Several studies across different agroecosystems worldwide have compared the effects of single soil tillage events to no-till on soil carbon (C) stocks. Yet, there is still significant uncertainty about how the frequency of ‘tillage + reseeding’ (e.g. number of reseeding events) might affect soil C stocks in agricultural grasslands in the long term. Here, we addressed this knowledge gap by sampling for the first time 500 grassland fields in Northern Ireland, UK, based on their management history including the number of tillage and reseeding events occurred in the previous 50 years. We show that soil C and N stocks within 0–30-cm depth were not significantly affected by the frequency of ‘tillage + reseeding’ events. We found, however, that soil C (%) and N (%) concentrations significantly decreased while soil bulk density increased with the frequency of soil till + grassland reseeding. Because soil C stocks are calculated by multiplying C (%) with bulk density, the opposite response of these two key factors has possibly contributed to ‘homogenise’ the soil C stock product partly explaining the lack of a significant relationship between soil C stocks and the frequency of soil till + reseeding events. Our evidence is that the most important variable affecting soil C (%) concentration was bulk density and thus soil compaction. We also show that grasslands mainly managed for grazing are significantly less tilled and reseeded and have soils with lower bulk density and higher C (%) than grasslands managed for silage production. Our findings suggest that while increases in the frequency of tillage and reseeding can negatively affect soil C (%), the soil C storage potential of agricultural grasslands can be more affected by increases in soil compaction associated with greater machinery traffic.

全球不同农业生态系统的几项研究比较了单一土壤耕作事件与免耕对土壤碳 (C) 储量的影响。然而，“耕作+重新播种”的频率（例如重新播种事件的数量）如何长期影响农业草地的土壤碳库仍然存在很大的不确定性。在这里，我们根据管理历史（包括过去 50 年发生的耕作和重新播种事件的数量）对英国北爱尔兰的 500 个草地进行了首次抽样，从而解决了这一知识差距。我们表明，0-30 厘米深度内的土壤碳和氮储量不受“耕作+重新播种”事件频率的显着影响。然而，我们发现，土壤 C (%) 和 N (%) 浓度显着下降，而土壤容重随着土壤耕作频率的增加而增加 + 草地重播。因为土壤碳库是通过将碳 (%) 乘以容重来计算的，这两个关键因素的相反响应可能导致土壤碳库产品“均质化”，部分解释了土壤碳库与土壤碳库之间缺乏显着关系的原因。土壤直到 + 重新播种事件的频率。我们的证据是影响土壤 C (%) 浓度的最重要变量是容重，因此是土壤压实度。我们还表明，与青贮饲料生产管理的草原相比，主要用于放牧的草原明显减少耕作和重新播种，土壤的容重较低，C (%) 较高。