importance of Nitrogen for plant growth; methods for measuring and estimating plant N content

1. Measuring and Estimating N
Levels in the Crop Canopy
Olga Walsh, PhD
Cropping Systems Agronomist & Extension Specialist
University of Idaho, Parma Research & Extension Center
FWAA Winter Conference, Boise, ID
January 12, 2017

2. BS Soil Sci: St Petersburg Russia – 1997; MS Soil Sci – 2007 and
PhD Soil Sci- 2009, OSU, Stillwater, OK;
Soil Nutrient Management - Montana State Univ - 2010 – 2014
Cropping Systems Agronomist, Univ Idaho – from 2014

3. Presentation Outline:
1. Nitrogen (N) role in plants
2. Plant N content
4. Measurement vs estimation
5. Measuring N: plant tissue testing
6. Estimating N: chlorophyll meters &
charts
7. Estimating N: crop sensors
8. Using UAVs (Drones)

4. Nitrogen role in plants

5. N function and deficiency
symptomsN is important for high photosynthetic activity,
vegetative growth and protein building

6. N and photosynthetic activity
 Process by which plants use the energy from
sunlight to produce sugar from CO2and H2O.
 Sugar is converted into energy in plant cells,
used for growth and development
 N – major component of Chlorophyll (green)
 Plants sufficient in N
are healthy and
vigorous and have
high photosynthetic
activity

7.  Chlorosis = yellowing of the leaves  Pale green
to yellow lower (older) leaves
 Why lower leaves? N is MOBILE in plant
 New leaves develop, take nutrients from the old
leaves and use them to grow. The old leaves are
left without enough nutrients  display the
symptoms.
N and chlorosis
Adequate
N
Limited
N
okstate.edu, 2005

8. N and vegetative growth
 Low N  smaller leaves, poor stand
establishment, stunted plants, slow growth
CYMMIT, 2006
Low
N
Adequate
N

9. N and vegetative growth
 N - essential element of all amino acids in plant
structures (building blocks of plant proteins)
 Important in the growth and development of vital
plant tissues and cells
 Enables plants to grow and reproduce
(component of DNA)

10. N and root growth
 Plants adapt to nutrient availability by
changing their root system architecture to
efficiently explore soil zones containing the
limited nutrient.
 Root growth affects
overall plant growth
 Root growth is
affected by N
Giehl & von Wirén, 2014

11. Plant N content

12. Plant N content
 Healthy plants often contain 3 to 4 % of N in
above-ground tissues.
 This is a much higher concentration compared
to other nutrients.
 N content is an important characteristic often
used for evaluation of crop health and nutrient
status.

13. N demand by crops
High
demand (> 120
lb N/a removed in 1
season
Moderate (50-
120 lb N/a removed
in 1 season
Low demand
(<50lb N/a removed
in 1 season

14. Sufficiency
 Deficient – nutrient is at low concentration,
severely limits yield, produces distinct deficiency
symptoms; Extreme deficiency plant death
 Insufficient - nutrient is below amount required for
optimum yields; Symptoms seldom evident
 Sufficient - nutrient present in adequate amounts
for optimum crop growth
 Excessive - nutrient is sufficiently high to result in
a corresponding shortage of another nutrient
 Toxic – element concentration is sufficiently high
to significantly reduce plant growth; Severe toxicity
 plant death

15. Measuring vs estimation

16. Measurement vs Estimation
 Several methods are available for direct
measurement and indirect estimation of N
content in plant biomass.
 Direct = measuring exactly the thing that
you're looking to measure
 Indirect = measuring something by
measuring something else

17. N measurement & estimation

18. Measuring N:
Plant tissue analysis
(potato petioles)

19. Plant tissue analysis
 Directly measures nutrient levels in the plant
 The supply of available nutrients is reflected in plant
nutrient content
 Use of plant tissue analysis allows producers to
evaluate the effectiveness of fertilizer
management
 N taken up by potatoes can be detected in petiole
nitrate analysis within 3-4 days after fertilizer
application
 Indicates the N status of the plant in the past 2-3
days, very good tool for in- season N decisions

20. Response to NResponsetoNitrogen
Deficiency
Sufficiency
Toxicity
Relative foliar N content

21. N content & fertilizer rates
 N content can be used to guide N fertilizer
applications
Increasing N fertilizer rate
Increasingcropyield Physiological optimum
Top yield
Bare
economic
optimum
Can cause
10-15% yield loss
BUT symptoms are
rare

22. N uptake in potatoesTotalNuptake,
kg/ha
200
100
50
0
N
uptake
Effective N management matches N

23. Petiole sampling Agvise Lab, 2017

24. Effect of petiole position on
nutrient concentration
Agvise Lab, 2017

25. Petiole N – lab test
• Petiole samples tested each week help
determine the current nitrogen status of the
potato crop
• N in the form of nitrate (NO3-N) is extracted
from potato leaf petioles with 2% acetic acid
(at room temperature) and analyzed by flow
injection

