Abstract
Infiltration and soil water content (SWC) are key concerns to
agro-hydrological researchers. Understanding of irrigation-induced
infiltration and soil water characteristics are fundamental to
irrigation management and improving agricultural Water Use Efficiency
(WUE) in arid and semi-arid areas. Based on measurements from a test
site in Xinjiang, China, numerical simulations have been performed to
investigate the infiltration processes under alternating drip irrigation
operations. The present study focuses on simulating infiltration physics
and analyzing its potential impacting factors, to shed light on the
design of irrigation systems that improve WUE. The results show that
irrigation schedules, surface sealing, residual water saturation, and
soil fractures have significant impacts on SWC patterns for both the
irrigation durations and intermittences. Low frequency irrigation with
high watering rates should be avoided due to its low irrigation
efficiency. Commencing with lower-rate irrigation is probably the best
practice for efficient irrigation for shallow-root crops. The soil
infiltrability drops exponentially or polynomially with the decrease in
permeability of the immediate surface. Introduction of a 5-mm soil
surface seal with a permeability of 5 mD leads to about 97.1% reduction
in the infiltrability. Residual water saturation Swr or water content
has positive correlations with Volumetric soil Water Content (VWC), due
to the trapping of the residual water. 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. The presence of soil fractures leads to
apparent preferential flows in the soil, which cause the wet fronts to
penetrate to 115.9% and 53.88% deeper depths at the 160 hr and 720 hr,
respectively.