Changes In Soil Organic Matter Quality Research Articles

Characteristics of humic acids isolated from burned and unburned topsoils in sub-boreal Scotch pine forests by 13C-NMR spectroscopy

Postpyrogenic soil dynamics is an informative tool for studying soil elementary processes in extreme temperature conditions and for predicting short time environmental changes in conditions of catastrophic landscape changes. Soil organic matter (SOM) system evolution is the most rapid process of postpyrogenic soil development. In this relation, the focus on humus structure is important for understanding these important dynamics. Soil restoration after spontaneous forest fires near Togljatty City (Samara Region, Russia) was abandoned in 2010 and further monitoring over the next ten years was organised to evaluate the speed of humus accumulation dynamics. The aim of this study was to apply the 13C-NMR (nuclear magnetic resonance) spectroscopy to analyse the effect of forest fires on SOM degradation in Scotch pine forests on Psamment Entisols of the fragmented steppe in the Samara Region. Three key soil plots were studied for estimating SOM quality changes under the forest fire effect: surface forest fire, crown forest fire and control, i.e. 18 soil samples of top soil horizons were analysed in three replicates. The data obtained indicate that the humus molecular composition was substantially affected by the wildfires. Investigation of the humic acids’ (HAs) molecular structure by 13C-NMR showed a relative increase in aromatic compounds and decrease in aliphatic ones. The aromaticity degree of HA molecules increases in 5.7 and 3.8 times in cases of surface and crown forest fires, correspondingly. In general, crown and surface fires plots are not very different in terms of 13C-NMR spectra of HAs (p = 0.34); however, HAs of control plot have essential differences from pyrogenic ones (p < 0.05). 13C NMR spectra have shown a change in the proportion of oxygen-containing functional groups as well. One of the most important effects observed in wildfire-affected SOM is that the proportion of lignin-like structures increases as a concomitant effect of depletion of C,H-alkyl groups, especially in the case of crown fires.

Biochemical Fractionation of Soil Organic Matter after Incorporation of Organic Residues

Soil organic matter (SOM) is a key factor for building and maintaining soil quality. The SOM quality is commonly assessed using densitometric and sieving separation methods, but such methods do not inform on the biochemical composition of SOM. Our objective was to evaluate the van Soest extraction procedure for soluble (SOL), holocellulose (HOLO) and lignin/cutin (LIC) fractions of SOM after incorporating crop residues and animal wastes into a C-depleted loamy sand. Millet cuttings, oat straw, fresh cattle manure and cattle manure compost were dried, sieved to obtain 53 - 250 and 250 - 2000 μm size fractions and characterized biochemically using a modified NDF-ADF-ADL van Soest method. Soil was also sieved into 53 - 250 and 250 - 2000 μm fractions. On a dry mass basis, crop residues contained 60% - 70% holocellulose while animal wastes contained more than 40% ash. Each soil fraction was combined with three rates of the corresponding organic fraction (2, 4, and 6 Mg&#183ha&#451 millet forage cuttings or oat straw and 5, 10, and 15 Mg&#183ha&#451 of cattle manure or cattle manure compost). Changes in soil biochemical components were analyzed using the balance method of compositional data analysis. Amendment, application rate and size fraction influenced significantly (p < 0.05) the [SOL | HOLO] balance but did not significantly affect the [SOL,HOLO | LIC] balance. The [SOL | HOLO] increased linearly with addition rate of crop residues, and decreased linearly with addition rate of animal wastes. This approach of balancing biochemical SOM components is a promising method to monitor the changes in SOM quality after the incorporation of organic residues and to elaborate beneficial practices for managing crop residues and animal wastes in agro-ecosystems.

