Abstract:
Abstract: Drought and water shortage have posed a great threat to the ecological and agricultural development in the semi-arid loess hilly region. Local vegetation normally determines the dynamic balance between natural precipitation and crop water demand. Since a long-term negative cycle of soil moisture can lead to serious soil desiccation, water supplies have a great impact on the ecological environment and sustainable agriculture. This study aims to explore the moisture recovery of dried soil under natural moisture conditions. An underground soil column was built up to 10 m in the Mizhi test station located in the north of Shaanxi Province, China. The soil moisture and the meteorological parameters had been observed by the CS650-CR1000 soil moisture automatic monitoring system and BLJW-4 meteorological observatory from 2014 to 2019. The results show that the distribution of natural moisture in the loess area was obviously uneven at various stages in different years. The moisture was divided into three stages in one year: the deficit moisture (from last November to March this year), the increasing moisture (from April to June), and the abundant moisture (from July to October). On a multi-year scale, high-, flat- and dry-water year alternately occurred. The distribution of moisture directly dominated the infiltration in the deeply dried soil. During the 6-year observation period, there were 56 times effective moisture events with a precipitation of 1 455.20 mm, which could infiltrate to 50cm or below. Specifically, the effective rates were 16.23% and 64.68%, respectively. On the monthly and yearly scale, the moisture had an independent influence on the infiltration in one month or year. The infiltration depths fluctuated with the precipitation in terms of the quadratic function. The maximum monthly precipitation (209.60 mm) occurred in July 2016, with the maximum depth of monthly infiltration (400 cm), and the maximum yearly moisture (590.80 mm) occurred in 2016, with the maximum infiltration depth of 400cm. Nevertheless, the cumulative infiltration depths continued to increase with time, due possibly to the interaction of each other under multi-month and multi-year moisture conditions. Particularly, the cumulative depths of moisture infiltration reached 1 000 cm by December of 2018. The entire profile of 1000cm dried soil was obtained at the different levels of water recovery. The complete recovery depths of dried soil under the natural moisture conditions from 2014 to 2019 were 140, 180, 300, 600, 700, and 700 cm, respectively. Compared with the soil moisture of farmland, the complete recovery degree could be 14%, 18%, 30%, 60%, 70%, and 70%, respectively. The findings are greatly significant to explore the water recovery of deeply dried soil under natural moisture conditions, thereby formulating some reasonable measures for the hydrological cycle in semi-arid loess areas.