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Remote Sensing

Aerial Color Infrared Photography to Optimize In-Season Nitrogen Fertilizer Recommendations in Winter Wheat

^a Canaan Valley Institute, USDA-ARS-PSWMRU, Bldg. 3702, Curtin Rd., University Park, PA 16802
^b NCDA&CS Agronomic Division, Greenville, NC 27858
^c Dep. of Crop Sci., North Carolina State Univ., Raleigh, NC 27695-7620
^d Dep. of Crop Sci., Vernon James Res. and Ext. Cent., 207 Research Rd., Plymouth, NC 27962
^e Dep. of Soil Sci., North Carolina State Univ., Raleigh, NC 27695-7619

^* Corresponding author (rps21{at}psu.edu)

Remote sensing in the form of aerial color infrared (CIR) photography has been shown to be a useful tool for in-season N management in winter wheat (Triticum aestivum L.). The objectives of this study were (i) to develop a methodology for predicting in-season optimum fertilizer N rates for winter wheat at growth stage (GS) 30 directly from aerial CIR photography and (ii) to quantify how the relationships between these optimum N rates and spectral indices respond to different levels of biomass of the wheat crop. Field studies were conducted for three winter wheat growing seasons (2002–2004) over a wide range of soil conditions across North Carolina using a split-split plot randomized complete block design. Different planting date–seeding rate (PDSR) combinations were applied to create a range of biomass levels at GS 30. Different levels of N were applied at GS 25 (N₂₅) to create a range of N supply and winter wheat radiance, and at GS 30 (N₃₀) to measure grain yield response to N₃₀. Aerial CIR photographs were obtained at each site at GS 30 before N applications. Significant biomass response to PDSR and yield response to N₂₅ and N₃₀ were observed. Optimum N₃₀ ranged from 0 to 124 kg ha^–1 with a mean of 55 kg ha^–1. Better prediction of optimum N₃₀ rates were obtained with spectral indices calculated relative to high-N reference strips compared to absolute bands or spectral indices. Biomass measured at GS 30 influenced the strength of the relationship between optimum N₃₀ and spectral indices. When the GS-30 biomass was >1000 kg ha^–1, the best predictor of optimum N₃₀ (R² = 0.85) was a quadratic model based on measured winter wheat radiance relative to mean radiance in the G band for the high N reference strip (Rel G_S).

Abbreviations: AOI, areas of interest • B, blue • C2002, Cunningham Research Station 2002 • C2003, Cunningham Research Station 2003 • C2004, Cunningham Research Station 2004 • CIR, color infrared • DGPS, differential global positioning system • DN, digital number • 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 • GS, growth stage • GSAVI, Green Soil Adjusted Vegetation Index • L2002, Lower Coastal Plain Tobacco Research Station 2002 • N₂₅, N applied at growth stage 25 • N₃₀, N applied at growth stage 30 • N_conc, tissue N concentration • NDVI, Normalized Difference Vegetation Index • NIR, near-infrared • Norm G, normalized green • Norm NIR, normalized NIR • Norm R, normalized red • NUE, nitrogen use efficiency • OSAVI, Optimized Soil Adjusted Vegetation Index • P2003, Piedmont Research Station 2003 • PDSR, Planting date–seeding rate • R, red • RDVI_R, Relative Difference Vegetation Index by Ratio • RDVI_S, Relative Difference Vegetation Index by Subtraction • Rel G_R, Relative Green by Ratio • Rel G_S, Relative Green by Subtraction • Rel NIR_R, Relative NIR by Ratio • Rel NIR_S, Relative NIR by Subtraction • Rel R_R, Relative Red by Ratio • Rel R_S, Relative Red by Subtraction • RGDVI_R, Relative Green Difference Vegetation Index by Ratio • RGDVI_S, Relative Green Difference Vegetation Index by Subtraction • RGNDVI_R, Relative Green Normalized Difference Vegetation Index by Ratio • RGNDVI_S, Relative Green Normalized Difference Vegetation Index by Subtraction • RGOSAVI_R, Relative Green Optimized Soil Adjusted Vegetation Index by Ratio • RGOSAVI_S, Relative Green Optimized Soil Adjusted Vegetation Index by Subtraction • RGRVI_R, Relative Green Ratio Vegetation Index by Ratio • RGRVI_S, Relative Green Ratio Vegetation Index by Subtraction • RGSAVI_R, Relative Green Soil Adjusted Vegetation Index by Ratio • RGSAVI_S, Relative Green Soil Adjusted Vegetation Index by Subtraction • RNDVI_R, Relative Normalized Difference Vegetation Index by Ratio • RNDVI_S, Relative Normalized Difference Vegetation Index by Subtraction • ROSAVI_R, Relative Optimized Soil Adjusted Vegetation Index by Ratio • ROSAVI_S, Relative Optimized Soil Adjusted Vegetation Index by Subtraction • RRVI_R, Relative Ratio Vegetation Index by Ratio • RRVI_S, Relative Ratio Vegetation Index by Subtraction • RSAVI_R, Relative Soil Adjusted Vegetation Index by Ratio • RSAVI_S, Relative Soil Adjusted Vegetation Index by Subtraction, RVI, Ratio Vegetation Index • SAVI, Soil Adjusted Vegetation Index • T2004, Tidewater Research Station 2004