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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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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.

Using a Grain Drill Grain Box for Fertilizer, Results and a Calibration guide.

For the last few years I have been challenging people to “Think Out Side the Box” when applying fertilizer. One of these application methods is to use a grain drill to put Nitrogen fertilizer into the soil. Just the act of getting N into the soil will immediately decrease the opportunity for losses. While it seems crazy many picked up on the idea of using grain drills for N applicators. The first year of a two-year study looking at documenting the practice is in the books. With data coming in from three locations, utilizing two drill types (double disk conventional and single disk no-till), the results are quite promising.  The biggest take home from year one was a 2 parter: 1) if conditions are conducive to nitrogen loss from urea volatilization, applying urea with a grain drill in the spring improved efficiency. Conversely if loss potential was low, there was no difference. 2) in some soil conditions the double disk drill could not close the furrow and this reduced the positive impact of using the drill.  The two tables below show the impact application and environment on yield.  Each of the treatments had 60 lbs of nitrogen (as Urea) applied per acre. At Chickasha the first application was made while it was fairly dry and then it rained, but the second application was made during a period in which there was no rain but a fairly significant dew each morning. This can be seen as the small effect volatilization played on the yields of the first application timing. At Lahoma, it was the early applications that had a higher risk of loss with no difference seen later.

 

Partial year one results from the topdress N with a grain drill at Chickasha OK. Timing 1 was late January and timing 2 was late February.

 

Partial year one results from the topdress N with a grain drill at Lahoma Ok. Timing 1 was early January and timing 2 was mid February, and timing 3 was early March.

 

With the results from the first year of the top-dressed drilled nitrogen studies in the books, the interest has been increasing. One question keeps popping up: for grain drills without a fertilizer box, what  do we put our grain box on to apply fertilizer.  At one point the number of inquires hit a critical mass and I sent out my crew to find grain drills and create calibration curves for DAP (18-46-0) and Urea (46-0-0).  The crew did just that.

Now please consider what is presented below is a general calibration. Much like the chart on your grain drills, it will hopefully get you close but the best-case scenario is that each drill is calibrate prior to running. As request are made we will try to add more drills to this list.

To create the following charts the guys located several different makes of drills around the OSU experiment stations. They were instructed to choose setting based on the manufacture seed rate charts in the range of 60, 90, 120 etc.  For each setting they caught a couple of row units for both Urea (46-0-0) and DAP (18-46-0). They caught each setting multiple times to get a good average.

If you look at the tables you can see the Landol 5211, Great Plains 1006NT, and International 5100 are fairly similar, with the John Deere 1560 being a little lower and the John Deere 450 significantly lower at the lower rates.  To use the tables below, consider what kind of grain drill you have and choose to follow one of the drills listed or the average of all five. If you use the average value I would expect most to find they applied a bit more than planned.  To make it even simpler, but less accurate, you can use the % wheat value.  To do this for DAP take your target rate and divide by .88, this value is what you want to set your drill to.  For example for a target rate of 100 lbs DAP per acre use the following formula:  100/.88 = 114.  Choose the manufacturer recommended settings 114 lbs wheat seed per acre.   If you are wanting to apply Urea take your target rate of urea and divide by 0.71.

 

DAP 18-46-0

Table showing the manufacturer wheat rate setting and the resulting amount of DAP 18-46-0.

Graph documenting the manufacturer wheat rate setting and the resulting amount of DAP 18-46-0.

UREA 46-0-0

Table documenting the manufacturer wheat rate setting and the resulting amount of Urea 46-0-0.

Graph documenting the manufacturer wheat rate setting and the resulting amount of Urea 46-0-0.

 

Again, I cannot state this enough, this is a general guide, each drill even of the same manufacture and model will likely be different.  The only way to be certain of the rate applied is to calibrate each drill individually.

