Soil compaction caused by the use of farm machinery is a widespread issue. Freeze–thaw cycles can improve the soil structure after compaction; however, the effect decreases as soil depth increases. Herein, we applied freeze–thaw cycle treatments to re-moulded compacted sandy loam soil (bulk density of 1.6 g/cm³) in two water content states (80 % and 30 % field capacities). Artificial perforation was performed to create long, straight pores in soil, which ensured that the soil mass was largely intact and unbroken, leaving the freeze–thaw cycles to complete the structural remediation and monitoring soil structure recovery. We measured the soil temperature, heat flux and thermal properties to explore the mechanisms of soil temperature regulation using artificial pores during freeze–thaw cycles. The pore and aggregate structure parameters before and after the freeze–thaw cycle treatment were measured. Under the freeze–thaw cycle treatment, the temperature in the bottom layer of compacted soil with artificial pores rapidly dropped below 0°C during the third and second cycles under high- and low-water-content conditions, respectively, whereas the temperature of soil without artificial pores decreased during the seventh and fourth cycles at the same water content states. Results indicated that the heat flux during the freezing phase was larger in the soil with artificial pores. However, no significant differences were observed in the thermal parameters, including thermal conductivity, volumetric heat capacity and thermal diffusivity, of soils with and without artificial pores at each water content state. The air-filled porosity, aggregate mean weight diameter and structure coefficient of the surface and bottom layers of the compacted soil columns were generally better in soil with artificial pores than in soil without artificial pores after repeated freeze–thaw cycles. This indicates that the artificial pores facilitated the restoration of compacted soil in the bottom layer during freeze–thaw cycles owing to the rapid drop in soil temperature. We deduced that the artificial long, straight pores in compacted soil created additional soil heat exchange areas in the heat transfer process to increase the rate of heat transfer, thus increasing soil heat exchange and causing the soil temperature of the bottom layer to drop rapidly during repeat freezing and thawing. However, further studies are required to investigate the remediation of artificial pores on compacted soils in fields and the optimal process for creating artificial pores in agricultural settings.

中文翻译：

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在冻融条件下使用人工孔隙修复压实土壤


使用农业机械引起的土壤压实是一个普遍存在的问题。冻融循环可以改善压实后的土壤结构;然而，这种影响会随着土壤深度的增加而减弱。在此，我们将冻融循环处理应用于两种含水状态（80% 和 30% 田间容量）的再成型压实沙壤土（堆积密度为 1.6 g/cm³）。进行人工射孔，在土壤中形成长而直的孔隙，确保土壤块基本完整和完整，留下冻融循环来完成结构修复和监测土壤结构恢复。我们测量了土壤温度、热通量和热特性，以探索冻融循环过程中利用人工孔隙调节土壤温度的机制。测量冻融循环处理前后的孔隙和聚集体结构参数。冻融循环处理下，在高含水率和低含水率条件下，第3次和第2次循环中人工孔隙压实土底层温度迅速降至0°C以下，而在相同含水状态下，无人工孔隙的土体温度在第7次和第4次循环中下降。结果表明：人工孔隙土壤中冻结期的热通量较大;然而，在每种含水状态下，有人工孔隙和无人工孔隙的土壤的热参数（包括热导率、体积热容和热扩散率）没有观察到显著差异。 经过反复冻融循环后，有人工孔隙的土壤、骨料平均重量直径和压实土柱表层和底层的结构系数普遍优于无人工孔隙的土壤。这表明，由于土壤温度的快速下降，人工孔隙在冻融循环期间促进了底层压实土壤的恢复。我们推断，压实土中的人工长而直的孔隙在传热过程中产生了额外的土壤换热区域，从而提高了传热速率，从而增加了土壤换热，导致表层土壤温度在重复冻融过程中迅速下降。然而，需要进一步的研究来调查田间压实土壤上人工孔隙的修复以及在农业环境中创建人工孔隙的最佳过程。