Active sensing of the N status of wheat using optimized wavelength combination: impact of seed rate, variety and growth stage

J. Jasper; S. Reusch; A. Link

Active sensing of the N status of wheat using optimized wavelength combination: impact of seed rate, variety and growth stage

In: Precision agriculture '09

Authors:

J. Jasper

J. Jasper Research Centre Hanninghof, Yara International ASA, 48249 Duelmen, Germany; joerg.jasper@yara.com

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S. Reusch

S. Reusch Research Centre Hanninghof, Yara International ASA, 48249 Duelmen, Germany; joerg.jasper@yara.com

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, and

A. Link

A. Link Research Centre Hanninghof, Yara International ASA, 48249 Duelmen, Germany; joerg.jasper@yara.com

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Type:: Chapter

Pages:: 23–30

DOI:: https://doi.org/10.1163/9789086866649_003

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Abstract

Variable rate nitrogen fertilizer application needs efficient determination of the nitrogen nutrition status of crops with high spatial and temporal resolution. A suitable approach to get this information fast and at low cost is proximal sensing of the light that is reflected from the crop canopy, either using the sunlight (passive sensors) or artificial light sources (active sensors). Previous research has indicated that an optimized spectral index based on one waveband in the NIR and the other close to the infrared shoulder of canopy reflectance might be superior to standard NDVI indices for both passive and active sensors. Since only little is known about the effect of agricultural practices on active measurements using different spectral indices, the accuracy of N uptake estimations by active remote sensing was investigated in two winter wheat field trials with varying N-rates, contrasting varieties and different seed densities in 2005 and 2007. As for passive canopy sensors, the sensitivity of active N uptake measurements depends on the choice of appropriate wavelength combinations. The optimized spectral index VI_opt (R760/R730) turned out to be superior to indices that combine wavelengths taken from the near infrared and the visible spectral range. It was found to be largely unaffected by variety properties and seed rates and showed less saturation at high N uptake levels later in the season, compared to the NDVI. The results furthermore indicate that the relationship between active reflectance measurement and N uptake depends on the physiological growth stage of the crop, regardless of the spectral indices used. Thus, algorithms to derive nitrogen fertilizer recommendations from the measurements need to be developed for N top dressings at respective specific growth stages separately.

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Precision agriculture '09

E-Book ISBN:: 9789086866649

Publisher:: Wageningen Academic

Print Publication Date:: 01 Jan 2009

Subjects
- Life Sciences
  - General
  - Agriculture & Environment

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Active sensing of the N status of wheat using optimized wavelength combination: impact of seed rate, variety and growth stage

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Precision agriculture '09

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