SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

Range (10 2 m)
Variance (% 2 )
Mean (%)
2.4
2.0
1.6
1.2
0.8
0.4
0.0
15
12
9
6
3
0
36
30
24
18
12
6
0
c
b
a
UG79 UG99 WG CG HG
2004-8-12 2005-6-16 2005-7-23 2006-5-28 2006-8-4 2006-9-5
2004-8-9 2005-6-11 2005-7-31 2005-9-19 2006-6-27 2006-8-16
2004-8-12 2005-6-16 2005-7-23 2006-5-28 2006-8-4 2006-9-5
2004-8-12 2005-6-16 2005-7-23 2006-5-28 2006-8-4 2006-9-5
Time (days)
Rainfall
Fig. 3.2. Time series of (a) mean soil moisture content, (b) soil moisture variance and (c) soil
moisture range for the different grazing intensities during the sampling period 2004-2006.
Although several investigators have also noted that variance increased with
increasing MSWC (Hills and Reynolds, 1969; Reynolds, 1970; Henninger et al.,
1976; Famiglietti et al., 1998; Parent et al., 2006), other studies have not
observed this trend (Hawley et al., 1983; Charpentier et al., 1992). From Fig. 3, it
appears that environmental disturbance, contributed by grazing intensity, could
influence the relationship. The HG plot showed the greatest trend, probably due
to the legacy of sheep trampling. In contrast to it, plots with longer recovery time
since last grazing (UG 79) have less of a positive relationship between MSWC
and variance. Our results indicated that variance of soil moisture in this semi-arid
region was higher under wet conditions since effects of main factors controlling
hydrological processes (e.g. soil heterogeneity) would be at a maximum under
wet conditions. Whereas it was lower under dry conditions due to a large water
deficit and a low evapotranspiration rate.
Table 2 lists the descriptive statistics of soil moisture for the different plots
following grouping into dry, medium and wet water statuses. Soil water content
(SWC) was greatest in UG 99, followed by UG 79, WG and CG, and smallest in
48
52
39
26
13
0
Rainfall (mm)