Bioavailability of N released from N-rich pyrogenic organic matter: An incubation study

In Mediterranean ecosystems, natural wildfires and prescribed burning play an important role. In order to obtain a better understanding of the impact of charcoal on the nitrogen (N) cycling in soil, ¹⁵N-enriched pyrogenic organic material (PyOM) obtained from “Lolium perenne” charred for 4 min at 350 °C was mixed with a typical Mediterranean agricultural soil and incubated for 72 days under controlled conditions. The main objectives were to analyze the availability of N from this material and to obtain more insight into the recalcitrance of PyOM in soils. Addition of artificially produced ¹⁵N-PyOM increased the biomass production and N retention. After 72 days of incubation time, 10% of the ¹⁵N added to the soil (¹⁵N_add) was incorporated into new grass biomass. Solid-state ¹⁵N NMR spectroscopy revealed that at least some of this N derived from the degradation of pyrrole-type structures. Increase of the amide-N intensity in the solid-state ¹⁵N NMR spectrum of the incubated soils indicated further that some ¹⁵N from the PyOM was also incorporated into new microbial biomass. Our results confirmed a relatively low recalcitrance of N-rich PyOM. Since during its degradation, N is only slowly transferred into a plant-available form, it may contribute to the observed improvement of soil fertility by avoiding fast N losses due to leaching and volatilization as a slow N-release fertilizer.     

Bioavailability of N released from N-rich pyrogenic organic matter: An incubation study

In Mediterranean ecosystems, natural wildfires and prescribed burning play an important role. In order to obtain a better understanding of the impact of charcoal on the nitrogen (N) cycling in soil, ¹⁵N-enriched pyrogenic organic material (PyOM) obtained from “Lolium perenne” charred for 4 min at 350 °C was mixed with a typical Mediterranean agricultural soil and incubated for 72 days under controlled conditions. The main objectives were to analyze the availability of N from this material and to obtain more insight into the recalcitrance of PyOM in soils. Addition of artificially produced ¹⁵N-PyOM increased the biomass production and N retention. After 72 days of incubation time, 10% of the ¹⁵N added to the soil (¹⁵N_add) was incorporated into new grass biomass. Solid-state ¹⁵N NMR spectroscopy revealed that at least some of this N derived from the degradation of pyrrole-type structures. Increase of the amide-N intensity in the solid-state ¹⁵N NMR spectrum of the incubated soils indicated further that some ¹⁵N from the PyOM was also incorporated into new microbial biomass. Our results confirmed a relatively low recalcitrance of N-rich PyOM. Since during its degradation, N is only slowly transferred into a plant-available form, it may contribute to the observed improvement of soil fertility by avoiding fast N losses due to leaching and volatilization as a slow N-release fertilizer.     

Structural and chemical changes in pyrogenic organic matter aged in a boreal forest soil

biochar;charcoal;chronosequence;porosity;prescribed burning;soil amendment;X-ray microtomography     

运用岩石热解产生的S3和S4信号进行土壤有机质特征研究

Variations in the abundance of soil organic matter（SOM） constituents with different stability have a major impact on important environmental processes, e.g., carbon dioxide（CO2） fluxes between the soil and the atmosphere. Recently, besides the bulk Rock-Eval（RE） data, the mathematical deconvolution of the signals derived from hydrocarbon-like compounds released by thermal cracking of SOM during RE pyrolysis has been increasingly used to estimate the relative contribution of the major SOM classes differing in origin and preservation. This study applied the mathematical deconvolution of the S3 and S4 signals of carbon monoxide（CO） and CO2, produced both by the pyrolysis of the oxygen-containing moieties and by the oxidation of the residual highly resistant organic matter, to characterize the stability of these components. Our results suggested that the stability of the oxygen-containing moieties was controlled by the precursor material and was strongly affected by the land use and the presence of humic substances in the surface horizon of some main soil types in Hungary. In consistence with the bulk RE data, results of the mathematical deconvolution also proved to be diagnostic markers for discriminating the aquatic or terrigenous plants as the main sources of SOM. The mathematical deconvolution of S4 signals derived from the highly resistant SOM fraction allowed us to quantify the contribution of constituents with different stability. Furthermore, the results of this study displayed that the stability of this highly abundant SOM fraction in the surface soil samples depended on source biomass and intensity of leaching.     

