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1.
Accurate measurement of soil organic carbon (SOC) is dependent on precise and fast methods for the separation of organic and inorganic carbon. The widely used methods involving thermal decomposition of soil samples at a specific temperature in an automated carbon (C) analyzer are susceptible to interference by carbonates and overestimation of organic C, and thus removal of carbonates by acid pretreatment of samples is recommended. Two carbonate-removal pretreatments including hydrochloric (HCl) acid addition and HCl fumigation are compared using the calcium carbonate (CaCO3) standard and soil samples of varying SOC contents. Both pretreatment methods provided similar measurements of organic C, indicating that both methods are efficient in removal of carbonates present in the soil. However, the HCl fumigation method exhibited greater accuracy and precision compared to the HCl addition method. Hence, SOC measurement procedure involving HCl fumigation as a pretreatment for the removal of carbonates is recommended for carbonate-rich soils.  相似文献   

2.
Siderite (FeCO3) is an iron carbonate mineral commonly found in sediments and soils. Similarly to other carbonates, such as calcite or dolomite, it may substantially affect the quantification of organic carbon (C) as well as determination of C isotope ratio of soil organic matter. Both analyses require effective removal of siderite by pretreatment with acid. However, little is known about the siderite removal efficiency of the acid pretreatment methods which have been previously proposed in the literature. In our study, we tested three previously proposed carbonate removal methods for siderite removal in siderite‐containing soils. Furthermore, we tested whether siderite C content in a soil sample can be detected as CO2 evolved after H3PO4 addition which would allow organic C determination from the difference between total and inorganic C. None of the three tested pretreatment methods led to sufficient removal of siderite C when applied on siderite alone. Therefore, we developed a new protocol for a 4‐day treatment with 10% HCl at 25°C. At siderite content of up to 10 wt.%, the removal efficiency of our method (99–100%) was sufficient both for organic C as well as for C isotope analyses. This was further confirmed with tests on siderite‐containing soils. These showed that the method of Larson et al. ( 2008 ) developed for sediments is also suitable. However, the new protocol provides advantage in terms of less microplate manipulation, capsule overflow and oven use. We found that CO2 is not evolved 2 minutes after H3PO4 addition from siderite in contrast to calcite and dolomite. This fact can be used for separate quantification of inorganic C from calcite/dolomite and siderite, e.g., in studies of their different role in soil development. We showed that siderite‐containing soils require special pretreatment procedure before organic C and 13C/12C analyses. We recommend using our protocol if techniques such as XRD or SEM‐EDS indicate the presence of siderite in soil.  相似文献   

3.
Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO2 produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO3), loess (0.2% CaCO3) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha−1). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O2 consumption and respiratory quotient (RQ=ΔCO2/ΔO2) were monitored, as well as the δ13C composition of the evolved CO2 to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO2 produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O2 consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO2 in alkaline soils. This CO2 excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ13C signatures confirmed that the CO2 produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO2 production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O2 consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data.  相似文献   

4.
Dolomite (CaMg(CO3)2) constitutes half of the global carbonates. Thus, many calcareous soils have been developing rather from dolomitic rocks than from calcite (CaCO3)‐dominated limestone. We developed a physical fractionation procedure based on three fractionation steps, using sonication with subsequent density fractionation to separate soil organic matter (SOM) from dolomite‐derived soil constituents. The method avoids acidic pretreatment for destruction of carbonates but aims at separating out carbonate minerals according to density. The fractionation was tested on three soils developed on dolostone parent material (alluvial gravel and solid rock), differing in organic‐C (OC) and inorganic‐C (IC) concentrations and degree of carbonate weathering. Soil samples were suspended and centrifuged in Na‐polytungstate (SPT) solutions of increasing density, resulting in five different fractions: two light fractions < 1.8 g cm–3 (> 20 μm and < 20 μm), rich in OC and free of carbonate, and two organomineral fractions (1.8–2.4 g cm–3 and 2.4–2.6 g cm–3), containing 66–145 mg g–1 and 16–29 mg g–1 OC. The organomineral fractions consist of residual clay from carbonate weathering such as clay minerals and iron oxides associated with SOM. The fifth fraction (> 2.6 g cm–3) was dominated by dolomite (85%–95%). The density separation yielded fractions differing in mineral compositions, as well as in SOM, indicated by soil‐type‐specific OC distributions and decreasing OC : N ratios with increasing density of fractions. The presented method is applicable to a wide range of dolomitic and most likely to all other calcareous soils.  相似文献   

