Raw data : "Soil organic carbon stocks and dynamics under contrasting organic matter management practices - Results from a 65-year-old experiment in Belgium"

Long-term field experiments (LTEs) are key for evaluating the long-term effect of agricultural practices on soil organic carbon (SOC) storage. In this work, we studied the long-term effect of organic matter (OM) management practices on SOC in a 65-year LTE under arable cropping in Belgium. To evaluate SOC dynamics, a time series (1959-2021) of topsoil SOC content was analyzed for three subperiods in which N fertilization remained unchanged. Topsoil and subsoil SOC stocks were calculated by the equivalent soil mass method for one individual sampling campain in 2018. Cattle manure (CM) application led to the most significant SOC storage, increasing topsoil SOC stock and content by approximately 20% over the long term. Other individual OM management practices – pig slurry (PS) application, cereal straw incorporation and cover crops (CC) cultivation – induced smaller, non-significant SOC increases of about 5%. Nevertheless, their combined effects were cumulative, resulting in significant SOC accruals. In contrast to the topsoil, SOC stock in the subsoil was unaffected by the OM management practices. Annual humified C inputs calculated from the amount and quality of livestock manures and (cover) crops residues correlated strongly with SOC content in the topsoil (r=0.8), which underlines that the amount and quality of C inputs are key drivers of SOC storage. Changes in N fertilization over time and N fertilization adjustments among treatments significantly affected SOC dynamics. This highlights the complexity of interpreting time series of data from LTEs, for which the evolution of management practices over time may act as confounding factors.长期田间试验（LTEs）是评估农业管理措施对土壤有机碳（SOC）储量长期影响的关键研究载体。本研究以比利时一处已开展65年的耕地长期田间试验为对象，探究了有机质（OM）管理措施对SOC的长期作用效果。为解析SOC动态变化，研究分析了1959年至2021年的表土SOC含量时间序列数据，并将其划分为三个氮肥施用水平保持恒定的子时段。2018年的单次采样中，研究采用等效土壤质量法计算了表土与底土的SOC储量。 施用牛粪（CM）可实现最为显著的SOC储量提升，长期内使表土SOC储量与含量均提升约20%。其余单一有机质管理措施——猪粪沼液（PS）施用、禾本科秸秆还田以及覆盖作物（CC）种植——仅带来约5%的SOC小幅增长，且未达到统计学显著性水平。不过，这些措施的组合效应具有累积性，可实现SOC的显著积累。与表土不同，底土SOC储量未受有机质管理措施的影响。 根据畜禽粪便及（覆盖）作物残体的数量与品质计算得到的年腐殖化碳输入量，与表土SOC含量呈极强相关性（相关系数r=0.8），这表明碳输入的数量与品质是SOC储量的关键驱动因子。氮肥施用的年度变化及不同处理间的氮肥调控措施，均会显著影响SOC动态变化。这一结果凸显了解读长期田间试验时间序列数据的复杂性——管理措施随时间的演变可能成为混淆性干扰因素。