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1.
Microbial communities are responsible for soil organic matter cycling and thus for maintaining soil fertility. A typical Orthic Luvisol was freed from organic carbon by thermal destruction at 600°C. Then the degradation and humification of 14C‐labelled maize straw by defined microbial communities was analysed. To study the role of microbial diversity on the humification of plant material, microcosms containing sterilized soil were inoculated with a natural microbial community or with microbial consortia consisting of bacterial and fungal soil isolates. Within 6 weeks, 41 ± 4% of applied 14C‐labelled maize straw was mineralized in the soil microcosms containing complex communities derived from a soil suspension, whilst the most efficient communities composed of soil isolates mineralized less than 35%. The humification products were analysed by solution state 13C‐NMR‐spectroscopy and gel permeation chromatography (GPC). The analyses of humic acids extracts by solution state 13C‐NMR‐spectroscopy revealed no difference in the development of typical chemical functional groups for humic substances during incubation. However, the increase in specific molecular size fractions of the extracted humic acids occurred only after inoculation with complex communities, but not with defined isolates. While it seems to be true that redundancy in soil microbial communities contributes to the resilience of soils, specific soil functions may no longer be performed if a microbial community is harshly affected in its diversity or growth conditions.  相似文献   

2.
The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by 13C‐dilution analysis and CPMAS‐13C‐NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year‐long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ13C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS‐13C‐NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic‐rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of 13C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.  相似文献   

3.
As a source of organic matter, crop residues affect the behaviour of pesticides in agricultural soils. The fate of [U‐ring‐13C] and [U‐ring‐14C] atrazine (6‐chloro‐N‐ethyl‐N‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) was investigated during laboratory incubation under controlled conditions in a loamy soil amended with wheat straw at two different states of decomposition: no preliminary decomposition or 6 months’ preliminary decomposition. After 3 months, non‐extractable, so‐called ‘bound’, 13C‐atrazine residues were recovered in three particle‐size fractions (> 200, 50–200 and < 50 μm), and investigated with solid‐state 13C‐NMR spectroscopy. Parallel incubations with [U‐ring‐14C] atrazine were carried out to quantify the bound residues as well as the extractable and mineralized fractions. The effect of straw residues on atrazine behaviour depended on whether they had been previously decomposed or not. When straw was decomposed for 6 months prior to incubation, atrazine mineralization was enhanced to 50% of the initial 14C in contrast to 15% of the initial 14C in soil alone and soil amended with fresh straw. In parallel, atrazine bound residues were formed in greater amount representing up to 20% of the initial 14C. CP/MAS 13C‐NMR on soil size fractions of soil–straw mixtures after incubation with 13C‐atrazine showed that bound residues contained mostly triazinic C, corresponding to atrazine or primary metabolites. Non‐humified organic materials recovered in size fractions > 200 and 50–200 μm contained significant amounts of bound residues, especially when straw was added to the soil. CP/MAS 13C‐NMR analysis of humic acids obtained from < 50‐μm fractions was difficult due to overlapping of the native carboxyl 13C signal with the 13C‐atrazine signal.  相似文献   

4.
Studies were made to determine the rate of decomposition of some 14C-labeled microbial polysaccharides, microbial cells, glucose, cellulose and wheat straw in soil, the distribution of the residual 14C in various humic fractions and the influence of the microbial products on the decomposition of plant residues in soil. During 16 weeks from 32 to 86 per cent of the C of added bacterial polysaccharides had evolved as 14CO2. Chromobacterium violaceum polysaccharide was most resistant and Leuconostoc dextranicus polysaccharide least resistant. In general the polysaccharides, microbial cells, and glucose exerted little effect on the decomposition of the plant products. Upon incubation the 14C-activity was quickly distributed in the humic. fulvic and extracted soil fractions. The pattern of distribution depended upon the amendment and the degree of decomposition. The distribution was most uniform in the highly decomposed amendments. After 16 weeks the bulk of the residual activity from Azotobacter indicus polysaccharide remained in the NaOH extracted soil. From C. violaceum polysaccharide both the extracted soil and the humic acid fraction contained high activity. About 50–80 per cent of the residual activity from the 14C-glucose, cellulose and wheat straw amended soils could be removed by hydrolysis with 6 n HCl. The greater part of this activity in the humic acid fraction was associated with the amino acids and that from the fulvic acids and residual soils after NaOH extraction with the carbohydrates. About 8 16 per cent of the activity of the humic acid fraction was present in substances (probably aromatic) extracted by ether after reductive or oxidative degradation.  相似文献   

