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osunpk

osunpk

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

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How long can wheat wait for Nitrogen? One more year of data.

Update to the delayed nitrogen study.

Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.

Due to the surprising results seen from the delayed N study that was first reported below we repeated the the study for a third year at two locations, the Lake Carl Blackwell Research farm near Perry OK and the Ballagh Research Farm near Newkirk OK. Due to the excessive rain fall the wheat was planted and trials established later than normal and a cool winter and spring and winter the crop green up (end of dormancy) was delayed compared with the two first cropping seasons. For this season we started applications before visual symptom difference between the N-rich Strip (pre-plant) and the rest of the field actually occurred. This can be seen with the pre-plant dates of late Oct-Early Nov and the notation of visual difference above the yield bars. Just as the other two previously crop years, the timing of the application did impact wheat yield and protein. In this season at LCB we see a increase in yield with application of N during the first part of March compared to the preplant with yields dropping off below the preplant when N was applied in mid April. At the Ballagh farm there is no yield benefit from delaying N after preplant but there was steady increase in protein, again at this location yield is lost when N was delayed past mid April. In both of these locations mid April was after the growth stage of Feekes 7. After three cropping seasons with some extremely different weather patterns we saw that in this work, pre-plant N was never better than in-season N applied prior to mid April, Feekes 7. In most cases N applied in-season yields and protein values were greater than that of the pre-plant treatment. My take home message from this project is multi fold; First, pre-plant may be cheaper and easier but it often falls short of in-season applications, Second that there should be no reason to rush putting top-dress nitrogen on. The application window is much wider than most ever expected and the closer we get to peak demand the better the yield and quality will likely be. And third, and final make the application of nitrogen when the conditions are the most conducive to getting the N in the ground and limiting losses.

Note: This trial used ammonium nitrate as its N source to evaluate the plants response and remove potential fertilizer efficiency problems. However while these trials were being conducted mirror studies using Urea as the N source were also being conducted. Those results are currently being compiled right now and we hope to share the results soon.

Grain yield and protein results from the delayed nitrogen study preformed at the Lake Carl Blackwell near Perry in 2018-2019. 11/7/2018 was the pre-plant application date.

 

Grain yield and protein results from the delayed nitrogen study preformed at the Ballagh research farm near Newkirk in 2018-2019. 10/24/2018 was the pre-plant application date.

Questions for comments feel free to contact me via email at b.arnall@okstate.edu

Original Post made Oct 1, 2018

How long can wheat wait for Nitrogen?

Joao Bigatao Souza, PhD. Student Precision Nutrient Management|
Brian Arnall Precision Nutrient Management Extension Specialist.

The N-rich strip method allows wheat producers a greater window of decision making regarding the application of nitrogen (N) fertilizers. Besides having greater accuracy in N rates than standard methods (based on the SBNRC – OSU) also helps to reduce costs in the production system and to preserve the environment avoiding over N applications.

With the experiments performed in the last two crop seasons (2016/18 and 2017/18), we can now be even more accurate with regard to the best application time to increase the N use efficiency by the crop. The objective of our study was to determine the impact of prolonged nitrogen deficiency on winter wheat grain yield and protein. Eight studies were conducted with 11 N application timings in no-till dryland conditions. A pre-plant treatment of 90 lbs ac-1 of N was broadcast applied as ammonium nitrate (AN). We used AN as our source because we wanted to measure the crops ability to recover and eliminate the impact of source efficiencies. When visual symptom differentiation (VSD) was documented between the pre-plant and the non-fertilized check, i.e the N-Rich Strip showed up, top-dress applications were performed every seven growth days (GDD> 0) (https://www.mesonet.org/index.php) until 63 growth days after VSD at all sites. The only N the treatments received where applied according to treatment structure. No preplant N was applied other than trt 1, and all locations had residual N under 15 lbs 0-6” sample.

The first visual response to fertilizer N ranged from November 11 to February 5 (Table 1). The soil can have residual N from the previous season which can supply the subsequent crop in the beginning of the development what makes the wheat not demonstrate any sign of stress in the early season. For example LCB2017 a and b which were located 100 yards apart but under a different point in the crop rotation (LCBa was wheat after wheat and LCBb wheat after canola) had a 30 day difference in date of first N response. This range in first and last dates allowed us to evaluate N application over a wide range of dates and determine whether the first sign of stress is actually the best indicator of top dress application timing.

