Dynamics of the microaggregate composition of chernozem in relation to changes in the content of organic matter

Monitoring of soil dispersivity and humus state has been performed in the stationary profile of ordinary chernozem in the Botanic Garden of the Southern Federal University in 2009–2014. The contents of physical clay and sand are almost stable in time, which indicates a quasi-static (climax) equilibrium in the soil. Another (reversible dynamic) process occurs simultaneously: seasonal and annual variation in the mass fractions of clay and silt in physical clay. Variations of humus content in the whole soil and in its physical clay are also observed on the background of seasonal changes in precipitation and temperature. A procedure has been developed for the analysis of the polydisperse soil system with consideration for the quasi-static and dynamic equilibriums. A two-vector coordinate system has been introduced, which consists of scales for changes in the contents of physical clay and physical sand in 100 g of soil and changes in the fractions of clay and silt in 100 g of physical clay. Co-measurements of two dispersivity series of soil samples—actual dynamic and calculated under quasi-static equilibrium (ideal)—have been performed. Dynamic equilibrium coefficients, which cumulatively reflect the varying proportions of physical clay and physical sand in the soil and the mass fractions of clay and silt in physical clay, have been calculated.     

Explaining soil organic matter composition based on associations between OM and polyvalent cations

Site conditions and soil management determine the content and the composition of soil organic matter (SOM). Organic matter (OM) is characterized by functional groups, which preferentially interact with polyvalent cations and soil minerals. These interactions could perhaps explain the site‐specific composition of bulk SOM and a pyrophosphate‐soluble OM fraction (OM‐PY) using basic soil properties. The objective of this study was to test a simplified model for the interactions between OM and polyvalent cations (i.e., Ca, Mg, Al, Fe, and Mn) by using data from soils from long‐term field experiments. The model considered (1) OM–cation, (2) OM–cation‐mineral, and (3) OM–mineral associations and assumed that the availability of the cation's coordination sites for the interaction with OM depends on these three types of associations. The test was carried out using data (topsoil) from differently fertilized plots from three long‐term field experiments (Halle, Bad Lauchstädt, Rotthalmünster). The composition of SOM and OM‐PY was characterized by the relationship of the ratio of the C=O (i.e., here indicating both carbonylic and carboxylic groups) versus C–O–C absorption band intensities obtained from the Fourier transform infrared (FTIR) spectra with the content of exchangeable, oxalate‐, and dithionite‐extractable polyvalent cations. The assumed associations between the OM and cations and the availability of the coordination sites explained most of the variations in the C=O/C–O–C ratios of the SOM, and fewer variations in the OM‐PY, when using the site‐specific exchangeable and oxalate‐extractable cation contents. The C=O/C–O–C ratios of the OM‐PY were site‐independent for samples from plots that regularly received farmyard manure. The results suggested that a simplified model that considers the polyvalent cation content weighted by the number of coordination sites per cation according to the type of association could be used to improve the explanation of site‐specific differences in the OM composition of arable soils.     

Temporal changes in distribution and composition of N from labeled fertilizer in soil organic matter fractions

Variations in the amount and composition of immobilized nitrogen (N) in major soil organic matter fractions were investigated in a 730-day soil incubation experiment using ¹⁵N-labeled urea and ¹⁵N nuclear magnetic resonance spectroscopy with the cross polarization/magic angle spinning (¹⁵N CPMAS NMR) method. After 730 days, 24.7% of the applied N was recovered from the soil as organic N. The urea-derived N recovered from humic acids and humin decreased from 11.2 and 33.8% of the applied amount after 14 days to 1.6 and 20.4% after 730 days, respectively. When these values were corrected for the microbial biomass (MB) N, they ranged from 9.0 to 1.2% and 28 to 18%, respectively. The proportion of urea-derived N recovered from fulvic acids was low, ranging between 0.4 and 5.8% (with MB N) or 5.6% (without MB N) of the applied amount, whereas that from water-soluble nonhumic substances (WS-NHS; NHS in the fulvic acid fraction) remained high, 28–33% of the applied amount after correction for the contribution of MB N up to day 365, and decreased to 0.9% thereafter. The ¹⁵N CPMAS NMR spectra of humic acids, fulvic acids, and humin showed the largest signal at −254 to −264 ppm, corresponding to peptide/amide N. The proportions of heterocyclic, peptide/amide, guanidine/aniline, and free amino N in the urea-derived humic acid N were 3–7, 83–90, 5–7, and 2–4%, respectively. More than 80% loss of the urea-derived humic acid N did not markedly alter their composition. No time-dependent variations were also observed for the proportions of respective N functional groups in humin N, which were 3–5, 71–78, 12–17, and 6–10% in the same order as above. These results suggest the greater importance of physical stability than structural variation for the initial accumulation of organic N in soil.     

