Use of near‐ and mid‐infrared spectroscopy to distinguish carbon and nitrogen originating from char and forest‐floor material in soils

The presence of relatively inert organic materials such as char has to be considered in calibrations of soil C models or when calculating C‐turnover times in soils. Rapid and cheap spectroscopic techniques such as near‐infrared (NIRS) or mid‐infrared spectroscopy (MIRS) may be useful for the determination of the contents of char‐derived C in soils. To test the suitability of both spectroscopic techniques for this purpose, artificial mixtures of C‐free soil, char (lignite, anthracite, charcoal, or a mixture of the three coals) and forest‐floor Oa material were produced. The total C content of these mixtures (432 samples) ranged from 0.5% to 6% with a proportion of char‐derived C amounting to 0%, 20%, 40%, 50%, 60%, or 80%. All samples were scanned in the visible and near‐IR region (400–2500 nm). Cross‐validation equations for total C and N, C and N derived from char (C_char, N_char) and Oa material were developed using the whole spectrum (first and second derivative) and a modified partial least‐square regression method. Thirty‐six samples were additionally scanned in the middle‐IR and parts of the near‐IR region (7000–400 cm^–1 which is 1430–25,000 nm) in the diffuse‐reflectance mode. All properties investigated were successfully predicted by NIRS as reflected by RSC values (ratio of standard deviation of the laboratory results to standard error of cross‐validation) > 4.3 and modeling efficiencies (EF) ≥ 0.98. Near‐infrared spectroscopy was also able to differentiate between the different coals. This was probably due to structural differences as suggested by wavelength assignment. Mid‐IR spectroscopy in the diffuse‐reflectance mode was also capable to successfully predict the parameters investigated. The EF values were > 0.9 for all constituents. Our results indicated that both spectroscopic techniques applied, NIRS and MIRS, are able to predict C and N derived from different sources in soil, if closed populations are considered.     

Sorption of iron‐cyanide complexes on goethite investigated in long‐term experiments

The iron‐cyanide complexes ferrocyanide, [Fe^II(CN)₆]^4–, and ferricyanide, [Fe^III(CN)₆]^3–, are anthropogenic contaminants in soil. We investigated their sorption on goethite, α‐FeOOH, in batch experiments in a time range from 1 d to 1 yr, their desorption by phosphate and chloride as well as their surface complexes on goethite by Fourier‐transform infrared spectroscopy (FTIR). The sorption of both complexes continued over the whole time range. Percent desorption of ferricyanide by phosphate decreased, whereas that of ferrocyanide increased until it amounted to approximately 87% for both complexes. By FTIR spectroscopy inner‐sphere complexation of both complexes on the goethite surface was indicated. With both complexes, a Berlin‐Blue‐like layer (Fe₄[Fe(CN)₆]₃) was formed initially on the goethite surface which disappeared with increasing reaction time. After at least 30 d reaction time, ferricyanide was the only sorbed iron‐cyanide complex detected even when ferrocyanide was initially added. This resulted from slow oxidation of ferrocyanide, most probably by dissolved oxygen. Based on all results, we propose that ferricyanide forms monodentate inner‐sphere complexes on the goethite surface.     

Humification indices of water‐soluble fulvic acids derived from synchronous fluorescence spectra — effects of spectrometer type and concentration

The high variability of dissolved organic matter (DOM) in natural systems (concentration, composition) means rapid methods are required for its characterization so that a high number of samples can be analyzed. The objective of the present study was to quantify the effects of spectrometer type and dissolved organic carbon (DOC) concentration on the humification indices of water‐soluble fulvic acids (FAs) derived from synchronous fluorescence spectra, and thus enable the broader application of this method for DOM characterization. We used three standard FAs from the International Humic Substances Society, 24 water‐soluble FAs isolated from topsoil, groundwater and surface water in a fen area, and two different spectrometers. The wavelengths at which bands occurred were similar for all the FAs. Therefore, the differences between the spectra of the FAs studied could be described by humification indices (band ratios). The humification indices calculated correlated very well between spectrometers despite small differences in the wavelengths of bands and shoulders. The absolute values of these indices deduced from two spectrometers can only be directly compared if the spectra are corrected using a standard substance. Increasing DOC concentration resulted in a linear increase in humification indices with a sample specific slope. Therefore, we recommend using an uniformly low DOC concentration of about 10 mg C l^—1 for recording the spectra of samples with typically low DOC concentrations (aquatic samples, soil solutions). This value is a compromise between relatively low absorption to minimize inner filter effects and a sufficient signal‐to‐noise ratio.     