5.
A 13C natural abundance experiment including GC-c-IRMS analysis of phospholipid fatty acids (PLFAs) was conducted to assess the temporal dynamics of the soil microbial community and carbon incorporation during the mineralization of plant residues under the impact of heavy metals and acid rain. Maize straw was incorporated into (i) control soil, (ii) soil irrigated with acid rain, (iii) soil amended with heavy metal-polluted filter dust and (iv) soil with both, heavy metal and acid rain treatment, over a period of 74 weeks. The mineralization of maize straw carbon was significantly reduced by heavy metal impact. Reduced mineralization rate of the added carbon likely resulted from a reduction of the microbial biomass due to heavy metal stress, while the efficiency of 13C incorporation into microbial PLFAs was hardly affected. Since acid rain did not significantly change soil pH, little impact on soil microorganisms and mineralization rate was found. Temporal dynamics of labelling of microbial PLFAs were different between bacterial and fungal PLFA biomarkers. Utilization of maize straw by bacterial PLFAs peaked immediately after the application (2 weeks), while labelling of the fungal biomarker 18:2ω6,9 was most pronounced 5 weeks after the application. In general, 13C labelling of microbial PLFAs was closely linked to the amounts of maize carbon present in the soil. The distinct higher labelling of microbial PLFAs in the heavy metal-polluted soils 74 weeks after application indicated a large fraction of available maize straw carbon still present in the soil.  相似文献   

6.
An incubation experiment was carried out with maize (Zea mays L.) leaf straw to analyze the effects of mixing the residues with soil and N amendment on the decomposition process. In order to distinguish between soil effects and nitrogen effects for both the phyllospheric microorganisms already present on the surface of maize straw and soil microorganisms the N amendment was applied in two different placements: directly to the straw or to the soil. The experiment was performed in dynamic, automated microcosms for 22 days at 15 °C with 7 treatments: (1) untreated soil, (2) non-amended maize leaf straw without soil, (3) N amended maize leaf straw without soil, (4) soil mixed with maize leaf straw, (5) N amended soil, (6) N amended soil mixed with maize leaf straw, and (7) soil mixed with N amended maize leaf straw. 15NH415NO3 (5 at%) was added. Gas emissions (CO2, 13CO2 and N2O) were continuously recorded throughout the experiment. Microbial biomass C, biomass N, ergosterol, δ13C of soil organic C and of microbial biomass C as well as 15N in soil total N, mineral N and microbial biomass N were determined in soil samples at the end of the incubation. The CO2 evolution rate showed a lag-phase of two days in the non-amended maize leaf straw treatment without soil, which was completely eliminated when mineral N was added. The addition of N generally increased the CO2 evolution rate during the initial stages of maize leaf straw decomposition, but not the cumulative CO2 production. The presence of soil caused roughly a 50% increase in cumulative CO2 production within 22 days in the maize straw treatments due to a slower decrease of CO2 evolution after the initial activity peak. Since there are no limitations of water or N, we suggest that soil provides a microbial community ensuring an effective succession of straw decomposing microorganisms. In the treatments where maize and soil was mixed, 75% of microbial biomass C was derived from maize. We concluded that this high contribution of maize using microbiota indicates a strong influence of organisms of phyllospheric origin to the microbial community in the soil after plant residues enter the soil.  相似文献   

