Sequestering organic carbon (C) in soil can help to combat land degradation, improve food security, and mitigate greenhouse gas emissions and climate change. But we need reliable, cost-efficient methods to assess, monitor, and verify the change. Here, we compared two methods for the direct measurement of soil organic C stocks and for monitoring the change. Our aims were to quantify the soil organic C stock in two carbon estimation areas, under cropping and grazing, using composite sampling with two designs and proximal sensing. We compared the two schemes in terms of the (a) accuracy of the estimated C stocks, the total cost, and the cost-efficiency, calculated as the ratio of the accuracy of the estimate and the total cost, and (b) uncertainty of the estimated standard error of the estimated C stocks. We found that compositing was cheaper but more inaccurate than sensing. Sensing was 1.2 to 2.1 times more cost-efficient than compositing. We also found that the uncertainty of the estimated standard errors from compositing was large and unreliable, which can hinder the quantification of a minimum detectable difference in organic C stocks. We show that the sensor-derived spatially explicit data can also be used to map the C stocks, which can help to optimise the sampling design in subsequent monitoring rounds. Our findings have important implications for the development of C measurement and monitoring methodologies. Visible–near infrared and gamma attenuation sensing can accurately, cost-efficiently, and reliably monitor and verify changes in soil C stocks.

中文翻译：

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两种测量土壤有机碳库和监测其变化的方法的成本效益和可靠性

封存土壤中的有机碳 (C) 有助于对抗土地退化、改善粮食安全以及减缓温室气体排放和气候变化。但我们需要可靠、经济高效的方法来评估、监控和验证变化。在这里，我们比较了两种直接测量土壤有机碳库和监测变化的方法。我们的目标是使用具有两种设计和近端传感的复合采样来量化种植和放牧下两个碳估算区域的土壤有机碳库。我们在 (a) 估计 C 库存的准确性、总成本和成本效率方面比较了两种方案，计算为估计的准确性与总成本的比率，以及 (b) 不确定性估计 C 库的估计标准误差。我们发现合成比传感更便宜但更不准确。传感的成本效益是合成的 1.2 到 2.1 倍。我们还发现，合成的估计标准误差的不确定性很大且不可靠，这会阻碍对有机 C 库中最小可检测差异的量化。我们表明，传感器派生的空间显性数据也可用于绘制 C 库，这有助于优化后续监测轮次中的采样设计。我们的发现对 C 测量和监测方法的发展具有重要意义。可见近红外和伽马衰减传感可以准确、经济、可靠地监测和验证土壤碳储量的变化。我们还发现，合成的估计标准误差的不确定性很大且不可靠，这会阻碍对有机 C 库中最小可检测差异的量化。我们表明，传感器派生的空间显性数据也可用于绘制 C 库，这有助于优化后续监测轮次中的采样设计。我们的发现对 C 测量和监测方法的发展具有重要意义。可见近红外和伽马衰减传感可以准确、经济、可靠地监测和验证土壤碳储量的变化。我们还发现，合成的估计标准误差的不确定性很大且不可靠，这会阻碍对有机 C 库中最小可检测差异的量化。我们表明，传感器派生的空间显性数据也可用于绘制 C 库，这有助于优化后续监测轮次中的采样设计。我们的发现对 C 测量和监测方法的发展具有重要意义。可见近红外和伽马衰减传感可以准确、经济、可靠地监测和验证土壤碳储量的变化。我们表明，传感器衍生的空间显性数据也可用于绘制 C 库，这有助于优化后续监测轮次中的采样设计。我们的发现对 C 测量和监测方法的发展具有重要意义。可见近红外和伽马衰减传感可以准确、经济、可靠地监测和验证土壤碳储量的变化。我们表明，传感器派生的空间显性数据也可用于绘制 C 库，这有助于优化后续监测轮次中的采样设计。我们的发现对 C 测量和监测方法的发展具有重要意义。可见近红外和伽马衰减传感可以准确、经济、可靠地监测和验证土壤碳储量的变化。