Oklahoma State University

1
Technologies to Increase Nitrogen Use Efficiency
Oklahoma State University Precision Agriculture /
Soil Fertility / Soil Nutrient Management

Why should Nitrogen Use Efficiencies be improved?
World wide nitrogen use efficiency (NUE) for
cereal grains is only 33. Oklahoma State
Universitys Precision Agriculture Team employs a
wide array of techniques and equipment in an
effort to improve NUE. Some of these techniques
include the use of the GreenSeeker and 4 band
sensors, both developed at OSU. When either of
these are used in conjunction with a N-Rich Strip
or a N-Ramp Calibration Strip, it allows
producers to make accurate midseason fertilizer
applications based on crop needs. The benefits
of implementing these methods results in more
accurate N rates, providing producers the same
yield with less fertilizer thereby, reducing
over application of fertilizer. Less N is lost
to runoff, leaching, volatilization, etc.,
resulting in a net savings for producers. Its
been calculated that a 20 increase in NUE world
wide would result in a savings of
US10,000,000,000 for producers. In addition,
these techniques benefit the environment. By
reducing runoff from agricultural lands, we can
reduce the estimated US1,000,000,000 worth of
fertilizer flowing down the Mississippi River
each year. The Precision Agriculture Team at OSU
continues to refine and develop new technologies
for improving NUE.
What technologies have been developed to increase
Nitrogen Use Efficiency?

• Some of the advanced technologies developed by
  OSU for improved fertilizer management are
• 1. By-Plant N Fertilization
• 2. GreenSeeker and 4 Band Sensor
• 3. N-Rich Strip and N-Ramp Calibration Strip

2. GreenSeeker and 4-Band Sensor
International Extension Activities
1. By-Plant N Fertilization
The GreenSeeker sensor is an active, optical
sensor that measures crop status. From these
measurements, a fertilizer recommendation can be
made based on the crop's N requirements. The
sensor works by using light emitting diodes (LED)
to generate red and near infrared (NIR) light.
The light generated is reflected off the crop and
measured by a photodiode located at the front of
the sensor head. Yield potential for a crop is
identified using a vegetative index known as NDVI
(Normalized Difference Vegetative Index) and an
environmental factor. GreenSeeker calculates
NDVI using both red and NIR light. Red light is
absorbed by plant chlorophyll as an energy source
during photosynthesis. Therefore, healthy plants
absorb more red light and reflect larger amounts
of NIR than unhealthy plants. NDVI is an
excellent indicator of biomass (amount of living
plant tissue), and is used in conjunction with
growing degree days greater than zero (GDDgt0) or
days from planting to accurately project yield
potential. Nitrogen is then recommended based on
yield potential and the responsiveness of the
crop to additional nitrogen. Using the
GreenSeeker has yielded significant savings.
Over the past 15 years, Soil Fertility graduate
students have been involved in international
programs and workshops to extend technologies
developed at OSU. To date, graduate students have
traveled to Argentina, Australia, Canada, China,
India, Mexico, Turkey, Uzbekistan, and Zimbabwe.

Mexico 2002
China 2004
Canada 2004
With an increase in precision farming practices
and improved remote sensing technology, the
ability to evaluate physiological differences at
the by-plant level, and on-the-go is now a
reality. This is increasingly important
following the findings from on-farm, by-plant
yield data collected in Argentina, Mexico, Iowa,
Nebraska, Ohio, Virginia, and Oklahoma. Over
all sites in all countries and states,
plant-to-plant variation in corn grain yield
averaged 44.1 bu/ac. In other words you can
expect one corn plant to differ from the other
on-average by more than 44 bu/ac, yet farmers
apply the same rate to each plant. Furthermore,
the yield range (maximum corn grain yield minus
the minimum corn grain yield per row) was found
to increase with increasing yield level.
Regardless of yield level, plant-to-plant
variability in corn grain yield can be expected.
Averaging yield over distances 1.5 ft removed the
extreme by-plant variability, thus, the scale for
treating other factors affecting yield should be
less than 1.5ft. Oklahoma State University has
developed an applicator that can effectively
sense and treat every 1.5 feet in corn fields
on-the-go at 5 mph. The future of precision
agriculture will ultimately end up at the
by-plant level since this is where the major
yield differences exist.
O K L A H O M A S T A T
E U N I V E R S I T Y
India 2005
Uzbekistan 2008
Zimbabwe 2008
Who has employed recent graduate students from
Soil Fertility?
The 4-band sensor utilizes four wavelength bands
(670nm, 780nm, 870nm, and 970nm) to determine
crop status. Another useful feature of the 4-band
sensor is its ability to determine plant tissue
temperature. The 4-band sensor is currently being
utilized as an aid to plant breeders in addition
to its utilization for nutrient management.
Since 1992, 64 students have completed or are
currently pursing a Master of Science (M.S.) or
Doctorate of Philosophy (Ph.D.) degree through
the Soil Fertility program at OSU. A few of the
companies recent graduates are employed with and
the graduates employed there is listed below.