Table 1 shows the planting date, date of first visual difference (0DAVD) and each of the application dates for all locations. Different colors represent individual months. Hollow stem occurred approximately Feb 20 in the 2017 crop and March 10th in the 18 crop.

 

Image of the 2016-17 Perkins location. Image collected March 21 2017.

As shown in the Tables 2 and 3 below only three of the 78 comparisons made back to the pre-plant application were significantly less in terms of grain yield. All three of these comparisons where from when N application was delayed until late March or April. When the delayed applications were compared to 0DAVD yields only two of the 68 comparisons showed a significant decrease on yield. One was the pre-plant application for LCB2017a while the other were the 63DAVD application for LCB2017b. In most locations applications made in March yields were at the highest point, however when delayed till April yield trends on the downward trend. The 2017 crop reached hollow stem (Feekes 6) around Feb 20th while the 2018 crop reached hollow stem around March 10th.

Grain protein concentration was decreased only once when compared to both the pre-plant and 0DAVD treatments. This one timing, LCB2018b 64DAVD, was the only application made in May. During this time the crop was in the early stages of grain-fill. In all locations delaying N application until February/March increased grain protein content above the check, and in most cases above the 0DAVD trt.

Tables 2-3 shows the winter wheat grain yield and protein concentration, respectively, of all treatments. The colors of the cells represent statistical difference from the Pre-plant treatment. Treatments with cells shaded yellow are equal to the pre-plant, Green is statistically greater than while red is statistically less than the pre-plant treatment.

 

2016-2017 Delayed nitrogen winter wheat grain yield and protein results. For the locations of Perkins and N40 the Dec-1 application has a higher yield due to a 2x application of N to equal 180 lbs.

 

2017-2018 Delayed nitrogen winter wheat grain yield and protein results. The Perkins location in 18 was the only location in the study which did not have a statistically significant response to added N.

All the data was combined and plotted by cumulative GDD’s>0 from planting (GDDFP) across all locations to determine a general “best” timing. Using the pre-plant application yield as a base there was no yield loss if the applications was made prior to the 143 GDDFP. When the results were normalized by 0DAVD N there was no yield loss if the applications were made prior to 130 GDDFP. The quadratic model created provides the opportunity to identify the point of highest grain yield, which was approximately 94 GDDFP. In terms of the relationship between the application of N based on GDDFP and % of protein content on the grain, a linear response of N delay application observed for grain protein concentration. Our results suggest that the later the application, the higher the protein % in the grains.

Growing degree days > 0 from planting and equivalent calendar days for all experimental sites (Lake Carl Blackwell, Perkins, Lahoma, Stillwater) utilized in the study evaluating the impact nitrogen fertilizer timing on winter wheat, conducted in north central Oklahoma over the 2016-2017 and 2017-2018 winter wheat growing seasons.

We have concurrent work looking at similar approaches with other sources of N such as Urea and UAN. While all of  these studies are being continued the past two years of work have presented some easy take homes.

First: Timing of N application does matter, but yellow wheat does not necessarily mean yield loss.
Second: Two years in a row ALL Nitrogen could be delayed until hollow stem without yield Loss, in fact yields of trts with N applied at this time typically better than that of the pre-plant.
Third: Protein content increased as N applications was delayed.
Fourth: The conclusions of this and other studies support that N-Rich Strip concept does not increase risk of lost yield.
Fifth: Applying the majority of the N at or just after hollow stem maximized grain yield and protein with a single shot.
Sixth and Final: Be more concerned about applying N in an environment conducive to increased utilization and less about applying at the first sign of N stress. Take a look at the wheat N uptake curve by K-State.The crop really doesnt get going in terms of N-uptake until jointing i.e. hollow Stem.

Wheat N-uptake. Figure adapted from Lollato et al.

