Remote sensing of plant nitrogen status in corn
1996
Bausch, W.C. | Duke, H.R.
Excessive nitrates in ground and surface water supplies are impacting nitrogen (N) fertilizer management schemes in many agricultural areas. Small amounts of N fertilizer applied "as needed" to a crop have potential for alleviating nitrate leaching below the crop root zone. To effectively apply this N management scheme, techniques must be developed that provide rapid assessment of the plant N status on a frequent basis. Ground-based canopy reflectance was measured perpendicular to the crop surface and in discrete wavebands over irrigated corn with several imposed N treatments for comparison to SPAD chlorophyll meter measurements and to plant tissue total N concentration. An N reflectance index (a ratio of a treatment near-infrared (NIR) to green (G) canopy reflectance to the NIR/G ratio of a well N-fertilized treatment) was developed. The N reflectance index produced a near 1:1 relationship with the N sufficiency index (average SPAD reading for a treatment divided by the average SPAD reading for a well N-fertilized treatment) for corn growth stages V11 to R4. For the N reflectance index to be a practical, useable technique, it must represent plant N status as early as the V6 growth stage. Soil background influence on canopy reflectance during early vegetative growth is a major obstacle; consequently, procedures must be developed to minimize its effect on this index.
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