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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 the GreenSeeker after Freeze Damage

After discussions with producers in southern Kansas I felt the need to bring back this past blog.  It seems that much of (not all) the early planted wheat lost a significant amount of biomass during the winter and the N-Rich Strip GreenSeeker approach is producing what looks to be low yield potentials and N-Rate recommendations.  This should be treated much like we do grazed wheat and the planting date should be adjusted, see below.  It is also important to note that in the past year a new wheat calculator was added to the NUE Site.  http://nue.okstate.edu/SBNRC/mesonet.php. Number 1 is the original OSU SBNRC but the #2 is calculator produced by a KSU/OSU cooperative project.  This is the SBNRC I recommend for use in Kansas and much of the norther tier of counties in OK.

Original Blog on Freeze Damage and the GreenSeeker.

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.

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.