Soil Organic Fractions Research Articles

Wildfires effects on organic matter of soils from Caramulo Mountain (Portugal): environmental implications.

The investigation about wildfires has demonstrated that research should include studies on the overall assessment of the processes, thus promoting the public awareness about impacts. The aim of this study is to assess the changes on the carbon content of soils affected by wildfires in Caramulo Mountain (Portugal) to therefore identify the environmental impacts arisen from those changes. Soils from different parent rocks, affected and non-affected by wildfires, were collected. Petrographic and geochemical methods were used to identify changes caused by the wildfires in the organic fraction of soils. The results demonstrate that changes in soils composition after wildfires include the production of charcoal and pyrogenic polycyclic aromatic hydrocarbons (PAH). The incorporation of charcoal from biomass burning in soils overtime and the production of pyrolytic PAH are of environmental concern since these compounds are known to be harmful to the environment and ecosystems and are human carcinogens. The concentration of BkF-benzo[k]fluoranthene, known as probable human carcinogen, exceeds the reference values for contaminated soils. Once in soils these compounds can be removed by percolation affecting waters and, consequently, biodiversity and human health.

Contrasting agricultural management effects on soil organic carbon dynamics between topsoil and subsoil

Agricultural practices (e.g. tillage, crop rotation and fertiliser application) have a strong influence on the balance between carbon (C) input and output by altering physicochemical and microbial properties that control decomposition processes in the soil. Recent studies suggest that the mechanisms by which agricultural practice impacts soil organic carbon (SOC) dynamics in the topsoil may not be the same as those in the subsoil. Here, we assessed SOC stock, soil organic fractions and nitrogen availability to 1.0 m in soils under a cotton (Gossypium hirsutum L.)-based cropping system, and assessed the impact of agricultural management (three historical cropping systems with or without maize (Zea mays L.) rotation) on SOC storage. We found that the maize rotation and changes in the particulate organic fraction influenced SOC stock in the topsoil, although the overall change in SOC stock was small. The large increase in subsoil SOC stock (by 31%) was dominated by changes in the mineral-associated organic fraction, which were influenced by historical cropping systems and recent maize rotation directly and indirectly via changes in soil nitrogen availability. The strong direct effect of maize rotation on SOC stock, particularly in the subsoil, suggests that the direct transfer of C into the subsoil SOC pool may dominate C dynamics in this cropping system. Therefore, agricultural management that affects the movement of C within the soil profile (e.g. changes in soil physical properties) could have a significant consequence for subsoil C storage.

Distribution Characteristics of Soil Organic Phosphorus Fractions in the Inner Mongolia Steppe

Phosphorus (P) is one of the limiting nutrients in Inner Mongolia steppe soil, which seriously affect steppe productivity. Therefore, it is necessary to understand the distribution characteristics of organic P (Po) fractions and their influencing factors in Inner Mongolia steppe soil and to identify the contribution of Po fractions to soil available P (AP) to maintain the sustainable development of the Inner Mongolia steppe by improving the utilization rate of Po. The contents of soil Po fractions such as H2O-extractable Po (H2O-Po), NaHCO3-extractable Po (NaHCO3-Po), HCl-extractable Po (HCl-Po), NaOH-extractable Po (NaOH-Po), and phytate P (Phyt-P) were determined in soil samples (0–15 cm) from 15 sampling sites representing three types of grassland (i.e., desert steppe, typical steppe, and meadow steppe) in Inner Mongolia. The influencing factors of the soil Po fractions were determined by redundancy analysis (RDA). Soil Po content accounted for 61.0% of the total P (TP) on average. NaOH-Po was the main fraction of Po, accounting for 49.1% of Po on average; H2O-Po content accounted for the least amount of Po (mean 1.3 mg kg−1). H2O-Po and HCl-Po were not significantly different among the three steppes. The contents of NaHCO3-Po increased in the order of desert steppe < typical steppe < meadow steppe, and the trend of NaOH-Po and Phyt-P contents were desert steppe < meadow steppe < typical steppe. Pearson correlation analysis showed that NaHCO3-Po was positively correlated with AP (r = 0.86, p < 0.01). HCl-Po was negatively correlated with AP (r = − 0.56, p < 0.05). NaOH-Po and Phyt-P were significantly positively correlated with NaHCO3-extractable inorganic P (NaHCO3-Pi); Phyt-P was also negatively correlated with HCl-extractable Pi (HCl-Pi) (r = − 0.61, p < 0.05). These correlations were mainly caused by differences in steppe types and soil properties caused by climatic conditions, as shown by the result of RDA analysis. Soil Po plays an indispensable role in the supply of soil P in the semi-arid steppe of Inner Mongolia, where NaHCO3-Po and HCl-Po strongly contributed to AP. In addition, NaOH-Po and Phyt-P as a part of stable pools are important for providing P to other P pools. Po fractions in steppe soils were mainly regulated by climatic conditions and are closely related to the soil organic matter and pH.

