Agriculture Reference
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20
15
simple averaging
10
5
0
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number of surveys averaged
Fig. 5.2 Errors with averaging methods used for field elevation data. Effect of combining repeated
elevation surveys of RTK-GPS by either simple averaging or by weighted averaging of the error
data (From Abd Aziz et al. 2009 , altered and simplified)
5.2
Sensing of Soil Properties on a Volume Basis
Natural soil properties such as texture, water, organic matter and salinity influence
the yield potential. Georeferenced knowledge about these properties can assist in
pinpointing the site-specific control of cultivation-, sowing-, fertilizing- and crop
protection operations.
Spatial variations within fields are frequent for all these soil properties.
Compared to this, temporal variations are important only for soil moisture.
This has implications for mapping practices. Maps about texture and organic
matter content are useful and once properly created can be up to date to assist
farming for decades. But because of the varying weather, maps about the site-
specific water content can be obsolete within a few days and in rain-fed areas
therefore seldom are of interest except for research purposes. However, the situ-
ation for soil water is completely different when online and on-the-go control of
farm operations and hence instant reaction is possible. This control can be very
useful for site-specific adjustments of irrigation operations, of the depth of culti-
vation or the depth of sowing.
In the past, the spatial resolutions in the recording of the data were insufficient.
The costs of manual soil sampling in the field and subsequent expensive analysing
in laboratories for texture, organic matter and water did not allow for high resolu-
tions. Often data from only one site per ha were analysed, which in most cases did
not at all provide a reliable basis for precision in site-specific operations. Handheld
measuring instruments can save sending the samples to laboratories, yet for high
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