Use of mid‐infrared spectroscopy in the diffuse‐reflectance mode for the prediction of the composition of organic matter in soil and litter

Mid‐infrared spectroscopy (MIRS) is assumed to be superior to near‐infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid‐infrared region including part of the near‐infrared region (7000–400 cm^–1) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by ¹³C CPMAS‐NMR spectroscopy. A partial least‐square method and cross‐validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid‐infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF ≥ 0.70, 0.8 ≤ a ≤ 1.2, r ≥ 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O‐alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl–to–aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse‐reflectance mode were generally not superior to those of NIRS.     

Phosphorus‐31–nuclear magnetic–resonance spectroscopy to trace organic dung phosphorus in a temperate grassland soil

Cattle dung contributes to hot‐spot inputs of nutrients to grassland systems, but not much is known about its organic P (P_o) composition and fate in the grassland soils. We used ³¹Phosphorus (P)–Nuclear Magnetic–Resonance (NMR) spectroscopy of alkaline soil extracts to examine potentials for tracing of different functional P_o forms into a temperate grassland soil amended with dung. The proportion of monoester, DNA‐diester, and phospholipid+teichoic acid P were comparable in dung extracts, but the soil was dominated by monoester P. The temporal trends in the DNA‐diester P–to–monoester P (D_DNAM) and diester P–to–monoester P (DM) ratio of dung, native soil, and soil amended with dung were monitored in the 70 d field experiment. The D_DNAM and DM ratio in the dung‐amended soil (0–1 and 1–5 cm depth) were always intermediate between the dung and (unamended) control soil. Clearly, extracted soil P was a mixture of incorporated dung‐derived P and native soil P. The dung‐P contribution in the 0–1 cm samples peaked at 47% of the total extracted P at day 70 and at 15% after 42 d in the 1–5 cm soil depth (based on the DM ratio). The proportions of dung‐derived P and C in the soil were positively correlated with: 1) topsoil, using the D_DNAM ratio (r² = 0.975), and 2) top‐ and subsoil, using the DM ratio (r² = 0.656). We concluded that our D_DNAM and DM‐P ratios approach (obtained from solution‐³¹P NMR) did trace successfully the short‐term dynamics and fate of dung P_o in soil. It indicated that dung‐derived P_o varied as rapidly in soil as the dung‐derived C.     

Usefulness of near‐infrared spectroscopy for the prediction of chemical and biological soil properties in different long‐term experiments

The prediction accuracy of visible and near‐infrared (Vis‐NIR) spectroscopy for soil chemical and biological parameters has been variable and the reasons for this are not completely understood. Objectives were (1) to explore the predictability of a series of chemical and biological properties for three different soil populations and—based on these heterogeneous data sets—(2) to analyze possible predictive mechanisms statistically. A number of 422 samples from three arable soils in Germany (a sandy Haplic Cambisol and two silty Haplic Luvisols) of different long‐term experiments were sampled, their chemical and biological properties determined and their reflectance spectra in the Vis‐NIR region recorded after shock‐freezing followed by freeze‐drying. Cross‐validation was carried out for the entire population as well as for each population from the respective sites. For the entire population, excellent prediction accuracies were found for the contents of soil organic C (SOC) and total P. The contents of total N and microbial biomass C and pH were predicted with good accuracy. However, prediction accuracy for the other properties was less: content of total S was predicted approximately quantitatively, whereas Vis‐NIR spectroscopy could only differentiate between high and low values for the contents of microbial N, ergosterol, and the ratio of ergosterol to microbial biomass C. Contents of microbial biomass P and S, basal respiration, and qCO₂ could not be predicted. Prediction accuracies were greatest for the entire population and the Luvisol at Garte, followed by the Luvisol at Hohes Feld, whereas the accuracy for the sandy Cambisol was poor. The poor accuracy for the sandy Cambisol may have been due to only smaller correlations between the measured properties and the SOC content compared to the Luvisols or due to a general poor prediction performance for sandy soils. Another reason for the poor accuracy may have been the smaller range of contents in the sandy soil. Overall, the data indicated that the accuracy of predictions of soil properties depends largely on the population investigated. For the entire population, the usefulness of Vis‐NIR for the number of chemical and biological soil properties was evident by markedly greater correlation coefficients (measured against Vis‐NIR predicted) compared to the Pearson correlation coefficients of the measured properties against the SOC content. However, the cross‐validation results are valid only for the closed population used in this study.     

