Results
1 The change of cumulative infiltration depths with time in red
plum apricot forest
Infiltration is a process in which water enter soil. The water
infiltrated into soil have two function. One is to increase soil water
content in a soil layer, and another is to increase cumulative
infiltration depth. The two curve was used to estimate the depth of
infiltration before and after a rain event or an infiltration process or
several days. The infiltration depth for a rain event is equal to the
distance from the surface to the crossover point between two soil water
distribution curves with depth measured in the soil profile before and
after a rain event or several days. A lot of the crossover points at the
same height in the soil profile makes up the wetting peak. The annual
precipitation is 536.2 mm, which is 120.6 mm more than the mean
precipitation 415.6 mm and close to the maximum rainfall record of 634.7
mm in the National high quality
red plum apricot demonstration area, see fig.1. After two effective rain
events, 9 mm in May 20 and 19.7 mm in April 13, infiltration depth reach
to 70 cm on April 28, 2018, see fig.2.
As time goes on, the cumulative infiltration depth increased with time
in 2018 because the infiltration includes two stages: rainfall
infiltration generally happening during a rain event and the cumulative
infiltration (Chowdary and others 2006) or reinfiltration (Corradini and
others 2000), which occurs in the period between two
(Fig.1 Here)
(Figures 2 Here)
rain events or a long term period in which there are more than two rain
events happens because there is a cumulative effect on the infiltration
process. After a heavy rain event, a high water-bearing soil layer
formed under land surface. With time going by, the soil water content in
the high water-bearing soil layer reduced because soil evaporate, plant
root water absorption, or infiltrate into deeper soil layer and form
another high water-bearing soil layer at deeper soil layer, and
cumulative infiltration depth increases in the soil profile (Guo and
Shao,2009; Guo 2017).When the soil water content in the upper layer of
wetting peak is equal to the lower layer of wetting peak, the cumulative
infiltration process stopped because there is not infiltration force,
and water potential difference between the upper layer of wetting peak
and the lower layer of wetting peak approaches to zero. At this time,
the cumulative infiltration depth is the maximum cumulative infiltration
depth (Guo 2020).That is to say, the maximum cumulative infiltration
depth is the maximum infiltration depth. The cumulative infiltration
depth arrives in 130 cm on May 28, up to 150 cm on June 16, get to 190
cm on July, 16 , and finally to 290 cm. So, the maximum infiltration
depth is 290 cm in red plum apricot forest, see Figure 3.
(Fig3 Here)