigerator set at 40 degrees F or less.

Please see the accompanying article “The challenge of collecting a representative soil sample” for guidance on field soil sampling practices.

For detailed instructions on submitting soil samples to the K-State Soil Testing Lab, please see the accompanying article “Fall soil sampling: Sample collection and submission to K-State Soil Testing Lab”.

For detailed information on how N credits are calculated please see the MF-2586 fact sheet: “Soil Test Interpretations and Fertilizers Recommendations”.

Bryan Rutter, PhD student and Soil Testing Lab Manager
rutter@ksu.edu

Dorivar Ruiz Diaz, Soil Fertility Specialist
ruizdiaz@ksu.edu

The original article can be found on the KSU Agronomy E-update site
https://eupdate.agronomy.ksu.edu/article_new/soil-sample-handling-practices-can-affect-soil-nitrate-test-accuracy-511-4

Phosphorus decisions, Is it worth cutting P?

August 30, 2022 9:26 am / 1 Comment on 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

Impact of Nitrogen timing 2021-22 Version

August 26, 2022 3:58 pm / 1 Comment on Impact of Nitrogen timing 2021-22 Version

Raedan Sharry, Ph.D. Student Precision Nutrient Management

As wheat planting rapidly approaches for some and gets underway for others, it is without a doubt worth considering the current moisture conditions, the near-term outlook, and how that might influence N management decisions. There is plenty of information located in this blog and many other resources that show the benefits of delayed N management in crops. This is particularly true when considering an extremely long growing season for winter wheat in the southern plains. Given our current soil moisture situation yield expectations given the current soil moisture may be limited until replenishing precipitation occurs. This has many questioning their N management plan.

Often when talking about the past N timing results How Late Can You Wait there are comments about the risk of waiting and the crop needing N to get going. Most of the work in the past looked at a single application of N applied at different times and didn’t address split application. But the data from a couple of trials located at Perkins and Perry Oklahoma in the 21-22 season is reinforcing what the past data suggest. These trials consisted of 2 varieties with a 0 N check and 9 combinations of N timings to at 90lbs rate and 3 timings at 140 lbs. of N. Ammonium nitrate (34-0-0) was the N source used in this study to limit the impact of urea volatilization. For both locations we have pre-plant soil test results for the 0-6 and 6-12 inch depths. Both locations at about 30 lbs of total N and OM of 2.0% in the top 6 inches.

Table 1. Treatments from 2 N studies located at Perkins and Perry Oklahoma. (TD=Top-Dress) Applications were made pre plant, 1/10/22, and 3/24/22.

The varietal component of this study doesn’t matter in this context so we will leave them unnamed as both cultivars responded very similar to nitrogen timing and rate within each location. The first thing to highlight is both trials were sown in mid-October. October 19^th and October 21^st to be exact. Both locations received timely rainfall to start the season with approximately 1.5 inches of precipitation falling in half-inch increments between October 25^th and November 10^th. Top-dress applications in January and March were made on 1/10/22 and 3/24/22 respectively. After the early rainfall events the season was largely dry up until the precipitation in mid-march. So pre-plant fertilizer was incorporated in a fairly timely manner however the January application was applied almost a month before meaningful precipitation occurred. The March application missed the only productive rainfall event until the end of April however this occurred solely due to the application trigger being based on reaching the jointing stage.

Figure 1. Rainfall (inch) for the 21-22 wheat growing season.

If we take what is stated above into consideration it would be hard to imagine that January applied N would provide a boost over pre-plant. The data says different. At both locations pre-plant N cost us bushels compared to treatments containing fertilizer only in January. Even splitting the application did not produce the same result as treatments that only apply N in-season. At the Perry location at the 90 lb. total rate there was no yield difference between any split applications and the 0-90-0 application making the January application more cost effective. While there were no split application treatments made at the 140 lb. rate the 0-140-0 treatment (140 lbs. applied in January) maximized yield. I also think it is important to note that if the March applications would have been applied prior to the rain event immediately preceding them the March application likely would have AT LEAST been competitive with the other treatments given previous research focusing on delayed N applications. Statistically the 90-0-0 and 0-0-90 were in the same grouping for both cultivars.

Figure 2. 2021-22 winter wheat grain yield at Perry, OK. Black bar variety 1, orange bar variety 2. Treats labels as rate of N (lbs N per acre Pre – Greenup – Jointing i.e. 0-0-0

At the Perkins location the results were not much difference as far as impact of timing. In-fact except for Var 1 at Perkins 0-140-0 was statistically better than all other treatments. Also expect for Var 1 at Perry the 0-90-0 and 140-0-0 were statistically the same. In all cases 90-0-0 yielded less than 0-90-0 but it was not statistical for all comparisons.

Figure 3. 2021-22 winter wheat grain yield at Perkins, OK. . Black bar variety 1, orange bar variety 2. Treats labels as rate of N (lbs N per acre Pre – Greenup – Jointing i.e. 0-0-0

The timing component is important as it shows that we are perfectly capable of applying N in-season and being successful. In-fact this work, and other work is starting to show that contrary to past beliefs, split application is not providing any benefit over a single well-timed application. The source of N of this project needs to be consider as the January top-dress application sat on the surface for almost a month before finally receiving just under two-tenths of an inch of precipitation. We will have another blog coming out soon looking at the impact of N sources urea versus UAN when applied in Fall, January, or March very soon.