Comparisons of soil organic matter and its fractions by pyrolysis mass-spectrometry

Pyrolysis mass-spectra from a sample of the A₁-horizon of a soil from southern Spain showed predominant peaks related to furan derivatives similar to those observed from complex polysaccharides in which not only hexoses but also pentoses and deoxyhexoses were constituent units. Smaller peaks, typical for protein materials and phenolic units, were also observed. On the other hand, typical peaks for the methoxyphenols of lignins were very small and indicated only limited amounts of undecomposed lignin residues in this soil sample. Peaks related to benzene or toluene were also very small.Humic acid samples from this soil showed much more prominent signals related to protein materials, benzene and phenolic derivatives and weaker polysaccharide-related signals than did the entire sample. Typical lignin related peaks were small or insignificant. Spectra from the grey or brown humidic acid fractions were much like those of the parent humic acid. Brown humic acid, however, showed stronger signals for nitrogen and sulphur compounds, indicating a higher content of protein-like materials in this fraction. Preparations of humic acid hydrolyzed by 6 N HCl showed in their pyrolysis products a marked increase in phenols and methoxyphenols.In its pyrogram, humin resembled humic acid, but signals for complex polysaccharides were more evident. Lignin-like materials seem not to be higher in this fraction. Hymatomelanic acid showed prominent signals related to polysaccharides and lignin. Pyrograms from the soil polysaccharides showed the characteristic pattern of a complex polysaccharide with the presence of fragments from polymers of amino acids or amino sugars. Fulvic acid spectra showed obvious dissimilarities to those from humic acid in that signals for protein, as well as those related to phenols, were low. Depending upon the isolation method, the fulvic acid preparations showed differing signals related to polysaccharide or phenolic materials.     

Dissolved organic matter and its parent organic matter in grass upland soil horizons studied by analytical pyrolysis techniques

We have sought to understand the molecular mechanisms by which dissolved organic matter (DOM) forms and soil organic matter (SOM) degrades in upland peaty gley soil under grass. Pyrolysis mass spectrometry (Py-MS) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) were applied to characterize the DOM collected from lysimeters and its parent SOM. The macromolecular organic matter in the litter and fermentation (Lf) horizon of the soil consists primarily of little decomposed lignocellulose from grass, whereas the humus (Oh) horizon is characterized by an accumulation of selectively decomposed lignocellulose material, microbial metabolites and bound fatty acids. The mineral horizon produced a relative enrichment of furan structures derived from microbial reworking of plant polysaccharides but virtually no lignin signals. A series of exceptional long chain C₄₃ to C₅₃ fatty acids with odd over even predominance, probably derived from mycobacteria, were also identified in the Oh horizon. Side-chain oxidation and shortening, increase of carboxyl functionality and selective removal of syringyl (S) > guaiacyl (G) > p-hydroxyphenyl (P) lignin units were the main reactions when lignin degraded. Compared with SOM, the DOM shows a large accumulation of more oxidized lignin and aromatic structures, especially those containing carboxylic and dicarboxylic acid functionalities and with shorter side-chain length. The polysaccharide-type compounds in the DOM were more modified (greater abundance of furan structures in pyrolysis products), and had significantly lower molecular weight and more diverse polymeric structures than did those in soils. Increased temperature and rainfall appeared to result in greater relative abundance of lignin degradation products and aromatic compounds in DOM.     