A new simple approach to assess sediment yield at a large scale with high landscape diversity: an example of Morocco

Sedimentation of dams and soil erosion remain a worldwide issue, this is especially true in countries characterized by great environmental diversity where their assessment remains a serious difficult issue. Morocco ranks among countries with the greatest achievements in the dams field in Africa, characterized by a great climate, vegetation cover and morphological diversity. The objective of this study was to identify the spatial distribution of Sediment Yield (SY) and Area-Specific Sediment Yield (SSY) on the country scale and to present a new simple approach by exploiting the statistical tool to assess their controlling factors. We collected and analyzed environmental data of 42 catchments of the biggest and most important dams of the country of Morocco. The adopted statistical methodology reveals that Moroccan catchments can be subdivided into 5 categories (depending on climate, morphology and vegetation cover conditions) in which SY is most related to the catchment area and drainage network length, while SSY is mostly related to the soil organic carbon stock, rainfall and clay fraction. Our approach provides important new insights regarding modelling catchment scale sediments dynamic to asses SY and SSY in different regions around the world, especially in large scale and where there is a great environmental diversity.

Long‐term fertilization does not affect soil carbon/nitrogen/sulfur ratios or the proportion between labile and nonlabile fractions in Mollisols

AbstractAgricultural management practices such as fertilization may affect the overall soil quality and nutrient supply capacity. In this study, we hypothesized that long‐term fertilization promotes (a) an increase in the proportion of easily degradable soil organic C, N, and S fractions and (b) changes in the soil C, N, and S stoichiometric ratios in the direction of favoring the specific nutrient added to the soil. We included S in our study due to the increasing importance of S fertilization in many agricultural soils. A long‐term experiment involving six fertilization treatments and maize (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) as cash crops was conducted for 14 yr in an on‐farm network located in the Pampean region (Argentina). Long‐term fertilization did not have a central role in defining the C, N, and S distribution between soil organic fractions or their stoichiometric ratios since the particulate organic matter (POM)‐C/total C, POM‐S/total S, C/N, C/N, and N/S ratios were not affected by fertilization treatments and the mineralizable N/total N ratio varied in a very short range. Instead, long‐term fertilization increased residue C inputs to the soil (8.7–19 Mg ha−1 over the unfertilized control) and, in turn, increases in soil total C, N, and S followed a linear relationship with residue inputs. This relationship was not affected by fertilization or site factors. These data contribute to understanding of the effects of continued fertilization on soil properties such as the distribution of fast‐ and slow‐cycling organic matter and nutrient concentrations, which are essential for effectively managing soils for sustainable agriculture.