Phosphorus speciation in cultivated organic soils revealed by P K‐edge XANES spectroscopy

Cultivated organic soils make a significant contribution to phosphorus (P) leaching losses from agricultural land, despite occupying a small proportion of cultivated area. However, less is known about P mobilisation processes and the P forms present in peat soils compared with mineral soils. In this study, P forms and their distribution with depth were investigated in two cultivated Histosol profiles, using a combination of wet chemical extraction and P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy. Both profiles had elevated P content in the topsoil, amounting to around 40 mmol kg^?1, and P speciation in both profiles was strongly dominated by organic P. Topsoils were particularly rich in organic P (P‐org), with relative proportions of up to 80%. Inorganic P in the profiles was almost exclusively adsorbed to surface reactive aluminium (Al) and iron (Fe) minerals. In one of the pro‐files, small contributions of Ca‐phosphates were detected. A commonly used P saturation index (PSI) based on ammonium‐oxalate extraction indicated a low to moderate risk of P leaching from both profiles. However, the capacity of soil Al and Fe to retain P in organic soils could be reduced by high competition from organic compounds for sorption sites. This is not directly accounted for in PSI and similar indices. Accumulation of P‐org in the topsoil may be attributable by microbial peat decomposition and transformation of mineral fertiliser P by both microbiota and crops. Moreover, high carbon–phosphorus ratio in the surface peat material in both profiles suggests reduced net mineralisation of P‐org in the two soils. However, advancing microbial peat decomposition will eventually lead to complete loss of peat horizons and to mineralisation of P‐org. Hence, P‐org in both profiles represents a huge potentially mobilised P pool.     

Assessment of biogeochemical trends in soil organic matter sequestration in Mediterranean calcimorphic mountain soils (Almería, Southern Spain)

Total soil organic matter levels and humic acid formation processes in mountain calcimorphic soils from Sierra María-Los Vélez Natural Park (Almería, Southern Spain) were found to differ depending on soil use (pine and oak forests, and cleared areas either cultivated or affected by bush encroachment). Biogeochemical indicators such as the concentration of exchangeable cations, or the concentration of the different types of humic substances were neither influenced by the type of vegetation nor soil use. In fact, multidimensional scaling and multiple correlations suggest that soil carbon sequestration processes are controlled by small-scale topographical features and their impact on water holding capacity. From a qualitative viewpoint, there were two more or less defined sets of soils: one set consisted of soils with humic acids with marked aliphatic character, displayed intense 2920 cm⁻¹ infrared band, and had low optical density. The resolution-enhanced infrared spectra suggested typical lignin patterns and well-defined amide bands, which point to a selective preservation of comparatively young organic matter. This situation contrasts with that in other set of soils with low C levels (<20 g kg⁻¹) where humic acids with featureless infrared spectra showed high aromaticity and were associated with perylenequinonic chromophors of fungal origin: this is considered the consequence of overlapping biogeochemical mechanisms involving both microbial synthesis and condensation processes. The results from visible and infrared derivative spectroscopies suggest that the reliability of statistically assessing the biogeochemical performance of the different uses on the site studied in terms of the intensity of the prevailing humic acid formation mechanisms, i.e., accumulation of inherited macromolecular substances in the former set, vs. microbial synthesis including the condensation of precursors of low molecular weight substances in the latter.     