Soil processes related to organic matter modifications following Douglas-fir mature reforestation

The aim of the study was to analyse the pedological, chemical and biochemical properties of soil in order to assess the effect of plant cover species (chestnut, Douglas-fir and mixed vegetation) on soil processes. The selected area under Douglas-fir reforestation was homogeneous for climate, morphology and parent material. The study involved three soils: under chestnut forest (CS), Douglas-fir reforestation (DF) and the transition zone (T). A soil profile differentiation occurred after 50 years of Douglas-fir plantation. The thickness of soil horizons at the surface varied, and the OH horizon in T site was fourfold thicker than that in DF site. The A1 mineral horizon in T site was also thicker than that in DF site. The Munsell value of mineral horizons was significantly lower in DF than CS site. Morphological differences (thickness and colour) probably reflect soil organic matter quality changes: in DF higher values of humification index were found in surface layers (OF/OH or OH and A1) and lower in deep organo-mineral and transition horizons (A2 and BA or AB) with respect to CS site. Also, a slight increase of weathering process was observed under Douglas-fir reforestation. The morphological, chemical and biological properties of soil were effective to assess the impact of various vegetation types on soil organic matter properties related to pedogenetic process. The various methodological approaches allow studying soil processes using a small–medium spatial scale sampling scheme.

Characterization of topsoils subjected to poorly controlled olive oil mill wastewater pollution in West Bank and Israel

Uncontrolled land disposal of olive mill waste water (OMW) can potentially result in soil pollution as a consequence of its high chemical and biochemical oxygen demand and high concentration of phytotoxic phenolic compounds. Although both positive and negative effects of OMW on soil quality have been reported, no clear consensus regarding its direct influence on soil hydrophobicity or soil organic matter (SOM) quality is apparent. An improved understanding of any changes in SOM quality would benefit from expanding current characterization approaches to include the determination of SOM stability and physico-chemical properties. In this screening study we investigated topsoils of sites in West Bank and Israel which have been subjected to a significant OMW disposal for several years. In most cases, amounts and disposal method are unknown. In addition to properties such as water repellency and sorption capacity, novel approaches that included carbon isotope ratio (δ13C), thermostability index (TS) and contact angle tensiometry were tested. All polluted soils exhibited stronger water repellency and, in multiple cases, higher sorptive capacity for agrochemicals and were depleted in δ13C. This coincided with higher organic carbon and water extractable organic matter contents with the magnitude of effects clearly stronger than those generally reported for controlled OMW disposal. Extractable organic matter of polluted soils contained higher amounts of non-aromatic compounds like fatty acids and sugars than their controls. Thermal analysis indicated a relative reduction of the recalcitrant OM compared to the controls although interestingly, individual calorific values were higher than those of the unpolluted controls. Water repellency correlated with the isotopic carbon ratio and with the calorific value of the recalcitrant OM, which are both useful indicators for the degree of decomposition of OMW organic matter. The calorific value of recalcitrant OM may also help describe the hydrophobic potential of OMW polluted soils.

Diffuse-Reflectance Fourier-Transform Mid-Infrared Spectroscopy as a Method of Characterizing Changes in Soil Organic Matter

Diffuse-reflectance Fourier-transform mid-infrared spectroscopy (MidIR) can identify the presence of important organic functional groups in soil organic matter (SOM); however, spectral interpretation needs to be validated to correctly assess changes in SOM quality and quantity. We amended soils with known standards, increasing the total C in the sample by 50%, and measured changes in MidIR spectra. Adenine, casein, cellulose, ergosterol, glucosamine, glycine, guanine, indole, methionine, palmitic acid, egg protein, chlorophyllin, tannic acid, xylose, urease, and vanillin standards were used. In addition, corn (Zea mays L.) stalk feedstock and two chars produced at different temperatures were studied. Two soils were used: a Hoytville, OH, soil (2.5% C and 36% clay) and an Akron, CO, soil (1.5% C and 14% clay). The addition of standards with >10% N content resulted in increased amide-like absorbance at 1670, 1588, and 1513 cm−1. Bands at 2970 to 2800, 2200 to 2000, and 1030 to 1160 cm−1 were sensitive to added polysaccharide. Protein addition increased absorption at 2970 to 2800 cm−1 but also increased the 1691 and 1547 cm−1 amide bands. Vanillin addition resulted in higher absorbance at the 1592, 1515, and 1295 cm−1 aromatic C=C bands. Biochars produced at 300°C resulted in increased absorbance at carbonyl and aliphatic bands, while addition of 500°C biochar increased aromatic absorbance. Our results showed that MidIR is sensitive to relatively small changes in SOM. If assumptions about the soil mineralogy are met, specific spectral bands can be used to follow changes in SOM chemistry.

