Assessment of Nitrogen Status in Wheat Using Aerial Photography

Abstract

Nontraditional technologies like aerial photography could be an interesting alternative for monitoring wheat nutritional status during the growing season. The objectives of this study were to determine the effect of nitrogen (N) rates and landscape position on the spectral indices obtained with color and color infrared aerial photographs and their relationships with N in a wheat crop. The experiment was conducted in the central western Pampas (35°27′S; 60°53′W) on two soils located in the same field. Nitrogen treatments were 0, 45, 85, and 125 kg N ha⁻¹ (N₀, N₄₅, N₈₅, and N₁₂₅) on two landscape positions in a field: upper land (U) and lower land (L). The N rate affected aboveground biomass, leaf area, N concentration, and chlorophyll at final tillering (GS 30) and grain filling (GS 73) stages, which indicated an improvement in crop N nutrition status proportional to the rate of fertilizer. The visible wavelength (red, green, and blue) reflectance decreased as N rate increased. Red digital counts (R) were better correlated with N concentration (r=0.75, p<0.05) than green (G) or blue (B) digital counts. For both crop stages, R explained approximately 72% of the N uptake. At GS 30, NNI and N uptake could be better predicted in season by using normalized difference vegetation index (NDVI) because the index also takes into account variations in N concentration and biomass. The nondestructive measurements of crop reflectance from aerial photography would appear to be appropriate indicators of the current N status in wheat crop.

Keywords:

• aerial photography
• nitrogen rates
• crop reflectance
• wheat crop

Acknowledgments

We thank Miguel Cabrera for his comments in an earlier manuscript. This experiment was made possible with support of the projects AG626 from the UBACyT and Don Adolfo S.A.