Spectroscopic characterization of mucilage (Chia seed) and polygalacturonic acid

Polygalacturonic acid (PGA) has frequently been suggested and used as a model substance for studying mucilage properties and effects in soil. While PGA has a defined chemical structure, the composition of mucilage as natural product can vary in space and time depending on the plant and soil conditions. However, it is still unclear if PGA can be used as surrogate for original mucilage when considering soil–mucilage interactions in the rhizosphere. Here the organic matter (OM) composition of PGA was compared with that of Chia seed mucilage and small‐scale spatial distribution of OM composition in mucilage droplets was analysed using Fourier transform mid infrared spectroscopy in KBr‐transmission technique (FTIR). Selected regions of dried Chia seed mucilage droplets were analysed using micro‐ Fourier transform mid infrared spectroscopy in transflection technique (micro‐FTIR). For PGA, the FTIR spectra revealed lower C–H/C=O and higher C=O/C–O–C ratios as compared to Chia seed mucilage, indicating a relatively lower potential hydrophobicity and higher sorption capacity of the OM in PGA than OM in mucilage. The micro‐FTIR spectra revealed that the potential hydrophobicity of a single freeze‐dried mucilage droplet was higher at the tip as compared to regions located above the tip. The results suggest that the use of PGA as model substance for mucilage is limited especially when trying to imitate the sorption and wettability properties of the Chia seed mucilage OM. The spatial heterogeneity in OM composition as well as shifts in maxima of C=O and O–H bands in micro FTIR spectra of the cross sectioned mucilage droplet suggest that the composition of mucilage is changing with time. These findings may help initiating future studies on the dynamics and variability of OM composition of mucilage.     

黄土的红外反射光谱与红外光声光谱特征及其差异研究

红外光谱法作为一种新的研究手段已经广泛应用于土壤分析,由其检测区域和手段的不同又可分为多种光谱类 型。本研究以第四纪黄土为例,系统地比较了近红外区和中红外区反射光谱和光声光谱的吸收特征及其差异。结果表明,中红外光谱比近红外光谱的信息更为丰富,且中红外光谱与样品中物质的特征吸收关系更加密切,从而更有利于土壤定性与定量分析。土壤的反射光谱和光声光谱表现出了明显不同的特征,在近红外区,反射光谱和光声光谱吸收明显不同,而在中红外区,反射光谱和光声光谱具有相对应的吸收,但相对吸收强度明显不同,且吸收峰的位置也发生改变,尤其在1 000 ~ 2 000 cm-1谱区,反射光谱相互干扰很强,而光声光谱的吸收特征更为明显。在黄土的分类鉴别上,反射光谱优于光声光谱。红外反射光谱和光声光谱在不同波段下具有不同的吸收灵敏度,在土壤定性与定量分析中各自都将具有其明显的优势。     

Phosphorus speciation of forest‐soil organic surface layers using P K‐edge XANES spectroscopy

The phosphorus (P) speciation of organic surface layers from two adjacent German forest soils with different degree of water‐logging (Stagnosol, Rheic Histosol) was analyzed by P K‐edge XANES and subsequent Linear Combination Fitting. In both soils, ≈ 70% of the P was inorganic phosphate and ≈ 30% organic phosphate; reduced P forms such as phosphonate were absent. The increased degree of water‐logging in the Histosol compared to the Stagnosol did not affect P speciation.     

Use of near‐infrared spectroscopy to distinguish carbon and nitrogen originating from char and forest‐floor material in soils: usefulness of a genetic algorithm

Several algorithms exist for the calibration procedures of near‐infrared spectra in soil‐scientific studies, but the potential of a genetic algorithm (GA) for spectral feature selection and interpretation has not yet been sufficiently explored. Objectives were (1) to test the usefulness of near‐infrared spectroscopy (NIRS) for a prediction of C and N from char and forest‐floor Oa material in soils using either a partial least squares (PLS) method or a GA‐PLS approach and (2) to discuss the mechanisms of GA feature selection for the examined constituents. Calibration and validation were carried out for measured reflectance spectra in the visible and near‐IR region (400–2500 nm) on an existing set of 432 artificial mixtures of C‐free soil, char (lignite, anthracite, charcoal, or a mixture of the three coals), and forest‐floor Oa material. For all constituents (total C and N, C and N from all coals and from the Oa material, C derived from mixed coal, charcoal, lignite, and anthracite), the GA‐PLS approach was superior over the full‐spectrum PLS method. The RPD values (ratio of standard deviation of the laboratory results to standard error of prediction) ranged from 2.4 to 5.1 in the validation and indicated a better category of prediction for three constituents: “approximate quantitative” instead of a “distinction between high and low” for C derived from mixed coal and “good” instead of “approximate quantitative” for C and N derived from all coals. Overall, this study indicates that the approach using GA may have a greater potential than the PLS method in NIRS.     