Use of specific peaks obtained by diffuse reflectance Fourier transform mid‐infrared spectroscopy to study the composition of organic matter in a Haplic Chernozem

This study assessed specific peaks obtained by diffuse reflectance Fourier transform mid‐infrared spectroscopy (DRIFTS) for characterizing the soil organic matter (SOM) composition of a Haplic Chernozem. Soils were collected from the Static Fertilization Experiment, Bad Lauchstädt, Germany, during 5 years from the farmyard manure (FYM), mineral fertilizer (NPK), combination (FYM + NPK) and no fertilizer (Control) treatments. Soils were extracted with hot water (HWE), and fractionated by size and density. Bulk soil and fractions were analysed by DRIFTS. Peak areas at 2930, 1620, 1530 and 1159 cm−1 were selected as a range of organic functional groups (with limited mineral interference), integrated with a local baseline (corrected peak area) and each was divided by the summed area of the four peaks (relative peak area). Positive correlations between carbon (C) in fractions representing labile OM (&lt;1.8 g cm−3, 1.8–2.0 g cm−3, CHWE) and the corrected peak area at 2930 cm−1 (3010–2800 cm−1) in the bulk soil indicated that this aliphatic peak corresponded to the more labile C compounds. Negative correlations between the same fractions and the corrected area of the predominantly aromatic peak at 1620 cm−1 (1660–1580 cm−1) in the bulk soil suggested a relationship with more stable SOM compounds. All relative peak areas were significantly affected by fertilizer treatment, with an increasing relative peak area at 2930 cm−1 in FYM compared with non‐FYM treatments. The ratio of the peaks at 1620 and 2930 cm−1 was positively correlated with the ratio of stable C (sum of C in &gt;1.8 g cm−3 and clay fractions) to labile C (C content of &lt;1.8 g cm−3 fraction) and thus taken as an indicator of SOM stability. The DRIFTS peak area method reflected changes in SOM quality and composition under long‐term management as measured by size and density fractionation, indicating heterogeneous chemical composition of the latter. Further, the DRIFTS analysis of undiluted soil samples can be used to assess SOM composition in small sample sets if specular reflection and mineral interferences are considered.

Treeline shifts in the Ural mountains affect soil organic matter dynamics

AbstractHistorical photographs document that during the last century, forests have expanded upwards by 60–80 m into former tundra of the pristine Ural mountains. We assessed how the shift of the high‐altitude treeline ecotone might affect soil organic matter (SOM) dynamics. On the gentle slopes of Mali Iremel in the Southern Urals, we (1) determined the differences in SOM stocks and properties from the tundra at 1360 m above sea level (a.s.l.) to the subalpine forest at 1260 m a.s.l., and (2) measured carbon (C) and nitrogen (N) mineralization from tundra and forest soils at 7 and 20 °C in a 6‐month incubation experiment. C stocks of organic layers were 3.6±0.3 kg C m−2 in the tundra and 1.9±0.2 kg C m−2 in the forest. Mineral soils down to the bedrock stored significantly more C in the forest, and thus, total soil C stocks were slightly but insignificantly greater in the forest (+3 kg C m−2). Assuming a space for time approach based on tree ages suggests that the soil C sink due to the forest expansion during the last century was at most 30 g C m−2 yr−1. Diffuse reflective infrared spectroscopy and scanning calorimetry revealed that SOM under forest was less humified in both organic and mineral horizons and, therefore, contained more available substrate. Consistent with this result, C mineralization rates of organic layers and A horizons of the forest were two to four times greater than those of tundra soils. This difference was similar in magnitude to the effect of increasing the incubation temperature from 7 to 20 °C. Hence, indirect climate change effects through an upward expansion of forests can be much larger than direct warming effects (Δ0.3 K across the treeline). Net N mineralization was 2.5 to six times greater in forest than in tundra soils, suggesting that an advancing treeline likely increases N availability. This may provide a nutritional basis for the fivefold increase in plant biomass and a tripling in productivity from the tundra to the forest. In summary, our results suggest that an upward expansion of forest has small net effects on C storage in soils but leads to changes in SOM quality, accelerates C cycling and increases net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass.