7.
甜玉米/白三叶草秸秆还田的碳氮矿化研究   总被引：4，自引：0，他引：4  
豆科/禾本科作物间套作后进行秸秆还田能补充土壤养分,缓解集约化农业生产对环境的压力.根据田间甜玉米/白三叶草套种各作物的秸秆产量,在恒温恒湿条件下进行室内培养,探讨秸秆不同方式还田后土壤微生物量碳、微生物量氮、呼吸产生的CO2和矿化产生的无机氮的变化规律.研究发现,各施肥处理的土壤微生物量碳、微生物量氮均在培养前期出现峰值,后期平稳降低;甜玉米秸秆和白三叶草绿肥同时还田的土壤微生物量碳、微生物量氮在各培养时期均最大,峰值分别达529.57 mg·kg-1和75.50 mg·kg-1,土壤呼吸产生的CO2最多;白三叶草绿肥单独还田有利于土壤无机氮的释放,培养第26 d 无机氮达到最大值,为29.81 mg·kg-1,之后一直在对照处理的1.60倍以上,第80 d达到2.48倍;甜玉米秸秆单独还田不利于土壤无机氮的释放,培养的第26 d至结束,甜玉米秸秆处理的无机氮为对照的13%～53%,最大为7.51 mg·kg-1;甜玉米秸秆配施尿素,短期内不利于土壤无机氮矿化.结果表明,施用有机物料能引起土壤有机质的短期快速转化,甜玉米秸秆和白三叶草绿肥配施有利于维持较大基数的土壤微生物量,单施白三叶草绿肥土壤微生物活性强,最有利于土壤速效氮的释放.  相似文献   

8.
黄淮海平原典型潮土上小麦和玉米收获后的秸秆往往直接还田,但驱动它们在不同质地潮土(砂质、壤质、黏质)中分解的微生物是否与残留秸秆养分含量有关尚不清楚。本研究基于尼龙网袋法,通过10个月的田间培育试验,监测秸秆分解率、残留秸秆养分含量及微生物群落组成,评估各指标在秸秆类型和土壤质地之间的差异,探究残留秸秆养分与微生物群落组成之间的关系。结果表明:小麦和玉米秸秆的分解率均随着土壤质地变黏重而增大,二者在砂质、壤质、黏质土壤中的平均分解率分别为73.66%和75.43%、74.19%和76.63%、77.68%和78.05%。小麦残留秸秆的平均氮、磷、钾含量分别比玉米残留秸秆的平均氮、磷、钾含量低12.0%、34.4%、16.7%(P0.05),但两者的碳含量无显著差异;在不同质地潮土间,除秸秆磷含量随土壤变黏重显著增加外,其余养分含量变化不显著。基于磷脂脂肪酸(PLFA)的微生物群落组成分析表明,小麦和玉米秸秆中的细菌、真菌、放线菌含量无显著差异,但小麦秸秆中革兰氏阳性菌(G~+)含量比玉米秸秆低20.26%,而革兰氏阴性菌(G~–)含量比玉米秸秆高16.35%,同时,G~+/G~–、真菌/细菌、单不饱和脂肪酸/饱和支链脂肪酸比在两种秸秆间存在显著差异;小麦和玉米秸秆在黏质潮土中的细菌、真菌、总PLFA的平均含量分别比砂质潮土中低25.1%、30.3%、22.9%(P0.05),而放线菌含量平均比砂质潮土高93.8%(P0.05)。冗余分析(RDA)分析表明,小麦与玉米残留秸秆中的微生物群落组成显著不同,主要与其G~+和G~–不同有关,其中小麦秸秆的微生物群落组成主要与秸秆的C/N、C/P、C/K比值有关,而玉米秸秆则主要与秸秆的氮、磷、钾含量和分解率有关,说明影响小麦和玉米秸秆微生物群落组成的养分参数不同。  相似文献   

9.
An experiment was carried out to investigate the decomposition and microbial use of maize leaf straw incubated in packed soil columns at different depths. The straw was incorporated into the top layer at 0–5 cm depth and into the bottom layer at 15–20 cm depth of a sandy or a loamy soil. Microbial biomass C was significantly increased after adding straw to the bottom layer of both soils. After adding straw to the top layer, this increase was significantly lower in the sandy soil and significantly higher in the loamy soil. Maize straw application significantly increased the ergosterol-to-microbial biomass C ratio in both soils from 0.26% to a mean content of 0.72% after adding straw to the top layer and to a mean content of 1.11% after adding straw to the bottom layer. The calculation of the maize-derived CO2 production revealed that the mineralization rates of maize C were always higher in the sandy soil, with a mean of 20%, than in the loamy soil, with a mean of 14%. The application of maize straw always significantly increased the soil organic matter-derived CO2 production. This increase was stronger in the loamy soil than in the sandy soil and stronger after application of the maize straw to the top layer than to the bottom layer. On average, 100% of the maize straw C was recovered in the different fractions analysed. In the layers with maize leaf straw application, 28% of the maize C was recovered as particulate organic matter (POM) > 2 mm and 32% as POM 0.4–2.0 mm, without a significant difference between the two soils and the depth of application. In the layers with maize leaf straw application, 19% of the maize C was recovered as microbial residue C and 3.1% as microbial biomass C. In the three layers without straw, the microbial biomass incorporated a further 2.4% of the maize C in the sandy soil, but only 0.9% in the loamy soil. Considerable amounts of substrate C were transferred within the microbial biomass over a decimetre distance. The finer pore space of the loamy soil seems to obstruct the transfer of maize-derived C. This was especially true if the maize leaf straw was added to the bottom layer.  相似文献   

