Organic Matter Fractions In Soils Research Articles

TOTAL AND PARTICULATE CONTENTS AND VERTICAL STRATIFICATION OF ORGANIC CARBON IN AGROFORESTRY SYSTEM IN CAATINGA

ABSTRACT The objective of this work was to evaluate the variation in total and particulate organic carbon contents, carbon vertical stratification, and sensitivity index of organic matter fractions in soils with organic residues arranged in alleys in an agroforestry system, with and without use of fire, in the Caatinga biome, in Brazil. The experiment was conducted in a split-plot arrangement with four replications, with the factor fire in the plots, and the factor organic residues in the subplots. The organic residues used consisted of Gliricidia sepium plants; G. sepium plants and carnauba processing residue; G. sepium plants and bio-compost; and G. sepium plants, carnauba processing residue, and bio-compost, which were evaluated in three soil layers. The alleys with carnauba processing residue, G. sepium plants, and bio-compost presented a better maintenance of particulate, and mineral-associated organic carbon contents. Thus, the agroforestry management in alleys using these three residues was efficient for the maintenance of labile and recalcitrant organic matter compartments. Particulate organic carbon was more sensitive to changes in soil management than total organic matter content, in all alleys, presenting higher sensitivity indexes.

A Dielectric Mixing Model Accounting for Soil Organic Matter

Core Ideas In the proposed model, the wilting point and porosity are a function of organic matter. In organic‐rich soil, the model improves accuracy of the microwave radiative transfer model. The model is applicable for both portable and satellite soil moisture sensors. Most dielectric mixing models have been developed for mineral soils without extensive consideration of organic matter (OM). In addition, when used for in situ measurement, most of these models focus only on the real part of the effective dielectric constant without the corresponding imaginary part. Organic matter fractions in soils are found globally (57%), with an especially significant amount in the boreal region (17%). Without proper consideration of OM in dielectric mixing models and subsequent microwave radiative transfer modeling, brightness temperature (TB) calculations may be erroneous. This would lead to uncertainties in the estimation of higher level products, such as soil moisture retrievals from portable soil moisture sensors (e.g., time‐domain reflectometers) or passive microwave sensors onboard the Soil Moisture Active Passive (SMAP), Soil Moisture and Ocean Salinity (SMOS), and Advanced Microwave Scanning Radiometer (AMSR2) satellites. We incorporated OM into a dielectric mixing model by adjusting the wilting point and porosity according to the OM content, i.e., the effective soil dielectric constant decreases with higher OM due to a decrease in the fraction of free water and an increase in bound water. With the proposed soil parameters in the dielectric mixing model, high levels of OM increase the TB for a specific soil moisture by decreasing the microwave effective dielectric constant. The simulated TB better reproduced SMAP‐observed TB (11% in RMSE) through the improvement of the effective dielectric constant (40% reduction in RMSE). We anticipate that the application of our approach can improve microwave‐based surface soil moisture retrievals in areas with high OM.

English

A speciation study of selected heavy metals in soil and stream sediments around a hospital waste dumpsite was investigated. Sequential extraction procedure was used to fractionate the metals into 4 fractions: Exchangeable and bound to carbonate, oxyhydroxide of Fe and Mn, organic matter and the residual fraction. Speciation analysis of Fe, Mn, Zn, Cu, Cd and Pb in soil revealed that a major portion of the metals were associated with the residual fraction. The exchangeable and carbonate fraction was the most important fraction for Mn(Dry/Wet) and Zn(Dry/Wet) with an average of (27%, 35.6%) Mn and (20.8%, 27.3% ) Zn. Cd, Fe and Cu were associated with the oxyhydroxide of Fe and Mn fraction with an average of (61%, 44.2%) Cd(Dry/Wet), (41%, 21%) Fe(Dry/Wet) and (25.3%, 22.5%) Cu(Dry/Wet). A significant amount of Pb(Dry/Wet) (10.7%, 21.8%) was bound to  organic fraction during dry and wet season respectively. In sediments, Mn(Dry/Wet) occurred mainly in exchangeable and carbonate fraction (45.2%, 29.3%), Fe(Dry/Wet) and Cd(Dry/Wet) in the oxyhydroxide of Fe and Mn fraction were (41%, 31.2%) and (26.6%, 93.6%) respectively and the amount of Pb(Dry/Wet) bound to the organic fraction was (86.9%, 27.3%). A significant amount of Cu(Dry/Wet) (20.8%, 29.4%) was bound to the organic fraction and Zn(Dry/Wet) (35.5%, 73%) was retained in the residual fraction. In soil and sediments, Mn was potentially more bioavailable.  However, the level of lead in organic matter fraction of soil suggest that it may be remobilized under oxidizing condition, hence, bioavailable.   Keywords: Speciation, hospital waste, heavy metal, sediments, soil.

