Evaluation of nitrogen treatment effects on the reflectance of cotton at different spatial scales
2018
Muharam, Farrah Melissa | Delahunty, Tina | Maas, Stephen J.
The importance of assessing nitrogen (N) status in cotton is important from economic and environmental standpoints. In this study, visible and near-infrared reflectance (NIR) data were collected at cotton leaf-, canopy- and scene-scales at three levels of N treatments to determine the best spatial scale and growth stage that most effectively indicate N treatment effects. While N fertilization affected relative chlorophyll content, leaf area index (LAI), and ground cover (GC) simultaneously, these factors portrayed different effects on cotton reflectance measured at the three spatial scales. Leaf-scale measurement was mainly affected by chlorophyll content. Canopy-scale reflectance was controlled by chlorophyll content and LAI. Scene-scale reflectance was predominantly controlled by GC and to the least extent by chlorophyll content. In terms of visible reflectance, chlorophyll absorption decreased with decreasing N at all spatial scales. Nitrogen treatment effects were most apparent at 550 and 700 nm at the leaf-scale, 610 and 700 nm at the canopy-scale, and 685–690 nm at the scene-scale (after per cent GC exceeded 64%). Only measurements taken at the scene-scale demonstrated a consistent relationship between N fertilization and NIR (800–1000 nm). This information could be useful in the development of N-sensitive indices.
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