METHODS (cont.)Field nadir and field off-nadir (approximately 60° from

nadir) pictures were taken of the canopy with an inexpensive digital camera (Canon PowerShot SD450, Lake Success, NY) against a neutral color board that included yellow and green disks which served as interval color standards (Fig. 2). Chlorophyll meter (Minolta SPAD-502, Konica Minolta Sensing, Inc., Tokyo, Japan) measurements and pictures of two most recently matured, fully expanded leaves 4-6 nodes from the terminal were taken under fluorescent lighting against a standardized color board (Fig. 2).

METHODS (cont.)Field nadir and field off-nadir (approximately 60° from

nadir) pictures were taken of the canopy with an inexpensive digital camera (Canon PowerShot SD450, Lake Success, NY) against a neutral color board that included yellow and green disks which served as interval color standards (Fig. 2). Chlorophyll meter (Minolta SPAD-502, Konica Minolta Sensing, Inc., Tokyo, Japan) measurements and pictures of two most recently matured, fully expanded leaves 4-6 nodes from the terminal were taken under fluorescent lighting against a standardized color board (Fig. 2).

INTRODUCTIONInadequate or excessive applications of fertilizer N in cotton are financially and environmentally costly. Timely in-season N determination in cotton (Gossypium hirsutum L.) can help producers combat these negative effects; however, current methods of determination are often time consuming and/or expensive. More instantaneous, accurate methods of determining N status which utilize equipment already in the possession of the producer are of particular interest. Recent work utilizing an inexpensive digital camera and image processing software to calculate the dark green color index (DGCI) has resulted in successful determination of corn and turf N status (Rorie et al., 2011; Karcher et al., 2003). This new method has the potential to provide producers with accurate, precise measurements of cotton N status in a quick enough manner to influence yield- impacting management decisions.

INTRODUCTIONInadequate or excessive applications of fertilizer N in cotton are financially and environmentally costly. Timely in-season N determination in cotton (Gossypium hirsutum L.) can help producers combat these negative effects; however, current methods of determination are often time consuming and/or expensive. More instantaneous, accurate methods of determining N status which utilize equipment already in the possession of the producer are of particular interest. Recent work utilizing an inexpensive digital camera and image processing software to calculate the dark green color index (DGCI) has resulted in successful determination of corn and turf N status (Rorie et al., 2011; Karcher et al., 2003). This new method has the potential to provide producers with accurate, precise measurements of cotton N status in a quick enough manner to influence yield- impacting management decisions.

OBJECTIVE The objective of this research was to examine the effectiveness of DGCI derived from standard digital photographs and commercially available image-analysis software to determine cotton N status and to compare sensitivities of calculated DGCI from laboratory, field nadir, and field off-nadir photographs with changes in leaf N and chlorophyll meter measurements.

OBJECTIVE The objective of this research was to examine the effectiveness of DGCI derived from standard digital photographs and commercially available image-analysis software to determine cotton N status and to compare sensitivities of calculated DGCI from laboratory, field nadir, and field off-nadir photographs with changes in leaf N and chlorophyll meter measurements.

METHODSA field trial was conducted in 2011 at the Lon Mann Cotton Research Station near Marianna, AR. Fertilizer N rates included 0, 30, 60, 90, 120, and 150 lb N/acre applied as urea in a single, pre-plant application to create a wide range of plant N status. Treatments were replicated four times. Leaf sampling, chlorophyll meter readings and digital pictures were taken at the third week of flowering. Leaf samples were dried and ground to pass a 20 mesh sieve and leaf N concentration of the ground sample was determined by the Agricultural Diagnostic Laboratory at the University of Arkansas in Fayetteville, AR.

METHODSA field trial was conducted in 2011 at the Lon Mann Cotton Research Station near Marianna, AR. Fertilizer N rates included 0, 30, 60, 90, 120, and 150 lb N/acre applied as urea in a single, pre-plant application to create a wide range of plant N status. Treatments were replicated four times. Leaf sampling, chlorophyll meter readings and digital pictures were taken at the third week of flowering. Leaf samples were dried and ground to pass a 20 mesh sieve and leaf N concentration of the ground sample was determined by the Agricultural Diagnostic Laboratory at the University of Arkansas in Fayetteville, AR.

CONCLUSIONSDigital image analysis is a practical and inexpensive method sensitive to cotton N status which could replace chlorophyll meters.Laboratory DGCIs correlate most strongly to changes in leaf N and SPAD readings, but field off-nadir DGCIs appear to be the most practical option for producers.An effective extension program could be set up to accept emailed or picture messaged off-nadir images of the crop of interest with a standardized color board for instantaneous determination of cotton N status.