Distribution and thermal stability of physically and chemically protected organic matter fractions in soils across different ecosystems

Accrual of carbon (C) and nitrogen (N) in soil is a significant and realizable management option to mitigate climate change; thus, a clear understanding of the mechanisms controlling the persistence of C and N in soil organic matter (SOM) across different ecosystems has never been more needed. Here, we investigated SOM distribution between physically and chemically stabilized fractions in soils from a variety of ecosystems (i.e., coniferous and broadleaved forest soils, grassland soils, technosols, and agricultural soils). Using elemental and thermal analyses, we examined changes in the quantity and quality of physically fractionated SOM pools characterized by different mechanisms of protection from decomposition. Independently of the ecosystem type, most of the organic C and total N were found in the mineral-associated SOM pool, known to be protected mainly by chemical mechanisms. Indexes of thermal stability and C/N ratio of this heavy SOM fraction were lower (especially in agricultural soils) compared to light SOM fractions found free or occluded in aggregates, and suggested a marked presence of inherently labile compounds. Our results confirm that the association of labile organic molecules with soil minerals is a major stabilization mechanism of SOM, and demonstrate that this is a generalizable finding occurring across different mineral soils and ecosystems.

Changes in the stocks of C and N in organic matter fractions in soil cropped with coffee and fertilized with sunn hemp and ammonium sulfate

Despite the potential to provide N to crops, the rapid incorporation of green manure nutrients into stable fractions of organic matter in the soil (SOM) may reduce the efficiency of green manuring. Thus, the objective of this work was to characterize the changes of C and N stocks in fractions of SOM cultivated with coffee (Coffea arabica L.) and fertilized with sunn hemp (Crotalaria juncea) and ammonium sulfate. To study the changes in organic C (OC) and total N (TN) in soil and fractions of SOM over time, soil samples were collected in the 0–5 and 5–10 cm layers, with the initial sampling done prior to the application of sunn hemp residues and ammonium sulfate. Five samples were collected every 2 months after the application of the legume and ammonium sulfate. The soil samples were submitted to densimetric and granulometric fractionation, obtaining the free light organic matter (F-LOM), particulate organic matter (POM), and organic matter associated with minerals (MAM). OC and TN stocks were then determined in soil and the SOM fractions. The changes in the stocks of OC (?StcC) in the soil in relation to time zero were positive in the evaluations carried out in the two layers. The fractions of SOM showed positive ?StcC at almost all of the evaluated times. The N supplied to the soil in the form of mineral and organic fertilizer promoted an increase of 0.24 Mg ha-1 of N in the 0–5 cm layer until after 60 days. Of this total, 0.03 Mg ha-1 was associated with F-LOM, 0.07 Mg ha-1 with POM, and the remainder was associated with MAM. Nearly 60% of the N that was supplied to the soil was drawn to the stable fractions of the SOM, indicating a rapid stabilization of this nutrient in the most recalcitrant organic compartments. Despite that, the variations in N stocks of MAM became smaller over time, and eventually became negative, in relation to time zero. This indicates the mineralization of N of this compartment. In the 5–10 cm layer, no effect of time was observed in the soil TN, N-POM, or N-MAM stocks. Additionally, under the conditions of this experiment, the majority of the N supplied to the soil was rapidly incorporated into the most stable fraction of SOM, and this might can reduced the efficiency of the green manuring.

Impacts of Smallholder Land Use on Physical-Based Soil Organic Matter Fractions in Soils with Varying Texture in Ecotopes of Eastern Cape Province, South Africa

ABSTRACTPhysical-based fractions of SOM were examined. Soil carbon (C) and nitrogen (N) across ecotopes were 17.22 g kg−1 and 3.73 g kg−1, respectively. Soil C and N were higher in conventional tillage (CT) than no-till (NT) by 2.94% and 0.94%, respectively. Soil C ranged from 11.09 g kg−1 in silt to 18.02 g kg−1 in coarse sand; from 12.89 g kg−1 in fine sand to 18.88 g kg−1 in clay under NT and CT, respectively. Soil N ranged from 4.54 g kg−1 in silt to 5.55 g kg−1 in clay; from 5.06 g kg−1 in coarse sand to 5.56 g kg−1 in silt under NT and CT, respectively. Soil N in bulk soil changed by −3.24% while soil C in bulk soil changed by −11.87%. The silt + clay was saturated; hence, studies on soil C and N dynamics in these ecotopes are advocated.

