Nitrogen Use Efficiency, Nitrogen Fertilizers, NUE, Nitrogen and the EnvironmentPredicting the Potential Response to Applied N  (Response Index) Using Nitrogen Rich Strips
Also see
Ramp Calibration Strips
    Tailoring Topdress Nitrogen                                                
Calibration Stamps for Improved Mid-Season Fertilizer N Recommendations in Corn and Wheat Production SystemsDhital, Sulochana and William Raun. 2016. Variability in optimum N rates for maize in the Central Great Plains. 

Variability in Optimum Nitrogen Rates for Maize. Agron. J. 108:2165-2173.

Wheat N Rich Strips for Corn

Early work where N Rich Strips were called 2X Strips

Calibration Stamps

Automated Calibration Stamp Technology for Improved In-Season Nitrogen Fertilization Agron J. 97:338-342. (pdf)

Wheat N Ramps

Ramp Calibration Strip Technology for Determining Midseason Nitrogen Rates in Corn and Wheat. Agron . J. 100:1088-1093.

Nitrogen Rich Strips for Improved Nitrogen Fertilizer Management   Get Your Nitrogen Rich Strips Out Early   Configuration of the RAMP or Ramp Calibration Strips for Improved N Management in corn and wheat  
Wheat Nitrogen Ramps

Response Index

Experiment 502, N fertilizer Response

N Rich Strip, Fairview Oklahoma

Image result for nitrogen rich strip montana
N Rich Strip, Montana



Indicator Crops Preplant

Indicator Crops
Increased NUE for mid-season topdress N rates
Tailoring Topdress Nitrogen (The Furrow, John Deere) (N Rich Strip Original Pictures)
Article from Pioneer, 2010 on Sensors for better N Management

Optical Sensor Based Algorithm for Crop Nitrogen Fertilization  Commun. Soil Sci. Plant Anal. 36:2759-2781

Automated Calibration Stamp Technology for Improved In-Season Nitrogen Fertilization Agron J. 97:338-342 

The demand for fertilizer nitrogen changes from year to year, even in long-term plots where the same fertilizer N rates are applied each year.  When winters are wet and warm, sufficient N can be mineralized from soil organic matter, and enough to nearly meet the demands for maximum yields (see 1973, 1979, 2001, and 2005)(Figure 1).  In these years, this is compounded by increased N deposition in the rainfall.  Our long-term winter wheat data confirms that the demand for N is variable from year to year, and that is unpredictable.  This exact same phenomenon was observed in the RC-RS long-term corn experiment conducted by the late Professor Robert A. Olson at the University of Nebraska where near maximum yields in the check plot were produced in 1978 (Figure 2).  Where did all the N come from if these check plots had not been fertilized for nearly 10 years?  The answer is N mineralization via an extremely wet and warm spring-summer. 

The influence of temporal variability on the need (or lack thereof) for fertilizer N is huge, yet our fertilizer N rate recommendations seldom account for this.  Soil testing (NH4-N and NO3-N) works, but when collected preplant, applying a static value on N demands that will become dynamic mid-season, makes no sense.   For precisely this reason, we have developed methods that account for the influence of temporal variability on N demands, by making better fertilizer N decisions mid-season when the growing crop can tell us precisely how much N was delivered for free (comparison between the N Rich Strip and the Farmer Practice, mid-season). 

The GreenSeeker sensor via NDVI measurements provides a highly accurate estimate of plant biomass, as a result, total N uptake can be estimated from mid-season measurements.  More importantly, yield potential can be predicted mid season using both sensor and known climatic data from planting to sensing.  By estimating yield, we can then estimate total grain N removed.  Yield potential (YP0) is then multiplied times the response index (estimated in-season from NDVI readings collected in the N Rich Strip and Farmer Practice) to obtain the yield obtainable if N fertilizer is to be applied (YPN).  The fertilizer N rate is determined by subtracting N uptake at YP0 from N uptake at YPN, and divided by an expected NUE. This entire algorithm is completely delineated in the "Optical Sensor Based Algorithm" article below. 

