Moving Beyond Nitrogen with Field Sensors

Jim Schepers (emeriti)Agronomy and Horticulture Dept.

University of Nebraska

Premise – in-season differences in crop vigor will be proportional to yield at harvest

≈

“ No correlation between looks (ears) and yield “Henry A. Wallace “ No correlation between looks and yield “Henry A. Wallace

0.4 0.5 0.6 0.7 0.8 0.9 1.00.0

0.2

0.4

0.6

0.8

1.0

1.2

f(x) = 1.62178061494712 x − 0.421987392841371R² = 0.913723152882455

f(x) = 1.7769944299956 x − 0.549233141583179R² = 0.841740414093161

V9

Sufficiency Index

Rela

tive

Yiel

d

Irrigated Corn - 2009

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.0

0.5

1.0

1.5

2.0

2.5

SI earlyRI earlySI lateRI late

NDVI

Rela

tive

NDV

I

~ V12~ V6

Relative Yield = Point Yield----------------------------------------------------------------

Reference Yield

RI yield =Reference Yield----------------------------------------------------------------

Point Yield

Back in 2003, 2004 and - - - - -

“Relative yield has no value” - Bill Raun

Why is Sensor Adoption Slow ?

• Lack of perceived spatial variability

• Time window is too short

• Don’t have a high-clearance sprayer

• Anhydrous ammonia is cheaper

• Too costly for small producers

• Other adaptive management options (fertigation)

• Intimidated by the technologies

• Not compatible with strip-tillage

Why is Sensor Adoption Slow ?

• Reports of reduced yields with sensors

• Marketed from an equipment perspective

• John Deere system is not compatible with AgLeader

• Flow-rate change is slow

• Don’t like N-rich strip requirement

• Don’t believe yield potential prediction is reliable

• Algorithm structure and options not explained

• Lack of technical assistance / publications

My Impressions - - - -

• N fertilizer is still an excellent investment

• Adaptive management aspect of sensors is not

perceived as environmental attribute

• Producers don’t understand NUE implications

• Crop canopy sensors are simply a TOOL

• Effective promotion resides with seed companies,

service agencies, and curious producers

0 50 100 150 200 25002468

10121416

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha)

“ Free Nitrogen “

NUE = 45%

Nitrogen Use Efficiency - NUE

0 50 100 150 200 25002468

10121416

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha)

“ Free Nitrogen “

NUE = 78%

NUE = 56%

NUE = 34%NUE = 11%

NUE = 45%

0 50 100 150 200 25002468

10121416

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha)

Mathematical Maximum

Net return of $6.13 for each$1.00 spent on fertilizer

Assume:$1.20 / kg N$240 / ton corn grain

0 50 100 150 200 25002468

10121416

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha) $7.90

$4.39 $-0.83

Assume:$1.20 / kg N$240 / ton corn grain

ECONOMICS - Return per $1.00 invested in N fertilizer

$11.51

0 50 100 150 200 25002468

10121416

f(x) = − 0.000177640591870031 x² + 0.0714676149607639 x + 6.54465338468529R² = 0.991975167483972

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha)

Mathematical Maximum

201

$-41.51/ha$7.33/ha

Effect of over or under-application by 10% ?

0 50 100 150 200 25002468

10121416

N Rate (kg/ha)

Corn

Yie

ld (

ton/

ha)

Economic Optimum N Rate

187

$-15.90/ha$-14.95/ha

Effect of over or under-application by 10% at EONR ?

EONR - where the cost of the last unit of N equals the increase in grain value.

Observation - After producers get past the intimidation of new software, they want to know more about how the algorithms work and how they can manipulate the inputs to accomplish their management objectives.

41.3658 41.3659 41.3660 41.3661 41.3662 41.3663 41.3664 41.3665

-97.866

-97.865

-97.864

-97.863

-97.862

-97.861

-97.860

-97.859

-97.858

-97.857

-97.856

Latitude

Long

itude

RapidSCAN Data - July 2, 2013

RapidSCAN - User Inputs

Reference Index (NDRE or NDVI)Minimum N rateMaximum N rateN creditsBack-off (none, slow, medium, fast)

60 80 100 120 140 160 180 200 220 240 2600

10

20

30

40

50

60

Series1

Series3

Series5

Series7

Series9

Series11

Sample Number

N R

ate

(lb/a

cre)

RapidSCAN Data - July 2, 2013

PLOTNRATE VREF

NDRE SI NDVIRE NIR R

LATITUDE

LONGITUDE

ELEVATION

HDOP

FIXTYPE DATETIMEN

MAXNDRE

MAXNDVI

MINNDRE

MINNDVI

STDNDRE

STDNDVI

CVNDRE

CVNDVI

Plot 38N-rate 23.8Virtual Reference 0.3520NDRE 0.3256SI 0.9250NDVI 0.7599Red-edge reflectance 19.434NIR reflectance 38.261Red reflectance 5.210Latitude 41.365873Longitude 97.864848Elevation 495.7HDOP 0.75Fixture type GP

Date 3/7/2013Time 14:13:15Number of readings* 17Maximum NDRE 0.3785Maximum NDVI 0.8259Minimum NDRE 0.2618Minimum NDVI 0.5907Stdev NDRE 0.0278Stdev NDVI 0.0486CV NDRE 0.0853CV NDVI 0.0639

Data Output

* Readings recorded at 2 Hz

Jim Schepers402-310-6150

james.schepers@gmail.com