Changes in Soil Organic Carbon Fractions Across a Loess Toposequence

Soil organic carbon fractions may vary with soil development and soil genesis controls its vertical distribution. The objectives of this study were to determine organic carbon fractions in soil derived from loess parent material and the role of relief in its vertical distribution. Five soil pedons, i.e., Typic Ustorthents (Rajar), Typic Calciustepts (Missa), Udic Calciustepts (Basal), Udic Haplustalfs (Guliana), and Typic Hapludalfs (Mansehra), were selected along a loess toposequence and sampled at genetic horizon level. Soils were characterized for texture, pH, calcium carbonate (CaCO3), and organic carbon fractions including total organic carbon (TOC), dissolved organic carbon (DOC), particulate organic carbon (POC), HCl-insoluble organic carbon, and density fractions, i.e., heavy fraction (HF) and light fraction (LF). Total organic carbon content ranged from 0.03 to 0.98% in these soils and significantly differed with soil depth within each soil and soil type. Mansehra and Guliana had 0.04 and 0.031% POC, respectively, which was greater compared to remaining soils. Dissolved organic carbon was greater in the Basal followed by Mansehra, Rajar, Missa, and Guliana soil profiles, and distribution remains uniform throughout the profile’s depth. Insoluble C fraction was 0.214% in Mansehra profiles followed by 0.156% in Rajar, 0.078% in Basal, 0.063% in Guliana, and 0.091% in Missa soil profiles. The Mansehra soil profiles had the highest (0.008 and 0.30%) content of both light and heavy fractions. Total organic carbon had little correlation with clay. Particulate organic carbon, DOC, and HCl-insoluble organic carbon had a significant correlation with TOC. The HF had the strongest correlation with TOC, while LF had a negative correlation. The soil organic fractions significantly differed with soil type and soil genesis. The soils at gentle slopes are dominant in most of the organic carbon fractions due to higher development stage.

Organo-metallic complex and its implications

Complex formation is the reaction of a metal ion and ligands through electron pair sharing and the resulting product is called the metal coordination compound. The metal ion is the electron-pair acceptor, and the ligand is the electron-pair donor. The metal ion serves as the central ion, and the organic ions are coordinated around it in a first coordination sphere.Covelo et al., 2008 studied the heavy metal sorption and desorption behavior of a Fibric Histosol with that of its organo mineral fraction (OMF) and reported that greatest sorption capacity was for lead and copper. Urrutia et al., 2013 studied the physico-chemical characteristics of diverse types of humic-metal-phosphate acid complexes and reported that molecular size distribution of humic-metal-phosphate as a function of pH is similar to that of potassium or sodium humates and metal-humate complexes. Eshwar et al., 2017 studied the stability constant of Fe(II), Cu(II), Mn(II) and Zn(II) metal ion complexes with HA/FA at pH 7 and at 30 ⁰C and reported that for humic acid the log k values was highest for Cu (II) and in case of fulvic acid the log k values was highest for Mn (II). Mukhopadhyay and Sanyal, 2004 studied the release potential of arsenic (As) from arsenic-humic/fulvic complexes by soluble phosphate nitrate salt and examined it in terms of the appropriate exchange isotherms and reported that phosphate had a greater degree of exchangeability with arsenic than did nitrate, at both the lower and higher concentrations and also reported that stability constant of synthetic HA/FA were greater than that of natural HA/FA.Sinha and Bhattacharyya, 2011 studied the release isotherm of As from the HA/FA complexes extracted from vermicompost and FYM in presence of molybdate, nitrate, phosphate, sulfate and borate and reported that the greatest tendency to displace As from the complexes was shown by sulphate, molybdate, and nitrate. Datta et al., 2001 studied the stability constant of complexes formed by the humic acid with Cd2+ ions in aqueous phase and reported that humic phenolic-OH group was involved in the formation of Cd2+ -humic complexShahid et al., 2012 studied the effects of different organic ligands like ethylene diamine tetra-acetic acid (EDTA), low molecular weight organic acids, humic substances on lead speciation and reported that EDTA forms soluble, stable, and phytoavailable Pb-chelates due to high binding lead affinity. He et al., 2016 studied the binding behavior of Cu+2 to all ten HA fraction and reported that the FTIR and SEM-EDX image of HA fraction revealed that carboxyl and phenolic groups were responsible for the Cu2+ sorption on the ten sequentially extracted HA fractions process. Higher molecular weight humic acids bind heavy metals more strongly than low molecular weight acids, and the study of soil organic fractions that can sorb heavy metals moderating its toxicity in the soil/crop system and preventing its entry in the food chain should be explored in future.

