Effects of residual water saturation
Residual water saturation Swr or water contentƟr is a hydraulic parameter defining SWCC. It is
dependent on various factors such as soil organic carbon and clay
content as well as other soil physical properties (e.g., Qin, 2003;
Poeplau et al., 2015). Soil with different Swr is
expected to have different pattern of SWC. Besides C0, additional two
simulations with differing designation of Swrwere run to investigate this effect. The differences in the profiles of
VWC due to differing Swr are clearly seen in Fig.
12. The curve for C0 is in the between of the other two lines at the
four times, because of its Swr has a value
between the other both. Higher Swr allows more
water to be retained in the pores and cannot be driven out by soil
gases. This explains why higher Swr leads to
higher VWC especially for the times free of irrigation (Fig. 12c, d).
Enhancement of one-fold magnitude of Swr causes
6.12% and 20.4% higher VWC for the loamy sand, but 7.57% and 5.71%
lower VWC for the underlying sandy loam, at the 160 hr and 720 hr
respectively. Given a certain irrigation water amount, fast downward
migration of the wet front and higher SWC in deep horizons are
implications of low irrigation water use efficiency. High residual water
saturation in the root zone benefits crop growth during rainless
periods. Speaking in this sense, it is encouraged to take practical
measures to alter the soil structure and physical properties (e.g. the
organic content) to ensure a higher Swr in the
root zone of the crops.
Figure 12. Profiles of VWC at various times for differing residual water
saturation settings for the loamy sand (C0: Swr=0.135;
C30: Swr=0.067; C31: Swr=0.270).