Questions for comments feel free to contact me via email at b.arnall@okstate.edu

Re-Post: Sensing the N-Rich Strip and Using the SBNRC

This the recent rains across the dry wheat belt the N-Rich Strips are going to start showing up. Because I am re-posting ans older blog that walks users through the sensing process and inputting data in to SBNRC. But since post we have also release a iOS version of the Online Calculator. iOS N-Rate Calc

Original Post:
With the significant swing in temperature over the last few weeks many are chomping at the bit to get outside.  The wheat is starting to respond to the good weather and N-Rich Strips are showing up around the state.  Over the past week I have had several calls concerning the impact of the cold weather on the N-Rich Strips.  Many of the fields either are still small due to limited days of warm weather and growth or may have a good deal of damage to the foliage.  If the field of concern has only a little or no damage and the strip is visible, the time to go is NOW, but if you cannot see the strip and your field has tissue damage or is small, similar to the first two images, then you will need to wait a week or two for sensor based recommendations.  Another situation fits with the third image, the field has freeze damage but the N-Rich Strip is also visible.   In this case the predicted yield level would be reduced do to the dead tissue making the N rate recommendation a little off.  I still however recommend using the sensor and online SBNRC (http://www.soiltesting.okstate.edu/SBNRC/SBNRC.php) to make or base top-dress N rate.  Even if the recommendation is a little off it will still be much more accurate than just guessing. However you must look at the SBNRC and ensure that it makes agronomic sense, if it does not consult your county educator or myself.   This is discussed in more detail in my earlier blog about freeze damage.  Keep in mind no matter what, if you can see the N-Rich Strip, everything outside of the strip is suffering from nitrogen deficiency.  Decisions and fertilizer applications need to be made soon, to maximize yield.

Winter Wheat and Nitrogen Rich Strips.

Winter Wheat and Nitrogen Rich Strips.

Regardless of whether or not the strip is visible you should be planning to sense with the GreenSeeker Handheld very soon. Remember the sensor has the ability to detect differences before your eyes can.   To sense the N-Rich Strip and Farmer Practice the user should carry the sensor approximately 30 to 40 inches above the crop canopy while holding the sensor level over the crop.  While you are walking the two area the trigger should be held the entire time.  I recommend walking at minimum 100 paces for each.    The average NDVI value seen on the screen will only stay on the screen for a few seconds.  Therefore it is critical you have a method of recording the number for later use. The sensor has limited memory so it will time out is the trigger is held for an extended period of time.  If you wish to collect more NDVI readings just do it in multiple trigger pulls recording each.  Once you have the average NDVI for the N-Rich Strip and Farmer Practice you can go to the SBNRC site mentioned above to retrieve the N rate recommendation.   Once in the calculator, for those in Oklahoma, choose the “within Oklahoma” option in the bottom left hand corner of the screen.  This will allow the calculator to access the Oklahoma Mesonet to determine growing degree days.  After the location is picked from the options you will need to enter Planting Date and Date Prior to Sensing.  Additional information requested is the expected grain and fertilizer prices.  While these inputs will provide some economic evaluations they will not impact recommended N rate.

GreenSeeker HandHeld NDVI Sensor

GreenSeeker HandHeld NDVI Sensor

Below is a YouTube video in which I describe how to use the GreenSeeker to collect NDVI readings, describe the data needed to complete the online calculator, and how to interrupt the calculators output.

2015-16 Wheat Crop Nitrogen Review

From trials to phone calls (and text messages, and tweets, and ect. ect) I have gathered a fairly good picture of this years winter wheat nitrogen story.  And as normal, nothing was normal.  Overall I seen/heard three distinct trends 1) Did not take much to make a lot 2) took a ton to make a lot 3) saw a response (N-rich strip or cow-pow) but fertilizer never kicked in. Covers most of the options, doesn’t it.

P1000542

The N-rich strips really came out over all very good this year.  N-Rich Strip Blog. On average many of those using the N-Rich Strip and SBNRC (SBNRC Blog) producers have been getting in the neighborhood of 1.0-1.3 lbs of N applied per bushel produced.  This year the numbers ran from 0.66 to 2.3 lbs of N per bushel.  In both extremes I believe it can be explained via the field history and the N-Cycle.

N-Cycle

Nitrogen Cycle Pete’s Sheet

In at least two fields, documented with calibrated yield monitors, the N-Rich Strip and SBNRC lead to massive yields on limited N. One quarter of IBA bumped 86 bpa average on 47 lbs of N while a second quarter, also IBA, managed 94 bpa average on about 52 units of N. We are currently running grain samples from these fields to look protein levels.

The other side of the boat were those with N-Rich strip calling for +2.0 lbs N per bushel.  I had received notes from producers without N-rich strips saying that they could predict yield based on the amount of N applied and it was a 2 to 1 ratio.  Not always but many of these high N demand fields where wheat following a summer or double crop or corn or sorghum. While many of the low N demand fields were wheat after wheat or wheat after canola. In a rotational study that had been first implemented in the 2014-15 crop year I saw big differences due to previous crop.  The picture below was taken in early March.  The straw residue in wheat after wheat had just sucked up the nitrogen.  While it was evident the residue from the canola broke down at a much more rapid pace releasing any and all residual nutrients early.

