To reveal the mechanisms of straw mulching amounts and mulching periods on soil moisture in the black soil zone of Northeast China. Three types of straw mulching (0.4, 0.8, and 1.2 kg/m²) and two mulching periods (sowing stage and three-leaf stage) were set up as interactive experiments, and no straw mulching was used as the control (CK) to analyze the response mechanisms of soil moisture content, water consumption, and water use efficiency to straw mulching periods and mulching amounts at different depths. The results showed that straw mulching improved the moisture storage capacity compared with no straw mulching, and the straw mulching rate of 0.8 kg/m² at the three-leaf stage improved the moisture storage capacity and reduced the water consumption capacity compared with the straw mulching at the sowing stage, CK and other straw mulching treatments at the three-leaf stage; the crop yield and water use efficiency increased and then decreased with the increase of straw mulching. The increase of crop yield and water use efficiency under the straw mulching treatments at the three-leaf stage was higher than that under the same straw mulching treatments at the sowing stage. The analysis of the dual effects of straw mulching amounts and mulching periods on moisture gain and loss showed that the straw mulching amounts of 0.8 kg/m² at the three-leaf stage had the best effect on soil moisture characteristics and water use efficiency.

Paddy cultivation in the black soil region of northeast China is faced with the problems of low irrigation water use efficiency (IWUE) and low temperature stress during sowing. Therefore, the combinations of film mulching and water-saving irrigation methods were adopted to adjust the balance between water and yield under the condition of suitable soil water and heat environment, and to quantify the relationship between irrigation water and yield formation. This study investigated the mechanisms of two kinds of biodegradable film mulching combined with two water-saving irrigation on soil hydrothermal conditions in cold-region paddy fields. The results show that film mulching improved the water retention capacity of the soil at different depths, with black film exhibiting better moisture conservation than white film. Overall, controlled irrigation resulted in higher soil moisture than ridge irrigation before the heading–flowering stage, but lower values in heading–flower stage and the later stage. Film mulching also increased soil temperature across different layers, with black film showing a more warming effect in the 0–5 cm soil layer. All combinations of biodegradable film mulching and water-saving irrigation enhanced the IWUE, with the ridge irrigation combined with black film mulching showing the most significant improvement. This research provides technical references for water-efficient rice cultivation in cold regions.