Questions or comments please email me at b.arnall@okstate.edu or call 405.744.1722

 

Herbicide and UAN tank mixed for top-dress

Spring is the time that many wheat producers apply herbicide and nitrogen (N) fertilizer.  For many this can be accomplished in a single pass by tank mixing the herbicide and UAN. In most cases this is an effective practice which eliminates one pass over the field.  There are some scenarios in which this practice is ill advised. One such scenario is high temperatures which would lead to excessive leaf burn and crop damage. The other scenario is no-till and that will be the focus of this article. Ruling out warm temperature tank mixing herbicides and nitrogen, assuming the herbicide can be tank mixed, is a good practice.  No-till on the other hand can be a different issue.

No till drill and ammonia oxide application

Situations with a lot of residue and smaller wheat is common during top-dress.

The problem in no-till comes from the liquid application method needed to apply herbicides, flat flan. To get a good kill with the herbicide the spray pattern needs to have good coverage, i.e a lot of small droplets to ensure maximum surface area impacted.  Unfortunately there are four primary fates of UAN  when applied via flat fan nozzles.  The UAN could be taken directly up into the wheat plant via absorption through the leaves, the UAN could reach the soil and go into the soil solution or absorbed onto the soil itself, the UAN can be taken up by weeds, or the UAN droplet may hit dead plant tissue and be adsorbed into the residue.

20090226-1864

UAN applied with a flat fan will hit a growing plant, the soil, or residue.

The fourth fate of UAN presented is what can make the tank mix less efficient than a two pass system.  In a no-till system any UAN that hits residue should be counted as lost, for the short term. The decision to go with a one pass or two pass system can be aided by evaluating the amount of canopy coverage.  For example if the no-till field has 50% canopy coverage then one could estimate 50% of the UAN applied via a one pass system would be tied up in the residue.  The cost of a second application could then be compared to the lost N.  If 15 gallon of 28-0-0 was being applied then approximately 22.5 lbs of N would be tied up by the straw. At a price of $0.40 per lb on N, that is $9.00 worth of N.  Conversely if the canopy coverage was 80% only 20% or 9 lbs of N would be tied up in the residue. Saving the $3.60 in nitrogen would not justify a second trip over the field. Luckily OSU recently released the Canopeo app which uses a cell phones camera to take pictures and quickly and accurately determine % canopy coverage.  Canopeo is available for iOS and android http://canopeoapp.com/.

In fields with a high amount of residue or limited canopy coverage UAN should be applied with streamer nozzles.  This will concentration the fertilizer into streams which will allow the UAN to have enough volume to move off the residue and into the soil.

So as the decision is being made to tank mix herbicide and UAN or make two passes take into consideration: % canopy coverage, rate of UAN (how much could be lost), cost of UAN per pound, and cost of a second trip over the field.

Below is an excerpt from the publication Best Management Practices for Nitrogen Fertilizer in Missouri; Peter C. Scharf and John A. Lory. http://plantsci.missouri.edu/nutrientmanagement/nitrogen/practices.htm

Broadcasting UAN solution (28 percent to 32 percent N) is not recommended when residue levels are high because of the potential for the N in the droplets to become tied up on the residue. Dribbling the solution in a surface band will reduce tie-up on residue, and knife or coulter injection will eliminate it. Limited research suggests that the same conclusions probably apply for grass hay or pasture. Broadcast UAN solution is also susceptible to volatile loss of N to the air in the same way as urea, but only half as much will be lost (half of the N in UAN solution is in the urea form).

Time to start topdressing wheat

Great write up by Dr. Edwards.

World of Wheat

There are few crop inputs that deliver as much return on investment as nitrogen fertilizer. It takes approximately two pounds of nitrogen, costing approximately $1.00, to produce one bushel of grain worth about $6.00. Of course, nitrogen is not the only yield determining factor in a wheat crop. Also, the law of diminishing marginal returns eventually kicks in, but nitrogen fertilizer is still one of the safest bets in the house.

Top dress nitrogen fertilizer is especially important because it is applied and utilized at a time when the plant is transitioning from vegetative to reproductive growth. Several things, including the number of potential grain sites, are determined just prior to jointing and it is imperative that the plant has the fuel it needs to complete these tasks. Jointing also marks the beginning of rapid nitrogen uptake by the plant which is used to build new leaves, stem, and the…

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