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

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

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

Yield Response to Application Timing

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

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

Influence of Rainfall

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


            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

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

Mechanics of Soil Fertility: The how’s and why’s of the things.

Ag Lime

The primary purpose of Ag lime is to increase to soil pH so before we talk ag lime, we need to talk soil pH. pH, regardless of what is being measured pH is the – log H+ ions. So how many followed that! Basically liquids, we are measuring the soil solution, are made up of a ratio of hydrogen (H+) cations and hydroxide (OH-) anions. When the two are at a even balance pH = 7. When OH out number H+ pH is greater than 7 (basic) and when H+ out numbers OH , the pH is less than 7 (acidic). When you send a soil sample off to the lab the most basic test preformed is pH. There are a few methods to do this but at Oklahoma State we take 10 grams of your soil and add 10 mls of water, stir it and record the pH with a probe. This pH reading is measuring the amount of H+ that is present in the soil solution, basically the H+ not attached to the soil, this is called active acidity. However, the amount of H+ in the soil solution is 1/100th the amount adsorbed on cation exchange sites. And if we want to change the pH we have to account for the H+ in the solution and the H+ that is on the exchanges sites. These H+ on the exchange sites will quickly pop off the CEC when the concentration of H+ in the soil solution is decreased. That is why when the pH is below a critical point the lab will run a buffer analysis. Think of it in this way, the lab adds what is equivalent to one ton of pure lime per acre to the cup, mixes well and re-measures the pH. The lab is looking to see how much the pH changes. Say there are two soils which both started at a pH of 4.3 and after the buffer solution was added with the first soil the pH changed to 6.7 while the second changed to 5.1. This tells us the second soil had a significantly greater amount of H stored on the CEC and therefore will take a lot more lime to change the pH in the field. Just a side note more than likely soil 1 was sandy, low CEC soil while soil 2 and fair amount of clay and significantly higher CEC. Therefore, we use the buffer index not the soil pH to make a lime rate recommendation.

Now that you have had a crash course in the chemistry of pH lets jump off the deep end of chemistry and talk Ag Lime. Ag lime is the short name for ground limestone used to change the soil pH of a field, garden, or lawn. We work heavily with calcitic (CaCO3) and dolomitic (MgCO3) lime. Both limes are basically a cation, calcium or magnesium, and a carbonate. The combo of a cation and carbonate is the winning ticket for pH change. However, many tend to think the cation is doing the work. Which is not true, if it was, we would be using gypsum (CaSO4) as the primary source of Ag lime, because it is slightly more soluble than limestone. {Side note sulfate (SO4) has already been oxidized and has no effect on pH, decreasing or increasing.} The cation does play an important role as its purpose is to kick the H+ off the soil particle. But removing H+ is easier said than done. Below is the lyotropic series, this represents the strength that cations are held to the CEC. Note the Al3+ and H+ is at the top of the list, meaning if all cations are present in equal amounts the Al3+ and H+ will bind to the CEC before any other.

Al 3+ = H+ > Ca 2+ = Mg 2+ > K+ = NH4+ > Na+

The one way the lyotropic series can be beat is by overwhelming the soil system with a cation lower on the list. In other words, we can put large quantities of Ca2+ and Mg2+ into the soil and they kick the H+ off the CEC. This is critical because the pH can not be changed unless the H+ enters the soil solution. This is where the CO3 does the heavily lifting of raising the pH. The CO3 reacts with H+ in the soil to form H2O and CO2.

2H+ + CO2 -> H2O + CO2

So, the amount of lime that the soil test recommends you apply is based upon the amount of H+ in the soil solution and on the soil CEC that needs to be neutralized to increase the pH to the desired level. Typically, these recommendations are made assuming a 6” incorporation depth, so that means we need to apply enough CO3 to neutralize the H+ in and on the two million pounds of soil.

Depiction of acidic soil particle interaction with Ag-Lime.

Below are two Sun-up videos where I discuss soil pH and lime.

If you have any questions or comments please feel free to reach out. b.arnall@okstate.edu

Jan 2023 edition of Wheat N management.

With the recent weather and lack of pre-plant N applied this fall I know a ton of rigs are running right now and I am handling a lot of questions about N rate, source, and time. So, while it might be a bit late I wanted to share a few thoughts.

First soil N: If you look back at the August 22 Blog, A Hiccup in the C cycle, well that cycle was put up on blocks for most of the wheat belt will late Oct. This had multiple ramifications, one; the summer crops suffered, two; mobile nutrients moved to the surface, and three; residue did not break down due to lack of moisture, the residue breakdown in turn ties up N into OM. These factors all resulted in above average soil test NO3 values. However, as I mentioned in that blog when the soils get moisture and warm temps that break down will ensue and short-term plant available N will drop until the OM mineralizes and releases NH4 sometime in the spring.

