Agriculture Reference
In-Depth Information
140
r
2
for the total field = 0.7454
130
120
110
100
90
80
70
r
2
= 0.8865
r
2
= 0.0007
r
2
= 0.3065
r
2
= 0.0367
r
2
= 0.0043
subfield A
subfield E
subfield B
subfield C
subfield D
60
10
20
30
40
50
electrical conductivity in mS/ m
Fig. 5.12
Effects of electrical conductivities on yields of winter-wheat in Schleswig-Holstein,
Germany for a field and its subfields. Regressions are shown for the total field as well as for its
subfields. The regression for subfield C is on the same line as the main regression for the whole
field and hence is difficult to depict. The
vertical lines
represent the respective standard deviations
(From Reckleben
2004
and Schwark and Reckleben
2006
, altered)
The change from a positive- to a negative effect on yield occurs in Fig.
5.11
at a
rather high level of conductivity, namely about 80 mS/m. It is reasonable to suspect
that the transition from rising to declining yields depends on the water supply during
the growing season.
In humid areas, the transition from a positive to a negative effect can already be
attained with an electrical conductivity of 40 mS/m or less (Domsch et al.
2003
;
Lueck et al.
2002
). And where a rather uniform soil prevails, the effects of its properties
on site-specific yields may fail to appear at all.
The regressions in Fig.
5.12
indicate how different the relation between electrical
conductivities and site-specific yields within a single field can be. The regression for
the total field suggests a distinct positive effect of conductivities in the range from
12 to 49 mS/m on wheat yields. However, the division into subfields shows that this
is largely due to the increasing yields between 12 and 19 mS/m and much less to
rising yields above this level. There are ranges above this level where no increases
occur. In this case, the decrease of yields probably starts somewhere between 44 and
49 mS/m. The standard deviations of the site-specific yields decrease with high
yield levels (Reckleben
2004
).
