The use of heavy forestry machines for clear-cutting and site preparation causes soil compaction, which can decrease forest productivity. This process becomes complicated in forests with high levels of precipitation due to the erosion and deposition of surface soil. Here, we investigated how soil compaction and slash dispersal on compacted soil affect soil nitrogen (N) mineralization in a high precipitation area with erodible volcanic soil in southern Japan. The physical and chemical properties of the soil were measured inside and outside the ruts of work roads in the presence and absence of dispersed slash in three Cryptomeria japonica plantations 9–10 months after clear-cutting and site preparation. We found that the soil N mineralization rate, particularly the soil nitrification rate, was lower in compacted soil, but the dispersal of slash after soil compaction enhanced the soil N mineralization and nitrification rates. Soil compaction also led to a low soil water permeability and high volumetric soil water content and was associated with the erosion and deposition of surface soil, with soil deposition including organic matter, being observed under dispersed slash. Additionally, the soil carbon (C) and N concentrations were lower in compacted soil but improved under dispersed slash. Principal component analysis showed that soil compaction and the soil C and N concentrations were closely related to each other on the first principal component (PC1), while the soil C/N ratio was separated from other factors on PC2. Furthermore, the scores of both PC1 and PC2 were related to soil N mineralization. These results suggest that soil compaction by forestry machines has a negative impact on soil N mineralization under high precipitation, but slash dispersal on the compacted soil is an effective approach for maintaining the soil N mineralization. The soil C/N ratio is likely related with N mineralization in the impacted soils, but the negative relationship between soil compaction and soil C and N concentrations through the movement of surface soil containing these elements should also be considered to fully understand the changes in soil N mineralization that occurs in forests under high precipitation.

中文翻译：

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高降水量下柳杉人工林压实和阔叶散布对土壤氮矿化的影响。

使用重型林业机械进行伐木和场地整备会导致土壤压实，从而降低森林生产力。由于表层土壤的侵蚀和沉积，在降水量高的森林中，此过程变得复杂。在这里，我们研究了压实土壤上的土壤压实和斜线散布如何影响日本南部易蚀火山岩高降水区的土壤氮（N）矿化。在3种柳杉散布的斜线存在与不存在的情况下，在工作道路的车辙内外测量了土壤的理化性质。砍伐和整地后9-10个月的人工林。我们发现，压实土壤中的土壤氮矿化率，特别是土壤硝化率较低，但压实后的斜线散布增加了土壤氮矿化率和硝化率。土壤压实还导致土壤水渗透率低和土壤水的体积含量高，并且与在分散的砍伐下观察到的表层土壤的侵蚀和沉积有关，包括有机物的土壤沉积。此外，压实土壤的土壤碳（C）和氮浓度较低，但在分散的砍伐下土壤碳（C）和氮的浓度有所提高。主成分分析表明，土壤压实度与土壤碳氮浓度在第一主成分（PC1）上密切相关，而PC2上的土壤碳氮比则与其他因素分开。此外，PC1和PC2的分数均与土壤氮矿化有关。这些结果表明，林业机械对土壤的压实作用对高降水量下的土壤氮矿化有负面影响，但在压实的土壤上进行斜线分散是保持土壤氮矿化的有效途径。土壤碳氮比可能与受灾土壤中的氮矿化有关，但应充分考虑土壤致密性与土壤中碳和氮浓度之间的负相关关系（通过包含这些元素的表层土壤的运动）在高降水量的森林中发生的氮矿化作用。PC1和PC2的得分均与土壤氮矿化有关。这些结果表明，林业机械对土壤的压实作用对高降水量下的土壤氮矿化有负面影响，但在压实的土壤上进行斜线分散是保持土壤氮矿化的有效途径。土壤碳氮比可能与受灾土壤中的氮矿化有关，但应充分考虑土壤致密性与土壤中碳和氮浓度之间的负相关关系（通过包含这些元素的表层土壤的运动）在高降水量的森林中发生的氮矿化作用。PC1和PC2的得分均与土壤氮矿化有关。这些结果表明，在高降水量下，林业机械对土壤的压实对土壤氮的矿化有负面影响，但在压实的土壤上进行斜线分散是保持土壤氮矿化的有效方法。土壤碳氮比可能与受灾土壤中的氮矿化有关，但应充分考虑土壤致密性与土壤中碳和氮浓度之间的负相关关系（通过包含这些元素的表层土壤的运动）在高降水量的森林中发生的氮矿化作用。但是，在压实的土壤上进行斜线扩散是保持土壤氮矿化的有效方法。土壤碳氮比可能与受灾土壤中的氮矿化有关，但应充分考虑土壤致密性与土壤中碳和氮浓度之间的负相关关系（通过包含这些元素的表层土壤的运动）在高降水量的森林中发生的氮矿化作用。但是，在致密土壤上进行斜线散布是保持土壤氮矿化的有效方法。土壤碳氮比可能与受灾土壤中的氮矿化有关，但应充分考虑土壤致密性与土壤中碳和氮浓度之间的负相关关系（通过包含这些元素的表层土壤的运动）在高降水量的森林中发生的氮矿化作用。