In-Season Nitrogen Fertilization Based on Sensor-Estimated

Potential Yield

In-Season Nitrogen Fertilization Based on Sensor-Estimated

Potential Yield

E.V. Lukina, K.W. Freeman,K.J. Wynn, W.E. Thomason, G.V. Johnson,

M.L. Stone, J.B. Solie, W.R. Raun

E.V. Lukina, K.W. Freeman,K.J. Wynn, W.E. Thomason, G.V. Johnson,

M.L. Stone, J.B. Solie, W.R. Raun

Oklahoma State UniversityOklahoma State UniversityDepartment of Plant and Soil SciencesDepartment of Plant and Soil Sciences

Introduction Introduction

Low nitrogen use efficiency for cereal production (33%) In-season reflectance readings from wheat at high

resolutions (1m2) have been shown to be highly correlated with biomass

Our present focus has been to apply N rates to each 1m2 area based on predicted potential yield Potential grain yield: yield predicted for a given year and

site, based on the assumption that the level of growth factors responsible for early stages of development of the crop will be maintained (limitations that existed at early stages of growth will continue to similarly influence development to maturity, e.g., N deficiency)

Low nitrogen use efficiency for cereal production (33%) In-season reflectance readings from wheat at high

resolutions (1m2) have been shown to be highly correlated with biomass

Our present focus has been to apply N rates to each 1m2 area based on predicted potential yield Potential grain yield: yield predicted for a given year and

site, based on the assumption that the level of growth factors responsible for early stages of development of the crop will be maintained (limitations that existed at early stages of growth will continue to similarly influence development to maturity, e.g., N deficiency)

ObjectiveObjective

To investigate the potential for N fertilization using in-season estimates of potential yield for every 1m2 based on plant reflectance readings

To investigate the potential for N fertilization using in-season estimates of potential yield for every 1m2 based on plant reflectance readings

Materials and MethodsMaterials and Methods

Winter wheat Coker, Custer, and 7853 Experimental design

Randomized complete block Four replications 4m x 7m plots 1m2 subplots for variable rate treatments

Spectral reflectance readings at 671nm (red) and 780nm (near infrared) taken at Feekes physiological growth stages 4 and 5

Winter wheat Coker, Custer, and 7853 Experimental design

Randomized complete block Four replications 4m x 7m plots 1m2 subplots for variable rate treatments

Spectral reflectance readings at 671nm (red) and 780nm (near infrared) taken at Feekes physiological growth stages 4 and 5

Optical sensor developed by OSUOptical sensor developed by OSU

Materials and MethodsMaterials and Methods

NDVI (Normalized Difference Vegetation Index) calculated for each subplot (1m2) by the equation (NIR-Red)/(NIR+Red)

For two of the treatments, N rates were determined based on tissue N need at F4 and F5, respectively

For the yield potential treatment, N rates were determined based on EY (estimated yield) index:

EY=(NDVIF4+NDVIF5)/GDDGDD=(Tmin+Tmax)/2- 4.4 °C

NDVI (Normalized Difference Vegetation Index) calculated for each subplot (1m2) by the equation (NIR-Red)/(NIR+Red)

For two of the treatments, N rates were determined based on tissue N need at F4 and F5, respectively

For the yield potential treatment, N rates were determined based on EY (estimated yield) index:

EY=(NDVIF4+NDVIF5)/GDDGDD=(Tmin+Tmax)/2- 4.4 °C

Materials and MethodsMaterials and Methods

Ammonium nitrate applied after sensing in early March (March 6-13)

Plots harvested by treatment (4m x 7m) in mid June

Grain weight and percent moisture automatically recorded

Total N in grain samples analyzed by dry combustion (Schepers et al., 1989)

Ammonium nitrate applied after sensing in early March (March 6-13)

Plots harvested by treatment (4m x 7m) in mid June

Grain weight and percent moisture automatically recorded

Total N in grain samples analyzed by dry combustion (Schepers et al., 1989)

Spatial variabilitySpatial variability

0.24

0.28

0.32

0.36

0.40

0.44

0.48

0.52

0.56

0.60

0.64

0.68

0.72

0.76

0.80Covington Feekes5 NDVI Contour MapCovington Feekes5 NDVI Contour Map

ResultsResults

Due to weed problems and high soil test N, one field experiment in 1998-99 did not respond to N fertilizer

Grain yield and N fertilizer requirement were highly correlated with yield potential-based N fertilization for both years at both locations.

Grain yield, N uptake and NUE were increased using EY compared to fixed rates in 1999, while the next year results were not consistent with the first year of study.

