Agriculture Reference
In-Depth Information
electrical conductivity
2 - 5 mS / m
8 - 10 mS / m
11 - 13 mS / m
16 - 19
24 - 31
vol. water content
8 - 12 %
14 - 15 %
16 - 17 %
19 - 21 %
25 - 30
horiz. penetration resistance
1.8 - 2.8 MPa
3.3 - 3.5 MPa
3.7 - 3.9 MPa
4.3 - 5.4
7.6 - 12.2
grain yield of wheat
0 - 5 t / ha
7 - 9 t / ha
9 - 10 t / ha
10 - 11 t / ha
14 - 20
0
120
240 m
Fig. 13.2
Maps of soil electrical conductivity, soil volumetric water content, soil horizontal pen-
etration resistance and wheat grain yield of a rainfed fi eld in Warleberg near Kiel, Germany. The
soil is a carbon depleted glacial loam. The electrical conductivity was recorded by an EM38 sensor
operating in a deep mode, while the water content and the penetration resistance were measured
via dual sensing of capacitance and force by a tine that operated at a depth of 20 cm from the sur-
face (see Sect.
5.2.3.4
). Note that for all soil- or crop properties the coloured scales are contiguous,
though the legends do not indicate this (From Sun et al.
2011
, rearranged and altered)
The maps in Fig.
13.2
are based on simultaneous sensing of electrical conductivity,
water content and horizontal penetration resistance (Sun et al.
2011
). The recording
took place immediately after the harvest of a winter-wheat crop so that a correlation
of its site-specifi c yield to the sensed properties still makes sense.
From the maps, it can be seen that similarities between the sensed soil properties
and the grain yield exist, however, the visual impression provides only very rough
estimates. The respective
coeffi cients of determination
(r
2
) in relation to the site-
specifi c wheat yield were
•
0.811 for the soil electrical conductivity
•
0.713 for the volumetric soil water content
•
0.501 for the horizontal soil resistance.
So from the signals recorded, the smallest infl uence on the yield comes from the
soil resistance. This soil property itself is highly dependent on the water content
(Sect.
7.2.1.5
). When taking into account the positive experiences that have been
made on a worldwide basis with reduced- or even no-tillage methods, the question
is, whether soil resistance is a property that needs to be sensed within the topsoil.
On the other hand, it is general experience that with well managed farming the
water
