Reduced use of fossil energy by removing cereal straw for bioenergy potentially threatens soil organic carbon (SOC) storage. Straw incorporation plays a key role for SOC storage in cereal-based cropping systems, but the use of cover crops (CCs) may compensate for straw removal. However, assessing the SOC sequestration potential of management changes requires field experiments with long continued treatments and frequent soil sampling. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual additions of spring barley straw (0, 4, 8 and 12 Mg ha⁻¹) and undersown ryegrass CC on SOC storage in the 0- to 20-cm layer. The effect of straw incorporation and CC on SOC was additive. At steady-state conditions, the SOC stock based on equivalent soil mass (SOC stock_FM) increased 3.9, 6.7 and 9.3 Mg C ha⁻¹ after annual incorporation of 4, 8 and 12 Mg straw ha⁻¹, respectively. The ryegrass CC increased SOC stock_FM by 3.3 Mg C ha⁻¹ and thus almost compensated for removal of 4 Mg straw ha⁻¹. An asymptotic regression model best described the temporal changes in SOC and showed that the effect of straw incorporation and ryegrass CC on SOC sequestration peaks after 10–15 years when a new equilibrium between input and output of C is reached. Clearly, reliable assessments of SOC sequestration potentials following changes in management require field experiments with frequent soil sampling until reaching steady-state conditions.

中文翻译：

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谷物秸秆掺入和黑麦草覆盖作物：土壤碳储存平衡的路径很短

通过去除谷物秸秆作为生物能源来减少化石能源的使用可能会威胁到土壤有机碳 (SOC) 的储存。秸秆掺入在谷物种植系统中 SOC 储存中起着关键作用，但覆盖作物 (CCs) 的使用可能会补偿秸秆的去除。然而，评估管理变化的 SOC 封存潜力需要长期持续处理和频繁土壤采样的现场实验。基于 1981 年在 Askov 试验站（丹麦）的沙壤土上进行的田间试验，我们检查了每年添加春大麦秸秆（0、4、8 和 12 Mg ha ^-1) 和在 0 到 20 厘米层的 SOC 存储上播种的黑麦草 CC。秸秆掺入和 CC 对 SOC 的影响是累加的。在稳态条件下，基于等效土壤质量的 SOC 储量（SOC 储量_FM ）在每年加入 4、8 和 12 Mg 秸秆 ha ^-1后分别增加了 3.9、6.7 和 9.3 Mg C ha ^-1。黑麦草 CC 使 SOC 储量_FM增加了 3.3 Mg C ha ^-1，因此几乎补偿了 4 Mg 秸秆 ha ^-1的去除. 渐近回归模型最好地描述了 SOC 的时间变化，并表明秸秆掺入和黑麦草 CC 对 SOC 固存的影响在 10-15 年后达到峰值，此时 C 的输入和输出之间达到新的平衡。显然，管理变化后对 SOC 封存潜力的可靠评估需要频繁进行土壤采样的现场实验，直到达到稳态条件。