Use of FTIR‐PAS combined with chemometrics to quantify nutritional information in rapeseeds (Brassica napus)

Fast acquisition of nutritional information of rapeseeds is important for rapeseed breeding programs, evaluation of soil nutrient conditions and even fertilization recommendations. Fourier transform mid‐infrared photoacoustic spectroscopy (FTIR‐PAS) was employed to determine nitrogen, phosphorus and potassium content in rapeseeds. Calibration models were developed using both partial least squares (PLS) and partial least squares combined with direct orthogonal signal correction (DOSC‐PLS). According to the values of RPD (ratio of prediction to deviation), the PLS models for nitrogen and phosphorus were acceptable, while the PLS model for potassium needed to be improved. By contrast, DOSC‐PLS models obtained the better predictive accuracy with RPD values of 2.54, 2.10 and 1.94 for nitrogen, phosphorus and potassium, respectively. This work demonstrates the good performance of FTIR‐PAS for rapid and non‐destructive quantification of nutritional information in rapeseeds.     

Sorption of HOC in soils with carbonaceous contamination: Influence of organic‐matter composition

Detailed information about structure and composition of organic sorbents is required to understand their impact on sorption capacity and sorption kinetic of organic pollutants. Therefore, the chemical composition of organic material from 18 geosorbents was investigated by solid‐state ¹³C nuclear‐magnetic‐resonance (NMR) spectroscopy. Structural parameters such as aromaticity, polarity, and alkyl‐C content were related to the Freundlich sorption exponent (1/n) and the sorption coefficient . The geosorbents included three natural and four combusted coals (carbonaceous material), three Histosols, five mineral soils from Germany containing inputs of technogenic carbonaceous material, derived from industrial activities, and four non‐contaminated mineral soils from Germany. Equilibrium sorption was measured for five hydrophobic organic compounds and analyzed with the solubility‐normalized Freundlich sorption isotherm. With increasing maturation degree, the proportion of polar constituents decreases from the natural soils to the coals. In contrast to the non‐polluted mineral soils, the soils with technogenic input are characterized by high aromaticity and low polarity. A positive correlation between sorption coefficient and aromaticity was found. The Freundlich exponent (1/n) is negatively correlated with the aromaticity, denoting an increase of adsorption processes with increasing aromaticity. Likewise, the contribution of partitioning decreases. This sorption mechanism predominates only if the organic matter in the samples contains a high proportion of polar compounds.     

拉曼光谱在精细农业土壤成分快速检测中的研究进展

拉曼光谱分析技术利用分子运动对入射光产生非弹性散射的原理对分子成分进行检测,具有受水分干扰小、样本预处理小、与红外光谱信息互补等特点,在土壤成分快速分析方面展现了很大的优势。但是拉曼光谱信号弱,受荧光干扰强,为土壤拉曼信号的有效获取带来困难。为了分析拉曼光谱在土壤成分检测中的应用潜力,该研究综述了移频激发差分拉曼光谱技术、共焦显微拉曼技术以及表面增强技术等基于拉曼光谱的土壤成分检测技术,分析了土壤成分拉曼光谱检测的研究进展,并提出进一步研究建议。结果表明：1)脂肪族化合物以及芳香族化合物都具有拉曼活性,为基于拉曼光谱的土壤有机质含量的定性、定量分析提供了理论依据。为了弥补拉曼光谱对有机质整体定量预测精度的不足,采用红外-拉曼光谱融合方式补偿单独拉曼光谱数据中缺失的土壤有机质信息,可显著改善预测精度。2)利用表面增强技术可以增强土壤溶液中可溶性氮与土壤有效氮拉曼特征波峰的强度,获得了良好的定量预测效果,回归模型决定系数R²达到0.91～0.99。3)土壤中很多含磷的化合物都具有拉曼活性,拉曼光谱是识别土壤中不同磷酸盐形态的极其有效的工具,在土壤磷素含量的分析中,应用...     

红外光谱在土壤学中的应用

红外光谱技术在土壤学中已得到较广泛的应用,它能够综合地反映土壤体系的物质组成及其相互作用,为研究土壤中物质循环及其作用过程提供了新的手段。本文回顾了近年来红外光谱技术在土壤学中的应用,包括透射光谱在土壤定性分析中的应用,并重点介绍红外反射光谱与化学计量学相结合的光谱建模技术发展情况及其在土壤定量分析中的应用。同时本文探讨了基于光声效应的红外光声光谱技术,红外光声光谱非常适合用于土壤这种复杂、非透明体系的研究,能够克服传统透射和反射光谱中存在的缺陷,测定快速方便,并具有较高的灵敏度和测量精确度,具有很大的应用潜力。     