长期施肥对黑土有机质及其组成的影响

以农业部哈尔滨黑土生态环境重点野外科学观测试验站长期定位试验为平台,研究了长期施肥对黑土有机质的影响.结果表明,长期施用不同肥料对土壤有机质含量的影响有较大差异,有机无机肥配合处理＞有机肥处理＞无机肥处理＞无肥处理.长期施肥对深层土壤有机质含量也有影响,施用有机肥作用尤其明显,并随着土层的加深施肥对土壤有机质含量的影响呈下降趋势.施用有机肥对有机质不同密度组分影响很大,对有机质含量增加最有效,而施用无机肥则有机质含量有所降低.     

Micromorphology and Late Glacial/Holocene genesis of Luvisols in Mecklenburg–Vorpommern (NE-Germany)

In the German soil science literature, Luvisols formed in Weichselian sediments (except from the Early Weichselian) are normally regarded as purely Holocene soils with the main period of development assumed to have been during the Atlantic phase. Although debated at some length since the 1960s, the genesis of the widespread albic Luvisols, with a simplified Ap/Bw/(Eb)/(EBtb)/Btb(g)/C horizon sequence and developed on the flat and slightly undulating till plains of the north German Mecklenburgian Stage (deglaciation 14 000 BP), has yet to be clarified. Periglacial climate during the Late Weichselian led to the formation of sand-filled wedge-shaped structures penetrating Bt horizons. Systematic micromorphologic investigations of soil profiles with sand wedges revealed the occurrence of numerous fragments of rounded limpid clay coatings within periglacial formed lenticular microplates as well as in and at the margins of the sand wedge infillings. Assuming the Younger Dryas as the latest possible phase of formation, the lenticular microplates and the undisturbed sand wedges postdate clay illuviation. Undisrupted clay coatings next to fragmented clay coatings prove a subsequent Holocene clay illuviation. Clay illuviation must have occurred at least in warmer phases of the Late Glacial, together with the already accepted pedogenic processes of decalcification, organic matter accumulation (Ahb horizons), podzolisation and silicate weathering (Bwb horizons) on sites not influenced by groundwater.     

Changes in the carbon and nitrogen isotopic composition of organic matter in soils of different thermal stability after free-air CO2 enrichment for three years

The hypothesis that the biological availability of soil organic matter (SOM) pools is inversely proportional to their thermal stability was tested using the isotopic difference between the atmospheric CO₂ (δ¹³C = ?8.0‰) and ¹³C-enriched CO₂ (δ¹³C = ?47‰) fertilizers, as well as ¹⁵N-labeled fertilizers. The soil samples from spring wheat plots subjected to treatment with ambient (370 ppm) and elevated (540 ppm) CO₂ concentrations for three years were analyzed by the thermogravimetric method. Based on the weight loss, five SOM pools were distinguished where the total C and N contents and isotopic compositions (δ¹³C and (δ¹⁵N) were determined. The contents of new C and N and their mean residence times in pools were calculated. The incorporation of ¹³C and ¹⁵N and their turnover rates did not depend on the thermal stability of the SOM pools, which disproved the hypothesis being tested.     

Long-term effects of crop rotation and fertilization on soil organic matter composition

Long‐term effects of crop rotation and fertilization are mostly observed with respect to the amount of soil organic matter (SOM) and measured in terms of soil organic carbon (SOC). In this paper, we analyze the SOM composition of samples from long‐term agricultural field experiments at sandy and clayey sites that include complex crop rotations and farm‐yard manure applications. The organic matter (OM) composition of the soil samples, OM(Soil), and that of sequentially extracted water, OM(W), and sodium pyrophosphate, OM(PY), soluble fractions was analyzed using Fourier Transform Infrared Spectroscopy (FTIR). The fraction OM(PY) represented between 13 and 34% of SOC, about 10 times that of OM(W). Site specific differences in OM(Soil) composition were larger than those between crop rotations and fertilizer applications. The smaller C=O group content in FTIR spectra of OM(W) compared with OM(PY) suggests that analysis of the more stable OM(PY) fraction is preferable over OM(W) or OM(Soil) for identifying long‐term effects, the OM(Soil) and OM(W) fractions and the content of CH groups being less indicative. Farm‐yard manure application leads to a more similar content of C=O groups in OM(PY) between crop rotations and fertilizer plots at both sites. Short‐term effects from soil tillage or potato harvesting on composition of OM require further studies.     