10.
Land use change, tillage practices and straw incorporation are known to affect soil organic carbon (SOC) as well as soil inorganic carbon (SIC) turnover in agricultural soils. SOC and SIC, particularly pedogenic carbonates (PC), were assessed in a semi‐humid region of China to a depth of 160 cm. δ13C values were used to calculate the percentage of PC and lithogenic carbonates (LC) in the total SIC. Over the 39‐y period of intensive agriculture including 14 y of tillage × straw experiment, three treatments, i.e ., tillage with wheat and maize straw return (TWM), tillage with wheat straw return (TW), and wheat and maize straw return with no‐tillage (WM) showed an increase of PC compared to a native plantation plot (NP). The significantly higher SOC stock via no‐tillage was limited to top 1 m soil and there was no significant difference between tillage and no‐tillage treatments at 0–160 cm depth. The changes of SOC caused by the tillage and maize straw addition were negligible compared to the gain in PC. Tillage, crop residues incorporation and irrigation played an important role in the turnover of PC and LC. SIC accumulation resulted from combination of neoformation of PC and conservation of LC. Neoformation of silicatic PC sequestered at least 0.49, 0.47, and 0.29 Mg C ha−1 y−1 in TWM, TW, and WM treatments, respectively, with reference to NP plot. We concluded that to evaluate the long term impacts of land use and farming practices on soil C storage, change of pedogenic and lithogenic carbonates and soil organic carbon in deeper soil profiles should be integrated on regional and global scales.  相似文献   

11.
The iron‐cyanide complexes ferricyanide, [FeIII(CN)6]3?, and ferrocyanide, [FeII(CN)6]4?, are anthropogenic contaminants in soil. We studied the interactions of ferricyanide with humic soils and charred straw (maize and rye, both charred at 300, 400 and 500°C) by batch experiments and Fourier transform infrared (FTIR) spectroscopy. All soil samples sorbed ferricyanide (up to 8.4 g kg?1). Precipitation of a manganese ferrocyanide after reduction of ferricyanide in the moderately acidic to neutral soils was deduced from both FTIR spectroscopy (CN absorption bands at 2069–2065 cm?1) and geochemical modelling. Ferricyanide was also adsorbed onto the charred straw. The amounts of iron‐cyanide complexes adsorbed increased with increasing charring temperature, with a maximum of 1.71 g kg?1. An absorption band at 2083 cm?1 indicated weakly adsorbed intermediates of the reduction of ferricyanide to ferrocyanide. This band disappeared in the samples charred at higher temperature, whereas a band at 2026 cm?1 was present in all spectra and became intensified in the high‐temperature straw. We attribute this band to ferrocyanide forming inner‐sphere complexes, presumably with quinone species of the organic matter. The band at 2026 cm?1 was also present in the spectra of the soils, indicating that soil organic matter also adsorbs ferrocyanide. However, in humic soils the main processes of ferricyanide interaction include reduction to ferrocyanide and precipitation as manganese ferrocyanide. Quantitatively, adsorption on highly aromatic substances plays only a less important role as compared with precipitation.  相似文献   

