Understanding the carbon fluxes and dynamics from a broad range of agricultural systems has the potential to improve our ability to increase carbon sequestration while maintaining crop yields. Short-term, single-location studies have limited applicability, but long-term data from a network of many locations can provide a broader understanding across gradients of climate and management choices. Here we examine eddy covariance measured carbon dioxide (CO₂) fluxes from cropland sites across the United States Department of Agriculture's Long-Term Agroecosystem Research (LTAR) network. The dataset was collected between 2001 and 2020, spanning 13 sites for a total of 182 site-years. Average seasonal patterns of net ecosystem CO₂ exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (R_eco) were determined, and subsequent regression analysis on these “flux climatologies” was used to identify relationships to mean annual temperature (MAT), mean annual precipitation (MAP), cropping systems, and management practices. At rainfed sites, carbon fluxes were better correlated with MAP (r2 ≤ 0.5) than MAT (r2 ≤ 0.22). Net carbon balance was different among cropping systems (p < 0.001), with the greatest net carbon uptake occurring in sugarcane (Saccharum spp. hybrids) and the least in soybean (Glycine max) fields. Crop type had a greater effect on carbon balance than irrigation management at a Nebraska site. Across cropping systems, grain crops often had higher GPP and were more likely to have net uptake when compared to legume crops. This multi-site analysis highlights the potential of the LTAR network to further carbon flux research using eddy covariance measurements.

了解来自广泛农业系统的碳通量和动态，有可能提高我们在保持作物产量的同时增加碳封存的能力。短期的单一地点研究的适用性有限，但来自多个地点的网络的长期数据可以提供对气候梯度和管理选择的更广泛理解。在这里，我们检查了来自美国农业部长期农业生态系统研究 (LTAR) 网络的农田地点的涡流协方差测量的二氧化碳 (CO _{2 ) 通量。}该数据集是在 2001 年至 2020 年间收集的，跨越 13 个站点，共 182 个站点年。净生态系统 CO ₂交换的平均季节模式 ( NEE)、总初级生产力 (GPP) 和生态系统呼吸 (R _eco )，然后对这些“通量气候学”进行回归分析，以确定与年平均温度 (MAT)、年平均降水量 (MAP)、种植面积的关系制度和管理实践。在雨养地区，碳通量与 MAP (r2 ≤ 0.5) 的相关性要好于 MAT (r2 ≤ 0.22)。种植系统之间的净碳平衡不同（p < 0.001），甘蔗（Saccharum spp . hybrids）的净碳吸收量最大，大豆（Glycine max) 字段。在内布拉斯加州，作物类型对碳平衡的影响比灌溉管理更大。在整个种植系统中，与豆类作物相比，谷物作物通常具有更高的 GPP 并且更有可能获得净吸收。这种多站点分析强调了 LTAR 网络在使用涡流协方差测量进一步研究碳通量方面的潜力。