5.
用激光衍射法评价有机物和和碳酸盐对土壤团聚的作用   总被引：5，自引：0，他引：5  
>Aggregation in many soils in semi-arid land is affected by their high carbonate contents.The presence of lithogenic and/or primary carbonates can also inffuence the role of soil organic matter(SOM) in aggregation.The role of carbonates and SOM in aggregation was evaluated by comparing the grain-size distribution in two carbonate-rich soils(15% and 30% carbonates) under conventional tillage after different disaggregating treatments.We also compared the effect of no-tillage and conventional tillage on the role of these two aggregating agents in the soil with 30% of carbonates.Soil samples were treated as four different ways:shaking with water(control),adding hydrochloric acid(HCl) to remove carbonates,adding hydrogen peroxide(H2O2) to remove organic matter,and consecutive removal of carbonates and organic matter(HCl + H2O2),and then analyzed by laser diffraction grain-sizing.The results showed that different contributions of carbonates and SOM to aggregate formation and stability depended not only on their natural proportion,but also on the soil type,as expressed by the major role of carbonates in aggregation in the 15% carbonate-rich soil,with a greater SOC-to-SIC(soil organic C to soil inorganic C) ratio than the 30% carbonate-rich soil.The increased organic matter stocks under no-tillage could moderate the role of carbonates in aggregation in a given soil,which meant that no-tillage could affect the organic and the inorganic C cycles in the soil.In conclusion,the relative role of carbonates and SOM in aggregation could alter the aggregates hierarchy in carbonate-rich soils.  相似文献   

6.
Isotopic fractionation of dissolved organic carbon percolating through the soil is often interpreted as due to microbial transformation. We investigated the potential effects of sorption on the δ13C of dissolved organic C in field and laboratory experiments. We sampled the organic C in soil water at two forested sites and measured sorption with intact mineral soil and individual minerals (dolomite, ferrihydrite, goethite, and quartz). The dissolved organic C was separated into hydrophilic and hydrophobic fractions using a resin approach. The δ13C values of bulk soils, alkaline‐extractable organic C, and dissolved organic C and its fractions were measured. Hydrophilic and hydrophobic fractions in forest floor seepage water were characterized by 13C‐NMR spectroscopy. At both sites, δ13C of dissolved organic C increased with increasing depth, suggesting that decomposition contributes to the loss of the dissolved organic C. However, there was an enrichment of hydrophilic organic C in the soil solution as the water moved down the soil. The δ13C values of hydrophilic fractions were less negative than those of hydrophobic fractions. The smaller δ13C in the hydrophobic fraction was due to the large contribution of compounds derived from lignin that are depleted in 13C. As the isotope composition of both fractions of dissolved organic C did not change throughout the profile, changes in δ13C of total organic C reflected changes in the relative proportions of its hydrophilic and hydrophobic fractions. The sorption experiments with minerals and soil cores gave similar results. When dissolved organic C came into contact with mineral material, the δ13C of that remaining in solution increased due to preferential sorption of the 13C‐depleted hydrophobic fractions. Moreover, the soils released hydrophilic organic C with large δ13C values, increasing the δ13C of organic C in effluents from soil compared with that in the inflow. Thus, selective sorption of organic C fractions changes δ13C in a way that mimics metabolic transformation and decomposition.  相似文献   