3. N-Rich Strip and N-Ramp Calibration Strip
N-Rich Strip The amount of N the environment
delivers changes from year to year. So, why do
you apply the same N fertilizer rate every year?
N-Rich Strips indicate how much N the environment
delivers. Using the web-based, Sensor Based
Nitrogen Rate Calculator, proper recommendations
of additional mid-season N fertilizer to be
applied to achieve maximum yields can be
obtained. How is this technology
established? Using the GreenSeeker hand-held
sensor, actual wheat or corn grain yield
potential can be estimated using the NDVI
readings (value output from the sensors) from the
Nitrogen Rich Strip compared to the Farmer
Practice and the number of days where growing
degree days are greater than zero (GDDgt0) or days
from planting to sensing. Essentially, the NDVI
value from the hand-held sensor outputs total
biomass.  For readings collected between January
and March (regardless of when the wheat was
planted), we can estimate biomass produced per
day.  This value is used to predict the wheat
grain yield obtainable.  With these numbers, the
yield and the need for additional N can be
predicted accurately. This approach is
established for other crops too. What can I
expect from using this technology? This method
determines the ideal top-dress N rate.  From
research conducted by OSU, this method is worth
over US10.00 per acre. When fertilizers are
applied in excess of that needed for maximum
yields, the potential for surface and subsurface
nitrate contamination of water supplies
increases. The amount of N that the environment
delivers is considered with this approach
therefore, the recommendation obtained accurately
estimates the additional N required, if any, by
the crop for the current growing season to
produce maximum yields. This approach can be
used in other crops as well, i.e. sorghum,
cotton, bermudagrass, etc.
Sensor Based N-Rate Calculator
Former Student Employed By Former Student Employed By
Dr. Brian Arnall Okla. State Jason Lawles West. Equip.
Dr. Brenda Tubaña LSU Clint Dotson Pioneer
Dr. Byungkyun Chung McNeese State Starr Holtz Monsanto
Dr. Kefyalew Girma Okla. State Clint Mack Monsanto
Dr. Kyle Freeman Monsanto Kyle Lawles Monsanto
Dr. Robert Mullen Ohio State Brandon England FSA
Dr. Paul Hodgen Monsanto Shambel Moges Accurate Labs
Dr. Jagadeesh Mosali Noble Foundation Pam Turner DEQ
Dr. Kent Martin Kansas State Keri Brixey NRCS
Dr. Wade Thomason Virginia Tech Cody Daft Monsanto
Dr. Steve Phillips IPNI Doug Cossey ServiTech
Dr. Fred Kanampiu CIMMYT Jeremy Dennis NRCS
Dr. Edgar Ascencio CARE Jeff Ball Estes Chem.
Dr. F. Gavi-Reyes Univ. Chapingo Curt Woolfolk SST
N-Ramp Calibration Strip The N-Ramp Calibration
Strip (RCS) allows the producer to visually
determine the appropriate mid-season N fertilizer
rate. Although use of the hand-held GreenSeeker
sensor is not required for evaluation, using the
sensor offers 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 in
vegetative growth to determine the appropriate
mid-season N application rate.  Whether
determined visually, or with a hand-held sensor,
the point where differences no longer exist is
the TOPDRESS N Rate for mid-season application. 
What was found? In some years, zero N check
plots can produce near maximum yields. Where
check plots (0-N) produced near maximum yields, a
RCS would have visibly illustrated limited
differences between the zero N segment and plots
in the RCS receiving N. As a result, in-season
observation would have recognized limited or no
demand for additional N fertilizer.
Current Students Olga Walsh, Daniel Edmonds,
Cody Daft, Birehane Desta,Yumiko Kanke, Emily
Ruto, Jake Vossenkemper, Jerry May, Guilherme
Torres