How are soil use and management reflected by soil organic matter characteristics: a spectroscopic approach

We studied the quantitative and qualitative changes of soil organic matter (SOM) due to different land uses (arable versus grassland) and treatments (organic manure and mineral fertilizer) within an agricultural crop rotation in a long‐term field experiment, conducted since 1956 at Ultuna, Sweden, on a Eutric Cambisol. The organic carbon (OC) content of the grassland plot was 1.8 times greater than that of the similarly fertilized Ca(NO₃)₂ treated cropped plots. The comparison of two dispersion techniques (a low‐energy sonication and a chemical dispersion which yield inherent soil aggregates) showed that increasing OC contents of the silt‐sized fractions were not matched by a linear increase of silt‐sized aggregates. This indicated saturation of the aggregates with OC and a limited capacity of particles to protect OC physically. Thermogravimetric analyses suggested an increase of free organic matter with increasing OC contents. Transmission FT‐IR spectroscopy showed relative enrichment of carboxylic, aromatic, CH and NH groups in plots with increasing OC contents. The silt‐sized fractions contained the largest SOM pool and, as revealed by ¹³C NMR spectroscopy, were qualitatively more influenced by the plant residue versus manure input than the clay fractions. Alkyl and O‐alkyl C in the silt‐sized fractions amounted to 57.4% of organic carbon in the animal manure treated plots and 50–53% in the other treatments.     

基于决策树模型的土壤有机质制图

Based on a case study of Longyou County, Zhejiang Province, the decision tree, a data mining method, was used to analyze the relationships between soil organic matter (SOM) and other environmental and satellite sensing spatial data.The decision tree associated SOM content with some extensive easily observable landscape attributes, such as landform,geology, land use, and remote sensing images, thus transforming the SOM-related information into a clear, quantitative,landscape factor-associated regular system. This system could be used to predict continuous SOM spatial distribution.By analyzing factors such as elevation, geological unit, soil type, land use, remotely sensed data, upslope contributing area, slope, aspect, planform curvature, and profile curvature, the decision tree could predict distribution of soil organic matter levels. Among these factors, elevation, land use, aspect, soil type, the first principle component of bitemporal Landsat TM, and upslope contributing area were considered the most important variables for predicting SOM. Results of the prediction between SOM content and landscape types sorted by the decision tree showed a close relationship with an accuracy of 81.1%.     

Soil organic matter maps by nuclear magnetic resonance

Preliminary studies are reported on a soil and a litter fraction which have the aim of exploring the potential of two-dimensional ¹³C nuclear magnetic resonance spectroscopy for the analysis of soil organic matter structure. It has been shown that contour plots can be obtained in which one co-ordinate gives chemical shift information and the other the magnitude of the dipolar interaction. For aromatic and oxygenated aliphatic carbon, the latter parameter is a measure of the degree of protonation. Hence the method is useful for distinguishing between soils containing highly substituted and condensed aromatic structures and those with protonated aromatic carbon. Likewise, it is possible to distinguish between soils containing dioxygenated carbon which is. protonated (e.g. ketal).     

Characterization of plant-derived water extractable organic matter by multiple spectroscopic techniques