半干旱土添加有机改良剂后有机质的化学结构变化

A 9-month incubation experiment using composted and non-composted amendments derived from vine pruning waste and sewage sludge was carried out to study the effects of the nature and stability of organic amendments on the structural composition of organic matter (OM) in a semi-arid soil.The changes of soil OM,both in the whole soil and in the extractable carbon with pyrophosphate,were evaluated by pyrolysis-gas chromatography and chemical analyses.By the end of the experiment,the soils amended with pruning waste exhibited less organic carbon loss than those receiving sewage sludge.The non-composted residues increased the aliphatic-pyrolytic products of the OM,both in the whole soil and also in the pyrophosphate extract,with the products derived from peptides and proteins being significantly higher.After 9 months,in the soils amended with pruning waste the relative abundance of phenolic-pyrolytic products derived from phenolic compounds,lignin and proteins in the whole soil tended to increase more than those in the soils amended with sewage sludge.However,the extractable OM with pyrophosphate in the soils amended with composted residues tended to have higher contents of these phenolic-pyrolytic products than that in non-composted ones.Thus,despite the stability of pruning waste,the composting of this material promoted the incorporation of phenolic compounds to the soil OM.The pyrolytic indices (furfural/pyrrole and aliphatic/aromatic ratios) showed the diminution of aliphatic compounds and the increase of aromatic compounds,indicating the stabilization of the OM in the amended soils after 9 months.In conclusion,the changes of soil OM depend on the nature and stability of the organic amendments,with composted vine pruning waste favouring humification.     

The composition of the functional pools of labile organic matter in the zonal range of automorphic soils of the central Russian Plain

The granule-densimetric fractionation method was used to identify the characteristic features of the composition of different functional pools of labile organic matter (OM) from the automorphic soils of a zonal range from the center of the Russian Plain. Labile OM included free organic matter (FM) represented by a light fraction (LFR) of a density lower than 1.8 g/cm³ and a size larger than 53 μm, and aggregated discrete organic matter (LF_AGR1) represented by an organic matter LF of a density lower than 1.8 g/cm³ and a size smaller than 53 μm and a phytolith LF (LF_AGR2) (density 1.8–2.0 g/cm³). The composition of the fractions isolated was studied using electron microscopy, microanalysis, and chemical analysis.     

Soil microbial biomass and organic matter composition in soils under cultivation

To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning ¹³C-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r=-0.960^***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.     

Soils of the subtaiga landscapes on the northern spurs of the Tsagan-Daban Ridge in the Selenga Mountains

The soil cover patterns in the subtaiga landscapes on the northern spurs of the Tsagan-Daban Ridge in the Selenga Mountains have been studied. Gray-humus lithozems and bedrock outcrops are typical of the steep south-facing slopes under herbaceous pine forests. Soddy iron-illuvial podburs are formed under forest vegetation on gentle slopes of northern and western aspects with a thick mantle of loose colluvial deposits. Dark-humus metamorphic soils occur on the slopes of western and northwestern aspects below 700 m a.s.l. under secondary forb-grassy communities that replaced the initial herbaceous pine forests. Windblown hollows (yardangs) are occupied by humus psammozems under steppe pine forests. The morphological and physicochemical characteristics of these soils are discussed in the paper.     

Seasonal changes in the content of dissolved organic matter in arable soils

Purpose

The aim of this paper has been to determine the seasonal changes in the content of dissolved organic matter (DOM) in the soils under agricultural use based on assaying changes in dissolved organic carbon (DOC) and dissolved nitrogen (DNt) as well as determining the factors which can define the DOM in soils.

Materials and methods

The research has involved the soils under agricultural use sampled in the Kujawsko-Pomorskie province (Poland). Phaeozems and Luvisols were sampled from the depth of 0–30, 30–60, and 60–100 cm, November 2011 through September 2013, in November, March, May, July, and September. The soil samples were assayed for the grain size composition, pH, dry weight content, content of total organic carbon, and total nitrogen. Dissolved organic matter was extracted with 0.004 mol dm³ CaCl₂; in the DOM extracts, the content of dissolved organic carbon (DOC) and dissolved nitrogen (DNt) were assayed. The research results were statistically verified.

