Studies On Water-Holding Properties Of Vegetative Litters And Their Influences On Gravity Irrigation In Ziquejie Terrace

As one of the sixth batch of national key scenic spots in China, Ziquejie Terrace is also famous in the world for its annual bumper harvest under natural gravity irrigation. The terrace has been farmed since 2000 years ago, and water-holding properties of litters play an important role in irrigation of this area. By means of field investigation and indoor experiment, the litters' water-holding properties including water uptake and releasing processes were explored, as well as their impacts on natural gravity irrigation in Ziquejie Terrace. It is found that there mainly exist 5 kinds of eco-community litters, namely spruce forest, spruce-bamboo mixed forest, bamboo forest, chestnut forest and grass ground. When immersed in water for over 8h all litters can be considered approximately saturated, and the maximum water-holding ratio of litters for spruce-bamboo mixed forest, bamboo forest, wild grass ground, spruce forest and chestnut forest is 420%, 310%, 283%, 252% and 226%, respectively. Releasing water in conditions of 20 degrees C and 24% humidity for 24h, the releasing process doesn't arrive at stability, and the releasing ratio of litters at that time for spruce forest, bamboo forest, chestnut forest, grass ground and spruce-bamboo mixed forest is 188%, 161%, 148%, 126% and 124%, respectively. According to regression analysis, there is a logarithmic function between water-holding ratio and immersed time, as well as between water-releasing ratio and releasing time. And a power relation is obtained between water-uptake rate and immersed time, as well as between water-releasing rate and releasing time. The water-uptake capability of litters differs from the water-releasing capacity, and the former is much stronger than the latter. At last, a physically meaningful formula for calculating the water resources reallocation ability of litters was proposed. Based on the formula it is calculated that favorable impacts of different litters on gravity irrigation in Ziquejie Terrace obeys the following order: spruce-bamboo mixed forest > spruce forest > bamboo forest > grass ground > chestnut forest.