Second soil water: For most of the wheat belt the Mesonet is showing a concerning trend in soil moisture. The 16” soil moisture map looks pretty good with exception of the panhandle. However, if you look at the difference between the 16” and 36” you can see there is not a lot of moisture at depth. If we maintain these warmer temps the crops going to keep growing and burning through the moisture. Our ground is going to require a good dose of spring rains to maintain the yield potential.

16 inch plant available water, retrieved from the mesonet on Jan 4th.
32 inch plant available water, retrieved from the mesonet on Jan 4th.

If you have read much of my work you know my opinion, supported by years of research, on nitrogen timing in wheat. In my perfect scenario I go with a in-furrow application and then hold off on any additional N application until just ahead of hollow stem for wheat under the 75-bushel range. And for anything over that yield level I like a shot of 30-50 at green-up with the remaining at jointing. With both approach I am utilizing reference strips. This timing approach allows for adjustments, which I believe this season will be needed.

So for me the trick with this season to maximize profit will be the flexibility. Going all in early locks you down. For those who haven’t applied yet but are about to, you should consider adding a zero N check or two. The zero N will help you see if all that residual N is still there for if the organic matter cycle has tied it back up. Basically, if the zero N shows early, that means your crop is dependent upon you for its N needs. If you get to hollow-stem and that zero N is still not visible, Pull Back the Reins on fertilizer N, the system is providing a fair amount. In the Arnall Utopia, the N you don’t apply in the Zero can go elsewhere and now you have a N-RICH Strip. With both of these options we can figure out a N rate based on GreenSeeker readings. If you have interest in applying reference strips let me know, I am happy to help create the applicator files that are used in the fertilizer rig.

Example of a field with a zero N and N-Rich strip. From this an applicator file can be created and sent to the fertilizer applicator.

Of course if your fertilizer management plan is in a holding pattern, the now is a perfect time to apply your N-Rich Strip. I have several blogs and extension materials which help describe the process N-Rich Blog.

If you’re going to go without the reference strip, then I say hold the majority of the N until we do or do not get spring rains. If it rains, let her rip. If not your probably sitting better with the N not on the field. Take a few lessons from the last wheat crop, heavy N was often more of a problem than being short on N when we were so dry.

Questions or comments feel free to reach out via email or social media.

Brian Arnall, Precision Nutrient Management b.arnall@okstate.edu

Related Blogs

Did in-furrow starter products increase yields?

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


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.

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

Soil sample handling practices can affect soil nitrate test accuracy

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 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

Dorivar Ruiz Diaz, Soil Fertility Specialist

The original article can be found on the KSU Agronomy E-update site

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

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 19th and October 21st 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 25th and November 10th. 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.

Nitrogen cycle hiccups and a lot of drying.

Normally this time of year the nitrogen and wheat seed is flowing. But the dry spell has a lot of the central plains wheat producers in a holding pattern. And right now many of the grain only producers are looking at soil test results to help make nutrient plans for Oct sown wheat.

Well the map below is the 24 inch fraction water index (8.24.22) and it tells the story of a dry soil to a significant depth. I wish I could say that below two feet we had good moisture. But, I would be lying.

Since June (see the soil moisture data below) we have been drying our soil to a significant depth. While the drying is a big story its not the one I am here to talk about. It is what has happened because of drying.

The soil is filled with mobile and immobile nutrients. Mobile nutrients move with soil moisture. That is why we suggest to take deep soil samples, for deep rooted crops like cotton and corn, before making nitrogen decisions. I have sampled a lot of fields over my career and seen a lot of very high nitrogen (NO3) and sulfur (SO4) values in the 18-36 inch depths. Well during June and July evaporation in fallow ground and evapotranspiration is cropped ground (or weedy ground) has been pulling moisture to the soil surface from the depths. This moisture moving up to the surface has brought all the mobile nutrients with it. Combine the movement via evapotranspiration by the lack of crop production (winter and summer) and we are seeing some VERY high NO3 values.

So what does that mean. Yes, there is a lot of residual N. Yes, I would agree that there is little need for pre-plant, although I have said regardless the conditions, see Is there still time for nitrogen. Does this mean I wont need any N, sorry you probably will. Why? This is where the Nitrogen Cycle and more correctly the Organic Matter Cycle comes into the picture. If you look above and see the long term soil moisture averages you’ll note most of June-Aug has 0.4 or better. our current track is not as pleasant. That means the system has not been functioning as normal due to lack of moisture. The system I am referring to is the microbial system. In an average year the soil microbial community is busy breaking down straw, roots, and residue over the summer months. When plant material high in carbon, low in nitrogen (like wheat straw) breaks down, the microbial community that is doing the work needs N. They get this N from the soil environment, and we not talking a pound or two, we are talking 20-80 pounds depending on residue load and type. But the microbes need moisture to do this and they have been without. So the immobilization portion of the N-cycle as yet to take full effect.