7.
Determination of the labile soil carbon (C) and nitrogen (N) fractions and measurement of their isotopic signatures (δ13C and δ15N) has been used widely for characterizing soil C and N transformations. However, methodological questions and comparison of results of different authors have not been fully solved. We studied concentrations and δ13C and δ15N of salt‐extractable organic carbon (SEOC), inorganic (N–NH4+ and N–NO3?) and organic nitrogen (SEON) and salt‐extractable microbial C (SEMC) and N (SEMN) in 0.05 and 0.5 m K2SO4 extracts from a range of soils in Russia. Despite differences in acidity, organic matter and N content and C and N availability in the studied soils, we found consistent patterns of effects of K2SO4 concentration on C and N extractability. Organic C and N were extracted 1.6–5.5 times more effectively with 0.5 m K2SO4 than with 0.05 m K2SO4. Extra SEOC extractability with greater K2SO4 concentrations did not depend on soil properties within a wide range of pH and organic matter concentrations, but the effect was more pronounced in the most acidic and organic‐rich mountain Umbrisols. Extractable microbial C was not affected by K2SO4 concentrations, while SEMN was greater when extracted with 0.5 m K2SO4. We demonstrate that the δ13C and δ15N values of extractable non‐microbial and microbial C and N are not affected by K2SO4 concentrations, but use of a small concentration of extract (0.05 m K2SO4) gives more consistent isotopic results than a larger concentration (0.5 m ).  相似文献   

8.
Profiles of semi-arid-zone soils in Punjab, northwestern India, were investigated for different forms of copper (Cu), including total Cu, diethylenetriaminepentaacetic acid (DTPA)–extractable Cu, soil solution plus exchangeable Cu, Cu adsorbed onto inorganic sites, Cu bound by organic sites, and Cu adsorbed onto oxide surfaces. When all soils were considered, total Cu content ranged from 7 to 37 mg kg?1, while DTPA-extractable and soil solution plus exchangeable Cu contents ranged from 0.30 to 3.26 mg kg?1 and from 0.02 to 0.43 mg kg?1, respectively. Copper adsorbed onto inorganic sites ranged from 0.62 to 2.6 mg kg?1 and that onto oxide surfaces ranged from 2.0 to 13.2 mg kg?1. The Cu bound by organic sites ranged from 1.2 to 12.2 mg kg?1. The magnitudes of different forms of Cu in soils did not exhibit any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Cu. The content of all forms of Cu was generally greater in the fine-textured Alfisols and Inceptisols than coarse-textured Entisols. Soil solution plus exchangeable Cu, Cu held onto organic sites, and and Cu adsorbed onto inorganic sites (crystalline) had significant positive correlations with organic carbon and silt contents.The DTPA Cu was positively correlated with organic carbon, silt, and clay contents. Total Cu content strongly correlated with silt and clay contents of soils. Among the forms, Cu held on the organic site, water soluble + exchangeable Cu, and Cu adsorbed onto oxide surface were positively correlated with DTPA-extractable Cu. The DTPA-extractable Cu and soil solution plus exchangeable Cu seems to be good indices of Cu availability in soils and can be used for correction of Cu deficiency in the soils of the region. The uptake of Cu was greater in fine-textured Inceptisols and Alfisols than coarse-textured Entisols. Among the different forms only DTPA-extractable Cu was positively correlated with total uptake of Cu.  相似文献   

9.
There is a need for a rapid, simple and reliable method of determining soil microbial biomass (SMB) for all soils because traditional methods are laborious. Earlier studies have reported that SMB‐C and ‐N concentrations in grassland and arable soils can be estimated by measurement of UV absorbance in soil extracts. However, these previous studies focused on soils with small soil organic matter (SOM) contents, and there was no consideration of SOM content as a covariate to improve the estimation. In this study, using tropical and temperate forest soils with a wide range of total C (5–204 mg C g?1 soil) and N (1–12 mg N g?1 soil) contents and pH values (4.1–5.9), it was found that increase in UV absorbance of soil extracts at 280 nm (UV280) after fumigation could account for 92–96% of the variance in estimates of the SMB‐C and ‐N concentrations measured by chloroform fumigation and extraction (P < 0.001). The data were combined with those of earlier workers to calibrate UV‐based regression models for all the soils, by taking into account their varying SOM content. The validation analysis of the calibration models indicated that the SMB‐C and ‐N concentrations in the 0–5 cm forest soils simulated by using the increase in UV280 and SOM could account for 86–93% of the variance in concentrations determined by chloroform fumigation and extraction (P < 0.001). The slope values of linear regression equations between measured and simulated values were 0.94 ± 0.03 and 0.94 ± 0.04, respectively, for the SMB‐C and ‐N. However, simulation using the regression equations obtained by using only the data for forest profile soils gave less good agreement with measured values. Hence, the calibration models obtained by using the increase in UV280 and SOM can give a rapid, simple and reliable method of determining SMB for all soils.  相似文献   