Organic matter fractions in soil under coffee with split applications of phosphorus and water regimes

Phosphorus fertilization and irrigation management are essential practices to increase coffee yields, though information is scarce about the effect of these practices on organic matter fractions of soils of the ‘Cerrado’ (savanna-like vegetation). The purpose of this study was to evaluate organic matter fractions of a clayey Oxisol under coffee with split applications of phosphorus (P) and water regimes. The experimental design was a randomized block with 3 x 2 factorial arrangement with three split applications of P (P1: 300 kg ha-1 P2O5 applied annually of which 2/3 applied in September and 1/3 in December; P2: 600 kg ha-1 P2O5 applied at planting and every two years, and P3: 1800 kg ha-1 of P2O5 applied only at planting, corresponding to a 6-year requirement), two water regimes (with and without irrigation) and three replications. Soil from the 0-5 and 5-10 cm layers was sampled. The total organic carbon (TOC), labile carbon (LC), microbial carbon (Cmic), and carbon fractions of fulvic acid (FA), humic acid (HA) and humin (HU) were determined. The irrigation regime of coffee increased the TOC, LC and Cmic levels and the humified fractions of soil organic matter. In general, the form of P splitting had little influence on the fractions of soil organic matter.

Fluorescence spectroscopic characterization of dissolved organic matter fractions in soils in soil aquifer treatment

This work investigated the effect of soil aquifer treatment (SAT) operation on the fluorescence characteristics of dissolved organic matter (DOM) fractions in soils through laboratory-scale soil columns with a 2-year operation. The resin adsorption technique (with XAD-8 and XAD-4 resins) was employed to characterize the dissolved organic matter in soils into five fractions, i.e., hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). The synchronous fluorescence spectra revealed the presence of soluble microbial byproduct- and humic acid-like components and polycyclic aromatic compounds in DOM in soils, and SAT operation resulted in the enrichment of these fluorescent materials in all DOM fractions in the surface soil (0-12.5 cm). More importantly, the quantitative method of fluorescence regional integration was used in the analysis of excitation-emission matrix (EEM) spectra of DOM fractions in soils. The cumulative EEM volume (Φ T, n ) results showed that SAT operation led to the enrichment of more fluorescent components in HPO-A and TPI-A, as well as the dominance of less fluorescent components in HPO-N, TPI-N, and HPI in the bottom soil (75-150 cm). Total Φ T, n values, which were calculated as [Formula: see text], suggested an accumulation of fluorescent organic matter in the upper 75 cm of soil as a consequence of SAT operation. The distribution of volumetric fluorescence among five regions (i.e., P i, n ) results revealed that SAT caused the increased content of humic-like fluorophores as well as the decreased content of protein-like fluorophores in both HPO-A and TPI-A in soils.

Frações de carbono em topossequências de solos sob eucalipto com diferentes históricos de uso

No Brasil, boa parte dos plantios florestais tem sido realizada em solos que apresentam algum grau de degradação física, química ou biológica. A proteção ao solo fornecida pelas árvores, em função da deposição de serapilheira, constitui um dos processos de recuperação de áreas degradadas, e, como a matéria orgânica está relacionada com muitos dos atributos físicos, químicos e biológicos do solo, ela se caracteriza como um fator-chave na manutenção da qualidade ambiental de sistemas florestais. Assim, objetivou-se neste trabalho caracterizar frações da matéria orgânica em solos sob cultivo mínimo de eucalipto com diferentes históricos de uso e posições na paisagem. O estudo foi realizado em três hortos florestais (HFs): Terra Dura, Canafístula e Sanga das Pedras, cultivados com eucalipto no Estado do Rio Grande do Sul. Os solos foram amostrados nas profundidades de 0-5, 5-20 e 20-40 cm. Na profundidade de 0-5 cm, a maioria dos Argissolos dos HFs estudados apresentou teores de carbono orgânico (CO) superiores aos de matas nativas adjacentes. Nas áreas cultivadas, há maior armazenamento de CO no HF Canafístula, sendo notados, em geral, menores teores de CO no terço inferior da encosta em relação às outras posições das topossequências avaliadas. O índice de humificação, em geral, é maior nas áreas de mata em comparação às áreas cultivadas; contudo, ele varia em função da profundidade do solo, da posição amostrada na topossequência e do HF avaliado. Nas profundidades de 0-5 e 5-20 cm, a abundância natural de 13C dos HFs é similar à das áreas de mata nativa, porém há maior teor de 13C na camada mais profunda dos solos cultivados, o que sinaliza para a contribuição à matéria orgânica do solo (MOS) de C oriundo das pastagens que antecederam o eucalipto.