With these results in mind and current moisture conditions it is only reasonable to consider delayed nitrogen application, not only to increase nitrogen use efficiency and possibly increase yields as well as a virtually guaranteed increase in grain protein, but also as a way to hedge your bet against fertilizer application cost. This work and all the past work support that grain only wheat does not benefit from the application of pre-plant N. By applying N fertilizer now there is a chance that it may become a sunk cost with a poor performing or even failed crop. And if it does start raining, well that pre-plant N will be right there ready to be leached. Being efficient is important in the tight years, and by delaying N application until you are sure the crop requires it may save you a pretty penny or more.

Questions or comments please feel free to reach out.
Brian Arnall b.arnall@okstate.edu
Acknowledgements: EDC Ag Products Co LLC for support of this project.
Oklahoma Wheat Commission and Oklahoma Fertilizer Checkoff for Funding.

Top-dress Wheat with P and K ??

June 29, 2022 11:31 am / 2 Comments on 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 1^st. 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 1^st) 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

In-season N application methods for Sorghum

April 8, 2022 1:55 pm / Leave a comment

Raedan Sharry, Ph.D. candidate under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist

The data about to be reported is from the study we have fondly named “Burn Baby Burn”, you will see why soon enough.

Grain Sorghum production continues to be an important component of many growers crop rotations in the Great Plains. However, for many growers who focus primarily on small grains production, equipment restraints may impose limits on in season nitrogen (N) management. When producers are able to delay the application until in-season it helps to ensure that N is available to the crop at the time of increased uptake during the reproductive stages of the crops life. Producers often have access to equipment and technologies that may be used to take advantage of improved N application timing, but may worry about the negative effects that nitrogen can have if the fertilizer is inadvertently applied to plant material. An experiment was initiated in Central Oklahoma to evaluate the yield response of grain sorghum to in-season nitrogen application methods.

Trials were placed at Lake Carl Blackwell near Stillwater, Perkins and Chickasha Oklahoma and included 9 in-season fertilization methods and a 0 nitrogen control. Treatments are listed in Table 1 below.

In total 120 lbs of N was applied to all treatments receiving in-season applications. 60 lbs was applied at planting to all treatments including the “Zero N Control”. The remaining 60 lbs. of N was applied according to application method in-season. The urea was applied by hand and the liquid treatments a push cart with adjustable boom height (Figure 1) was used to apply the UAN. Applications were made mid day at V8 growth stage. The temperature at the time of all applications was about 90 F and humidity below 75%. Nozzle position for 30″ and 60″ was set for between rows.

Figure 1 In-season nitrogen application using the T-bar 20″ treatment.

At two of the three locations (Stillwater and Perkins) the addition of 60 lbs. of N in-season increased yield above the control treatment. At the Stillwater (Lake Carl Blackwell) location there were no statistical differences (α=0.05) between in-season fertilized treatments except the T-Bar 20” treatment (Figure 2). The Perkins location (Figure 3) provided a similar result in which again there was no statistical difference between fertilized treatments, excluding the T-Bar 20” treatment.

Figure 2. Grain yield (bu/ac) in a grain sorghum N application study located near Stillwater, OK.

Figure 3. Grain yield (bu/ac) in a grain sorghum N application study located at Perkins, OK.

The Chickasha location differed in that additional in-season nitrogen did not improve yield (Figure 4). While we want a response to applied N, in the case it allows use to solely evaluate the impact of burn associated with N application. The T-bar 20” treatment statistically negatively impacted grain yield and the FlatFan-20″ did at α=0.10, which means we are only 90% confident the yield lose was due to treatment. This response has been consistent across all three locations, on average decreasing yield approximately 21 bu/ac relative to the individual site grain yield average.

Figure 4. Grain yield (bu/ac) of a grain sorghum N application study at Chickasha, OK.

Even though it was mentioned for Chickasha, it is also important to note that while it was not statistically significant (α=0.05) the FF- 20” treatment (Flat Fan nozzles above canopy on 20” spacing) trended towards decreasing yields at all 3 locations and is likely detrimental to crop performance. At all locations substantial damage to leaf material was observed, similar to that pictured in Figure 5 below. Several of the treatments damaged leaf material on the plant through burn injury, but most were not negatively impactful on grain yield in the 2021 growing season. Grain sorghum yield did not benefit from moving the application point below the canopy using drop attachments, nor did adjusting nozzle spacing from 30 to 60”. Source was not a significant factor impacting grain yield regardless of it application method.

Figure 5. Aerial image of plots located at Perkins, OK in a grain sorghum in-season nitrogen application study.

The observations from this study show that many of the in-season nitrogen application methods that are available to growers will not negatively impact yield. This however does not apply to tools such as the T-Bar. Similar tools that concentrate large amounts of N to leaf material are also likely to produce similar results. It is important to note that the T-bar was used on 20” spacings and not tested otherwise. Moving the spacing of the T-bar may lead to different results.

Growers who are looking to move N applications in their grain sorghum crop to in-season to capture the benefits associated will likely be able to with equipment that is already available to them. While leaf damage may be observed under sub-optimal application methods, damage is unlikely to contribute to significant yield loss. However, growers should keep in mind that environmental conditions may have a significant impact on the results seen from these types of application as growers should always look to limit stress to the plant when possible.

We of course will be putting out a second year of this study and will share the results when we can.

For more information or questions contact
Brian Arnall b.arnall@okstate.edu 405.744.1722

https://osunpk.com/2022/04/07/can-grain-sorghum-wait-on-nitrogen-one-more-year-of-data/

Can Grain Sorghum Wait on Nitrogen? One more year of data.

April 7, 2022 6:49 pm / 1 Comment on Can Grain Sorghum Wait on Nitrogen? One more year of data.