Legume-based silvopastoral systems drive C and N soil stocks in a subhumid tropical environment

Silvopastoral systems include trees or shrubs and grasses and are considered a sustainable method of restoring degraded pastures and increasing carbon and nitrogen stocks in tropical soils. We hypothesize that establishing shrub-tree legumes in a signalgrass pasture has the potential to increase soil C and N stocks. Thus, we investigated a silvopastoral system over four years in a subhumid tropical zone in northeastern Brazil to determine the soil C and N stocks and the organic matter chemical fractions. The experimental design consisted of i-pure signalgrass (Brachiaria decumbens), ii-signalgrass intercropped with gliricidia (Gliricidia sepium) and iii-signalgrass intercropped with sabiá (Mimosa caesalpiniaefolia). Measurements were taken at 0, 4 and 8 m away from the legume rows and at random in the pure signalgrass pasture. Soil samples were obtained in the second and fourth years after silvopastoral system implementation at 0–10, 10–20, 20–40, 40–60 and 60–100 cm soil depths at each distance in triplicate to produce compound samples. These were used to determine the C and N contents and stocks, as well as the soil organic matter chemical fractions. Within two years, the gliricidia and sabiá soil C stocks directly below the legume row at 100 cm depth increased by 45% and 35%, respectively, while the soil N stock tripled at all distances. The soil organic matter increased over the two years, and the humin proportion in the soil organic matter (SOM) increased in the silvopastoral system soils. Overall, after four years of silvopastoral system establishment, this system showed the potential to store N and achieve soil C stock levels that are within the global average range for these systems.

Polycyclic aromatic hydrocarbon concentrations in soils of greenhouses located in Aksu Antalya, Turkey.

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic organic compounds that are generally absorbed on organic fraction of soils. It is known that some PAHs, which can pass to air, soil, water and food as a result of natural or anthropogenic processes, have carcinogenic, toxic and mutagenic effects on humans and animals. One of the important steps that is identified in the transition takes place during agricultural production. Greenhouses are commonly used as a type of agricultural production especially during the winter season in mid and temperate climates. Greenhouse cultivation is abundant in Antalya Aksu Region in Turkey. Two sampling campaigns (autumn and winter) were carried out to sample the soils in 53 glass and polyethylene covered greenhouses. The samples were analysed with gas chromatography-mass spectrometry (GC/MS) for 16 PAHs. The result showed that four ring PAHs were dominant in the region. In the winter season, PAHs concentrations increase because of low volatility of motor vehicle exhaust related PAHs in the atmosphere and of coal and wood combustion emissions used in the heating of greenhouses and surrounding village houses. The cross plots of diagnostic ratios also confirmed coal and wood combustion and traffic emissions in the region.

Effects of long-term fertilization on soil organic phosphorus fractions and wheat yield in farmland of Loess Plateau

Understanding the effects of long-term fertilization on soil organic phosphorus fractions and wheat yield in the Loess Plateau can provide theoretical support for improving phosphorus conversion, utilization, and rational use of fertilizer. We examined the effects of different fertilizer treatments on soil organic phosphorus fractions, wheat yield and soil properties of a farmland in the long-term (1984-2016) positioning test station of Changwu loess soil. There were eight treatments, including no fertilizer (CK), single application of nitrogen fertilizer (N), single application of phosphorus fertilizer (P), application of nitrogen and phosphorus fertilizer (NP), single application of organic fertilizer (M), nitrogen combined with organic fertilizer (MN), phosphorus combined with organic fertilizer (MP), nitrogen and phosphorus combined with organic fertilizer (MNP). The results showed that the range of soil organic phosphorus content was 244.7-429.1 mg·kg-1 after long-term fertilization. Except for the N treatment, organic phosphorus content was significantly increased by 15.4%-47.9% compared to CK. Long-term application of phosphorus fertilizer changed the content of organic phosphorus fractions in the surface soil (0-20 cm). The treatments of MP and MNP significantly increased the contents of labile organic phosphorus and moderately labile organic phosphorus. The treatments of N, P and NP significantly reduced the content of moderately stable organic phosphorus. The treatments of N, P, NP, MN, MP, MNP all significantly increased the highly stable organic phosphorus. The ratio of soil organic phosphorus fractions to total organic phosphorus content was in order of moderately labile organic phosphorus > highly stable organic phosphorus > labile organic phosphorus > moderately stable organic phosphorus. After long-term fertilizer application, the combination of nitrogen and phosphorus fertilizers, especially with organic fertilizers, significantly increased wheat biomass yield and grain yield. Among all the examined soil properties, organic matter, Olsen-P and total inorganic phosphorus were significantly positively correlated with wheat yield. MP and M could significantly increase the content of Olsen-P, total phosphorus, total inorganic phosphorus, labile organic phosphorus and moderately labile organic phosphorus in the loess soil of Loess Plateau. Our results indicated that the organic and phosphorus fertilizers could improve soil phosphorus components that could be more easily absorbed by crops. In summary, the combination of nitrogen and phosphorus fertilizers, especially with organic fertilizers, could increase soil phosphorus supply in the region and promote the wheat yield, which is important for improving soil quality in the Loess Plateau.

