The sustained intensification of agricultural production to meet increasing food, feed and fibre demands has aggravated soil deformation, thereby accelerating soil degradation. The conversion of some of these degraded arable lands to permanent grassland has been recommended to recover the soil functions. However, there is still a considerable gap in understanding the timeline for the effective recovery of degraded land in terms of its stability (resistance and resilience to disturbance). Moreover, the dynamics of the recovery process in ameliorative grasslands are still not fully understood. In this study, the physical, hydraulic, and mechanical properties including the coefficient of compressibility (Cn) and precompression stress were investigated in degraded arable land at three different depths (0–5, 10–15 and 20–25 cm) after 1-, 2-, 8-, 13-, 19-, and 25-years ameliorative grassland conversion. To fully understand and finalise the dynamics of the recovery process as a function of time since the amelioratory conversion, we combined the analysed data from 2 different sets of measurements (loading conditions) on samples predrained to − 60 hPa matric potential. The loading conditions were (a). static - confined compression with normal stresses applied for 4 h in steps of 1, 20, 50, 100, 200, and 400 kPa without stress relaxation on each sample, and (b). dynamic - cyclic loading at 50 kPa with 30 seconds of loading and unloading (relaxation). We included data concerning porewater pressure dynamics under the cyclic loading condition to document possible changes in elasticity. Our results showed that settlement during loading and the elastic rebound during unloading were related to the sward age and the sampled depth. Before the cyclic loading experiment, higher values of effective stress were recorded in the older swards, but the values changed after loading in response to the change in the porewater pressure. The effective stress values were less negative during loading than when unloading. At soil depth of 0–5 cm in the 25 years old sward, the rebound rate (values) and the coefficient of compressibility were higher due to changes in soil properties, particularly the soil bulk density, while at the 10–15 and 20–25 cm depths, the mean values were much closer. When the rebound rate was considered, the highest mean value occurred at 13 years after conversion. In addition, significantly higher values of pre-compression stress were observed in the 8-year-old sward under static loading, which decreased by 19 years. Higher values of pre-compression stress were mostly recorded at the lower depths under static loading. Finally, the results showed that a period between 8 and 13 years is needed to document the starting of strength regain and the recovery of the physical properties and functions, after conversion to grassland. This recovery was observed even up to deeper depths of 20–25 cm for precompression stress and for the soil compressibility/rebound in the top 5 cm

中文翻译：

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长期草原经营下退化耕地力学和韧性特性的变化


为了满足日益增长的粮食、饲料和纤维需求，农业生产的持续集约化加剧了土壤变形，从而加速了土壤退化。建议将其中一些退化的耕地转变为永久草地，以恢复土壤功能。然而，在理解退化土地的稳定性（抵抗力和对干扰的恢复力）方面的时间表方面，仍然存在相当大的差距。此外，改善草原恢复过程的动力学仍未完全了解。本研究以退化耕地为研究对象，研究了 1 年、2 年、8 年、13 年、19 年和 25 年改良草地后，3 种不同深度（0-5、10-15 和 20-25 cm）退化耕地的物理、水力和力学性能，包括压缩系数 （Cn） 和预压应力。为了充分理解和最终确定自改善转换以来恢复过程随时间变化的动态，我们结合了来自 2 组不同测量（加载条件）的分析数据，这些数据对预排水至 − 60 hPa 矩阵电位的样品。加载条件为 （a）。静态 - 以 1、20、50、100、200 和 400 kPa 的步长施加法向应力的约束压缩 4 小时，每个样品没有应力松弛，以及 （b）。动态 - 50 kPa 的循环加载，加载和卸载（松弛）30 秒。我们纳入了有关循环载荷条件下孔隙水压力动力学的数据，以记录弹性的可能变化。结果表明，加载过程中的沉降和卸载过程中的弹性回弹与洼期和采样深度有关。 在循环加载试验之前，较旧的草坪记录了较高的有效应力值，但在加载后，这些值会随着孔隙水压力的变化而变化。加载期间的有效应力值比卸载时负值小。在 25 年生草地中，在 0-5 cm 的土壤深度，由于土壤特性的变化，特别是土壤容重的变化，回弹率（值）和可压缩系数更高，而在 10-15 和 20-25 cm 深度，平均值更接近。当考虑反弹率时，最高平均值出现在转化后 13 年。此外，在静载荷下，在 8 年生草坪中观察到的预压应力值显着升高，下降了 19 年。在静载荷下，较高的预压缩应力值主要记录在较低的深度。最后，结果表明，需要 8 到 13 年的时间来记录转变为草原后力量恢复的开始以及物理特性和功能的恢复。即使在 20-25 cm 的更深深度下，也能观察到预压应力和顶部 5 cm 的土壤压缩性/回弹