Agriculture Reference
In-Depth Information
60
without corrections for site-specific variations
of water content in soil samples
40
20
y = 0.727 + 1.09 x
r
2
= 0.905
0
including corrections for site-specific variations
of water content in soil samples
60
40
20
y = 0.490 + 0.89 x
r
2
= 0.910
0
0
10
20
30
40
50
60
soil nitrate N sensed in a site-specific mode by ion-sel. electr. in mg per kg
Fig. 9.7
Soil nitrate N sensed in a site-specific mode either electrochemically or by a standard
method in a laboratory. The soil samples came from the same site-specific locations of several
fields in Nova Scotia, Canada (From Sibley et al.
2010
, altered)
The operation implies that the natural moisture content of the soil samples
can vary depending on the location in the field. With a fixed ratio between the
naturally moist soil volume and the amount of water added, this also means that
small variations in the final water content of the slurry in the electrochemical
cell can result. However, these rather small variations in the water content of the
slurry due to differences in the moisture of the soil do not deteriorate the
accu-
racy of sensing
.
This can be seen from comparisons of soil nitrate N that was sensed in a site-
specific mode either electrochemically by ion-selective electrodes or by standard
methods in a laboratory. These comparisons were made with or without corrections
for the varying natural moisture of the soil samples. Both cases resulted in very high
correlations to the findings for the same site-specific locations from the standard
laboratory methods. Differences that might be due to the corrections for the respec-
tive soil moisture of the samples do not show up (Fig.
9.7
, top and bottom). This is
probably because the water that is added for preparing the slurry counts much more
than the natural soil moisture. Yet this does not alter the fact that substantial changes
in the water content of the sensed soil have an effect on the output of ion-selective
electrodes (Fig.
9.3
).