Rotation

The yield differences were striking. The canola rotation benefited the un-fertilized plots by 22 bpa and even with 90 lbs of N applied having canola in the rotation increased yields by 12 bpa.  We are looking and grain quality and residual soil sample now. I am sure there will be a more indepth blog to follow.

Canola Wheat Rotation study year two yield average. yields average across previous years N-rates.

Canola Wheat Rotation study year two yield average. yields average across previous years N-rates.

Another BIG story from the 2015-16 wheat crop was the lack of benefit from any N applied pre-plant. It really took top-dress N this year to make a crop.  Due to our wet early fall and prolong cold winter N applied pre was either lost or tied up late.  Work by Dr. Ruans Soil Fertility Program really documented the lack luster pre-plant N effect. The figure below shows 4 location of a rate by timing student.  The number at the bottom of each graph is a rate by time (30/0 means 30 lbs Pre-0 lbs Top, 60/30 means 60 lbs Pre-30 lbs Top).  At every single location 0/60 beat 60/0. Top-dress N was better than Pre-plant N.

Driver_Raun

Figure 1. Work from Ethan Driver and Dr. Bill Raun. Study looked at rate and timing of N fertilization in wheat. Treatments are ordered by total N applied.

The last observation was lack of response from applied N even though the crop was deficient.  Seen this in both the NE and NW corners.  I would hazard with most of the circumstance it was due to a tie up of applied N by the previous crops residue.  The length at which the winter stretched into spring residue break down was also delayed.

Take Home 

Here it is folks APPLY NITROGEN RICH STRIPS.  Just do it, 18 years of research preformed in Oklahoma on winter wheat says it works. Hold off on heavy pre-plant N even if anhydrous is cheap.  It does matter how cheap it is if it doesn’t make it to the crop.  Will we see another year like 2015-16, do not know and not willing to place money on either side. What we do know is in Oklahoma split applying nitrogen allows you to take weather into account and the N-Rich strip pays dividends.

There are several fact sheets available on top-dressing N and the application of N-Rich strips.  Contact your local Oklahoma Cooperative Extension Service county educator to get a copy and see if they have a GreenSeeker sensor on hand.

Sensing the N-Rich Strip and Using the SBNRC

Original Post:
With the significant swing in temperature over the last few weeks many are chomping at the bit to get outside.  The wheat is starting to respond to the good weather and N-Rich Strips are showing up around the state.  Over the past week I have had several calls concerning the impact of the cold weather on the N-Rich Strips.  Many of the fields either are still small due to limited days of warm weather and growth or may have a good deal of damage to the foliage.  If the field of concern has only a little or no damage and the strip is visible, the time to go is NOW, but if you cannot see the strip and your field has tissue damage or is small, similar to the first two images, then you will need to wait a week or two for sensor based recommendations.  Another situation fits with the third image, the field has freeze damage but the N-Rich Strip is also visible.   In this case the predicted yield level would be reduced do to the dead tissue making the N rate recommendation a little off.  I still however recommend using the sensor and online SBNRC (http://www.soiltesting.okstate.edu/SBNRC/SBNRC.php) to make or base top-dress N rate.  Even if the recommendation is a little off it will still be much more accurate than just guessing. However you must look at the SBNRC and ensure that it makes agronomic sense, if it does not consult your county educator or myself.   This is discussed in more detail in my earlier blog about freeze damage.  Keep in mind no matter what, if you can see the N-Rich Strip, everything outside of the strip is suffering from nitrogen deficiency.  Decisions and fertilizer applications need to be made soon, to maximize yield.

Winter Wheat and Nitrogen Rich Strips.

Winter Wheat and Nitrogen Rich Strips.