10.
The fate of carbon (C) in grassland soils is of particular interest since the vast majority in grassland ecosystems is stored below ground and respiratory C‐release from soils is a major component of the global C balance. The use of 13C‐depleted CO2 in a 10‐year free‐air carbon dioxide enrichment (FACE) experiment, gave a unique opportunity to study the turnover of the C sequestered during this experiment. Soil organic matter (SOM), soil air and plant material were analysed for δ13C and C contents in the last year of the FACE experiment (2002) and in the two following growing seasons. After 10 years of exposure to CO2 enrichment at 600 ppmv, no significant differences in SOM C content could be detected between fumigated and non‐fumigated plots. A 13C depletion of 3.4‰ was found in SOM (0–12 cm) of the fumigated soils in comparison with the control soils and a rapid decrease of this difference was observed after the end of fumigation. Within 2 years, 49% of the C in this SOM (0–12 cm) was exchanged with fresh C, with the limitation that this exchange cannot be further dissected into respiratory decay of old C and freshly sequestered new C. By analysing the mechanistic effects of a drought on the plant‐soil system it was shown that rhizosphere respiration is the dominant factor in soil respiration. Consideration of ecophysiological factors that drive plant activity is therefore important when soil respiration is to be investigated or modelled.  相似文献   

11.
《Geoderma》2006,130(1-2):35-46
Tropical soils are generally depleted in organic carbon (OC) due to environmental conditions favouring decomposition and mineralisation of soil organic matter (SOM). In Northern Laos, sloping soils are subjected to slash and burn agriculture, which leads to production of black carbon (BC), a stable SOM fraction. BC may directly influence the quantity and quality of SOM sequestered in tropical soils. The aim of this study was to quantify BC content and evaluate its impact on the chemical and stable isotope composition of SOM along a catena composed of Dystrochrepts at the bottom of the slope, Alfisols (midslope) and Inceptisols at the top of the slope for different burning frequencies. Six soil profiles, situated on a slope ranging from a river bank to the summit of a hill, were sampled. The stable isotope compositions (13C and 15N) of samples from both organo-mineral A and mineral B and C horizons were determined. The chemical composition of SOM analysed by 13C CPMAS NMR spectroscopy and the contribution of BC determined by dichromate oxidation were compared to OC and iron oxide content as well as land management including the burning cycle.The highest C contents were recorded at midslope positions. At any position on the slope, δ13C and δ15N ratios showed an enrichment in 13C and 15N with increasing soil depth. The OC content of soil horizons was related to their aryl C content, which is the component most likely driven by BC inputs. The BC contributions analysed by dichromate oxidation ranged from 3% to 7% of total OC. A positive correlation was obtained between aryl C and the BC content of SOM. Comparison of BC content and stable isotope composition of SOM showed that BC influenced the δ13C and the δ15N stable isotope ratios of these soils. BC was not associated with the mineral phase. The highest BC contents were measured under intensive slash and burn practice in the vicinity of the boundary of Alfisols at the top of the slope, where erosion was severe. Therefore, BC, a SOM component strongly influencing OC sequestration of these soils, is susceptible to translocation down the slope.  相似文献   

