Agriculture Reference
In-Depth Information
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r 2 = 0.81
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predicted nitrate-N in ppm (spectroscopic results)
Fig. 9.15 Sensing nitrate-N in samples of soil paste by mid-infrared reflectance with 7,148 nm
wavelength versus results from traditional analyses in a laboratory (From Jahn and Upadhyaya
2006 , altered)
Table 5.4 ) . The soil spectra in the mid-infrared range just have more distinct peaks
and dips than those in the near-infrared region, and this improves the estimation
results. However, a disadvantage is the higher investment for the sensing equipment
compared to near-infrared spectroscopy. The second step pertains to the processing
of the spectral data. This processing provides the means for the third step, finding
the most effective wavelength for sensing nitrate ions.
So the procedure is that the calibration starts with the full mid-infrared spectrum
from 2,500 to 25,000 nm wavelength, but the final validation is effected just by a
discrete narrow waveband. For soil samples from several Californian fields, the
result was a wavelength of 7,148 nm . The relation between the predicted nitrate
from the spectral sensing with this wavelength and the traditional results from the
chemometric analyses in a laboratory is shown in Fig. 9.15 .
The relevance of this method of soil nitrate sensing rests not only on the reliabil-
ity of the correlation between the spectral sensing and the traditional analyses in
laboratories (Jahn et al. 2006 ). Important is also that it allows to simplify the sensing
via mid-infrared radiation by employing a discrete narrow waveband , which in
effect is a drastic reduction of the measuring range. This in turn can provide pros-
pects to reduce the sensing cost for a final site-specific application of mid-infrared
radiation.
However, site-specific spectral sensing of soil nitrate-N in an on-the-go manner
has not yet been realized in practice. A question is at which depth from the soil
surface the sensing should take place. Nitrate-N can be relocated rather fast within
the soil profile since it moves with the waterfront. And it might be taken up by crops
from depths well below the topsoil (Shanandeh et al. 2011 ). It is for this reason that
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