Regardless of whether or not the strip is visible you should be planning to sense with the GreenSeeker Handheld very soon. Remember the sensor has the ability to detect differences before your eyes can.   To sense the N-Rich Strip and Farmer Practice the user should carry the sensor approximately 30 to 40 inches above the crop canopy while holding the sensor level over the crop.  While you are walking the two area the trigger should be held the entire time.  I recommend walking at minimum 100 paces for each.    The average NDVI value seen on the screen will only stay on the screen for a few seconds.  Therefore it is critical you have a method of recording the number for later use. The sensor has limited memory so it will time out is the trigger is held for an extended period of time.  If you wish to collect more NDVI readings just do it in multiple trigger pulls recording each.  Once you have the average NDVI for the N-Rich Strip and Farmer Practice you can go to the SBNRC site mentioned above to retrieve the N rate recommendation.   Once in the calculator, for those in Oklahoma, choose the “within Oklahoma” option in the bottom left hand corner of the screen.  This will allow the calculator to access the Oklahoma Mesonet to determine growing degree days.  After the location is picked from the options you will need to enter Planting Date and Date Prior to Sensing.  Additional information requested is the expected grain and fertilizer prices.  While these inputs will provide some economic evaluations they will not impact recommended N rate.

GreenSeeker HandHeld NDVI Sensor

GreenSeeker HandHeld NDVI Sensor

Below is a YouTube video in which I describe how to use the GreenSeeker to collect NDVI readings, describe the data needed to complete the online calculator, and how to interrupt the calculators output.

Freeze Injury and N-Rich Strips,

 

Dr. Jeff Edwards “OSUWheat” wrote about winter wheat freeze injury in a receive blog on World of Wheat, http://osuwheat.com/2013/12/19/freeze-injury/.  As Dr. Edwards notes injury at this stage rarely impact yield, therefore the fertility requirements of the crop has not significantly changed.  What will be impacted is how the N-Rich Strip and GreenSeeker™ sensor will be used.  This not suggesting abandoning the technology in fact time has shown it can be just as accurate after tissue damage.   It should be noted GreenSeeker™ NDVI readings should not be collected on a field that has recently been damaged.

A producer using the N-Rich Strip, GreenSeeker™, Sensor Based N-Rate Calculator approach on a field with freeze damage will need to consider a few points.  First there need to be a recovery period after significant tissue damage; this may be one to two weeks of good growth.   Sense areas that have had the same degree of damage as elevation and landscape position often impacts the level of damage.  It would be misleading to sense a area in the N-Rich strip that was not significantly damaged but an area in the Farmer Practice that took a great deal of tissue loss.

Finally we must consider how the SBNRC, available online at http://nue.okstate.edu/SBNRC/mesonet.php, works.  The calculator uses NDVI to estimate wheat biomass, which is directly related to grain yield.  This predicted grain yield is then used to calculate nitrogen (N) rate.  So if biomass is reduced, yield potential is reduced and N rate reduced.  The same issue is seen in dual purpose whet production.  So the approach that I recommend for the dual purpose guys is the same that I will recommend for those who experienced significant freeze damage.  This should not be used for wheat with just minimal tip burn.

To account for the loss of biomass, but not yield, planting date needs to be adjusted to “trick” the calculator into thinking the crop is younger and has greater potential.   Planting date should be move forward 7 or 14 days dependent  For example the first screen shot shows what the SBNRC would recommend using the real planting date.  In this case the potential yield is significantly underestimated.

The second and third screen shots show the impact of moving the planting date forward by 7 and 14 days respectively.  Note the increase in yield potential, which is the agronomically correct potential for field considering soil and plant condition, and increase in recommended N-rate recommendation.  Adjust the planting date, within the 7 to 14 day window, so that the yield potential YPN is at a level suitable to the field the yield condition and environment.  The number of days adjusted is related to the size and amount of loss.  The larger the wheat and or greater the biomass loss the further forward the planting date should be moved.  In the example below YPN goes from 37 bu ac on the true planting date to 45 bu ac with a 14 day correction.  The N-rate changes from 31 lbs to 38 lbs, this change may not be as much as you might expect.  That is because YP0, yield without additional N, also increases from 26 to 32 bushel.

freeze Zero day moveImage 1. Planting date 9/1/2013.  YPN 37 bu ac-1 and N-Rec 31 lbs ac-1.

Freeze 7 day moveImage 2. Planting date 9/8/2013.  YPN 40 bu ac-1 and N-Rec 34 lbs ac-1.

Freeze 14 day moveImage 3. Planting date 9/15/2013.  YPN 45 bu ac-1 and N-Rec 38 lbs ac-1.

This adjustment is only to be made when tissue has been lost or removed, not when you disagree with the yield potential.  If you have any questions about N-Rich Strips, the GreenSeeker™, or the online SBNRC please feel free to contact me at b.arnall@okstate.edu or 405.744.1722.