Agriculture Reference
In-Depth Information
content of soils increases the yield potentials - within limits. But this advantage can
turn into the opposite if the clay sensed is concentrated in a dense pan that restricts
drainage as well as root development. More sensing and processing techniques for
precise site-specific mapping of such layers and pans within the rooted soil volume
should be developed. This could help to precisely evaluate the agronomic effects of
uneven texture and water situations within the sensed soil volumes in a vertical
direction.
In
arid regions
, the interpretion of the signals that are obtained is somewhat
simpler as a result of the overriding influence of salinity (Table
5.2
). And because
of this, maps of the means might not be necessary. Yet the benefits from salinity
mapping in arid regions can be huge, since this is the starting basis for precise site-
specific soil reclamation and soil fertility.
Presently less evident are the perspectives for electrical conductivity sensing
in
dryland regions
without irrigation, where effects of salinity and of soil water
are difficult to assess (McCutcheon et al.
2006
). Yet the perspectives for the use
in these regions might get better when precise separating of the effects that these
soil constituents exert on the signals becomes state of the art (see Sect.
5.2.2.2
,
bottom).
5.2.3
Water Sensing Based on Permittivity and Capacitance
5.2.3.1
Basics
Soil sensing via electrical conductivity presently is mainly used for getting site-
specific information in an integrated and summarizing way about the factors tex-
ture, organic matter and water. This integrated and summarizing information helps
to assess the yield potential
a priori
. But there exist situations when information
about the site-specific situation for a single factor alone - water - is needed.
The water content can be regarded as the most transient soil property. It can
increase drastically within a few hours because of rain and decrease again within
some days during dry spells. From this follows that a map about the respective water
situation might help to explain the yield of a crop
ex post
, but the use of the same
map for site-specific control of farming operations hardly ever can be extended over
long time periods. Yet there can be occasions where a more precise knowledge
about the temporal soil water content can help substantially,
e.g.
• when
cultivations
must be scheduled since the breakup of clods that is needed as
well as the prevention of compaction due to the weight of farm machines for
many soils can depend on the water content.
• for
sowing- and planting
in the defining of the best time and in the control of the
site-specific depth since the seeds need water for emergence.
• in the scheduling and site-specific control of
irrigation
. Agricultural crops
extract most - but not all - of their water requirements from the top 30 cm soil