Early response of organic matter dynamics to pine‐biochar in sandy soil under peach trees

AbstractBiochar may enhance soil health in sandy soils under peach [Prunus persica (L.) Batsch] tree production. A study was initiated in the Sandhills of North Carolina by applying pine‐biochar at two different rates (5 and 10%, v/v) and types of application (incorporation to 30 cm [‐Inc] and surface [‐Sur]) in 2017. Soil organic matter (SOM) dynamics was assessed via soil organic carbon (SOC), total nitrogen (TN), permanganate‐oxidizable carbon (POXC), aggregate fractions (macro‐, micro‐aggregates, and clay + silt particles), and enzyme activities (CNPS activity) at 0–15 and 15–30 cm in 2018 and 2019. After the first year of pine‐biochar application, POXC decreased in all biochar treatments, SOC was higher in the 10%‐Inc treatment, whereas CNPS activities and macroaggregates were highest in the 5%‐Sur compared with the non‐treated control. These results suggest early changes in SOM dynamics and biogeochemical cycling and have the potential to guide producers with the long‐term application of pine‐biochar to sandy soils.

Soil and Tree Nutrient Status of High Elevation Mixed Red Spruce (Picea rubens Sarg.) and Broadleaf Deciduous Forests

Anthropogenic and industrial emissions have resulted in historically high levels of acidic deposition into central Appalachian forests. Despite the reduction in acidic inputs due to legislation curbing industrial emissions in the United States, continued N deposition may impact forest ecosystems. Soil and foliar samples were collected from four high elevation red spruce sites along a modeled gradient of historic N deposition. The three most abundant tree species at all sites, Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg., were sampled. Bulk soil beneath the canopies of individual trees were collected from the top 15-cm and separated into organic and mineral fractions for analysis. Mehlich-III soil extracts of soil fractions and foliar digests from these trees were subjected to elemental analysis. Soil N concentrations supported the presence of a N deposition gradient: in organic horizon soil fractions, N concentrations were driven by precipitation volume and elevation; whereas in mineral soil fractions, N concentration was explained by modeled N deposition rate and elevation. In organic fractions, significant reductions in Ca, K, and P were evident as N deposition increased, whereas the Ca:Sr ratio increased. Foliar Ca, K, and Sr declined in foliage with increasing N deposition, with concomitant increases in foliar Ca:Sr ratios. Although the three species were sympatric in mixed stands at all four sites, the foliar–soil nutrient associations differed among them across the gradient, indicating differential uptake and cycling of nutrients/metals by these forest tree species.

Impact of deadwood decomposition on soil organic carbon sequestration in Estonian and Polish forests

