Comparison of Commercial Crop Canopy Sensors Ken Sudduth Newell Kitchen Scott Drummond USDA-ARS, Columbia, Missouri

Began on-farm research using canopy sensors in 2004 Field-length sensor-controlled strips and imbedded small plots to define N response variability across landscapes Data were collected with GreenSeeker and Crop Circle ACS-210; N application based on CC data Missouri VR-N research

ARS-Missouri system Implemented on a Spra-Coupe Used a “binary nozzle” concept with 3 different valve manifolds

Spra-Coupe application system Drop nozzles with 1x, 2x, and 4x orifice plates were installed in row middles to cover 6-row strip plots Nominal application rates: 1x = 30 lb N/acre 2x = 603x = 90 4x = 1205x = 1506x = 1807x = 210

Are Crop Circle and GreenSeeker sensor readings different? They’re not identical, but since they follow a straight line, we can use either one – if the rate equation is adjusted correctly

Comparison of application rates – Not much difference Crop Circle GreenSeeker

Most of our early data analysis and interpretation was with Crop Circle (ACS-210) data – how do GreenSeeker and Topcon CropSpec sensors compare? A 2009 study comparing commercial sensors gave unexpected results Study was redesigned and repeated in 2010 Three commercial sensors were compared based on: Relative NDVI Temporal stability Correlation to SPAD and crop height Missouri VR-N research

Materials and methods - Sensors

Holland Scientific Crop Circle ACS-210 NTech Industries GreenSeeker Model 505 Topcon CropSpec Visible wavelength 590 ± 5.5 nm660 ± 15 nm735 ± 5 nm NIR wavelength880 ± 10 nm770 ± 15 nm805 ± 5 nm Height above target 0.25 to 2.1 m0.6 to 1.6 m2 to 4 m View directionNadir Oblique, 45 to 55º Field of view / sensing footprint 32º x 6º 61 x 1.5 cm (~ constant over height range) 2 to 4 m wide (~ proportional to height above target)

Materials and methods - Sensors Holland Scientific Crop Circle ACS-210 NTech Industries GreenSeeker Model 505 Topcon CropSpec Visible wavelength 590 ± 5.5 nm660 ± 15 nm735 ± 5 nm NIR wavelength880 ± 10 nm770 ± 15 nm805 ± 5 nm Height above target 0.25 to 2.1 m0.6 to 1.6 m2 to 4 m View directionNadir Oblique, 45 to 55º Field of view / sensing footprint 32º x 6º 61 x 1.5 cm (~ constant over height range) 2 to 4 m wide (~ proportional to height above target)

Sensor geometry as used in previous field research: Crop Circle and GreenSeeker on rows 2 and 5 of 6- row pass; CropSpec from adjacent runs Data collected at 10 Hz from Crop Circle and GreenSeeker; 1 Hz from CropSpec

Data collection plots Response blocks with 8 N rates 0 to 235 kg/ha on 34 kg/ha increments applied soon after planting (0 to 210 lb/ac on 30 lb/ac increments) Each plot 12 rows (9 m) wide by 15 m long Two data passes with 6-row machine in each plot 2.5 m of data trimmed from each end, leaving center 10 m Reflectance data collected multiple times Corn height ~ 1 to 1.5 m Pass averages calculated and used for analysis

Auxiliary data collection Corn height Indicator of total biomass SPAD chlorophyll meter reading Indicator of leaf N concentration from Sudduth et al., 2010

Results

Comparing Crop Circle and GreenSeeker relative NDVI

Comparing Crop Circle and CropSpec relative NDVI Mean crop height = 0.9 m Mean crop height = 1.4 m

Different sensed areas Crop Circle and GreenSeeker at 10 Hz (~60 points/sensor/plot) CropSpec at 1 Hz (~6 points/sensor/plot)

Comparing relative NDVI GreenSeeker and Crop Circle highly correlated More differences between CropSpec and the two nadir sensors Sensed area of the two sensors Data not collected simultaneously (generally from adjacent run, < 5 min time difference) Slope and offset considerations

Temporal stability of sensor data

Data from all three sensors exhibited stability over a period of >7 hours (r ≥ 0.92) GreenSeeker slightly more variable over time Possible reasons for temporal differences: Driving misalignment between runs (nadir sensors) Sensor variations (ambient light effects) Ambient condition changes (leaf surface moisture, plant alignment due to wind, etc.) Physiological changes in the plants Effects were not large in this study

Relating sensor data to SPAD CropSpec most strongly related to SPAD

Relating sensor data to crop height GreenSeeker and Crop Circle more strongly related to corn height

Sensors vs. biophysical data CropSpec more predictive of SPAD (N) Oblique view minimized height/distance effect Sensed lower leaves where N was more strongly expressed Crop Circle and GreenSeeker more predictive of height (biomass) Effects of distance and also mixed soil/plant scene

Summary In a comparison of three commercial crop canopy sensors: Pass-average relative NDVIs from all three sensors were strongly correlated Highest correlation between Crop Circle and GreenSeeker Relative NDVI from all sensors was stable over time Slightly more temporal variability with GreenSeeker Relative NDVI from all sensors was related to both crop height (biomass) and SPAD (N concentration) CropSpec data most strongly affected by SPAD CC and GS more strongly affected by crop height/biomass

Summary Can CropSpec data be used in existing algorithms developed for Crop Circle or GreenSeeker? Appropriate slope and offset compensation would be required Additional field research is needed to determine stability of slope and offset values over different crop conditions Because effects of biophysical parameters are different for CropSpec than for Crop Circle and GreenSeeker better results may be obtained with sensor-specific algorithms

2011 Sensor comparison Very narrow range in 2011 sensor data Similar growth stage and crop height to 2010 data #1?#

Missouri algorithm graphically

Missouri algorithm developed from previous plot research Equations for calculating N rates (lbs N/acre) from active canopy sensors Corn Growth Stage Sensor TypeV6-V7 (1 to 1.5-ft tall corn)V8-V10 (2 to 4-ft tall corn) Crop Circle(330 x ratio target / ratio reference ) - 270(250 x ratio target / ratio reference ) GreenSeeker(220 x ratio target / ratio reference ) - 170(170 x ratio target / ratio reference ) Notes: Maximum N rate should not exceed 220 lbs N/acre. For V6-V7 corn, the value of ratio reference should not exceed 0.37 for Crop Circle and 0.30 for GreeenSeeker. Set this as a ceiling. For V8-V10 corn, the value of ratio reference should not exceed 0.25 for Crop Circle and 0.18 for GreeenSeeker. Set this as a ceiling.