Prediction of model pools for a long‐term experiment using near‐infrared spectroscopy

Fourty‐one soil samples from the “Eternal Rye” long‐term experiment in Halle, Germany, were used to test the usefulness of near‐infrared spectroscopy (NIRS) to differentiate between C derived from C₃ and C₄ plants by using the isotopic signature (δ¹³C) and to predict the pools considered in the Rothamsted Carbon (RothC) model, i.e., decomposable plant material, resistant plant material, microbial biomass, humified organic matter, and inert organic matter. All samples were scanned in the visible‐light and near‐infrared region (400–2500 nm). Cross‐validation equations were developed using the whole spectrum (first to third derivative) and a modified partial least‐square regression method. δ¹³C values and all pools of the RothC model were successfully predicted by NIRS as reflected by RSC values (ratio between standard deviation of the laboratory results and standard error of cross‐validation) ranging from 3.2 to 3.4. Correlations analysis indicated that organic C can be excluded as basis for the successful predictions by NIRS in most cases, i.e., 11 out of 16.     

Compositional and functional features of humic acids from organic amendments and amended soils in Minnesota, USA

The use of organic amendments requires an adequate control of the chemical quality of their humic acid (HA)-like fractions and of the effects that these materials may have on the status, quality, chemistry and functions of native soil HAs. In this work, the compositional, functional and structural properties of the HA-like fractions isolated from a liquid swine manure (LSM), a municipal sewage sludge (SS), and two municipal solid waste composts (MSWCs) were evaluated in comparison to those of HAs isolated from three unamended soils and from the corresponding soils amended with LSW, SS, and MSWC at various rates in three field plot experiments conducted in Minnesota, USA. With respect to the unamended soil HAs, the HA-like fractions of the three amendments featured a greater aliphatic character, a marked presence of proteinaceous, S-containing and polysaccharides-like structures, an extended molecular heterogeneity, small organic free radical contents and a small degree of humification. The MSWC-HAs featured a larger degree of humification than LSM-HA and SS-HA. The three amendments affected in different ways and by various extents the compositional, structural and functional properties of soil HAs depending upon the nature, origin and application rate of the amendment. In general, the data obtained suggested that proteinaceous, S-containing and aliphatic structures contained in HA-like fractions of organic amendments were partially incorporated into native soil HAs.     

Droplet infiltration and organic matter composition of intact crack and biopore surfaces from clay‐illuvial horizons

The organic matter (OM) in biopore walls and aggregate coatings may be important for sorption of reactive solutes and water as well as for solute mass exchange between the soil matrix and the preferential flow (PF) domains in structured soil. Structural surfaces are coated by illuvial clay‐organic material and by OM of different origin, e.g., earthworm casts and root residues. The objectives were to verify the effect of OM on wettability and infiltration of intact structural surfaces in clay‐illuvial horizons (Bt) of Luvisols and to investigate the relevance of the mm‐scale distribution of OM composition on the water and solute transfer. Intact aggregate surfaces and biopore walls were prepared from Bt horizons of Luvisols developed from Loess and glacial till. The mm‐scale spatial distribution of OM composition was scanned using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ratio between alkyl and carboxyl functional groups in OM was used as potential wettability index (PWI) of the OM. The infiltration dynamics of water and ethanol droplets were determined measuring contact angles (CA) and water drop penetration times (WDPT). At intact surfaces of earthworm burrows and coated cracks of the Loess‐Bt, the potential wettability of the OM was significantly reduced compared to the uncoated matrix. These data corresponded to increased WDPT, indicating a mm‐scaled sub‐critical water repellency. The relation was highly linear for earthworm burrows and crack coatings from the Loess‐Bt with WDPT > 2.5 s. Other surfaces of the Loess‐Bt and most surfaces of the till‐derived Bt were not found to be repellent. At these surfaces, no relations between the potential wettability of the OM and the actual wettability of the surface were found. The results suggest that water absorption at intact surface structures, i.e., mass exchange between PF paths and soil matrix, can be locally affected by a mm‐scale OM distribution if OM is of increased content and is enriched in alkyl functional groups. For such surfaces, the relation between potential and actual wettability provides the possibility to evaluate the mm‐scale spatial distribution of wettability and sorption and mass exchange from DRIFT spectroscopic scanning.