Key messageThe deadwood of different tree species with different decomposition rates affects soil organic carbon sequestration in Estonian and Polish forests. In warmer conditions (Poland), the deadwood decomposition process had a higher rate than in cooler Estonian forests. Soil organic matter fractions analysis can be used to assess the stability and turnover of organic carbon between deadwood and soil in different experimental localities.ContextDeadwood is an important element of properly functioning forest ecosystem and plays a very important role in the maintenance of biodiversity, soil fertility, and carbon sequestration.AimsThe main aim was to estimate how decomposition of deadwood of different tree species with different decomposition rates affects soil organic carbon sequestration in Estonian and Polish forests.MethodsThe investigation was carried out in six forests in Poland (51° N) and Estonia (58° N). The study localities differ in their mean annual air temperature (of 2 °C) and the length of the growing season (of 1 month). The deadwood logs of Norway spruce (Picea abies (L.) Karst.), common aspen (Populus tremula L.), and silver birch (Betula pendula Roth) were included in the research. Logs in three stages of decomposition (III–V) were selected for the analysis.ResultsThere were differences in the stock of soil organic carbon in two experimental localities. There was a higher soil carbon content under logs and in their direct vicinity in Polish forests compared to those in the cooler climate of Estonia. Considerable differences in the amount of soil organic matter were found. The light fraction constituted the greatest quantitative component of organic matter of soils associated with deadwood.ConclusionA higher carbon content in surface soil horizons as an effect of deadwood decomposition was determined for the Polish (temperate) forests. More decomposed deadwood affected soil organic matter stabilization more strongly than less decayed deadwood. This relationship was clearer in Polish forests. Higher temperatures and longer growing periods primarily influenced the increase of soil organic matter free light fraction concentrations directly under and in close proximity to logs of the studied species. The slower release of deadwood decomposition products was noted in Estonian (hemiboreal) forests. The soil organic matter mineral fraction increased under aspen and spruce logs at advanced decomposition in Poland.

Effects of Manure Application Rates on the Soil Carbon Fractions and Aggregate Stability

An incubated study was conducted to explore the effect of different manure application dosages (0%, 1%, 2%, and 4%, referred to as T0, T1, T2, and T4, respectively) on dynamic changes in the organic carbon fraction and aggregate stability of soil under different incubation times (120, 180, 240, 300, and 360 days). Soil organic carbon (SOC) and its fractions, such as light fraction organic carbon (LFOC), and polysaccharides, cellulose, water-soluble substance (WSS), fulvic acid carbon (FAC), humic acid carbon (HAC) content, and aggregate stability were measured. The results showed that SOC and its fractions were increased with increasing manure application rates. The SOC, LFOC, polysaccharides, cellulose, WSS, FAC, HAC contents and the HAC/FAC ratio increased by 15.3%-83.2%, 6.8-15.9 times, 8.5%-46.4%, 39.3%-122.6%, 35.7%-112.9%, 3.3%-46.9%, 42.5%-88.3%, and 28.5%-38.6% under T1-T4 treatments, respectively, compared to the T0 treatment at the end of the incubation period. With a longer period of incubation, the contents of SOC and HAC showed a decreasing trend, the LFOC increased first and decreased. The FAC content and the HAC/FAC ratio showed a fluctuation trend, but the content of polysaccharides showed an increasing trend. The application of manure decreased the content of >2 mm mechanically stable aggregates but increased the content of > 0.25 mm water stable aggregates in the soil. The mean weight diameter of water stable aggregate (WMWD) increased by 58.6%, while by the end of the incubation period, the percentage aggregate destruction rate (PAD) decreased by 22.2% under the T4 treatment compared to the T0 treatment. Correlation analysis showed that there was a significant correlation between SOC and its fractions, and between organic carbon fractions (except polysaccharides) and aggregate stability. Path analysis showed that the content of HAC and > 2 mm mechanically stable aggregate had a significant direct impact on the mean weight diameter of mechanically stable aggregate (DMWD) (P<0.05). Furthermore, the content of > 2 mm and < 0.25 mm water stable aggregates had a significant direct impact on the WMWD (P<0.01). The content of<0.25 mm water stable aggregates had a significant direct impact on the PAD (P<0.01), while the content of SOC and WSS had a significant indirect impact on the PAD via a direct effect on the content of<0.25 mm water stable aggregate (P<0.05).