27. Potato petiole levels

28. Potato petiole sampling
 Early in the season - petiole nitrate levels are
expected to be high (20,000 - 30,000 ppm)
 During rapid vegetative growth & beginning of
tuber bulking - petiole levels are expected to
drop
 If temp warms up quickly after cool period –
explosive rapid vine growth  drop in petiole N
levels to 5000 ppm or lower = dilution of the
nitrate in the potato petiole, BUT the canopy
can look lush and green
 Apply more N? - If the total soil N >60 lb/a  No
need to additional N fertilizer

29. Estimating N:
Chlorophyll meters &
Leaf color charts

30. Chlorophyll & Plant N
• Chlorophyll is positively and linearly correlated
with plant leaf N – can use chlorophyll to
estimate NChlorophyll
concentration
Leaf N concentration

31. How Chlorophyll meters work
 The meter measures the ratio of radiation
transmittance from two wavelengths:
 red……..strongly absorbed by chlorophyll,
and
 near infrared……..not absorbed by
chlorophyll
 Meters expose a portion of a leaf to
abundant light and measure how much was
NOT captured by chlorophyll in the
photosynthetic process

32. Chlorophyll Meters
FieldScout,
$2,850
Spectrum Technologies; Apogee Instruments, atLeaf
2017
SPAD,
$2,700

33. SPAD meter accuracy
Xiong et al,
2017
• SPAD values are highly correlated with
chlorophyll content (left) AND with plant N
content (right)

34. Chlorophyll Meters
 SPAD, FieldScout - values proportional to amount
of chlorophyll in the leaf
 MC-100 – values of actual chlorophyll
concentration
Primack, 2015
atLeaf readings
SPADreadings
$2,700 vs $250

35. From Chlorophyll to N rate
• 6 years of field trials
• Relationship between Chlorophyll and
Economic N rate (Figure 1)
• Developed N recommendations (Table
1)

36. Leaf color charts
Board + App =
$150
IRRI; Spectrum Technologies,
2017
As low as $1.00/unit

37. Estimating N:
Crop Sensors

38. Optical
Crop
Sensors
hollandscientific.com; topconpositioning.com; nue.okstate.edu; agleader.com

39. Sensor-Based N Rate
1. We need
a lot
2. We don’t need
much
3. We need
a little1. High Yield
Potential,
plants some-
what deficient
in N
2. Very high
Yield Potential,
almost
adequate N
nutrition
3. Low Yield
Potential,
plants are very
deficient

40. Sensor Basics
• Emits light and measures reflectance from plants
• Red light is used for photosynthesis (absorbed)
• NearInfrared light – not enough energy, not
used (reflected)
• Sensor reading - Similar to a plant physical
examination
www.nue.okstate.edu, 2014

41. Sensor Basics
• Sensor can detect:
 Plant Biomass
 Plant Chlorophyll
 Crop Yield
 Water Stress
 Plant diseases, and
 Insect damage
 Sensors are used by agronomists, breeders, plant
pathologists, weed scientists, crop consultants,
growers
www.nue.okstate.edu, 2014

42. red
redNIR
NIR
30%50%
60% 8%
NDVI = (NIR-red)/(NIR+red)
Sensor detects the amount of light reflected from
the crop and calculates NDVI Tubana, 2007
NDVI = 0.76
NDVI = 0.25

43. What the GreenSeeker sensor “Sees”
The vigor of the leaves
and
the ratio of plant to soil
affect NDVI values
N-Tech Ind., 2009

44. N-Tech Ind., 2009
What the GreenSeeker sensor “Sees”

45. From sensor to N Rate
 Established Reference Strip (at seeding)
 Compared to the rest of the field (sensed at tillering)
 Now we know: yield potential and crop
responsiveness to N
 How do we determine the needed N rate?
 Need a formula (algorithm) to translate
sensor readings into N recommendation

46. NDVI vs crop yield
NDVI sensors
can estimate
crop yield with
90-95% accuracy
Walsh et al,
2013

47. NDVI vs yield
NDVI explained 68%
of variation in wheat
yield.
Combining NDVI and
plant height increased
accuracy of yield
prediction to 73%.
Walsh et al,
2015

48. Using UAVs (Drones)

49. DRONE STUDY - Objectives
To establish a UAV-based methodology for
in-season prediction of:
 wheat N content
 grain yield potential, and
 and prescribing N fertilizer rates

50. Drone Study

51. N rates and crop sensor data
UAV-based NDVI map
showing N rates
applied
Map showing UAV-
based NDVI values
Walsh et al,
2016
Spring wheat, Parma, ID,
2016

52. 3-D view of wheat plots,
Rupert, ID

53. NDVI data collected with UAV

54. Measured vs estimated plant N
Walsh et al,
2017
Drone
images
provide
accurate
estimation
of plant N
content

55. Thank you!
Questions?
Olga Walsh
owalsh@uidaho.edu
University of Idaho, Parma R&E Center
Tel: (208)722-6701
Web: IDCrops
(http://idcrops.blogspot.com/) Twitter:
@IDCrops