N Rich Strip, EFAW


Figure 1.  Wheat grain yields in the check (0 kg N/ha) and the N rich (112 kg N/ha) plots, and the associated response index (grain yield N rich, divided by the grain yield in the check) from 1971 to 2007 in the Stillwater 222 long-term winter wheat experiment.

Figure 2.  Corn grain yields in the check (0 kg N/ha) and the N adequate or N rich (180 kg N/ha) plots, and the associated response index (grain yield N rich, divided by the grain yield in the check) from 1969 to 1983 in the RC-RS long-term corn experiment conducted by Professor R.A. Olson near Mead, Nebraska.


Experiment 502, long term nitrogen response in winter wheat

Figure 3.  Wheat grain yields in the check (0 kg N/ha) and the N rich (112 kg N/ha) plots, and the associated response index (grain yield N rich, divided by the grain yield in the check) from 1971 to 2010 in the Lahoma 502 long-term winter wheat experiment.

RI_NDVI versus RI_Harvest, Experiment 502 RI NDVI versus RI Harvest, Experiment 222


439, Continuous Cotton


Relationship between RINDVI and RIHarvest at Feekes 5 across 62 locations in Oklahoma, 1998-2003.

Relationship between the estimated responsiveness to applied N or response index (RI-NDVI) from sensor readings (RI-NDVI = NDVI in the N Rich strip divided by the NDVI in the farmer practice) and the response index determined at harvest (Grain yield in the N rich strip plot divided by the N Rich strip in the farmer practice), 2004 Corn Trials.  Clearly, the responsiveness to N can be determined from mid-season sensor measurements collected between V8 and V9.

2007: Relationship between the response index measured in season, (NDVI of fertilized plot / NDVI of check plot) from readings of cotton at growth stages from 60 to 80 days after planting, and measured lint yield and the response index measured at harvest (yield of fertilized plot / yield of check plot) from all site years.



Optical Sensor Based Algorithm

Ramped Calibration
Nitrogen Ramp Calibration Strip applied in Winter Wheat


The new Ramped Calibration Strip Applicator applies increasing levels of N in a strip across a fixed distance (160 to 320) feet.  The levels applied range from 0 at the start of the strip to the maximum that could ever be expected to be used.  This fertilizer is applied pre-plant or in a very early crop growth stage.  An N-rate recommendation can be determined by visual inspection or with a hand-held sensor by walking the strip from the low rate toward the high rate and stopping at the point where there are no further changes in crop growth or NDVI.  The N-rate applied at that spot (where no further changes in NDVI were noted) is the N-rate recommendation.  

Brent Rendel, Rendel Farms has Built a Producer Version of the RAMP Applicator (low cost, manually controlled version that virtually anyone could build) (Spring 2007)
   6504 South 600 Road
   Miami, OK 74354
Curtis and Levi Johnson (Johnson Farms) J2 RAMP Applicator (Spring 2007)
   R.Rt 1, Box 82
   Helena, OK 73741
How to build your own RCS Applicator (OSU, 2006)
   Randy Taylor
   Department of Biosystems and Agricultural Engineering
   Oklahoma State University
   Stillwater, OK 74078
   405 744 5277
RAMP Page (Brian Arnall)
Jason Lawles (RAMP Applicator) Spring 2007
Western Equipment
4501 E. Main, P.O. Box 391
Weatherford, OK 73096
580 772-5578

N Rich Strip Adopters

Steinert’s near Hennessey

Brent Rendel (see link below where he has developed several rampers)

Jimmy Wayne Kinder, near Walters

Panhandle via extension presentations Brian gave in Boise City and Woodward

Jason Lawles via Western Equipment (several hundred)
Levi and Curtis Johnson Brothers (developed the J2 ramper, , see below, Helena, OK)
Joe Biggerstaff, Engineering Student of Solie’s (every field they owned and rented)

Curtis Fischer (Kingfisher)

Devin Weeder (Buffalo)
Kim Metcalf (now with Estes Chemical)
Gerald Wynes (Ponca City), many
Jagadeesh Mosali (N rich strips in Bermuda, many locations)
Roger Gribble (many)
Ivan Peck (many on his own for the last 5 years)
Monsanto (many via Kyle Freeman, Kyle Lawles, and Paul Hodgen)

Delaware County, Bermudagrass, 2007 (RAMP peaked at 200 lb N/ac, with a range from 0 to 350 lb N/ac.

