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Quantitative Approaches for Using Color Infrared Photography for Assessing In-Season Nitrogen Status in Winter Wheat

^a USDA-ARS, Air Quality–Plant Growth and Development Research Unit, 3908 Inwood Rd., Raleigh, NC 27603
^b Dep. of Crop Science, North Carolina State Univ., Box 7620, Raleigh, NC 27695-7620
^c Dep. of Crop Science, North Carolina State Univ., Vernon James Res. and Ext. Center, 207 Research Rd., Plymouth, NC 27962

View larger version (9K): [in a new window]   Fig. 1. Map of North Carolina. Site names are given adjacent to stars indicating site location.

View larger version (11K): [in a new window]   Fig. 2. The coefficient of determination (R2) for the linear or quadratic model between growth stage (GS)-30 whole-plant N concentration and the normalized difference vegetation index (NDVI) vs. mean GS-30 biomass.

View larger version (29K): [in a new window]   Fig. 3. The normalized difference vegetation index (NDVI) vs. growth stage (GS)-30 whole-plant N concentration for the four site–years with high (>1000 kg ha-1) mean GS-30 biomass.

View larger version (23K): [in a new window]   Fig. 4. The normalized difference vegetation index (NDVI) vs. growth stage (GS)-30 N uptake for five site–years without Hessian fly infestations. Note P-1 was not separated by variety.

View larger version (29K): [in a new window]   Fig. 5. The normalized difference vegetation index (NDVI) sufficiency index vs. growth stage (GS)-30 whole-plant N concentration for four site–years with high (>1000 kg ha-1) GS-30 mean biomass.

View larger version (18K): [in a new window]   Fig. 6. The normalized difference vegetation index (NDVI) sufficiency index vs. growth stage (GS)-30 N uptake for four site–years with high (135 kg N ha-1) reference locations and without Hessian fly infestations.

View larger version (29K): [in a new window]   Fig. 7. Relationship between PredNRateNConcentrationBased vs. the normalized difference vegetation index (NDVI) for four site–years with high (>1000 kg ha-1) growth stage (GS)-30 biomass. Equation [7] was used to calculate PredNRateNConcentrationBased based on GS-30 whole-plant N concentration.

View larger version (26K): [in a new window]   Fig. 8. Relationship between PredNRateNUptakeBased vs. the normalized difference vegetation index (NDVI) for five site–years. Equation [8] was used to calculate PredNRateNUptakeBased based on growth stage (GS) 30 N uptake. Note P-1 was not separated by variety.

View larger version (34K): [in a new window]   Fig. 9. Failure of growth stage (GS)-30 N uptake to distinguish between N deficient and N sufficient sample locations. Data are identical to those shown in Fig. 5 and 8; however, filled symbols represent sample locations with N deficiency based on the critical value of 39.5 g kg-1 for GS-30 whole-plant N concentration (Scharf et al., 1993). Open symbols represent sample locations with sufficient N also based on 39.5 g kg-1 for GS-30 whole-plant N concentration. (A) NDVI vs. GS-30 N uptake; (B) PredNRateNUptakeBased calculated from GS-30 N uptake (Eq. [8]) vs. NDVI.