Soil CO2 Emissions from Northern Andean Páramo Ecosystems: Effects of Fallow Agriculture

The effects of fallow agriculture on soil organic matter (SOM) dynamics and CO2 emissions were assessed in the tropical Andean páramo ecosystem. Possible changes during the cultivation-fallow cycle were monitored in four areas of the Quebrada Piñuelas valley (Venezuela). Uncultivated soils and plots at different stages of a complete cultivation--fallow cycle were incubated, and SOM mineralization kinetics was determined. Soils exhibited a low SOM mineralization activity, total CO2 evolved never reaching 3% of soil carbon, pointing to a stabilized SOM. Potential soil CO2 effluxes differed significantly according to their plot aspect: northeast (NE)-aspect soils presented higher CO2 effluxes than southwest (SW)-aspect soils. Soil CO2 emissions decreased after ploughing as compared to virgin páramo; low CO2 effluxes were still observed during cropping periods, increasing progressively to reach the highest values after 4-5 y of fallow. In all cases, experimental C mineralization data was fitted to a double exponential kinetic model. High soil labile C pool variability was observed, and two different trends were identified: NE-oriented soils showed more labile C and a wider range of values than SW-facing soils. Labile C positively correlated with CO2 effluxes and negatively with its instantaneous mineralization rate. The instantaneous mineralization rate of the recalcitrant C pool positively correlated with %C evolved as CO2 and negatively with soil C and Al2O3 contents, suggesting the importance of aluminum on SOM stability. The CO2 effluxes from these ecosystems, as well as the proportion of soil C released to the atmosphere, seem to depend not only on the size of the labile C pool but also on the accessibility of the more stabilized SOM. Therefore, fallow agriculture produces moderate changes in SOM quality and temporarily alters the CO2 emission capacity of these soils.

Tropical agriculture and global warming: impacts and mitigation options

The intensive land use invariably has several negative effects on the environment and crop production if conservative practices are not adopted. Reduction in soil organic matter (SOM) quantity means gas emission (mainly CO2, CH4, N2O) to the atmosphere and increased global warming. Soil sustainability is also affected, since remaining SOM quality changes. Alterations can be verified, for example, by soil desegregation and changes in structure. The consequences are erosion, reduction in nutrient availability for the plants and lower water retention capacity. These and other factors reflect negatively on crop productivity and sustainability of the soil-plant-atmosphere system. Conversely, adoption of "best management practices", such as conservation tillage, can partly reverse the process - they are aimed at increasing the input of organic matter to the soil and/or decreasing the rates at which soil organic matter decomposes.

Soil organic matter status of Chernozem soil in North Kazakhstan: effects of summer fallow