Calibration Stamps for Improved Mid-Season Fertilizer N Recommendations in Corn and Wheat Production Systems
Wheat N Ramp
Ramp Usage and Demonstartion

N rates using the Ramped Calibration Strip 

Are you Spending Too Much on Nitrogen Fertilizer?


How to obtain highly accurate mid-season fertilizer N rates using the Ramped Calibration Strip 

The new Ramped Calibration Strip Applicator applies 16 different N rates (10 to 20 foot intervals), over 160 to 320 feet (actual rates and distances can be adjusted depending on the crop).  Companies interested in building variants of this applicator can adjust distances, N rates, intervals, etc., as they see fit.  The Ramped Calibration Strip is used to visually determine precise mid-season fertilizer N rates for wheat and corn production.  Although the use of hand-held GreenSeeker sensors are not required, the sensors offer the opportunity to sense the entire "RAMP" and thus accurately determine where the peak in NDVI exists over the range of N rates applied.  Without the sensor, farmers can simply walk from one end of the RAMP to the other and stop where they no longer see any differences.  Whether determined visually, or with a handheld sensor, the point where no differences no longer exist, is the TOPDRESS N Rate. 

This methodology is a variant of what has been developed using the N Rich Strip and the handheld sensing technology that relies on predicted yields and the Sensor Based Nitrogen Rate Calculator (

Looking at the graph above, you can see exactly why this is the case.  By stopping at the point (recording distance in feet) where there are no longer visible or recorded differences in NDVI, you can plot a line directly down to "distance" that has a predetermined N rate associated with it.  That N rate (depending on how you set up the intervals to change the rate, and the actual rates chosen) is the TOPDRESS N Rate to be recommended.  For the 3 fields above where NDVI values were plotted with distance (green squares, red triangles, and blue circles), the recommended topdress N rates would have been 40, 80, and 100 lbs N/ac, respectively.  Why?  You have to remember that the Ramped Calibration Strip is applied "ON-TOP" of the farmer practice (whatever that may be).  Assuming that we can "catch up" and/or achieve maximum yields from the mid-season N application, and assuming that yield potentials were not severely restricted by excess early season N stress, the RAMP interpolated rate is how much you would need to apply on the rest of the field to achieve the same "visible" or "NDVI recorded" response. 

In corn, some would argue that this methodology is flawed, because you don't know whether or not this rate will "run out" later in the season.  This is to a certain extent correct, but if the farmer is wanting to avoid that potential "risk" the topdress N rate can be increased by whatever amount he/she deems appropriate.  However, the RAMP is an incredible starting point for determining the optimum mid-season N rate.  Why?  Because we have now evaluated enough corn and wheat data to know that in several long-term experiments (corn, NE, WI, MX; wheat, OK), there were years where the check plot (No N Fertilizer ever applied) produced near maximum yields.  A RAMP N Rich Strip in those fields would have told us "MID-SEASON" that there were no visible differences between the 0-N and all other plots within the RAMP receiving N.  Wouldn't farmers want to know that?  Wouldn't this be important to know?  If the check plots with no fertilizer N looked as good as the fertilized plots, where was their N coming from?  Over the years, we have learned that warm wet winters (winter wheat) and warm wet springs and early summer (corn) are conducive to increasing the amount of N mineralized from soil organic matter, and that N deposition in rainfall increases significantly in these years.  Because we have years where the demand for fertilizer N is less (and highly dependent on the environment), and other years where it is cool and dry and the demand for fertilizer N is greater.  The only way to determine how much the environment delivered for free is to have a Ramped Calibration Strip in each and every field. 