12.
ABSTRACT

A field evaluation of the stable isotopes (δ13C and δ15N) and their relationship among physicochemical and enzyme activities was conducted in Indian semi-arid agricultural soils. Composite soil samples were collected based on organic management (ORG), inorganic management (IM), integrated crop management (ICM) and precision farming (PF) experimental plots from the fall of September 2017 to October 2018. δ15N was significantly higher (13.85 %) in ORG soils compared with ICM (13.28 %), IM (12.84 %) and PF (12.75 %). In contrast δ13C was higher (?13.25%) in PF soils than IM (?13.6 %), ICM (?15.07 %) and ORG (?15.23 %). Soils from ORG had significantly higher levels of total N, total C, total S, organic carbon, available N, extractable P, Soil organic carbon stock, exchangeable K and enzyme activities compared to IM, ICM and PF. Urease, β – glucosidase, acid phosphatase, alkaline phosphatase, invertase, cellulase and dehydrogenase activities significantly increased the δ15N and reduced δ13C in agricultural soils. Our results suggested that organic management had improved the δ15N, plant available nutrients and soil enzyme activities. Stable δ13C and δ15N isotopes are good indicators of monitor the soil health, carbon, and nitrogen biogeochemical cycles in Indian semi-arid agricultural soils.  相似文献   

13.
ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ13C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ13C values and the amounts of HWEOC or WEOC. The δ13C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ13C values and amounts.  相似文献   

14.
 Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg–1 soil in unfertilized soil to 423 mg kg–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by use of organic amendments along with inorganic fertilizers. Received: 6 May 1998  相似文献   

15.
不同磷源对设施菜田土壤速效磷及其淋溶阈值的影响   总被引：2，自引：0，他引：2  
土壤中磷的移动性不仅取决于磷的数量且与磷肥形态有关。了解不同磷源（有机肥和化肥）对设施菜田土壤磷素的影响对于指导科学施肥和面源污染防治至关重要。本文选取河北省饶阳县3种不同磷含量的农田土壤（未种植过蔬菜的土壤、种植蔬菜30年的塑料大棚土壤和种植蔬菜4年的日光温室土壤）为研究对象,采用室内培养试验和数学模型模拟方法研究有机无机磷源对设施菜田土壤磷素的影响,确定无机肥和有机肥源土壤磷素淋溶的环境阈值。结果表明添加有机肥和无机磷肥都会显著增加3种不同种植年限设施菜田土壤速效磷（Olsen-P）和氯化钙磷（CaCl2-P）含量,但增加速度不同。对于未种植过蔬菜的低磷对照土壤,磷投入量高于50 mg·kg-1（干土）后,无机肥比有机肥显著提高了土壤Olsen-P含量。对于已种植蔬菜30年的塑料大棚土壤,高磷投入时[300 mg·kg-1（干土）和600 mg·kg-1（干土）],无机肥比有机肥显著提高了土壤Olsen-P含量,低于此磷投入量时有机肥和无机肥处理之间没有显著差异。3种不同农田土壤CaCl2-P的含量所有处理均表现出无机肥显著高于有机肥处理,尤其是在高磷量[>300 mg·kg-1（干土）]投入时表现更加明显。两段式线性模拟结果表明,设施菜田土壤有机肥源磷素和无机肥源磷素淋溶阈值分别为87.8 mg·kg-1和198.7 mg·kg-1。随着土壤Olsen-P的增加,添加无机肥源磷对设施菜田土壤CaCl2-P含量的增加速率是有机肥源磷的两倍。因此,建议在河北省高磷设施菜田应减少无机磷肥的投入,特别是土壤速效磷高于198.7 mg·kg-1的设施菜田应禁止使用化学磷肥和有机肥,在土壤速效磷低于198.7 mg·kg-1的设施菜田应加大有机肥适度替代无机肥技术的推广。  相似文献   

16.
The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon (SOC) in terrestrial ecosystems. In this study, a multi‐form, small‐input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH4Cl, (NH4)2SO4 and KNO3, were applied at four rates: 0, 10, 20 and 40 kg N ha?1 year?1. One hundred and eight soil samples were collected at 10‐cm intervals to a depth of 30 cm in 2011. Contents and δ13C values of bulk SOC were measured, as well as three particle‐size fractions: macroparticulate organic C (MacroPOC, > 250 µm), microparticulate organic C (MicroPOC, 53–250 µm) and mineral‐associated organic C (MAOC, < 53 µm). The results show that 5 years of N addition changed SOC contents, δ13C values of the bulk soils and various particle‐size fractions in the surface 10‐cm layer, and that they were dependent on the amounts and forms of N application. Ammonium‐N addition had more significant effects on SOC content than nitrate‐N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m?2), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m?2) and 8.8% (0.85 kg C m?2), respectively. The critical load of N deposition appears to be about 20 kg N ha?1 year?1. The newly formed C in the small‐input N treatment remained mostly in the > 250 µm soil MacroPOC, and the C lost in the medium or large N treatments was from the > 53 µm POC fraction. Five years of ammonium‐N addition increased significantly the surface soil POC:MAOC ratio and increased the instability of soil organic matter (SOM). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term.  相似文献   