In North Kazakhstan there is concern about the degradation of Chernozem soil and agricultural sustainability by the inclusion and frequency of summer fallows in crop rotations in terms of their influence on the changes of soil organic matter (SOM) quality and quantity. We examined five fallow-wheat ( Triticum aestivum L.) cropping systems with different frequencies of the fallow phase in Chernozem soil of North Kazakhstan; continuous wheat (CW), 6-y rotation (6R), 4-y rotation (4R), 2-y rotation (2R) and continuous fallow (CF). Soil samples were collected from the two phases of each rotation, pre- and post-fallow, and analyzed for potentially mineralizable C (PMC) and N (PMN), ‘light fraction’ organic matter (LF-OM), C (LF-C) and N (LF-N). Potentially mineralizable C was inversely proportional to the frequency of fallow and was highest in CW. Mineral N (min-N) and PMN were more responsive to rotation phase than other indices of SOM. Mineral N was higher in the post-fallow phase while PMN was higher in the pre-fallow phase. Light fraction organic matter was negatively correlated to the frequency of fallow and was higher in the pre-fallow than in the post-fallow phase in a rotation. The results suggested that the yearly input of plant residue in a less frequently fallowed system built up more PMC, whereas PMN was closely correlated to recent inputs of substrate added with plant residues. We conclude that a frequent fallow system may deplete SOM via accelerated mineralization. Also that LF-OM, PMC and PMN are more sensitive to detect subtle changes in SOM quality than total SOM. Our results may provide prediction of SOM response to fallow frequency in wheat-based rotation systems in Chernozem soils of semi-arid regions.

Effect of natural and agricultural factors on long-term soil organic matter dynamics in arable soddy-podzolic soils—modeling and observation

Changes in topsoil C content were measured in 60 experiments on soddy-podzolic soils in the Russian Federation, Belarus, Ukraine, Lithuania and Latvia with different management characteristics. The data were compiled with a range of actual climatic parameters for the years of the experiments. The combined impact of different management practices (inorganic fertilizers, organic manure and different rotations), climate gradients and soil properties (initial soil C, clay content) was analysed using a static model. The importance of initial C level interactions with the soil and climatic variables are demonstrated as one of the major factors of soil organic matter (SOM) dynamics. The effect of different treatments for seven long-term experiments at the same site (Barybino, the Moscow Region) was explored using both static and dynamic modeling approaches. The SUNDIAL dynamic model was used to estimate the dynamics of different C pools for the whole 35-year experimentation period. Some adjustments to parameters were necessary to obtain satisfactory results. The management practices tested lead to changes not only in total SOM but also in SOM quality parameters. This was established using a complex of chemical and biological methods. For cropping systems with 50% of row crops manure application increased steady state C values by about 0.2%. High inorganic N fertilization decreased the steady state C values. The negative effect of high inorganic N fertilization was seen to be more pronounced on soil with a higher C content. This influence might be a result of increased organic C mineralization after autumn application of mineral N where there may be no crop present to utilize the fertilizer, resulting in adverse changes in SOM quality. The mineral fertilization contributes significantly to the formation of labile humic substances at the expense of Ca-forms of SOM which are more resistant to microbial decomposition and act as the binding agents of aggregate stability.

How does residue management impact soil organic matter composition and quality under Eucalyptus globulus plantations in southwestern Australia?

This study investigated the influence of harvest residue management practices on soil organic matter (SOM) composition and quality from two second-rotation Eucalyptus globulus plantations in southwestern Australia, using solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy with cross-polarisation and magic-angle-spinning (CPMAS). Soil samples (0–5 cm) were collected every 12 months for 5 years from two sites that had contrasting soil types and fertility. Harvest residue management treatments established at both sites were (a) no harvest residues; and (b) double harvest residues. The use of 13 C CPMAS and DD NMR spectroscopy enabled the successful non-destructive detection of SOM quality changes in the two E. globulus plantations. Relative intensities of 13 C CPMAS NMR spectral regions were similar at both sites, and for both harvest residue treatments, indicating that SOM composition was also similar. Dipolar dephasing (DD) NMR spectra revealed resonances in SOM assigned to lignin and tannin structures, with larger resonances in the carbonyl and alkyl C regions that were indicative of cuticular material, enabling detection of changes in SOM quality. Retention of double harvest residues on the soil surface increased the soil quality compared with removal of all harvest residues at both sites as indicated by the NMR aromaticities, but this was most noticeable at Manjimup, which had greater initial soil fertility.