Olga S. Walsh, Western Triangle Agricultural Research Center, Conrad, MontanaMal Westcott, and Martha Knox, Western Agricultural Research Center, Corvallis, Montana

Evaluation of Sensor-Based Technologies and Nitrogen Sourcesfor Improved Recommendations for Dryland and Irrigated

Spring Wheat Production in Montana

JUSTIFICATION

DISCUSSION

MATERIALS AND METHODS

3 experimental sites: 2 dryland (WTARC, and on-farm study (Pat Wheeler, Valier, Pondera County), and 1 irrigated (WARC)Choteau spring wheat variety4 preplant N rates (22, 45, 67, and 90 kg N ac-

1)2 topdress N fertilizer sources (granular –

urea, 46-0-0, and liquid – urea ammonium nitrate (UAN), 28-0-0)1 unfertilized check and 1 non-limiting N-

Rich plots(246 kg N ac-1 preplant) per replication Topdress N fertilizer rate determined using

NDVI obtained using GreenSeeker and Pocket Sensor at Feekes 5 growth stage

To evaluate two sensors (GreenSeeker and Pocket Sensor) for developing NDVI-based topdress fertilizer N recommendations in spring wheat in MontanaTo determine whether sensor-based

recommendations have to be adjusted depending on what N fertilizer source (liquid UAN, or granular urea) is used

OBJECTIVES

PRECISION SENSING EQUIPMENT

GreenSeeker Real-time active light

source sensorEmits light at 670nm (red)

and 780nm (NIR)Measures crop canopy reflectance at 200

readings /secOutputs Normalized Difference Vegetative

Index (NDVI)Equivalent to a plant physical examination

Pocket SensorReal-time active light source

sensorCan be calibrated to any

NDVI sensorNDVI can be directly

compared independent of what sensor is used to sense the crop

Spring wheat - key cereal crop grown in MontanaGreat demand for up-to-date information on

crop-specific and site-specific fertilizer use is strongly apparent among Montana crop producersIn general, N fertilizer rates for cereal crops

in Montana are determined as following: NR = YP x 2.5-3.0, (NR=N fertilizer rate (lbs/a), YP=yield potential (bu/a)When wheat yield potential (YP) is higher-

than-average, early-season N application may not be adequate for sufficient protein accumulation Late-season N fertilizer application can

boost protein level by 0.5-2.0%

Quantitatively measures vegetation indices such as the Normalized Difference Vegetation Index (NDVI) (Tucker, 1979)A non-destructive methodology developed

for precise estimation of crop’s YP mid-seasonUtilize spectral measurements which are

used to develop an algorithm for mid-season topdress N fertilization (Raun et al., 2001) Allow to accurately access the crop’s nutrient status and account for spatial and temporal variabilityEnable fertilization based on crop

need/yield potentialadjusting fertilizer application rates

according to site-specific conditions Result = more efficient, profitable, and

sustainable crop production

RESULTS

Figures 1a and 1b. Relationship between spring wheat grain yield and GreenSeeker NDVI (1a) and Pocket Sensor NDVI (1b) at WTARC and WARC, 2011.

Collecting GreenSeeker NDVI readings from spring wheat plots, Montana, spring 2011

GreenSeeker NDVI values obtained at Feekes 5 growth stage were strongly correlated with spring wheat grain yield (R2 = 0.95)Pocket Sensor NDVI values collected at

Feekes 5 growth stage were able to predict 87% of spring wheat grain yield (R2 = 0.87)The Sensor-Based Nitrogen Optimization

Algorithm (USA/Canada/Mexico) recommended application of 35 to 157 kg N ha-1 at WTARC and from 29 to 80 kg N ha-1 at WARC depending on the NDVI valuesMuch more pronounced response to N was

observed at WARCThe highest observed NDVI at WARC was

0.7, the plots with NDVI of 0.3, 0.4, and 0.5 were prescribed 29, 57, and 80 kg N ha-1 topdress rates respectively. No topdress was recommended for plots with NDVI values >0.5

AKNOWLEDGEMENT: We are grateful to Montana Fertilizer Advisory

Committee for funding this project

SENSOR-BASED TECHNOLOGY

CONTACT INFORMATION: Dr. Olga S. Walsh, Western Triangle Agricultural Research Center, MSUtelephone: (406)278-7707; e-mail: olga.walsh@montana.edu; web: http://ag.montana.edu/wtarc/

0.2 0.3 0.4 0.5 0.6 0.71000

1500

2000

2500

3000

3500

4000

f(x) = 5480.681124 x² + 1916.42099 x + 424.0816605R² = 0.944462306181873

GreenSeeker NDVI

Sp

rin

g w

he

at

gra

in y

ield

, k

g h

a-1

Figure 1 a

0.2 0.3 0.4 0.5 0.6 0.71000

1500

2000

2500

3000

3500

4000

f(x) = 19516.97783 x² − 10535.86697 x + 2937.806512R² = 0.872632361243899

Pocket Sensor NDVI

Sp

rin

g w

he

at

gra

in y

ield

, k

g h

a-1

Figure 1 b