Results and discussion

It has been demonstrated that in the first year of research, the content of dissolved organic carbon in the soils was changing throughout the year. The highest differences in the content of that carbon fraction occurred across the soil sampled in autumn and the soil sampled in spring. In the second year of research, an inverse dependence was noted. DOC was migrating to deeper layers of the soil profile; yet, the migration got more intensive in summer. The content of dissolved nitrogen was not changing significantly throughout the year. Higher DNt content in the surface layer, in general, resulted in a higher content of dissolved nitrogen in deeper profile layer, which could have been due to leaching of the nutrient deep down the soil profile.

Conclusions

The content of dissolved organic carbon was significantly related to the content of total organic carbon and total nitrogen. Significant changes in the content of dissolved forms of nitrogen were reported in the profile of Phaeozems due to mineral fertilization and irrigation. The soils where irrigation and higher nitrogen rates had been applied demonstrated a higher content and share of soluble forms of nitrogen, as compared with the soils non-irrigated and the soils where lower nitrogen rates had been supplied.

     

Changes in the chemical composition of soil organic matter after application of compost

Is the composition of soil organic matter changed by adding compost? To find out we incubated biowaste composts with agricultural soils and a humus‐free mineral substrate at 5°C and 14°C for 18 months and examined the products. Organic matter composition was characterized by CuO oxidation of lignin, hydrolysis of cellulosic and non‐cellulosic polysaccharides (CPS and NCPS) and ¹³C cross‐polarization magic angle spinning nuclear magnetic resonance (CPMAS ¹³C‐NMR) spectroscopy. The lignin contents in the compost‐amended soils increased because the composts contained more lignin, which altered little even after prolonged decomposition of the composts in soil. A pronounced decrease in lignin occurred in the soils amended with mature compost only. Polysaccharide C accounted for 14–20% of the organic carbon at the beginning of the experiment for both the compost‐amended soils and the controls. During the incubation, the relative contents of total polysaccharides decreased for 9–20% (controls) and for 20–49% (compost‐amended soils). They contributed preferentially to the decomposition as compared with the bulk soil organic matter, that decreased between < 2% and 20%. In the compost‐amended agricultural soils, cellulosic polysaccharides were decomposed in preference to non‐cellulosic ones. The NMR spectra of the compost‐amended soils had more intense signals of O–alkyl and aromatic C than did those of the controls. Incubation for 18 months resulted mainly in a decline of O–alkyl C for all soils. The composition of the soil organic matter after compost amendment changed mainly by increases in the lignin and aromatic C of the composts, and compost‐derived polysaccharides were mineralized preferentially. The results suggest that decomposition of the added composts in soil is as an ongoing humification process of the composts themselves. The different soil materials affected the changes in soil organic matter composition to only a minor degree.     

Tillage practice influences on the physical protection, bioavailability and composition of particulate organic matter

 This study was conducted to determine whether separation of particulate organic matter (POM) that is biologically labile from aggregate entrapped material improves the usefulness of POM as an index of soil C and N dynamics. The effects of conventional (CT) and no-tillage (NT) practices on POM were assessed using soils from three 10-year trials in Illinois. Loose and occluded POM in the 0–5 cm depth were separated from 1994 samples. Use of NT practices increased C and N contents at 0–5 cm relative to CT practices and those increases were most apparent in the occluded POM fraction. The correlation between total POM-N and potentially mineralizable N (PMN) was stronger than that between PMN and either the loose or occluded-POM fractions. In 1995, both the microbial biomass, estimated as chloroform-labile C (CFEC), and PMN were correlated with POM-C and N, but the relationship was weak when data (from different tillage and depth combinations) were not treated in aggregate. POM-C and CFEC were most strongly correlated in surface depths and in CT treatments. In NT 0–5 cm samples, PMN contents were similar (≈27 mg N kg^–1 soil) at all sites despite notable differences in POM-N concentrations; PMN was not related to POM-N in CT samples. There was no consistent relationship between PMN and POM-N contents in 5–30 cm samples. DRFTIR spectra indicated that carbohydrates were most abundant in POM at 0–5 cm. Relatively low PMN rates and enrichment of polysaccharides in POM in the sicl soil suggest that physical protection of labile organic substrates was more important at that site than at sites with lighter textured soils. Improved fractionation and incubation techniques and alleviation of laboratory artifacts will improve our ability to relate POM quantity, distribution and composition to biologically mediated C and N dynamics occurring in the field. Received: 2 December 1999     

