Agriculture Reference
In-Depth Information
10 years, the costs per year resulting from the contracting expenses would only be
between 1 and 2 Euros per ha.
An interesting perspective would be the creation of conductivity maps from
repeated readings as a
byproduct
of other farm operations. With the increasing
use of GNSS- or GPS based precision guidance, it might become feasible to
record signals about soil conductivities as well as about topography while mov-
ing across the fields for other farming purposes. Hence more reliable maps for
yield predictions could be obtained by averaging of signals from the same spot
(Figs.
5.1
and
5.2
).
It is general experience that the soil's potential for high yields depends largely on
its ability to store and provide water for plant growth. The objective of averaging
conductivity signals would be not to eliminate the water effect, but instead to remove
the influence of its variation. The water tension in soils differs greatly, depending on
whether the water is absorbed by soil particles, is in soil capillaries or moves freely.
Apart from the weather or irrigation, it is the soil texture that determines the amount
of water that is absorbed, stored and available for plant growth. So in short, it is an
interaction between soil and water
that defines largely the development of crops
- aside from the application of agrochemicals.
Sensing of electrical conductivities in humid areas relies to a large extent on this
interaction between soil texture and water. The conductivity signals quasi integrate
the effects of clay and moisture. And fortunately, the effects of increasing clay- and
water content on electrical conductivities on the one hand and on yields on the other
hand point in the same direction, if soils with very high clay contents are excluded.
Consequently, if by mapping of the means the temporally varying water effect can
be removed, the signals obtained from conductivity sensing principally might be
better suited for estimating yield potentials than the traditional analyses of only soil
textures in laboratories. Hence maps of the mean electrical conductivity might
become
yield-predicting-maps
.
And traditional maps about soil texture instead
probably will only serve as supplementing references in the future.
So sensing of electrical conductivities instead of the traditional analyzing of tex-
tures has distinct advantages:
•
The signals are easily mapped online and on-the go instead of taking samples in
the field and analyzing them in laboratories. Thus data from hundreds of sites per
ha instead of one or two sites per ha can be afforded, which is a prerequisite for
subsequent site-specific operations.
•
The sensing criterion is not only texture, but in addition the water situation in
soils. In principle, this complies with agronomic needs.
However, any attempt to derive site-specific yield potentials from electrical con-
ductivities must take into consideration that - without being aware of this - sensing
of
soil layers
may be included. In case soil layers in the subsoil are sensed that exist
as pans, restrict the drainage of water and are not penetrated by the roots, the results
can be very misleading. This is because the response curves of the presently domi-
nating conductivity sensing systems (Figs.
5.3
,
5.4
,
5.5
, and
5.6
) pretend uniform
soil properties within the vertical area that is sensed. Generally, an increasing clay
