Designed experiments for optimizing infrared spectroscopic characterizations and quantifications of soil organic matter at scales of increasing complexity: importance of band shifts, spectral variable selection and subtraction approaches

设计实验，以在复杂性不断增加的范围内优化土壤有机质的红外光谱表征和定量：带移、光谱变量选择和减法方法的重要性

• 批准号: 501354812
• 负责人: Dr. Ruth Ellerbrock
• 金额: --
• 依托单位: Arbeitsgruppe Hydropedologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/501354812?language=en
• 关键词: Designed; experiments; optimizing; infrared; spectroscopic

The accuracy of visual and near infrared (Vis/NIR) and mid-infrared (MIR) spectroscopy for soil organic matter (SOM) characterization and quantification has been very variable in a large number of observational studies and there is insufficient knowledge on the underlying reasons for this variation in performance. The reasons are mainly related to IR-active properties of SOM and SOM fractions being affected by interactions of SOM with (mineral-bound) ions that result in shifts of bands in the Vis/NIR and MIR spectra relative to those without cations, minerals and soils. This proposal aims by means of designed experiments (i) to improve the mechanistic understanding of the interaction between organic matter (OM) and cations using Vis/NIR, MIR and micro-MIR; (ii) to subsequently develop an adjustment procedure to quantify effects of cations on shifts and intensities of OM bands; and (iii) to finally optimize linear and non-linear chemometric regression approaches for the prediction of contents of bulk soil organic carbon (SOC) and SOC fractions using the adjustment procedure and optimized spectral variable selections. Salts, minerals, and soils will be added to predefined organic components to obtain different OM-cation associations. The complexity of OM in the experiments will increase from low molecular weight organic substances to commercial humic acid, pre-incubated wheat straw and forest floor Oa material. The Vis/NIR and MIR spectra (including micro-MIR) of the mixtures will be compared with those of the OM to advance the mechanistic understanding of the relations between OM-cation interactions and band shifts. The adjustment procedure, which quantifies the effects of cations on band shifts and intensities, will be based on the Lambert-Beer law and will use the data of the OM-cation experiments to calculate wavenumber-dependent weighting factors that reflect the cation effects on the band intensities. The weighting coefficients will be used to recalculate the band intensities of the OM components. The accuracy of re-calculated OM spectra will be checked by comparing them with the spectra of the original OM and in case of native OM by a spectral subtraction procedure after chemical oxidation. Linear and non-linear chemometric regression approaches for the prediction of contents of bulk SOC and SOC fractions in soils at field and regional scales will be subsequently optimized. For the optimizations, the usefulness of band-shift corrections and improved chemometric regressions that consider advanced spectral variable selection approaches and cation-/mineral-related information will be explored. Overall, the spectral data from experiments designed at scales of increasing complexity are expected to advance the understanding of effects of OM-cation interactions on band shifts which can then be applied for improving the signal to noise ratios and optimizing linear and non-linear chemometric regression approaches.

在大量的观测研究中，可见光和近红外（维斯/NIR）和中红外（MIR）光谱用于土壤有机质（SOM）表征和定量的准确性变化很大，并且对这种性能变化的根本原因缺乏足够的了解。其原因主要与有机质和有机质组分的红外活性受到有机质与（矿物结合）离子的相互作用的影响，从而导致维斯/NIR和MIR光谱中的谱带相对于不含阳离子、矿物和土壤的谱带发生位移有关。该建议旨在通过设计实验（i）利用维斯/NIR、MIR和micro-MIR提高对有机物（OM）和阳离子之间相互作用的机理理解;（ii）随后开发一种调整程序以量化阳离子对OM谱带位移和强度的影响;优化线性和非线性化学计量学回归方法预测土壤有机碳含量和SOC分数使用调整程序和优化的光谱变量选择。盐，矿物质和土壤将被添加到预定义的有机组分，以获得不同的OM-阳离子协会。实验中有机质的复杂性将从低分子量有机物增加到商品腐殖酸、预培养的小麦秸秆和森林地面Oa材料。混合物的维斯/NIR和MIR光谱（包括微MIR）将与OM的光谱进行比较，以推进OM-阳离子相互作用和带移之间关系的机械理解。调整程序，量化的影响，阳离子的带位移和强度，将根据朗伯-比尔定律，并将使用OM-阳离子实验的数据来计算波数依赖的加权因子，反映阳离子的影响带强度。加权系数将用于重新计算OM组分的谱带强度。通过将重新计算的OM光谱与原始OM光谱进行比较，检查重新计算的OM光谱的准确性，如果是天然OM，则通过化学氧化后的光谱相减程序进行检查。线性和非线性化学计量学回归方法的预测散装SOC和SOC组分在田间和区域尺度的土壤中的含量将随后优化。对于优化，带移校正和改进的化学计量学回归，考虑先进的光谱变量选择方法和阳离子/矿物相关的信息的有用性将被探索。总的来说，从实验设计的光谱数据的复杂性不断增加的规模，预计将推进的OM-阳离子相互作用的带移，然后可以应用于提高信噪比和优化线性和非线性化学计量学回归方法的影响的理解。