17.
Abstract

The objective of this study was to compare mid‐infrared (MIR) an near‐infrared (NIR) spectroscopy (MIRS and NIRS, respectively) not only to measure soil carbon content, but also to measure key soil organic C (SOC) fractions and the δ13C in a highly diverse set of soils while also assessing the feasibility of establishing regional diffuse reflectance calibrations for these fractions. Two hundred and thirty‐seven soil samples were collected from 14 sites in 10 western states (CO, IA, MN, MO, MT, ND, NE, NM, OK, TX). Two subsets of these were examined for a variety of C measures by conventional assays and NIRS and MIRS. Biomass C and N, soil inorganic C (SIC), SOC, total C, identifiable plant material (IPM) (20× magnifying glass), the ratio of SOC to the silt+clay content, and total N were available for 185 samples. Mineral‐associated C fraction, δ13C of the mineral associated C, δ13C of SOC, percentage C in the mineral‐associated C fraction, particulate organic matter, and percentage C in the particulate organic matter were available for 114 samples. NIR spectra (64 co‐added scans) from 400 to 2498 nm (10‐nm resolution with data collected every 2 nm) were obtained using a rotating sample cup and an NIRSystems model 6500 scanning monochromator. MIR diffuse reflectance spectra from 4000 to 400 cm?1 (2500 to 25,000 nm) were obtained on non‐KBr diluted samples using a custom‐made sample transport and a Digilab FTS‐60 Fourier transform spectrometer (4‐cm?1 resolution with 64 co‐added scans). Partial least squares regression was used with a one‐out cross validation to develop calibrations for the various analytes using NIR and MIR spectra. Results demonstrated that accurate calibrations for a wide variety of soil C measures, including measures of δ13C, are feasible using MIR spectra. Similar efforts using NIR spectra indicated that although NIR spectrometers may be capable of scanning larger amounts of samples, the results are generally not as good as achieved using MIR spectra.  相似文献   

18.
Red soils in subtropical regions are often low in available phosphorus (P), a vital plant nutrient. Phosphate-solubilizing microorganisms (PSMs) can release P from phosphate reservoir, making it accessible to plants. However, the complex interactions between PSMs and minerals in red soils are not yet fully understood. In this study, we investigated the effects of Aspergillus niger, a typical phosphate-solubilizing fungus (PSF), on phosphate dissolution in two representative red soils – an acidic soil and an alkaline soil. In the acidic red soil, the fungal abundance reached 3.01 × 10 7 cfu g−1 after a 28-day incubation period, with respiration of ~2000 mg C kg−1. The secretion of oxalic acid promoted P release from inorganic phosphate (from ~1 to 187 mg kg−1). Additionally, the contents of amorphous Fe/Al oxides decreased, which otherwise could have contributed to P sorption in the soil. In contrast, P availability declined in the alkaline red soil after the addition of A. niger, regardless of the P source (inorganic or organic phosphate). Meanwhile, the fungal respiration decreased to ~780 mg C kg−1. Therefore, alkaline red soils with abundant carbonates are susceptible to P deficiency due to both the diminished function of PSMs and strong soil buffering. These findings have important implications for sustainable agriculture on alkaline red soils, as they suggest that the use of PSMs to improve P availability may be limited.  相似文献   