CONCLUSIONSDigital image analysis is a practical and inexpensive method sensitive to cotton N status which could replace chlorophyll meters.Laboratory DGCIs correlate most strongly to changes in leaf N and SPAD readings, but field off-nadir DGCIs appear to be the most practical option for producers.An effective extension program could be set up to accept emailed or picture messaged off-nadir images of the crop of interest with a standardized color board for instantaneous determination of cotton N status.

REFERENCESBell, P. F., D. J. Boquet, E. Millhollon, S. Moore, W. Ebelhar, C. C.

Mitchell, J. Varco, E. R. Funderburg, C. Kennedy, G. A. Breitenbeck, C. Craig, M. Holman, W. Baker, and J. S. McConnell. 2003. Relationships between leaf-blade nitrogen and relative seedcotton yields. Crop Sci. 43:1367-1374.Karcher, D. E., and M. D. Richardson. 2003. Quantifying turfgrass

color using digital image analysis. Crop Sci. 45: 943-951.Rorie, R. L., L. C. Purcell, M. Mozaffari, D. E. Karcher, C. A. King,

M. C. Marsh, and D. E. Longer. 2011. Association of “Greenness” in corn with yield and leaf nitrogen. Agron. J. 103: 529-535.

REFERENCESBell, P. F., D. J. Boquet, E. Millhollon, S. Moore, W. Ebelhar, C. C.

Mitchell, J. Varco, E. R. Funderburg, C. Kennedy, G. A. Breitenbeck, C. Craig, M. Holman, W. Baker, and J. S. McConnell. 2003. Relationships between leaf-blade nitrogen and relative seedcotton yields. Crop Sci. 43:1367-1374.Karcher, D. E., and M. D. Richardson. 2003. Quantifying turfgrass

color using digital image analysis. Crop Sci. 45: 943-951.Rorie, R. L., L. C. Purcell, M. Mozaffari, D. E. Karcher, C. A. King,

M. C. Marsh, and D. E. Longer. 2011. Association of “Greenness” in corn with yield and leaf nitrogen. Agron. J. 103: 529-535.

RESULTSResponse of leaf N to applied fertilizer N was moderate (r2=0.55, visual differences evident in Fig. 2).Field nadir and field off-nadir DGCIs did not correlate as strongly to leaf N as laboratory DGCIs

(Fig. 3).Laboratory DGCIs and SPAD measurements responded similarly to changes in leaf N (r2=0.603, r2=0.561, respectively).Laboratory DGCIs were very strongly correlated to SPAD readings (r2=0.914, Fig. 3).Field nadir and field off-nadir DGCIs were moderate and strongly correlated to SPAD readings (r2=0.680, r2=0.818, Fig. 3).

RESULTSResponse of leaf N to applied fertilizer N was moderate (r2=0.55, visual differences evident in Fig. 2).Field nadir and field off-nadir DGCIs did not correlate as strongly to leaf N as laboratory DGCIs

(Fig. 3).Laboratory DGCIs and SPAD measurements responded similarly to changes in leaf N (r2=0.603, r2=0.561, respectively).Laboratory DGCIs were very strongly correlated to SPAD readings (r2=0.914, Fig. 3).Field nadir and field off-nadir DGCIs were moderate and strongly correlated to SPAD readings (r2=0.680, r2=0.818, Fig. 3).

Tyson B. Raper, Derrick M. Oosterhuis, Upton Siddons, Larry C. Purcell, and Morteza MozaffariTyson B. Raper, Derrick M. Oosterhuis, Upton Siddons, Larry C. Purcell, and Morteza MozaffariUniversity of Arkansas, Fayetteville, AR 72701University of Arkansas, Fayetteville, AR 72701

SPAD READING

35 40 45 50

r ²=0.914n=28

r ²=0.680n=28

r ²=0.818n=28

LA

B D

GC

I

0.5

0.6

0.7

0.8

0.9

1.0

r ²=0.603n=28

NA

DIR

DG

CI

0.4

0.5

0.6

0.7

0.8

0.9

r ²=0.440n=28

LEAF N, %

1.5 2.0 2.5 3.0 3.5 4.0

OF

F N

AD

IR D

GC

I

0.4

0.5

0.6

0.7

0.8

0.9

r ²=0.480n=28

ACKNOWLEDGEMENTSSpecial thanks to Upton Siddons for his assistance in data

analysis and to Dr. Morteza Mozaffari for allowing data collection on his field.

ACKNOWLEDGEMENTSSpecial thanks to Upton Siddons for his assistance in data

analysis and to Dr. Morteza Mozaffari for allowing data collection on his field.

SPECTRAL REFLECTANCE RESPONSE TO N

WAVELENGTH, nm

500 600 700 800

RE

FL

EC

TA

NC

E, %

0.0

0.2

0.4

0.6

0.8

N DEFICIENT N SUFFICIENT