Separation of light and heavy organic matter fractions in soil — Testing for proper density cut-off and dispersion level

Density fractionation is frequently applied to separate soil organic matter according to the degree and the mode of interaction with minerals. Density fractions are operationally defined by density cut-off and sonication intensity, which determine the nature of the separated material. However, no tests or general agreements exist on the most appropriate density cut-off as well as on method and intensity of dispersion. Numerous variants have been proposed and applied, with results often contrasting each other and being hard to interpret. Here, we aimed at separating two light fractions (free and occluded into aggregates) composed of almost pure organic material, and one heavy fraction comprising the organic–mineral associations. We tested effects of different density cut-offs and sonication intensities, in combination and separately, on fraction yields, as well as on the fractions' organic carbon, total nitrogen and lignin-derived phenols. We tried to find optimum density cut-offs and sonication intensities, providing light fractions with maximum organic material and minimum contamination by mineral material. Under the test conditions, a density of 1.6gcm−3 gave best results for all test soils, allowing for separation of maximums amounts of almost pure organic material. The density cut-off at 1.6gcm−3 is well in line with previous studies and theoretical considerations, therefore we recommend the use of this density as most suitable for separation of organic debris. Sonication levels for aggregate disruption to achieve complete separation of occluded light organic matter varied amongst soils. The necessary intensity of dispersion relates to the type of soil, depending on the stability of contained aggregates. The application of one single dispersion energy level to different soils may result either in mineral contamination or in incomplete separation of light and heavy fractions as well as in redistribution of organic material amongst fractions. This means there is no single sonication level that can be applied to all soils. Thus, obtaining a meaningful light fraction residing within aggregates (occluded light fraction) requires assessment of the dispersion energy necessary to disrupt the aggregate system of a given soil without dispersion of organic–mineral associations. This can be done in pre-experiments where the soil is fractionated at different sonication levels. The appropriate dispersion is determined by mass yields and OC content of the obtained occluded fractions.

Sorption of atrazine and phenanthrene by organic matter fractions in soil and sediment

Atrazine and phenanthrene (Phen) sorption by nonhydrolyzable carbon (NHC), black carbon (BC), humic acid (HA) and whole sediment and soil samples was examined. Atrazine sorption isotherms were nearly linear. The single-point organic carbon (OC)-normalized distribution coefficients ( K OC) of atrazine for the isolated HA1, NHC1 and BC1 from sediment 1 (ST1) were 36, 550, and 1470 times greater than that of ST1, respectively, indicating the importance of sediment organic matter, particularly the condensed fractions (NHC and BC). Similar sorption capacity of atrazine and Phen by NHC but different isotherm nonlinearity indicated different sorption domains due to their different structure and hydrophobicity. The positive relationship between (O + N)/C ratios of NHC and atrazine log K OC at low concentration suggests H-bonding interactions. This study shows that sediment is probably a less effective sorbent for atrazine than Phen, implying that atrazine applied in sediments or soils may be likely to leach into groundwater.

The behavior of clomazone in the soil environment

Clomazone is a herbicide used to control broadleaf weeds and grasses. Clomazone use in agriculturally important crops and forests for weed control has increased and is a potential water contaminant given its high water solubility (1100 microg mL(-1)). Soil sorption is an environmental fate parameter that may limit its movement to water systems. The authors used model rice and forest soils of California to test clomazone sorption affinity, capacity, desorption, interaction with soil organic matter and behavior with black carbon. Sorption of clomazone to the major organic matter fraction of soil, humic acid (HA) (K(d) = 29-87 L kg(-1)), was greater than to whole soils (K(d) = 2.3-11 L kg(-1)). Increased isotherm non-linearity was observed for the whole soils (N = 0.831-0.893) when compared with the humic acids (N = 0.954-0.999). Desorption isotherm results showed hysteresis, which was greatest at the lowest solution concentration of 0.067 microg mL(-1) for all whole soils and HA extracts. Aliphatic carbon content appeared to contribute to increased isotherm linearity. The results indicate that clomazone does not sorb appreciably to sandy or clay soils. Its sorption affinity and capacity is greater in humic acid, and consequently clomazone has difficulty desorbing from soil organic matter. Sorption appears to follow processes explained by the dual-mode model, the presence of fire residues (black carbon) and a recently proposed sorption mechanism.