Water extractable organic matter (WEOM) derived from fresh- or early-stage decomposing soil amendment materials may play an important role in the process of organic matter accumulation. In this study, eight WEOM samples extracted with a 40:1 (v/w) water to sample ratio from alfalfa (Medicago sativa L.), corn (Zea mays L.), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa L.), lupin (Lupinus albus L.), soybean (Glycine max L. Merr.), wheat (Triticum aestivum L.), and dairy manure were investigated using ultraviolet (UV)–visible, Fourier transform infrared (FT-IR), solution ³¹P nuclear magnetic resonance (NMR), and solid state ¹³C NMR spectroscopies. UV–visible and FT-IR spectra of the plant-derived WEOM samples were typical for natural organic matter, but possessed less humic-like characteristics than dairy manure-derived WEOM. Solution ³¹P NMR spectra indicated that WEOM samples extracted from alfalfa, corn, and soybean shoots contained both orthophosphate and monoester P. Of the monoester P in WEOM from soybean shoot, 70% was phytate P. WEOM from crimson clover, hairy vetch, lupin, and wheat shoots contained orthophosphate only. The solid-state ¹³C NMR spectra of the seven plant-derived WEOM samples indicated that they all were primarily composed of sugars, amino acids or peptides, and low molecular mass carboxylic acids. Carbohydrates were dominant components with very few aromatics present in these samples. In addition, WEOM from crimson clover and lupin, but not other three leguminous plant WEOM samples, contained significant asparagine. On the other hand, WEOM from corn and wheat contained less amino acids or peptides. The spectra of WEOM of dairy manure revealed the presence of significant amounts of nonprotonated carbons and lignin residues, suggesting humification of the manure-derived WEOM. Significant carbohydrates as well as aromatics were present in this WEOM. The P and C bonding information for these WEOM samples may be useful for understanding the effects of WEOM on soil nutrient availability to plants. Trade or manufacturers' names mentioned in the paper are for information only and do not constitute endorsement, recommendation, or exclusion by the USDA-ARS.     

A 13C-NMR study on the formation of soil organic matter from grass residues

The development of C-distribution on functional groups in soil organic matter (SOM) was investigated in whole soil samples and organomineral particle-size fractions from the 34-year-old pot experiment Hu3-Loamy marl at Rostock. CPMAS-¹³C-NMR spectra of grass roots and whole soil samples indicated the enrichment of carboxyl-C, aliphatic C and aromatic C in SOM, Only minor changes were observed in the SOM-C distribution on functional groups between 13th and 34th experimental year. The investigation of organomineral clay and silt-size fractions showed a specific retention of aliphatics in clay. The most obvious changes in organic matter composition in size-fractions were the increase of carbohydrate-C and decrease of aromatic C.     

Soil organic matter composition and soil lightness

Relationships between soil lightness, soil organic matter (SOM) composition, content of organic C, CaCO₃, and texture were studied using 42 top‐soil horizons from different soil types located in southern Germany. SOM composition was determined by CPMAS ¹³C NMR spectroscopy, soil color was measured by diffuse‐reflectance spectrophotometry and given in the CIE L*a*b* color coordination system (Commission Internationale de l'Eclairage, 1978). Multiple‐regression analysis showed, that soil lightness of top‐soil horizons is principally determined by OC concentration, but CaCO₃ and soil texture are also major variables. Soil lightness decreased with increasing OC content. Carbonate content had an important effect on soil lightness even at low concentrations due to its lightening property. Regressions between soil lightness and organic C content were strongly linear, when the soils were differentiated according to texture and CaCO₃ content. The aryl‐C content was the only SOM component which correlated significantly with soil lightness (r_S = –0.87). In the linear regressions carried out on the different soil groups, soil aryl‐C content was a more significant predictor for soil lightness than total OC content.     

Soil organic matter, effects on soils and crops

Abstract. Manurial treatments and cropping history have remained unchanged for many years in classical and long-term experiments at Rothamsted and Woburn, in some cases for more than 100 years. Soil samples taken periodically have been analysed to follow changes in organic carbon content with time and treatment. Data presented here clearly show effects of carbon input and soil texture on equilibrium organic matter content.
Until recently increasing amounts of soil organic matter had little effect on yields of arable crops especially if fertilizer nitrogen dressings were chosen correctly. However the yield potential of many crops has increased and various agronomic inputs have become available to achieve that potential. Yields of many crops are now larger on soils with extra organic matter both on the sandy loam at Woburn and the silty clay loam at Rothamsted. Some of the effect appears to be related to extra water holding capacity, some to availability of nitrogen in ways which cannot be mimicked by dressings of fertilizer N, and some to improved soil physical properties. Responses to fertilizer N have been larger on soils with more organic matter.     

