Intensively managed grasslands have been found to be either carbon (C) sources or sinks depending on management and climate. This study reports the net ecosystem production (NEP) and latent heat fluxes () from a managed forage field at a dairy farm in Agassiz, British Columbia, Canada. The forage crop (ryegrass and tall fescue) was harvested up to 6 times a year. The field received multiple applications of dairy manure slurry and was also fertilized with inorganic nitrogen. Eddy-covariance measurements of NEP were combined with C imports (manure additions) and exports (harvested biomass) to determine the net ecosystem C balance (NECB), and values of gross primary production (GPP) and were used to determine water use efficiency (WUE). In terms of environmental controls on NEP, variability of daytime NEP was well described by fitting measured incoming photosynthetically active radiation with a rectangular hyperbolic light-response curve, but variability in nighttime NEP was less effectively described by soil temperature and soil moisture. After accounting for C imports and exports, the NECB of the field was -315 ± 141 and -51 ± 148 g C m y (± indicates the uncertainty range) during the 2020 and 2021 study years, respectively, indicating C was lost from the field and was strongly influenced by C imports and exports relative to NEP. Higher than normal soil moisture and precipitation as well as higher than normal air temperature were both found to suppress GPP and ecosystem respiration (), but annual NEP was more impacted by soil moisture in the first year (2020) due to its effect of lowering GPP compared to high air temperature (including the 2021 Pacific Northwest heat dome) and low soil moisture in the second year due to their greater impact on relative to GPP. Crop harvests were found to substantially reduce both GPP and WUE which suggests that the intensity of management in terms of harvest frequency could be modified to improve long-term C sequestration.

中文翻译：

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加拿大不列颠哥伦比亚省弗雷泽河谷下游集约化管理的饲料作物的碳平衡和水分利用效率


人们发现，集约化管理的草原要么是碳（C）源，要么是碳汇，具体取决于管理和气候。本研究报告了加拿大不列颠哥伦比亚省阿加西一家奶牛场管理牧草场的净生态系统产量 (NEP) 和潜热通量 ()。饲料作物（黑麦草和高羊茅）每年收获多达 6 次。该田多次施用奶牛粪浆，并施用无机氮肥。 NEP 的涡度协方差测量与碳输入（粪便添加）和输出（收获的生物量）相结合，以确定净生态系统碳平衡（NECB）和总初级生产值（GPP），并用于确定水利用效率（水分利用效率）。在NEP的环境控制方面，通过将测量的入射光合有效辐射与矩形双曲光响应曲线拟合可以很好地描述白天NEP的变化，但土壤温度和土壤湿度不能有效地描述夜间NEP的变化。考虑C进口和出口后，2020年和2021年研究年该油田的NECB分别为-315±141和-51±148g C my（±表示不确定性范围），表明C从油田丢失并受到相对于 NEP 的 C 进出口的强烈影响。研究发现，高于正常的土壤湿度和降水量以及高于正常的气温都会抑制 GPP 和生态系统呼吸（），但年度 NEP 在第一年（2020 年）受土壤湿度的影响更大，因为它具有降低 GPP 的作用与第二年的高气温（包括2021年太平洋西北热穹）和低土壤湿度相比，由于它们相对于GPP的影响更大。 研究发现，作物收获会大幅降低 GPP 和 WUE，这表明可以调整收获频率方面的管理强度，以改善长期碳固存。