Agriculture Reference
In-Depth Information
10
10
near-infrared reflectance
r
2
= 0.50
visible reflectance
r
2
= 0.25
8
8
6
6
4
4
2
45678910
2
4
6
8
10
lime by buffer pH lab method in t /ha
lime by buffer pH lab method in t /ha
10
visible + near-infrared
+ mid-infrared refl.
r
2
= 0.74
mid-infrared reflectance
r
2
= 0.75
10
8
8
6
6
4
4
4
56
78
9 0
4
6
8
10
lime by buffer pH lab method in t /ha
lime by buffer pH lab method in t /ha
Fig. 9.11
Comparing the lime requirement as determined in laboratories either by standard meth-
ods or by reflectance of full spectra (From Viscarra Rossel et al.
2006
, altered)
resulted in an improved yet still not satisfying correlation. But the mid-infrared
spectroscopy (2,500-25,000 nm) finally supplied a coefficient of determination
(r
2
= 0.75) that offered prospects for application. Using all these three spectral
ranges in a combined manner together provided a similar result. Consequently,
the mid-infrared region
per se
alone should be the best choice. This superiority of
sensing in the mid-infrared range is in agreement with results that have been
is more expensive to sense in this spectral region than to use visible radiation or
the near-infrared range. Even more important is that up to now mid-infrared
reflectance needs rather dry soil, which prevents the application for proximal
on-the-go sensing.
The soil properties that are important for the control of liming do not present
the same conditions on a time scale. With professional farming, checking the soil
water pH might be reasonable every 3-5 years. Compared to this, the soil proper-
ties that must be known in addition to define the
buffer situation
- like
e.g.
cation-exchange-capacity, texture and organic carbon - remain constant over
much longer time periods. Hence a possible approach would also be to sense the
soil water pH on a site-specific basis via reflectance in real-time while liming
takes place, but to rely for the required buffer corrections on simultaneously used
maps. These georeferenced digital maps with data about long-term soil properties
