Low soil fertility is challenging the sustainable production of yam and other staple crops in the yam belt of West Africa. Quantitative soil measures are needed to assess soil fertility decline and to improve crop nutrient supply in the region. We developed and tested a mid-infrared (mid-IR) soil spectral library to enable timely and cost-efficient assessments of soil properties. Our collection included 80 soil samples from four landscapes (10 km × 10 km) and 20 fields per landscape across a gradient from humid forest to savannah and 14 additional samples from one landscape that had been sampled within the Land Health Degradation Framework. We derived partial least squares regression models to spectrally estimate soil properties. The models produced accurate cross-validated estimates of total carbon, total nitrogen, total sulfur, total iron, total aluminum, total potassium, total calcium, exchangeable calcium, effective cation exchange capacity, and diethylenetriaminepentaacetic acid (DTPA)-extractable iron and clay content (R²>0.75). The estimates of total zinc, pH, exchangeable magnesium, bioavailable copper, and manganese were less predictable (R²>0.50). Our results confirm that mid-IR spectroscopy is a reliable and quick method to assess the regional-level variation of most soil properties, especially the ones closely associated with soil organic matter. Although the relatively small mid-IR library shows satisfactory performance, we expect that frequent but small model updates will be needed to adapt the library to the variation of soil quality within individual fields in the regions and their temporal fluctuations.

中文翻译：

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用中红外土壤光谱法估计西非山药生产景观的土壤特性

低土壤肥力正在挑战西非山药带的山药和其他主要作物的可持续生产。需要采取定量土壤措施来评估土壤肥力下降并改善该地区的作物养分供应。我们开发并测试了一个中红外 (mid-IR) 土壤光谱库，以实现对土壤特性的及时且具有成本效益的评估。我们的收藏包括来自四个景观（10 公里 × 10 公里）和每个景观 20 个田地，跨越从潮湿森林到稀树草原的梯度，以及来自在土地健康退化框架内采样的一个景观的 14 个额外样本。我们推导出偏最小二乘回归模型来光谱估计土壤特性。这些模型对总碳、总氮、总硫、总铁、总铝、总钾、总钙、可交换钙、有效阳离子交换容量和二亚乙基三胺五乙酸 (DTPA) 可提取的铁和粘土含量进行了准确的交叉验证估计( R ² >0.75 )。总锌、pH、可交换镁、生物可利用铜和锰的估计值不太可预测（R ² >0.50）。我们的结果证实，中红外光谱是评估大多数土壤特性的区域级变化的可靠且快速的方法，尤其是与土壤有机质密切相关的特性。尽管相对较小的中红外库表现出令人满意的性能，但我们预计需要频繁但较小的模型更新以使库适应该地区各个田地内土壤质量的变化及其时间波动。