For those farmers/producers interested in using the sensors for determining their topdress N rates, all they have to do is mark the start and end of the Ramped Calibration Strip (preplant), and collect sensor data using the handheld GreenSeeker sensor walking at a constant speed over the length of the ramp.  Using the program below, they can automatically read that file, and it will compute the optimum N rate.  We recommend the use of the sensors simply because our eyes are not as sensitive in picking up these differences.

NOTE:  This approach (interpreting the Ramped Calibration Strip) is for determining field rate application (flat rates) and accounts for only temporal variability.  Simultaneous consideration of temporal and spatial variability requires on-the-go prediction of yield potential (YP0) and use of the response index for each 0.4m2 area (wheat), and every 2-3 plants in corn.

Oklahoma State University recently released the first automated calibration stamp applicator for improving in-season fertilizer N rates and ultimate Nitrogen Use Efficiency.

Accurate determination of mid-season fertilizer N rates for cereal production is complicated.  Mid-season fertilizer N is currently recommended using a wide range of soil-test and soil-N mineralization procedures, with no fundamental scientific agreement anywhere in the world on the methodology.  A conventional 2003 Honda FourTrax Foreman ES 4-wheeler (433cc, 127cm wheel base, 116cm wide) with a 3 m wide spray boom and a 1 m spacing between nozzles was modified to deliver a range of fixed N rates as urea ammonium nitrate (28%N) within a 9m2 grid.  Within each grid, 9 separate 1m2 areas exist, whereby each of the 4 corners receive no fertilizer N.  Rates of 22, 45, 67, 90, and 112 kg N ha-1 occupy the other 5, 1m2 areas within the 9m2 grid (termed as an N rate calibration stamp).   Traveling at 5 mph, consecutive 9m2 grids can be applied continuously.  The calibration stamps should be applied preplant and superimposed on top of the farmer practice.  By mid-season, differences between the 1m2 N rate areas can be visualized and a field-specific topdress N rate can be prescribed by choosing the lowest N rate where no visual differences were observed between it and the next highest rate.  Using preplant or early-season applied calibration stamps, topdress N rates can be determined that precisely account for N mineralization, and atmospheric N deposition from planting to the time mid-season N is applied.

Click here for VIDEO of the Calibration Stamp!

Clint Mack prepares to apply calibration stamps in Western Oklahoma

Calibration Stamp in Western Oklahoma showing the 3 strips with decreasing N rates.

Calibration Strips applied just north of Experiment #222, fall 2004, read on March 18, 2005

Dr. Marvin Stone, Dr. John Solie, David Zavodny, and Kyle Freeman stand in front of the very first CST applicator.

Jerrel Powell and Tom Denker discuss the N Rich Strip Program

Figures (above and below).  Calibration stamps applied soon after planting (left) and visual stamp differences mid-season (right) that are used to prescribe accurate mid-season N fertilizer rates.


Continuous calibration stamps (9m2) applied at Perkins, OK on top of winter wheat at Feekes growth stage 4, and superimposed schematic of actual N rates in kg N/ha using urea ammonium nitrate applied as a foliar spray.

UAN with Blue Dye applied soon after wheat planting such that calibration stamps can be visualized by cooperators/farmers.

Kyle Freeman and Brian Arnall adjust the air pressure for the spraying system that requires 30 PSI.  Next to his left hand is the controller which can be operated with 3 switches (power, purge, and spray).  The controller automatically cycles if the spray button is held down.  Each cycle includes a stamp with 9 squares (4 checks of 0, and one each of 20, 40, 60, 80, and 100 lbs N/ac).  Each square measures 1 x 1 m, while the entire stamp measures 3 x 3 m. 

Prior to putting out the calibration stamps, Kyle Freeman purges the system with UAN.
Montana, N Rich Strip

Montana N Rich Strip'
2014 Data

RI NDVI vesus RI Harvest, 2014

Comprehensive information on Nitrogen Use Efficiency for cereal crop production