19.
Long‐term dynamics of amino acids (AAs), from a bare fallow soil experiment (established in 1928 at INRA‐Versailles, France), were examined in unamended control (Con) plots and plots treated with ammonium sulphate (Amsul), ammonium nitrate (Amnit), sodium nitrate (Nanit) or with animal manure (Man). Topsoil (0–25 cm) from 1929, 1963 and 1997 was analysed for C, N and 15N content and distribution of 18 amino acids recovered after acid hydrolysis with 6 m HCl. With time, soil N, C and AA content were reduced in Con, Amsul, Amnit and Nanit, but increased in Man. However, the absolute N loss was 3–11 times larger in Man than Nanit, Amsul, Amnit and Con, due to the much higher N annual inputs applied to Man. From 1929 to 1997 in Con, Amsul, Amnit and Nanit the whole soil and non‐hydrolysable‐N pool δ15N increased associated with the loss of N (indicative of Rayleigh 15N/14N fractionation). No δ15N change from 1929 to 1997 was found in the hydrolysable AA‐N (HAN) pool. Fertilizer N inputs aided stabilization of soil AA‐N, as AA half‐life in the mineral N fertilizer treatments increased from 34 years in 1963 to 50 years in 1997. The δ15N values of alanine and leucine reflected both source input and 15N/14N fractionation effects in soils. The δ15N increase of ornithine (～6‰) was similar to the whole soil. The δ15N change of phenylalanine in Con (decrease of 7‰) was related to its proportional loss since 1929, whereas for Amsul, Amnit, Nanit and Man it was associated with isotope effects caused by the fertilizer inputs. However, the soil δ15N value of most individual amino acids (IAAs) did not significantly change over nearly 70 years, even with mineral or organic N inputs. We conclude for these bare fallow systems that: (i) δ15N changes in the whole soil and non‐hydrolysable AA pool were solely driven by microbial processes and not by the nature of fertilizer inputs, and (ii) without plant inputs, the δ15N of the HAN pool and (most) IAAs may reflect the influence of plant–soil interactions from the previous (arable cropping) rather than present (fallow) land use on these soil δ15N values.  相似文献   

20.
Different forms of manganese (Mn) were investigated, including total, diethylenetriamine penta-acetic acid (DTPA) extractable, soil solution plus exchangeable (Mn), Mn adsorbed onto inorganic sites, Mn bound by organic sites, and Mn adsorbed onto oxide surfaces, from four soil taxonomic orders in northwestern India. The total Mn content was 200–950 mg kg?1, DTPA-extractable Mn content was 0.60–5.80 mg kg?1, soil solution plus exchangeable Mn content was 0.02–0.80 mg kg?1, Mn adsorbed onto inorganic sites was 2.46–90 mg kg?1, and Mc adsorbed onto oxide surfaces was 6.0–225.0 mg kg?1. Irrespective of the different fractions of Mn their content was generally greater in the fine-textured Alfisols and Inceptisols than in coarse-textured Entisols and Aridisols. The proportion of the Mn fractions extracted from the soil was in the order as follows: Adsorbed onto oxide surfaces > adsorbed onto inorganic site > organically bound > DTPA > soil solution + exchangeable. Based on coefficient of correlation, the soil solution plus exchangeable Mn, held onto organic site and oxide surface (amorphous) and DTPA-extractable Mn, increased with increase in organic carbon of the soil. The two forms, adsorbed onto inorganic site (crystalline) and DTPA extractable, along with organic carbon, increased with increase in clay content of the soil. DTPA-Mn and Mn adsorbed onto oxide surfaces and held on organic site decreased with increased with an increase in calcium carbonate and pH. Total Mn was strongly correlated with organic carbon and clay content of soil. Among the forms, Mn held on the organic site, water soluble + exchangeable and adsorbed onto oxide surface were positively correlated with DTPA-extractable Mn. DTPA-extractable Mn seems to be a good index of Mn availability in soils and this form is helpful for correction of Mn deficiency in the soils of the region. The uptake of Mn was greater in fine-textured Inceptisols and Alfisols than in coarse-textured Entisols and Aridisols. Among the different forms only DTPA-extractable Mn was positively correlated with total uptake of Mn. Among soil properties Mn uptake was only significantly affected by pH of the soil.  相似文献   

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