Chemical and spectroscopic characterization of soil organic matter fractions isolated by sequential extraction procedure

Soil organic matter fractions were isolated from three soils by the application of a sequential extraction procedure employing a series of 10 mild organic solvents of different polarity. The isolated organic materials were characterized by elemental, infrared and electron spin resonance analyses. They showed different chemical and structural properties which varied according to the progression of the solvent series, with some similarities between two successive extracts. The corresponding fractions extracted from the three soils were substantially similar to each other in chemical character. Along each series of extracts aliphaticity appeared to decrease, whilst aromaticity, polar oxygenated and nitrogenated functional groups, transition metal ion content and organic free radical concentrations increased. ESR spectra were structured and were put in four different classes, according to their characteristic resonances. Although the yields of extracted organic material were not high, the fractions could be considered representative of the soil organic matter composition and furnish new chemical information on its nature and properties.     

Soil organic matter distribution as influenced by enchytraeid and earthworm activity

Loam and sandy soils, and the earthworm casts produced with ¹⁴C-labelled plant material in both soils, were incubated in airtight glass vessels with and without enchytraeids to evaluate the effects of soil fauna on the distribution and fragmentation of organic matter. After 1, 3, and 6 weeks, the amount of C mineralised was determined in soils and earthworm casts, and the soil was fractionated into particulate organic matter (POM), the most active pool of soil organic matter, after complete physical dispersion in water. The percentage weight of fine fractions (0-50 µm) was 67.4% in the loam soil. Sand (coarse, i.e. 150-2,000 µm and fine 50-150 µm) represented 87.2% of total weight in sandy soil, while the percentages of C (PC) were 23.2% in coarse POM (2,000-150 µm) and 11.9% in fine POM (150-50 µm). These percentages were higher than those in loam soil, i.e. 3.4% (coarse POM) and 5.4% (fine POM). The PC in coarse POM (9.50%) and fine POM (16.4%) remained higher in casts from sandy soil than in casts from loam soil (4.7% in coarse and 14.3% in fine POM). The highest percentages of ¹⁴C-labelled leaves were found in fine fractions, 55.9% in casts from loam soil and 48.8% in casts from sandy soil. The C mineralisation of the added plant material was higher in casts from the sandy soil (20.3%) than from the loam soil (13.5%). Enchytraeids enhanced C mineralisation in the bulk sandy soil, but did not affect the mineralisation of added plant material in either soil. The main enchytraeid effect was enhancement of the humification process in the bulk sandy soil, the casts from this soil, and the bulk loam soil.     

Soil organic matter chemistry in allophanic soils: a pyrolysis-GC/MS study of a Costa Rican Andosol catena

Soil organic matter (SOM) in allophanic soils is supposed to accumulate due to protection caused by binding to allophane, aluminium and iron. We investigated a catena of allophanic and non‐allophanic soils in Costa Rica to determine the effect of such binding mechanisms on SOM chemistry. These soils contain no contribution of black carbon. Molecular characterization of litter, extractable and dispersed organic matter was done by Curie‐point pyrolysis‐GC/MS. The molecular chemistry of the organic fractions indicates a strong decomposition of plant‐derived organic matter and a strong contribution of microbial sugars and N‐compounds to SOM. Both the decomposition of plant‐derived SOM – including that of relatively recalcitrant compounds – and the relative contribution of microbial SOM were greater in allophanic samples than in non‐allophanic ones. This suggests that chemical protection does not act on primary OM, although it may influence the accumulation of secondary OM in these soils. The effect of allophane on SOM contents in such perhumid soils is probably through incorporation of decomposition products and microbial SOM in very fine aggregates that – in a perhumid environment – remain saturated with water during much of the year. Greater concentrations of aliphatics are found in allophanic residues, but there is no evidence of any specific mineral‐organic binding. The results do not support the existing theory of chemical protection of plant‐derived components through binding to allophane, iron and aluminium.     