Due to weed problems and high soil test N, one field experiment in 1998-99 did not respond to N fertilizer

Grain yield and N fertilizer requirement were highly correlated with yield potential-based N fertilization for both years at both locations.

Grain yield, N uptake and NUE were increased using EY compared to fixed rates in 1999, while the next year results were not consistent with the first year of study.

ResultsResults

The highest grain yield and N uptake during the second year of experiment was obtained on the plots with fixed N rate of 90 kg N per ha.

The highest NUE’s were observed on the yield potential-based N fertilization plots at Morrison location, and 45 kg of N per ha (fixed rate) at Covington.

The highest grain yield and N uptake during the second year of experiment was obtained on the plots with fixed N rate of 90 kg N per ha.

The highest NUE’s were observed on the yield potential-based N fertilization plots at Morrison location, and 45 kg of N per ha (fixed rate) at Covington.

Grain yield response to N rates,Covington, 1999

Grain yield response to N rates,Covington, 1999

Yield response to fixed N rates

y = 0.1074x2 - 1.5561x + 1122.6

R2 = 0.2773

0

1000

2000

3000

0 20 40 60 80 100

N Rate (kg/ha)

Gra

in Y

ield

(kg

/ha

)

Yield response to fixed N rates

y = 0.1074x2 - 1.5561x + 1122.6

R2 = 0.2773

0

1000

2000

3000

0 20 40 60 80 100

N Rate (kg/ha)

Gra

in Y

ield

(kg

/ha

)

Yield response to YP-based N rates

y = -1.7659x2 + 343.3x - 13177

R2 = 0.9576

0

1000

2000

3000

4000

50 60 70 80 90 100 110

N Rate (kg/ha)G

rain

Yie

ld (

kg

/ha

)

Yield response to YP-based N rates

y = -1.7659x2 + 343.3x - 13177

R2 = 0.9576

0

1000

2000

3000

4000

50 60 70 80 90 100 110

N Rate (kg/ha)G

rain

Yie

ld (

kg

/ha

)

Grain yield response to N rates,Covington, 2000

Grain yield response to N rates,Covington, 2000

Yield response to fixed N rates

y = -0.2082x2 + 33.03x + 1406.5R2 = 0.851

1000

2000

3000

4000

5000

0 20 40 60 80 100

N Rate (kg/ha)

Gra

in Y

ield

(kg

/ha

)

Yield response to YP-based N rates

y = 2.5076x2 - 154.99x + 3837.8

R2 = 0.9996

1000

2000

3000

4000

5000

30 40 50 60

N Rates (kg/ha)G

rain

Yile

d (k

g/ha

)

Grain yield response to N rates,Morrison, 2000

Grain yield response to N rates,Morrison, 2000

Yield response to fixed N rates

y = -0.0354x2 + 14.323x + 2926.9R2 = 0.5245

1000

2000

3000

4000

5000

0 20 40 60 80 100

N Rate (kg/ha)

Gra

in Y

ield

(kg

/ha

)

Yield response to YP-based N rates

y = 40.824x2 - 1928.1x + 26061R2 = 0.7514

1000

2000

3000

4000

5000

20 22 24 26 28 30

N Rate (kg/ha)

Gra

in Y

ield

(kg

/ha

)

N fertilizer requirement as influenced by N rates, Covington, 1999

N fertilizer requirement as influenced by N rates, Covington, 1999

N requirement vs YP-based N rates

y = 0.0277x2 - 4.878x + 239.07

R2 = 0.8416

0

10

20

30

40

50

50 60 70 80 90 100 110N Rate (kg/ha)

kg

of N

/ to

n o

f w

he

at

N requirement vs YP-based N rates

y = 0.0277x2 - 4.878x + 239.07

R2 = 0.8416

0

10

20

30

40

50

50 60 70 80 90 100 110N Rate (kg/ha)

kg

of N

/ to

n o

f w

he

at

N requirement vs fixed N rates

y = -0.0043x2 + 0.9904x - 1E-13

R2 = 0.8009

0

20

40

60

80

100

0 50 100

N Rate (kg/ha)

kg

of N

/ to

n o

f w

he

at

N requirement vs fixed N rates

y = -0.0043x2 + 0.9904x - 1E-13

R2 = 0.8009

0

20

40

60

80

100

0 50 100

N Rate (kg/ha)

kg

of N

/ to

n o

f w

he

at

N fertilizer requirement as influenced by N rates, Covington, 2000

N fertilizer requirement as influenced by N rates, Covington, 2000

N requirem ent vs fixed N rates

y = -0.0008x2 + 0.4429x - 6E-14R2 = 0.9807

0

10

20

30

40

50

0 20 40 60 80 100

N Rate (kg/ha)