Mecanismos de remoção de Cromo(VI) do solo pela interação entre matéria orgânica e Ferro(III)

A contaminação do solo e águas por cromo (Cr) tem ocorrido frequentemente em áreas industriais e em suas proximidades, muitas vezes devido a acidentes e, também, ao mau gerenciamento de seus resíduos. O cromo na forma hexavalente (Cr(VI)) é extremamente tóxico e cancerígeno, enquanto que na forma trivalente (Cr(III)) e em níveis traço é considerado benéfico aos seres humanos e animais. O presente estudo apresenta uma revisão sobre os principais mecanismos relacionados à interação do Cr(VI) com alguns componentes do solo, quando associado a um evento de contaminação do meio. Observa-se que os principais agentes responsáveis pela remoção do Cr(VI) do meio são aqueles capazes de reduzi-lo à forma trivalente (Cr(III)), como a fração orgânica do solo e o Fe(II). No entanto, minerais e compostos ricos em Fe(III) também podem auxiliar na redução do Cr(VI). Nesse caso, o Fe(III) pode ser reduzido pelo carbono orgânico à forma divalente que, por sua vez, reduz o cromo à forma trivalente, imobilizando-o no solo. Para que isso ocorra, além da presença de matéria orgânica, o pH ácido do meio também auxilia nesse processo – cujas condições são comumente encontradas em solos tropicais, como o Latossolo Vermelho. Portanto, entender como o Cr(VI) reage com os principais componentes do solo é muito importante para auxiliar nos processos de remediação de áreas contaminadas.

Production and Decomposition of Cover Crop Residues and Associations With Soil Organic Fractions

The decomposition of plant residues, the changes in the total organic carbon (TOC) and the fractions of soil organic matter (SOM) occur differently in irrigated areas. The objective of this study was to quantify the biomass production, the decomposition of cover crops residues and relate them with the changes n the content and fractions of SOM in an irrigated area of vegetable crops. Six types of cover crop treatments were evaluated: brachiaria (B); sunn hemp (S); millet (M); B + S; B + M; S + M, plus an additional treatment (native area), with 4 repetitions. The production of fresh (FB) and dry biomass (DB), the rate of plant residue decomposition, TOC, SOM fractions and the coefficient of SOM (QSOM) were quantified. It was observed that the greatest and the lowest volume of crop residues were from the B and S cover crop, respectively. The cover crops in monoculture presented great decomposition rates and short half-life when compared to mixtures of cover crop. The TOC and QSOM were great in the 0 to 0.05 m soil layer, and in the M + S cover crop mixture, when compared to the 0.05 to 0.1 m soil layer and to other cover crops. Among the SOM fractions, the humin predominated in the most superficial soil layer (0 to 0.05 m).

Assessing the effects of 17 years of grazing exclusion in degraded semi-arid soils: Evaluation of soil fertility, nutrients pools and stoichiometry

Grazing exclusion (GE) has been used as a strategy to restore degraded pastures worldwide. In this study, the effects of 17 years of GE on a) soil fertility, b) stoichiometric ratios between soil nutrients and c) carbon (C) and nitrogen (N) storage in particulate and mineral-associated organic matter soil fractions were assessed in an area degraded by overgrazing (OG) in a semi-arid region in Brazil. For this purpose, three sites with two treatments (exclusion and overgrazing) were studied at three sampling depths (0–10, 10–20 and 20–40 cm). Our results showed that pH, total organic carbon, particulate organic carbon, total N, particulate organic nitrogen, Ca2+ and K+ increased, whereas the Al3+ content decreased with GE. Conversely, the available P content, Mg2+ and Na+ showed no significant variations as a function of GE. A relatively constant C:N:P ratio (30:4:1) was observed, with little variation as a function of GE or OG, indicating a high total P content in the soil. Labile fractions (particulate) of C and N increased with GE. According to our results, GE can be used as a strategy to restore degraded natural pastures in arid and semi-arid ecosystems.