From the litter layer to the saprolite: Chemical changes in water-soluble soil organic matter and their correlation to microbial community composition

Organic matter content and chemistry is vital to the structure and function of soil systems, but while organic matter is recognized as biogeochemically important, its chemical interaction with soil processes is not well understood. In this study we used fluorescence spectroscopy, which has been used extensively for understanding the role of organic matter in aquatic systems, to identify chemical changes in organic matter with depth in a soil system. Soil was collected from nine different pits in a first-order montane catchment in the Colorado Front Range. The water-soluble soil organic matter was extracted from each sample and fluorescence and UV–vis spectroscopy was used to analyze its chemical character. While organic matter chemistry had little correlation with landscape location and local vegetation, there were noticeable consistent trends between soil horizon and organic matter chemistry in each pit. Total organic matter decreased with depth and became less aromatic with increasing depth. This less aromatic material in the saprolite also had a greater microbial signature. The redox character of the organic matter accompanied this change in source and molecular structure, with more oxidized character corresponding with organic matter with more microbial input and more reduced character corresponding to organic matter with more plant input. A concurrent investigation of the microbial population of the same soil samples also showed microbial population composition varying more with soil depth than landscape position, and depth changes in microbial diversity occurred concomitantly with depth changes in organic matter chemistry.     

长期施用有机肥和磷肥对潮褐土土壤有机质及腐殖质组成的影响

采用长期肥料定位试验,研究了施用有机肥和磷肥对土壤有机质、腐殖质含量与组成的影响。结果表明:与本试验布置时的基础土样相比,连续10年隔年施用有机肥、有机肥和磷肥配施使土壤有机质增加了8.4%~17.3%,单施磷肥土壤有机质下降了7.8%~10.7%,其差异均达显著水平;与P0M0相比,单施磷肥、有机肥、有机肥和磷肥配施处理的土壤中有机质分别增加了2.9%~6.2%、24.8%~29.8%、25.2%~35.1%;土壤腐植酸总量及胡敏酸含量与土壤有机质含量呈显著正相关关系;施用磷肥利于土壤富里酸的积累,并影响土壤胡富比。     

Effect of the chemical composition of industrial dusts on forest floor organic matter accumulation

The influence of dusts from aluminium (AP), zinc and lead (ZP1, ZP2), sintering (SP) and power (PP) plants on organic matter accumulation on the forest floor of a mixed oak-pine forest was studied in Niepo?omice Forest near Kraków, Poland. An artificial application of the dusts on experimental plots was used corresponding to 100, 500, 1000, 2000, and 5000 t km^?2. Increased organic matter accumulation was observed 5 yr following the addition of AP, ZP1 and ZP2 dusts, while SP and PP dusts at levels > 100 t km^?2 caused a slight decrease in litter accumulation. Statistical analysis indicated that Cd, Mn, Pb and Zn present in industrial dusts were responsible for the increase in litter accumulation, while some nutrients (e.g. K, Mg, Na) contained in the dusts might decrease organic matter storage to some extent.     

Chemical composition of the organic matter in forest soils: The humus layer

Decomposition and humification were studied within three types of forest humus (mull, moder, and mor) by means of CPMAS ¹³C NMR spectroscopy combined with degradative methods. The NMR data show that O-alkyl carbon decreases in all soils, and alkyl as well as carboxyl carbon increase as depth and decomposition increase; the percentage of aromatic carbon remains constant at about 25%. With increasing depth the amount of carbon that can be identified as belonging to specific compound classes by wet chemical methods decreases from 60% to 40%. Microbial polysaccharides and the proportion of non polysaccharide O-alkyl carbon increase with depth. A selective preservation of recalcitrant, condensed lignin structural units is also observed. In order to relate the spectroscopic and chemical data from investigations of whole soils with studies of humification, samples were fractionated into fulvic acid, humic acid, and humin fractions. The fulvic acid fraction contains large concentrations of carbohydrates irrespective of the soil horizon. The humic acid fraction contains less polysaccharides, but high amounts of alkyl carbon and aromatic structures. The percentage of aromatic carbon existing in the humic acid fraction increases with depth, probably reflecting the amount and degree of oxidative decomposition of lignin. A loss of methoxyl and phenolic groups is evident in the ¹³C NMR spectra of the humic acid fraction. The humin fraction resembles relatively unchanged plant-derived materials as evident from the lignin parameters and carbohydrate contents. All the observed data seem to indicate that humic acids originate form oxidative degradation of humin or plant litter.