Soil C status is acritical component of greenhouse gas mitigation efforts, and supports food security through affecting crop growth and management. In much of the world, laboratory-based measures of soil C are expensive and logistically challenging, whereas map-based predictions generated at the continental scale (e.g., African Soil Information Service [AfSIS]; www.soilgrids.org) may be unreliable at the management-relevant, policy-relevant, field, and regional scales. We test whether an USD 350, open source, field portable reflectometer can provide site-specific estimates of soil C status, and also predict whether a crop will respond to fertilizer across 1,155 sites in central and southern Malawi based on an established threshold of 9.4 g C kg⁻¹ soil. When compared with soil C measured by combustion, the scanner calibrated with covariates of field-estimable texture class and slope class provides unbiased (0.42 ± 0.44 g C kg⁻¹ soil; p = .06), precise (R² = .57), and actionable (area under the receiver operating characteristic curve [AUC] = 0.88) data at the field scale, including at unmeasured locations (relative prediction error 19–23%) and at the village scale. The reflectometer outperformed predictions from the continental-scale AfSIS database, which were neither precise (R² = .044) nor actionable (AUC = 0.63) at the field scale, and underestimated soil C in the region by 2.5 ± 0.5 g C kg⁻¹ soil (p < .001). The reflectometer is an accessible tool to monitor soil C in sub-Saharan Africa to improve field-level management, and guide regional policies that support food security while combating climate change.

中文翻译：

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用于撒哈拉以南非洲可持续管理的可获取、负担得起、精细规模的土壤碳估算

土壤碳状况是温室气体减排工作的一个关键组成部分，并通过影响作物生长和管理来支持粮食安全。在世界大部分地区，基于实验室的土壤碳测量成本高昂且在逻辑上具有挑战性，而在大陆范围内生成的基于地图的预测（例如，非洲土壤信息服务 [AfSIS]；www.soilgrids.org）在管理相关、政策相关、领域和区域尺度。我们测试价值 350 美元的开源田间便携式反射计是否可以提供特定地点的土壤碳状况估计，并根据既定的 9.4 g 阈值预测一种作物是否会对马拉维中部和南部 1,155 个地点的肥料产生反应公斤^-1土壤。与通过燃烧测量的土壤 C 相比，使用现场可估计纹理等级和坡度等级的协变量校准的扫描仪提供无偏 (0.42 ± 0.44 g C kg ^-1土壤；p  = .06)、精确 ( R ²  = .57)和可操作的（接收者操作特征曲线下面积 [AUC] = 0.88）数据，包括未测量的位置（相对预测误差 19-23%）和村庄规模。反射计的表现优于大陆尺度 AfSIS 数据库的预测，后者 在现场尺度上既不精确 ( R ² = .044) 也不可操作 (AUC = 0.63)，并且将该地区的土壤 C 低估了 2.5 ± 0.5 g C kg ^{- 1}土壤 ( p < .001）。反射计是一种易于使用的工具，用于监测撒哈拉以南非洲地区的土壤碳含量，以改善田间管理，并指导支持粮食安全同时应对气候变化的区域政策。