The effect of vegetation change in C and N contents in litter and soil organic fractions of a Northern Iran temperate forest

The properties of litter and soil, which are probably influenced by vegetation traits, have an effect on the fractions of C and N and ultimately global warming. In this study, litter and soil samples were collected from representative forestlands, including a mixed natural forest dominated by hornbeam‑ironwood and tree plantations of ash, maple, cypress and pine which are situated in a temperate area of Northern Iran. Main litter characteristics, soil aggregation and fractions of C and N were studied. Pine had the highest values of litter thickness (14.46 cm), C (60.31%) and C/N ratio (81.77 and 20.28 for litter and soil, respectively). However, litter N (2.20%), micro aggregates of total soil (39.75%), aggregate stability (73.86%) and macro aggregates of total soil (54.87%) were found significantly higher under the natural stands. Total C (2.58%), C in macro and micro aggregates (0.31 and 0.33 respectively), POM-C (4. 68 g/kg), DOC (125.54 mg/kg) and C sequestration (45.34 Mg/ha) were considerably higher under pine (for POM-C, pine ≈ cypress) and the greater values of total N (0.34%), N in macro and micro aggregates (0.10 and 0.08 respectively), POM-N (0.47 g/kg), DON (33.80 mg/kg) and N sequestration (6.86 Mg/ha) were observed under natural stands. Under our conditions, conversion of natural forest is due to reduction of soil N fractions and C increased under pine tree plantations.

Integrated Management of Pig Residues and Copper Mine Tailings for Aided Phytostabilization.

There is high demand for identifying socio-environmentally sound ways to dispose of large quantities of offensive odor-generating organic residues produced by intensive livestock farming. The use of these residues as amendments at large-scale mine tailings storage facilities for in situ plant-based reclamation may be a useful alternative. We performed a greenhouse assay to evaluate effectiveness of pig slurries and the solid organic fraction of aerobic-aerated pig slurries, both treated and not treated for odor emission, as amendments for copper tailings. Different doses of slurries or the solid organic fraction of the slurries, untreated and treated with either ozone or a commercial product used to manage strong odors (Just a Drop), were incorporated into tailings and stabilized (15 d) under greenhouse conditions. L. (ryegrass) was used as bioindicator for Cu and Zn toxicity. Plant performance (shoot and root dry biomass, Cu and Zn content in leaves) and general physicochemical characteristics of substrates were evaluated. Our results showed that odor management of pig residues was possible with commercial products, and their incorporation into tailings rapidly and effectively reduced odor emission. The solid organic fraction of the slurries neutralized acidic tailings, and both pig residues increased organic matter and nutrient content in tailings while reducing extractable Cu. As a result, ryegrass productivity was significantly improved by incorporation of either slurries or their solid organic fraction into tailings in a dose-dependent form. Foliar Cu content in ryegrass was not affected but foliar Zn content increased; however, Zn remained within acceptable ranges. Both the pig slurries and their soil organic fractions proved to be valuable residues for tailings reclamation.

Effects of irrigation and nitrogen fertilization on greenhouse soil organic nitrogen fractions and soil-soluble nitrogen pools

Soil organic nitrogen fractions and soil-soluble nitrogen pools are important indicators of soil fertility and plant nutrition requirements. However, little is known about soil organic nitrogen fractions and their correlations with soil mineral nitrogen (SMN) and soluble organic nitrogen (SON). A five-year field experiment was conducted to determine the effects of lower irrigation limits (25, 35, and 45 kPa) and nitrogen fertilization (75, 300, and 525 kg ha−1) rates on greenhouse soil organic nitrogen fractions and soil-soluble nitrogen pools. The results indicated that the soil organic nitrogen fractions and soil-soluble nitrogen pools were significantly affected by the irrigation and nitrogen fertilization rates and their interactions at various greenhouse soil depths (P < 0.01). The soil organic nitrogen occurred mainly in the form of acid-hydrolyzable N (AHN). The soil organic nitrogen fractions other than the amino sugar N (ASN) and the soil-soluble nitrogen pools (SMN and SON) decreased with increasing soil depth. Our findings suggest that ammonium N (AN), amino acid N (AAN), and SMN may predict the soil nitrogen supply potential in greenhouse agroecosystems. Soil total nitrogen (Ntotal), soil organic carbon (SOC), and nitrate nitrogen (NO3−-N) appeared to be the major factors explaining the soil organic nitrogen fractions. Considering water saving, nitrogen reduction, and soil nitrogen supply optimization, it was concluded that the best schedules to use in the greenhouse were I2N1 and I2N2 treatments.