Aims Predictions of medium to long-term changes in soil organic carbon (SOC) stocks involve simulation models with plant carbon (C) inputs estimated from crop yields using crop harvest indices and allometric scaling involving fixed root-to-shoot ratios. The choice of allometric approach and initial distribution of SOC among model pools is crucial for model estimates. Methods We evaluated the impact of a modified allometric approach for grass leys and initial model set-up using the C-TOOL model. Four European agricultural long-term experiments were considered including three experiments with different frequency of grass leys in the crop rotation and one permanent grassland. Results The modified allometric function for ley relied on fixed below-ground C input regardless of mineral fertilizer inputs and modified pool initialization involved available site history. Including available, but insufficient, pre-experiment history to adjust the initial set-up of model SOC pools did not improve to the C-TOOL simulations. Changing the allometric approach for ley from fixed shoot-to-root ratios to fixed below-ground C input decreased the soil C input dramatically and improved the C-TOOL simulation of SOC stocks for fertilized treatments in all experiments when combined with standard model set-up. For unfertilized treatments, however, the efficiency of the standard allometric function was superior to the modified one. Conclusions Our results challenge the prevalent use of allometric approaches based on fixed root-to-shoot in SOC simulation models. The potential of modifying the initial distribution of SOC among model pools by accounting for historic land use remains in the dark.

中文翻译：

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访问欧洲温带农业土壤碳储量模型模拟的阴暗面：异速生长函数和模型初始化

目标 对土壤有机碳 (SOC) 库中长期变化的预测涉及模拟模型，其中植物碳 (C) 输入使用作物收获指数和涉及固定根茎比的异速生长比例从作物产量估计。异速生长方法的选择和 SOC 在模型库中的初始分布对于模型估计至关重要。方法 我们使用 C-TOOL 模型评估了改良异速生长方法对禾本科植物和初始模型设置的影响。考虑了四个欧洲农业长期试验，包括三个在轮作中不同频率的草地试验和一个永久性草地。结果 改良的 ley 异速生长函数依赖于固定的地下 C 输入，而不管矿物肥料输入和修改后的池初始化涉及可用的站点历史。包括可用但不足的预实验历史来调整模型 SOC 池的初始设置并没有改进 C-TOOL 模拟。将莱伊的异速生长方法从固定的芽根比改为固定的地下 C 输入显着降低了土壤 C 输入，并在与标准模型集相结合时改进了所有实验中施肥处理的 SOC 储量的 C-TOOL 模拟 -向上。然而，对于未受精处理，标准异速生长函数的效率优于修改后的函数。结论 我们的结果挑战了基于 SOC 模拟模型中固定根到芽的异速生长方法的普遍使用。通过考虑历史土地利用来修改模型池中 SOC 初始分布的潜力仍然未知。