12.
A combination of solid‐state CPMAS‐13C‐NMR and TMAH thermochemolysis‐GC/MS was applied to investigate the molecular composition of particulate organic matter (POM) separated from a Chinese paddy soil, from the Tai Lake region, under a long‐term field experiment with different fertilizer treatments. The treatments were: (i) no fertilizer application (NF), (ii) chemical fertilizers only (CF), (iii) chemical fertilizer plus pig manure (CFM) and (iv) chemical fertilizer plus crop straw (CFS). CPMAS‐13C‐NMR spectra showed that POM from all treated plots was rich in O‐alkyl‐C compounds, followed by alkyl‐C and aromatic‐C compounds. However, as compared with a control (NF), POM under CFM and CFS treatments exhibited a smaller relative O‐alkyl‐C content and a larger contribution of aromatic‐C and alkyl‐C, thus increasing both aromaticity and hydrophobicity and, hence, recalcitrance of POM samples. Thermochemolysis of POM from all treatments demonstrated a dominance of aliphatic and lignin‐derived compounds. However, the distribution of lignin monomers (p‐hydroxyphenyl, P, guaiacyl, G, and syringyl, S) revealed significant differences among the treatments. The relative distribution of lignin P, G and S monomers in NF, CF and CFS indicated a preferential contribution of annual crops and maize straw, as compared with that found for CFM. Concomitantly, a larger content of aliphatic thermochemolysis derivatives was found for CFS and CFM. The relative increase of aliphatic molecules in CFS was attributed to hydrophobic polyesters from higher plants. In the CF and CFM systems, the presence of aliphatic components of microbial origin suggested a greater microbial activity in comparison with NF and CFS. The combined application of solid state CPMAS‐13C‐NMR and TMAH thermochemolysis‐GC/MS can be used to assess effectively the accumulation of recalcitrant organic compounds in soil POM under long‐term fertilizer application with organic biomass. It is thus inferred that soil organic matter stabilization by molecular recalcitrance contributes to carbon sequestration in Chinese paddy soils under long‐term managements.  相似文献   

13.
A 28-day incubation experiment at 12°C was carried out on the decomposition of maize leaf litter to answer the questions: (1) Is the decomposition process altered by chemical manipulations due to differences in the colonization of maize leaf litter? (2) Do organisms using this maize material contribute significantly to the soil microbial biomass? The extraction of the maize straw reduced its initial microbial biomass C content by 25%. Fumigation and extraction eliminated the microbial biomass by 88%. In total, 17% of added maize straw C was mineralized to CO2 during the 28-day incubation at 12°C in the treatment with non-manipulated straw. Only 14% of added C was mineralized in the treatment with extracted straw as well as in the treatment with fumigated and extracted straw. The net increase in microbial biomass C was 79 μg g?1 soil in the treatment with non-manipulated straw and an insignificant 9 μg g?1 soil in the two treatments with manipulated straw. However, the net increase did not reflect the fact that the addition of maize straw replaced an identical 58% (≈180 μg g?1 soil) of the autochthonous microbial biomass C3-C in all three straw treatments. In the two treatments with manipulated straw, the formation of maize-derived microbial biomass C4-C was significantly reduced by 25%. In the three straw treatments, the ratio of fungal ergosterol-to-microbial biomass C ratio showed a constant 60% increase compared to the control, and the contents of glucosamine and muramic acid increased by 18%. The average fungal C/bacterial C ratio was 3.6 in the soil and 5.0 in the recovered maize straw, indicating that fungal dominance was not altered by the initial chemical manipulations of the maize straw-colonizing microorganisms.  相似文献   

14.
In highly weathered tropical conditions, soil organic matter is important for soil quality and productivity. We evaluated the effects of deforestation and subsequent arable cropping on the qualitative and quantitative transformation of the humic pool of the soil at three locations in Nigeria. Cultivation reduced the humic pool in the order: acetone‐soluble hydrophobic fraction (HE) > humic acid (HA) > humin (HU) > fulvic acid (FA), but not to the same degree at all three sites. The C and N contents, as well as the C/N ratios of humic extracts, were large and not substantially influenced by land use. The δ13C values of the humic extracts were invariably more negative in forested soils thereby showing a dilution of δ13C signature with cultivation from C3 to C4 plants. The δ13C values of apolar HE fractions were generally more negative, indicating a reduced sensitivity compared with other humic fractions to turnover of crop residues. The contents of hydrophobic constituents (alkyl and aromatic C), as revealed by cross‐polarization magic angle spinning (CPMAS) 13C‐NMR spectroscopy, in HA, FA and HU were generally < 50%, with the exception of larger hydrophobicity in HU in the forested soil at Nsukka and HA in that at Umudike. The HE fraction contained significantly more apolar constituents, and consequently had a larger intrinsic hydrophobicity than the other humic fractions. The larger reduction of apolar humic constituents than of the less hydrophobic humic fractions, when these soils were deforested for cultivation, indicates that at those sites the stability of accumulated organic matter is to be ascribed mainly to the selective preservation of hydrophobic compounds.  相似文献   