Frações da matéria orgânica do solo após três décadas de cultivo de eucalipto no Vale do Rio Doce-MG

As mudanças nas distintas frações da matéria orgânica do solo (MOS) sob cultivo do eucalipto são pouco conhecidas. Assim, o presente trabalho teve como objetivo avaliar o impacto do cultivo do eucalipto nos estoques de C das diversas frações da MOS, em solos ocupados anteriormente por pastagens degradadas, bem como verificar qual fração da MOS constitui-se um indicador mais sensível à mudança de uso do solo. O estudo foi realizado em plantações comerciais de eucalipto em dois locais na região do Vale do Rio Doce-MG (Belo Oriente e Virginópolis), onde foram determinados em amostras dos solos: C orgânico total (COT), C da fração leve (leve livre - FLL e leve oclusa - FLO), da fração pesada (areia - AR, silte + argila - S + A e argila - ARG), da biomassa microbiana (BM) e das frações húmicas (ácidos fúlvicos - FAF, ácidos húmicos - FAH e huminas - FH). Os resultados indicaram que, de maneira geral, os solos sob os diferentes tipos de uso em Virginópolis, em virtude da menor temperatura média anual e maior teor de argila, apresentaram maiores estoques de C em todas as frações da MOS em relação a Belo Oriente. Assim, o seqüestro de C no solo pelo cultivo do eucalipto foi maior em Virginópolis (14,2 t ha-1) que em Belo Oriente (10,0 t ha-1), resultando numa taxa de seqüestro de C de aproximadamente 0,42 e 0,29 t ha-1 ano-1 , respectivamente. Em Belo Oriente, o cultivo do eucalipto favoreceu o aumento no estoque de C das frações ARG, S + A e FH no solo. Comportamento semelhante foi observado para o C das FLL, FAF e FAH, em Virginópolis. Dentre todas as frações da MOS analisadas, a BM e a FLO foram indicadores menos sensíveis às alterações na MOS após três décadas da mudança de uso do solo. Com isso, o COT e a fração leve livre, ácidos fúlvicos, ácidos húmicos e humina foram mais eficientes nesse sentido.

Determination of potentially mineralizable nitrogen and nitrogen in particulate organic matter fractions in soil by visible and near-infrared reflectance spectroscopy

Visible (VIS) and near-infrared reflectance spectroscopy (NIRS) combined with multivariate data analysis was used to predict potentially mineralizable nitrogen (PMN) and nitrogen in particulate organic matter fractions (PSOM-N). Soil samples from a long-term experiment (n=24) as well as soils under commercial management (n=160) in Uruguay (South America) were analysed. Samples were scanned in a NIRS 6500 monochromator instrument by reflectance (400–2500 nm). Modified partial least square regression (MPLS) and cross validation were used to develop the calibration models between NIRS data and reference values. NIRS calibration models gave a coefficient of determination for the calibration (R2CAL)>0·80 and the standard deviation of reference data to standard error in cross validation (RPD) ratio ranging from 2 to 5·5 for the variables evaluated. The results obtained in the study showed that NIRS could have the potential to determine PMN and PSOM-N fractions in soils under different agronomic conditions. However, the relatively limited number of samples led us to be cautious in terms of conclusions and to extend the results of this work to similar conditions.

Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .VI. Loss of total nitrogen from different particle size and density fractions

The dynamics of total N in particle-size and density fractions of six major soils which have been used for cereal cropping for 20-70 years were studied in order to identify the labile organic matter fractions in soil. For virgin soils, no single particle-size was consistently enriched in N as compared with the whole soil. The clay fraction contained the largest proportion (53% overall) of total N. Silt-size and sand-size N fractions accounted for 26% and 21% of total N, respectively. Upon cultivation, the sand-size fraction lost most of its N (as much as 89% in Langlands-Logie soil). However, N losses also occurred from silt-size and clay-size fractions in most soils. Changes in C : N ratios of different particle-size fractions upon cultivation were not consistent in all soils, possibly because of the transfer of organic C and N among these fractions. Therefore, the separation of labile organic matter fractions from the whole soil based upon particle-size may not be successful in all soils. On the other hand, the density fractionation of soil into a light fraction (<2 Mg m-3) containing relatively labile organic matter (76-96% lost upon cultivation) and a heavy fraction (>2 Mg m-3) containing less labile organic matter appears to be more successful in most soils. It is suggested that the cultural practices that enhance the amount of light fraction would increase the rate of nutrient cycling through microbial biomass and may increase the overall availability of nutrients in soil.