Agriculture Reference
In-Depth Information
5.1
Sensing of Topography
Soil properties depend to a large extent on nature, yet partly also on human activi-
ties. Both nature as well as human activities can result in spatial variations of soil
properties that should be taken into account for site-specific farming. This chapter
deals with properties that mainly depend on nature such as
•
topography
•
texture
•
organic matter content
•
cation-exchange-capacity
•
water content
•
salinity.
Soil properties that in modern farming predominantly depend on human activi-
ties, such as the supply with nutrients, are dealt with in later chapters.
Topography
affects farming in many aspects. Its long-term influence on run-off
of water and thus on erosion results in distinct differentiation of soil qualities
between uphill- and downhill locations. Short-term effects come from the fact that
the inclination of fields to the sun influences the temperature of the soil. The less
oblique the solar radiation hits the soil surface, the more energy is transferred per
unit area and hence the higher the soil temperature is. This explains why generally
fields with slope aspects that are oriented to the South are preferred in most areas of
the Northern latitudes of the sphere. It is
vice versa
in areas of the Southern lati-
tudes, here fields that are oriented to the North are more valuable in most cases.
The resulting effect of
slope orientation
on crop growth can be vast. In some
areas of the Northern hemisphere, wine is only grown on slopes that are oriented to
the South. Even with small cereals, the effect of slope orientation on yield can be
significant. Studies of Geary (
2003
) with a CERES wheat model show a loss in
grain yield of 1 t/ha on a slope of 10 % oriented to the North in England.
Implications for precision farming come from the influence of topography on
soil qualities, on water run-off and on yield potential. When the yield potential of a
field changes as a result of varying field inclinations as well as of slope orientations,
both the economy and the environment ask for adapting the input of agrochemicals
to this. Site-specific operations in fertilizing and crop-protection can provide for
that. Variations in soil qualities, in water run-off and thus on the prerequisites for
erosion within a field call for site-specific responses in cultivation intensities.
Yet reliable site-specific data about the relief of fields are prerequisites for any
responses to topography. Traditionally, these data for relief- or contour maps have
been obtained via conventional manual techniques by using theodolites and level
surveying. Modern techniques for sensing and recording of topography are widely
automated and include sensing methods such as
•
radar interferometry
(comparing phases as well as amplitudes of outgoing-
and reflected satellite radar radiation)
