Analysis of Soil Water and Salt Redistribution during the Freeze-thaw Period in “Autumn Watering-spring Irrigation” under Local Autumn Watering Conditions

Abstract

【Objective】 The objective of this study is to investigate the water and salt movement during freeze-thaw period under partial autumn watering conditions in the Hetao Irrigation District. Specifically, the study focuses on comparing the water and salt dynamics between autumn irrigated farmland and non-autumn irrigated farmland (spring irrigated the following year). 【Method】 Field sampling observations and laboratory experiments were conducted to analyze the variations in soil temperature, soil moisture, and soil salinity during the freeze-thaw period under autumn watering and non-autumn watering conditions. 【Result】 After partial autumn irrigation, the temperature gradually decreased from the surface to the deeper layers in autumn irrigated farmland, while it decreased gradually in spring irrigated farmland. During the freezing process, the soil temperature in the 0~60 cm layer of autumn irrigated farmland dropped below 0 ℃ 30 days earlier than in spring irrigated farmland. In the melting process, the temperature in the 0~60 cm layer of autumn irrigated farmland rose above 0 ℃ 10 days later than in spring irrigated farmland. The desalination of the 0~100 cm soil layer in autumn irrigated farmland occurred mainly after autumn watering and during the freezing period, resulting in a desalting percentage of 47.38%. However, spring irrigated fields experienced salt accumulation of 35.68% and 16.87% during the freezing and melting stages, respectively. Throughout the freeze-thaw period, the net salt flux in each layer of both autumn irrigated and spring irrigated fields was negative, but it increased with soil depth. However, in spring irrigated farmland, the net salt flux initially increased and then decreased with increasing soil depth. 【Conclusion】 The water and salt migration patterns during the freeze-thaw period were influenced by the water level differences between autumn irrigated and spring irrigated fields. The time difference between the freezing and melting processes led to salt accumulation in spring irrigated fields before the next year’s spring irrigation. These findings provide valuable insights into the water and salt migration dynamics in irrigated and non-irrigated farmland, as well as the optimal development of autumn irrigation and spring irrigation practices under local autumn watering conditions.

Keywords

• local autumn watering
• spring irrigation
• freeze-thaw period
• water-salt migration