The oxidation products formed from: Soil organic matter by hydrogen peroxide treatment

The oxidation products formed from soil organic matter during hydrogen peroxide digestion were studied by means of analyses of carbon and nitrogen, thin layer chromatography, infrared Spectroscopy, and redox titration.

The carbon remaining after hydrogen peroxide digestion, as expressed in percentage by WeIght of the original soil was 0.57 to 4.09, corresponding to 17.81 to 29.00 per cent of the carbon fOUnd in the original soil. The nitrogen remaining after the same treatment was 75 to 100 per cent of total nitrogen in the original soil. The greater part of the remaining water soluble nItrogen was NH₃-N. The thin layer chromatography showed the presence of oxalic acid and V.V. light-ahsorbing substances in the oxidation products. No organic matter other than oxalate Was indicated on the infrared spectra. The amount of water soluble oxalate formed from 100 g of soil determined by means of redox titration was 5.7 to 117.0 mmole. Assuming that the ratio of solution: soil is 5:1 at the final stage of per oxidation, the concentration of oxalate in the SUpernatant solution was in the range from 0.011 to 0.234 M.     

基于高光谱特征的土壤有机质含量估测研究

在室内条件下,利用ASD2500高光谱仪测定了潮土和水稻土自然风干土壤样品的光谱。通过系统分析两种不同类型土壤的高光谱特征差异及其有机质含量的敏感波段区位,建立了土壤有机质含量的光谱估测模型。结果表明,具有相同有机质含量的两种类型土壤整体光谱变化趋势无明显差别,但反射率表现出明显差异,一阶导数变换能较好地显现谱图中的肩峰。潮土和水稻土有机质的敏感波段集中在相同区域,原始反射率在685 nm处相关性最高,而一阶导数光谱在554 nm处相关性最高。通过对整体样本的多元逐步回归分析,筛选出两种土壤有机质相同的敏感波段为800 nm、1 398 nm和546 nm。进一步以一阶导数为自变量,基于1 400nm和554 nm两个波段构建了土壤有机质差值指数SOMDI及估测模型,即Y=4.19 12.85×(R_FD554 R_FD1 400)。利用独立的样本对建立的光谱模型进行了检验,预测决定系数均达0.79以上。上述结果表明,利用高光谱技术可实现土壤有机质的快速监测与诊断。     

Carbon and nitrogen forms in soil organic matter influenced by incorporated wheat and corn residues

We have investigated molecular-scale changes in soil organic matter (SOM) as incorporated wheat and corn residues decompose and whether those changes are correlated with soil nitrogen forms. The ‘initial litter quality hypothesis’ that compositional variations in plant residues may persist during decomposition of these residues as they are transformed to SOM was tested. We studied soils in 6-year field experiments of a double-cropped corn–wheat rotation system designed with the following treatments: no crop residue and no chemical fertilizer, chemical fertilizer alone, wheat straw + chemical fertilizer, corn stover + chemical fertilizer, and corn plus wheat residue + chemical fertilizer. Organic carbon and nitrogen forms were assessed, and SOM chemical structures were examined by Fourier transform infrared and solid-state nuclear magnetic resonance spectroscopy. We found that concentrations of organic-N in corn residues plus fertilizer treatment were significantly larger than those in wheat straw plus fertilizer treatment. In addition, concentrations of amide groups and NCH in SOM with corn residue treatment were larger than those in SOM with wheat residue treatment. Incorporation of both corn and wheat residues led to an increase in carbohydrate-derived components of SOM. Compared with the check treatment, aromaticity, alkyl C/O-alkyl C, and hydrophobicity/hydrophilicity indices of the SOM were lower with addition of residue. Aromaticity was greater in corn residue treatment than in wheat residue treatment. This study provides support for the hypothesis that the variation in chemical composition of SOM reflected the incorporation of distinct chemical structures in wheat and corn straw residues.