Data from: Soil carbon maintained by perennial grasslands over 30 years but lost in field crop systems in a temperate Mollisol

To mitigate climate change, some seek to store carbon from the atmosphere in agricultural soils. However, our understanding about how agriculture affects soil organic carbon is muddied by studies (1) lacking longitudinal data, (2) ignoring bulk density changes, or (3) sampling only surface soils. To better understand soil organic carbon trends, here we measured changes over 30 years in density-corrected, full-soil-depth (90 cm) soil organic carbon stocks under 6 cropping systems and a restored prairie in a Mollisol of southern Wisconsin, USA. Cash-grain systems and alfalfa-based systems lost soil organic carbon. Prairie and rotationally-grazed pasture maintained soil organic carbon. Average soil organic carbon losses for cash-grain and alfalfa-based systems were −0.82 (±0.12) and −0.64 (±0.17) Mg C ha-1 yr-1, respectively. Sensitivity analysis showed that incomplete methodologies overestimated soil organic carbon improvements. Our findings using more comprehensive methods demonstrate the inadequacy of row-crop systems and the need for well-managed grasslands to protect soil organic carbon in productive agricultural soils of the Upper Midwest USA.

为减缓气候变化，部分研究尝试将大气中的碳封存于农业土壤之中。然而，现有三类研究的不足使得我们对农业如何影响土壤有机碳（soil organic carbon）的认知仍存在混淆：一是缺乏纵向数据（longitudinal data），二是忽略土壤容重（bulk density）变化，三是仅采集表层土壤样本。为更清晰地厘清土壤有机碳变化趋势，本研究针对美国威斯康星州南部的软土（Mollisol），对6种种植制度（cropping systems）与1块恢复草原（restored prairie）下经容重校正的全土层（90 cm）土壤有机碳储量进行了长达30年的监测。结果显示：经济谷物种植体系与苜蓿基种植体系（alfalfa-based systems）出现了土壤有机碳流失，而恢复草原与轮牧牧场（rotationally-grazed pasture）则维持了土壤有机碳储量。经济谷物种植体系与苜蓿基种植体系的土壤有机碳平均年流失率分别为-0.82（±0.12）与-0.64（±0.17）Mg C ha⁻¹ yr⁻¹。敏感性分析（sensitivity analysis）结果显示，采用不完整研究方法的研究往往会高估土壤有机碳的提升幅度。本研究采用更为全面的研究方法所得出的结论表明：在美国中西部北部（Upper Midwest USA）的高产农业土壤中，条播种植体系（row-crop systems）存在明显不足，亟需通过科学管理的草原来保护土壤有机碳储量。