significantly different (p b 0.01) among all four soil layers and increased
with increasing soil layer depth (Fig. 4b). Similarly, in the shelterbelt
subplot (Fig. 4c), mean SWCs followed the same pattern of increase
with soil depth. However, the mean SWCs were only slightly greater
in the 30–120 cm soil layer than in the 0–30 cm layer during most of
the observation period. Mean SWCs in the deepest soil layer were significantly
greater (p b 0.01, N = 67) than those in the upper layers.
Variations in SWC in each soil layer presented similar trends for all
land use types during 2012 and 2013 (Fig. 4). In 2012, SWCs tended to
initially decrease throughout the profile before increasing from about
June 5, reaching maximum values on slightly different dates just before
July 10; they then tended to decrease while fluctuating. In 2013, SWCs
tended to decrease throughout the whole profile before June 13th, although
the minimum values were attained in the deepest layer by the
end of May. After mid-June, SWCs tended to increase to different extents
and to fluctuate due to irrigation and rainfall events.
3.1.2. Profile distribution of soil water
The profiles of the mean SWCs are shown in Fig. 5 for the three land
use subplots. The soil water profiles could be divided into two layers
under the spring wheat and shelterbelt. The uppermost of these soil
layers (0–120 cm) was characterized by SWCs at different depths that
were similar. Consequently, the SWC within this layer was almost
constant but tended to increase with increasing depth. In the second
layer (120–260 cm), the SWC increased more rapidly with depth,
from 0.147 to 0.314 cm3 cm−3 under spring wheat and from 0.116 to
0.362 cm3 cm−3 under the shelterbelt. In contrast, under maize, the
SWC tended to increase at a relatively steady rate. However, there was
a notable decline in the SWC at depths between 200 and 210 cm. The
mean SWCs in the 0–200 cm layer were significantly different
(p b 0.01) among the three land use types. However, in the profile
below a depth of 200 cm, there were no significant differences among
the SWCs under the three land use types.
The variations in the soil water profiles on different dates for the
three land use types are presented in Fig. 6. For both the spring wheat
and shelterbelt subplots, the changes in the soil water profiles among
different dates were similar (Fig. 6a and b). In the 60–170 cm layer,
there was little change in the SWC over time. However, the SWCs
below 170 cm were significantly different (p b 0.01) on different dates
under both spring wheat and trees. In contrast, the soil water profile
under maize exhibited greater changes over time that were due,