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

The last time I saw conditions like this I was working in a wheat field that the year before had 80 bpa wheat cut but had 80 lbs of N in the 6″ preplant soil sample. When sowing the my crop I noted there was still a ton of residue left in the soil that had not broken down over the very dry summer. Well the fall was beautiful, great rains and warm temperatures. By Thanksgiving the crop was yellow and the N-Rich strip showing up really well. A soil sample taken Dec 1 showed there was only 5 lbs of N left in the soil, by my estimate the crop had only used 30. It was the microbes tyeing up the rest.

I was asked at a field day, would the immobilized N be mineralized and made plant available. That answer is easy Yes. Then I was asked when and that answer is tough unless you can predict the weather. The cycle is dependent upon moisture and soil temp. Warm wet fall/winter means better chance for early spring mineralization. Dry and or very cold winter looking at a delayed release. Also the spring weather pattern will influence the release. So here are my thoughts on what to do.

First: Given the lack of subsoil moisture at the time of this blog, I see little reason for any plant N to be applied in grain only wheat. For the forage systems I’d keep it at or under 50 lbs until we build our moisture profile.
Second: Do not forgo the in-furrow. A good root system could be critical this season, so make sure your Phosphorus is taken care of. If you ground is marginally acidic 6.0 or less this is even more important.
Third: If I’ve said it once I’ve said it one hundred times. PUT OUT N-Rich strips. Even if you don’t plan to use use the online tool, a consultant or a service provider, putting a strip out in your field will provide SO much information about what your crop and soil is experiencing. All about N-Rich Strips.
Fourth: If wheat is in a tug of wag match with microbial community, the microbes win. This is by no means a bad thing, but the numbers we see today, will not be indicative of what’s available once the N-Cycle kicks back into gear.

Thanks to the Oklahoma Mesonet for always having just the graphs I need.
Questions or comments please feel free to reach out.
Brian Arnall b.arnall@okstate.edu

To bale or not to bale.

This blog is unfortunately too late for many of those in central and southern plains but as the drought continues to grip the Plains states many are determining on whether to bale failed crops or leave them stand.

I can not argue that given the current forage situation that baling the failed crop will have a high value. I remember in 2011/2012 hearing about how baling failed crops resulted in much needed revenue. I also cannot argue with anyone who says they would prefer to leave the standing crop to maintain some leave of residue. Given our weather pattern since the fall many places are short on cover. Of course, a nice balance could be grazing the failed crop, given consideration is given to the nitrate levels.
Factsheet on Nitrate Toxicity

While the above conversation on revenue versus soil cover is likely the most important, I wanted to shed some insight on the nutrient value of the crop being discussed. A quick guide to nutrient removal can be found in the Nutrient Management Field Guide, link. While the numbers are estimated averages, they can provide a general starting point.

The nutrient values used in the Pete Sheet came from a collection of publications and surveys. You will note a significant difference in the corn silage values and sorghum-sudan values, this is primarily due to moisture content silage being high 55-65% and sorghum-sudan as a dry weight 0% moisture. I believe the two provide pretty good book ends for a high and low moisture content. But for this blog I added a Mid, which is just the halfway point between the two. So depending on the moisture content of what you are doing there is a good range. I pulled the nutrient fertilizer values from the Two Rivers Co-op page.

Nutrient removal values for several feed and fiber crops. Values from the nutrient removal Pete Sheet which can be found in the Oklahoma Nutrient Field Guide http://www.npk.okstate.edu

With the rising price of hay and fertilizer all aspects should be considered before pulling the trigger. The purpose of this blog was not to support one choice or the other, just to provide information. The table below shows the value of nitrogen, phosphorus, potassium, and sulfur per ton of biomass of corn silage (Wet Weight Basis 55-65% moisture), sorghum-sudan (Dry Weight Basis 0% moisture) and a mid point that may be more along the lines of some of the corn being chopped.

Nutrient content ton and value per ton for Corn silage (Wet Weight basis 55-65% moisture), Sorghum Sudan (Dry Weight Basis) and a nutrient content mid point. Prices based on two rivers coop website quote retrieved July 23. Website state prices update July 8, 2022.

I was asked about soybean hay. The literature was a little sparse of data so what is in the table comes from three sources (Listed as 1,2,3), the first source only had crude protein.

Nutrient content per dry ton and value per dry ton for Soybean hay harvest from R3-R7 stages from three sources in the literature. Prices based on two rivers coop website quote retrieved July 23. Website state prices update July 8, 2022.

Also I found this Factsheet out of Missouri. Extremely important to consider if you applied herbicides to the failed crops. Considering-Your-Grazing-Haying-and-Silage-Options-for-Herbicide-treated-Corn-and-Soybean
More important links related to herbicides.




If you have any questions or comments please feel free to reach out to me.
Brian Arnall

Top-dress Wheat with P and K ??

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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