15.
Land-use conversion affects the soil community and microbial abundance, which are essential dynamic indicators of soil quality and sustainability. However, little to no work has been performed to analyse the impact from different land-use histories (i.e. fallow, tea, rice, banana, and maize) on the microbial abundance and diversity in the soil of sacha inchi (Plukenetia volubilis L.). Real-time quantitative PCR (qPCR) was performed to quantify soil bacterial and fungal abundance. Denaturing gradient gel electrophoresis (DGGE) combined with cloning and sequencing was used to assess the microbial communities. Our results showed that the bacterial and fungal abundance in fallow land-use conversion soils was significantly lower than that in the other four land-use conversion soils (tea, rice, banana, and maize). Moreover, the highest abundance of bacteria and fungi was detected in the soils converted from maize to sacha inchicultivation. In addition, canonical correspondence analysis (CCA) showed that the total N and pH were significantly related to bacterial and fungal community structures. These results suggest that land-use conversion from maize fields to sacha inchi farms is an effective way to maintain the soil microbial quantity and hence the sustainability of the soil.  相似文献   

16.
Fundamental knowledge about the complex processes during the decomposition, mineralization and transfer of residue organic matter in soils is essential to assess risks of changes in agricultural practices. In a double tracer (13C, 15N) experiment the effect of maize straw on the mineralization dynamics and on the distribution of maize-derived organic matter within particle size fractions was investigated. Maize straw (a C4 plant) labelled with 15N was added to soils (13.2 g dry matter kg–1 soil) which previously had grown only C3 plants, establishing two treatments: (i) soil mixed with maize straw (mixed), and (ii) soil with maize straw applied on the surface (surface). Samples were incubated in the laboratory at 14°C for 365 days. The size fractions (> 200 μm, 200–63 μm, 63–2 μm, 2–0.1 μm and < 0.1 μm), obtained after low-energy sonication (0.2 kJ g–1), were separated by a combination of wet-sieving and centrifuging. The mineralization of maize C was similar in the two treatments after one year. However, decomposition of maize particulate organic matter (predominantly in the fraction > 200 μm) was significantly greater in the mixed treatment, and more C derived from the maize was associated with silt- and clay-sized particles. A two-component model fitted to the data yielded a rapidly mineralizable C pool (about 20% of total C) and a slowly mineralizable pool (about 80%). Generally, the size of the rapidly mineralizable C pool was rather small because inorganic N was rapidly immobilized after the addition of maize. However, the different mean half-lives of the C pools (rapidly decomposable mixed 0.035 years, and surface-applied 0.085 years; slowly decomposable mixed 0.96 years, and surface-applied 1.7 years) showed that mineralization was delayed when the straw was left on the surface. This seems to be because there is little contact between the soil microflora and plant residues. Evidently, the organic matter is more decomposed and protected within soil inorganic compounds when mixed into the soil than when applied on the soil surface, despite similar rates of mineralization.  相似文献   

17.
The soil conditioners anionic polyacrylamide (PAM) and dicyandiamide (DCD) are frequently applied to soils to reduce soil erosion and nitrogen loss, respectively. A 27‐day incubation study was set up to gauge their interactive effects on the microbial biomass, carbon (C) mineralization and nitrification activity of a sandy loam soil in the presence or absence of maize straw. PAM‐amended soils received 308 or 615 mg PAM/kg. Nitrogen (N)‐fertilized soils were amended with 1800 mg/kg ammonium sulphate [(NH4)2SO4], with or without 70 mg DCD/kg. Maize straw was added to soil at the rate of 4500 mg/kg. Maize straw application increased soil microbial biomass and respiration. PAM stimulated nitrification and C mineralization, as evidenced by significant increases in extractable nitrate and evolved carbon dioxide (CO2) concentrations. This is likely to have been effected by the PAM improving microbial conditions and partially being utilized as a substrate, with the latter being indicated by a PAM‐induced significant increase in the metabolic quotient. PAM did not reduce the microbial biomass except in one treatment at the highest application rate. Ammonium sulphate stimulated nitrification and reduced microbial biomass; the resultant acidification of the former is likely to have caused these effects. N fertilizer application may also have induced short‐term C‐limitation in the soil with impacts on microbial growth and respiration. The nitrification inhibitor DCD reduced the negative impacts on microbial biomass of (NH4)2SO4 and proved to be an effective soil amendment to reduce nitrification under conditions where mineralization was increased by addition of PAM.  相似文献   