kg o

f N /

ton

of w

heat

N requirem ent vs YP-based N rates

y = -0.0257x2 + 2.0346x - 16.27R2 = 0.9993

20

21

22

23

24

25

30 35 40 45 50 55N Rate (kg/ha)

kg o

f N/ t

on o

f whe

at

N fertilizer requirement as influenced by N rates, Morrison, 2000

N fertilizer requirement as influenced by N rates, Morrison, 2000

N requirement vs fixed N rates

y = -0.0008x2 + 0.3252x - 5E-14R2 = 0.9894

0

5

10

15

20

25

30

0 20 40 60 80 100

N Rate (kg/ha)

kg o

f N /

ton

of w

he

at

N requirement vs YP-based N rates

y = -0.0688x2 + 3.4837x - 36.652R2 = 0.2325

0

2

4

6

8

10

20 22.5 25 27.5 30

N Rate (kg/ha)

kg o

f N /

ton

of w

he

at

Grain yield response to TreatmentGrain yield response to Treatment

Grain Yield & N Rate vs TreatmentCovington, 1999

0500

10001500200025003000

45 90 YP F4 F5

Treatment

Gra

in Y

ield

(k

g/h

a)

0

20

40

60

80

100

N r

ate

ap

plie

d

(kg

/ha

)

Grain Yield

N Rate

Grain yield response to TreatmentGrain yield response to Treatment

Grain Yield & N Rate vs TreatmentCovington, 2000

0

1000

2000

3000

4000

5000

0 45 90 YP1 YP2 F5

Treatment

Gra

in Y

ield

(k

g/ha

)

0

20

40

60

80

100

N ra

te a

pplie

d (k

g/ha

)

Grain Yield

N Rate

Grain Yield & N Rate vs TreatmentMorrison, 2000

0

1000

2000

3000

4000

5000

0 45 90 YP1 YP2 F5

TreatmentG

rain

Yie

ld

(kg/

ha)

0

20

40

60

80

100

N r

ate

appl

ied

(kg/

ha)

Grain Yield

N Rate

YP1 (based on 98, 99, 00 forage N uptake data)YP2 (based on 00 N uptake data only)YP1 (based on 98, 99, 00 forage N uptake data)YP2 (based on 00 N uptake data only)

N uptake response to TreatmentN uptake response to Treatment

N uptake & N Rate vs TreatmentCovington, 1999

0

10

20

30

40

50

60

45 90 YP F4 F5

Treatment

Tot

al N

upt

ake

by

grai

n (k

g/ha

)

0

20

40

60

80

100

N r

ate

appl

ied

(kg/

ha)

N uptake

N Rate

N uptake response to TreatmentN uptake response to Treatment

N uptake & N Rate vs TreatmentCovington, 2000

0

10

20

30

40

50

0 45 90 YP1 YP2 F5

Treatment

To

tal N

up

tak

e

by

gra

in (

kg

/ha

)

0

20

40

60

80

100

N r

ate

ap

plie

d

(kg

/ha

)

N uptake

N Rate

N uptake & N Rate vs TreatmentMorrison, 2000

0

20

40

60

80

100

0 45 90 YP1 YP2 F5

TreatmentT

ota

l N u

pta

ke

b

y g

rain

(k

g/h

a)

0

20

40

60

80

100

N r

ate

ap

plie

d

(kg

/ha

)

N uptake

N Rate

NUE response to TreatmentNUE response to Treatment

NUE & N Rate vs TreatmentCovington, 1999

0

10

20

30

40

50

45 90 YP F4 F5

Treatment

NU

E

0

20

40

60

80

100

N r

ate

ap

plie

d

(kg

/ha

)

NUE

N Rate

NUE response to TreatmentNUE response to Treatment

NUE & N Rate vs TreatmentCovington, 2000

0

10

20

30

40

45 90 YP1 YP2 F5

Treatment

NU

E

0

20

40

60

80

100

N r

ate

ap

pli

ed

(kg

/ha

)

NUE

N Rate

NUE & N Rate vs TreatmentMorrison, 2000

0

20

4060

80

100

120

45 90 YP1 YP2 F5

Treatment

NU

E

0

20

40

60

80

100

N r

ate

ap

pli

ed

(kg

/ha

)

NUE

N Rate

ConclusionConclusion

EY may be used as a predictor of potential yield and for adjustment of in-season N fertilization rates

Yield potential-based in-season N fertilization may increase grain yield, N uptake and NUE

EY may be used as a predictor of potential yield and for adjustment of in-season N fertilization rates

Yield potential-based in-season N fertilization may increase grain yield, N uptake and NUE