Reeves James B, Francis Barry A, Hamilton Stephen K
Animal Manure and By-Products Laboratory, Building 306, Room 101, BARC East, Beltsville, MD 20705, USA.
Appl Spectrosc. 2005 Jan;59(1):39-46. doi: 10.1366/0003702052940431.
Studies on the occurrence and effects of specular reflection in midinfrared spectra of soils have shown that distortions due to specular reflection occur for both organic (humic acid) and non-organic fractions (carbonates, silica, ashed fraction of soil). The results explain why the spectra of CaCO(3) in limed soils do not match published spectra and offer an explanation as to why the presence of inorganic C interferes with the development of calibrations for organic C. These results may also have implications for the use of mid-infrared spectra for quantitative and qualitative analysis of soils. For example, libraries of spectra collected by means other than diffuse reflectance would be largely useless for comparing mineral spectra to soil spectra. To obtain the best results with forages and grains, it is necessary to develop separate calibrations for different products, but this has not seemed to be a problem for diverse sets of soil samples with C contents of 0 to 5%. Mid-infrared calibrations have also appeared to be more robust than the corresponding near-infrared calibrations in that fewer outliers are found. However, the results discussed here indicate that at least for some soil types (e. g., large differences in mineralogy or C contents), separate calibrations may be necessary.
对土壤中红外光谱镜面反射的发生及影响的研究表明，镜面反射导致的畸变在有机（腐殖酸）和无机成分（碳酸盐、二氧化硅、土壤灰分）中均会出现。这些结果解释了为什么石灰性土壤中碳酸钙的光谱与已发表的光谱不匹配，也解释了为什么无机碳的存在会干扰有机碳校准的建立。这些结果可能还对利用中红外光谱进行土壤定量和定性分析有影响。例如，通过漫反射以外的其他方式收集的光谱库，在将矿物光谱与土壤光谱进行比较时基本上是无用的。为了在草料和谷物上获得最佳结果，有必要针对不同产品建立单独的校准，但对于碳含量为0%至5%的各种土壤样品来说，这似乎不是一个问题。中红外校准似乎也比相应的近红外校准更稳健，因为发现的异常值较少。然而，这里讨论的结果表明，至少对于某些土壤类型（例如，矿物学或碳含量差异很大），可能需要单独的校准。