18.
The objective of this study is to develop a method to follow the dynamics of sludge‐derived organic carbon, which will allow us to understand the behaviour of trace metals in the sludge‐treated soils. We studied, in a sandy agricultural soil of southwest France, cultivated with maize and amended with sewage‐sludge over 20 years, the dynamics of different sources of organic matter and compared this with a control, which had never received any treatment. For the first time, a method is proposed that will distinguish and quantify sludge‐derived organic carbon, maize‐derived organic carbon, and native organic carbon. This method is based on the mean differences in δ13C abundances between native (−26.5‰), maize (−12.5‰) and sludge (−25.4‰) organic carbon. Three hypotheses on the dynamics of soil organic matter sources are proposed: (i) isotopic differences observed between control and sludge‐treated soils are due only to the incorporation of sludge C, whereas in the others, the control was used to model the incorporation of (ii) maize C or (iii) native C in the sludge‐treated soils. The comparison of the stocks of each source (native C, maize C and sludge C) found in the bulk soil with the sum of corresponding stocks found in particle‐size fractions allowed us to reject the two first hypotheses and to validate the last one. Repeated applications of sewage‐sludge induced accumulation of sludge‐derived organic carbon in the topsoil, and simultaneously contributed to the preservation of maize‐derived organic carbon. When sludge applications ceased, the rapid decrease in soil organic matter stocks was mostly caused by the degradation of the sludge‐derived organic carbon sources. At the same time, the maize‐derived organic carbon shifted from the coarsest fraction (200–2000 μm) to the finest fraction (0–50 μm). Therefore, this study has shown that repeated applications of sewage‐sludge induced changes in soil organic matter dynamics over time.  相似文献   

19.
To assess the effect of continuous organic material (OM) application on soil humic acids, the amount and chemical characteristics of humic acids in various types of soils (n = 10) were compared between plots treated with farmyard manure (FYM) or rice straw compost (RSC) plus chemical fertilizer (CF) and plots treated with CF alone. The degree of humification (degree of darkening), molecular size distribution and 13C cross polarization/magic angle spinning nuclear magnetic resonance spectra of humic acids from CF‐treated soils showed wide variation among the soils. Humic acid content was generally larger in OM + CF soils than in corresponding CF soils, and the stable C isotopic ratio suggested partial replacement of indigenous humic acids with OM‐derived ones even where no apparent increase in humic acid content was observed. The rate of OM application and the indigenous humic acid content were related positively and negatively, respectively, to the apparent accumulation rate of humic acids among soils. The degree of humification of humic acids was generally smaller in OM + CF soils than in CF soils. Humic acids extracted from FYM and RSC exhibited chemical characteristics typical of humic acids having a smaller degree of humification, which suggested the contribution of OM‐derived humic acids to the differences between OM + CF and CF soil humic acids, such as larger average molecular sizes and smaller and larger proportions of aromatic C and O‐alkyl C, respectively, relative to total C in the OM + CF soil humic acids. Little change was observed in the chemical characteristics of humic acids when the degree of humification of indigenous humic acids was small. The effect of OM application on the chemical characteristics of humic acids was most conspicuous in soils containing humic acids having an intermediate degree of humification, possibly resulting from the combination of accelerated degradation of indigenous humic acids and the accumulation of OM‐derived humic acids.  相似文献   

20.
14C-tracer technique and closed incubation method were used to study straw 14C decomposition and distribution in different fractions of newly formed humus under different moisture regimes. Decomposition of straw 14C was faster during the initial days, and slower thereafter. Decay rate constants of straw 14C varied from 3.29 × 10-3 d-1 to 7.06 × 10-3 d-1. After 112 d incubation, the amount of straw 14C mineralized was 1.17~1.46 times greater in submerged soils than in upland soils. Of the soil residual 14C, 9.08%~15.73% was present in humic acid (HA) and 31.01%~37.62% in fulvic acid (FA). Submerged condition favored the formation of HA, and HA/FA ratio of newly formed humus (labelled) was greater in submerged soils than in upland soils. Clay minerals affected the distribution of straw 14C in different humus fractions. Proportion of 14C present in HA to 14C remaining in soil was greater in Vertisol than in Ultisol.  相似文献   

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