Dynamics of Soil Temperature Under Different Methods of Straw Restoration in Black Soil During Seasonal Freeze-Thaw Period

[Objective] To investigate the effects of different straw returning methods on the temperature of black soil during seasonal freeze-thaw period. [Methods] By monitoring the field temperature, the soybean field was selected as the research object, and two types of returning methods were set, namely, straw mulching (FG) and straw mixing(FH). The amount of returned straw was 30% (59 670 kg/hm2), 60% (119 340 kg/hm2) and 90% (179 010 kg/hm2), respectively, and the bare land was designated as the control treatment (CK) in a total of seven treatments. Four soil depths of 5, 10, 20 and 30 cm below the surface along the vertical profile of soil were set to analyze the characteristics of soil temperature changes during the freezing and thawing period under different straw return methods and amounts. [Results] (1) Straw returning to the field resulted in the soil entering various freeze-thaw stages at a time lagging behind that of the bare land, and effectively raised the range of the minimum soil temperature and lowered the maximum temperature, of which both the maximum temperature raising and lowering occurred in the FG90 treatment, which were 3.0~6.1 ℃ and 1.5~5.2 ℃, respectively. (2) Straw returning weakened the soil temperature variability and correlation with air temperature. The maximum coefficient of variation and coefficient of variation and correlation occurred in the bare soil layer of 5 cm, which were 6.54 and 0.82, respectively. The minimum occurred in the 30 cm soil layer of the FG90 treatment, with values of 0.82 and 0.26, respectively. The relationship between soil temperature variability was CK>FG30>FH30>FH60>FG60> FH90>FG90, and the relationship between soil temperature and air temperature was CK>FH30>FG30>FH60>FH90>FG60>FG90>FG90. (3) The freezing and thawing rates of bare land were the highest and the freezing-thawing periods were the shortest, with a freezing rate of 0.19 ℃/h and thawing rate of 0.60 ℃/h. The minimum freezing rate occurred in FH90 treatment (0.04 ℃/h) and the minimum thawing rate occurred in FG90 treatment (0.05 ℃/h). (4) With the increase of soil depth, the soil freezing stage and thawing stage gradually increased, but the freezing duration gradually decreased. The effect of delaying freeze-thawing was most obvious in the FG90 treatment, with the freezing stage and thawing stage of 8 and 10 days, respectively. [Conclusion] The results of the research quantitatively described the temperature characteristics of black soil under different straw return measures during freezing and thawing periods, and clarified the differences in soil temperature effects between different straw return measures, which is of great significance in guiding the rational use of straw resources and conservation tillage in black soil areas.