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Remote Sensing

Aerial Color Infrared Photography for Determining Early In-Season Nitrogen Requirements in Corn

^a Dep. of Crop Sci., North Carolina State Univ., Raleigh, NC 27695-7620
^b Dep. of Crop Sci., Vernon James Res. and Ext. Cent., 207 Research Rd., Plymouth, NC 27962
^c Dep. of Soil Sci., North Carolina State Univ., Raleigh, NC 27695-7619

^* Corresponding author (Ravi_Sripada{at}ncsu.edu)

Received for publication July 1, 2005. In-season determination of corn (Zea mays L.) N requirements via remote sensing may help optimize N application decisions and improve profit, fertilizer use efficiency, and environmental quality. The objective of this study was to use aerial color-infrared (CIR) photography as a remote-sensing technique for predicting in-season N requirements for corn at the V7 growth stage. Field studies were conducted for 2 yr at three locations, each with and without irrigation, in the North Carolina Coastal Plain. Experimental treatments were a complete factorial of four N rates at planting (N_PL) and five N rates at V7 (N_V7). Aerial CIR photographs were taken at each of the locations at V7 before N application. Optimum N_V7 ranged from 0 to 207 kg N ha^–1 with a mean of 67 kg N ha^–1. Significant but weak correlations were observed between optimum N_V7 rates and the band combinations relative green, Relative Green Difference Vegetation Index, and Relative Difference Vegetation Index as measured in CIR photos. High proportions of soil reflectance in the images early in the corn growing season (V7) likely confounded our attempts to relate spectral information to optimum N_V7 rates. The primary obstacles to applying this technique early in the season are the use of relative digital counts or indices that require high-N reference strips in the field and strong background reflectance from the soil. When the N_PL treatments that were nonresponsive to N_V7 (i.e., optimum N_V7 = 0) were removed from the analysis, the normalized near infrared, the Green Difference Vegetation Index, the Green Ratio Vegetation Index, and the Green Normalized Difference Vegetation Index were the best predictors of optimum N_V7 rate (r² = 0.33).

Abbreviations: AOI, areas of interest • B, blue • CIR, color infrared • DVI, Difference Vegetation Index • G, green • GDVI, Green Difference Vegetation Index • GNDVI, Green Normalized Difference Vegetation Index • GOSAVI, Green Optimized Soil Adjusted Vegetation Index • GRVI, Green Ratio Vegetation Index • GSAVI, Green Soil Adjusted Vegetation Index • NDVI, Normalized Difference Vegetation Index • NIR, near infrared • Norm G, normalized green • Norm NIR, normalized near infrared • Norm R, normalized red • N_PL, nitrogen applied at planting • NRI, Nitrogen Reflectance Index • NSI, Nitrogen Sufficiency Index • N_V7, nitrogen applied at V7 • OSAVI, Optimized Soil Adjusted Vegetation Index • PBRS, Peanut Belt Research Station • R, red • RDVI, Relative Difference Vegetation Index • Rel G, relative green • Rel NIR, relative near infrared • Rel R, relative red • RGDVI, Relative Green Difference Vegetation Index • RGNDVI, Relative Green Normalized Difference Vegetation Index • RGOSAVI, Relative Green Optimized Soil Adjusted Vegetation Index • RGRVI, Relative Green Ratio Vegetation Index • RGSAVI, Relative Green Soil Adjusted Vegetation Index • RNDVI, Relative Normalized Difference Vegetation Index • ROSAVI, Relative Optimized Soil Adjusted Vegetation Index • RRVI, Relative Ratio Vegetation Index • RSAVI, Relative Soil Adjusted Vegetation Index • RVI, Ratio Vegetation Index • TRS, Tidewater Research Station • SAVI, Soil Adjusted Vegetation Index

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