首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 202 毫秒
1.
The soils of three fields under continuous maize culture for 2,4 and 15 yr, and the soil of an adjacent hayfield were analyzed for carbohydrates by gas chromatography. A sharp decrease (30%) in total carbohydrates, paralleled by a smaller decrease in organic matter (9%), was observed after 2 yr of maize cultivation. The 4-yr maize soil showed an upward trend in both organic matter and carbohydrate content but this was subsequently reversed. The 15-yr highly-compacted maize soil had 40% less organic matter and 40% less carbohydrates than the hay soil. When compared to the well structured 2-yr maize soil, this compacted soil had less arabinose, xylose, glucose, galactose and mannose; carbohydrates which are probably of plant root origin. These sugars are likely to be involved in the structural stability of soil aggregates. Conversely, neither the amino sugars nor the uronic acids seemed to contribute to good soil structure.  相似文献   

2.
The humic acids (HAs) isolated by conventional procedure from rhizosphere (r) and bulk (c) soils were analyzed by means of chemical and physico-chemical techniques. Two different crops were selected, tomato (T) and artichoke (A), and each HA was fractionated by size-exclusion chromatography (SEC) into three fractions with increasing molecular size, respectively, Fraction I (FrI) < Fraction II (FrII) < Fraction III (FrIII). Elemental analysis data indicated greater N and S contents in the rhizosphere T-HAs, with respect to rhizosphere A-HA, which suggests the occurrence in the former ones of a large amount of organic nitrogen- and sulfur-containing compounds that are released by the rhizodeposition processes. Further, the three HA fractions from the bulk soils of the two series showed a gradual increase of C, H, and N contents, and a decrease of O and S contents and C/N and C/H ratios. These results suggested that the lowest molecular size fractions are richer in oxygenated functional groups, whereas the higher molecular size fractions are richer in N-containing groups and structural C- and H-containing units. The three HA fractions from the rhizosphere soils of the two series showed a gradual decrease in C content, and an increase of H, N, and O contents, which suggests the possible incorporation into soil HAs of a multitude of C-containing compounds of low molecular size released by plant roots. The FT-IR data, in general, suggested that the contents of carboxylic, phenolic and N-containing groups and polysaccharide-like components in HAs from rhizosphere soils are larger than those of HAs from the corresponding bulk soils. Further, the FrI fraction consisted mainly of simple structural units, likely quinonic and phenolic units with a prevalent aromatic character, whereas the FrII and, especially, FrIII fractions featured a mixed aliphatic/aromatic nature and a greater molecular complexity. The extent of these differences appeared to depend on the plant species and age, and is mainly due to the partial incorporation into rhizosphere HAs of typical root exudate components, such as amino acids, amides, aliphatic and aromatic acids of low molecular size, polysaccharides and sugars, fatty acids and sterols, and enzymes.  相似文献   

3.
Many questions have surfaced regarding long-term impacts of land-use and cultivation system on soil carbon (C) sequestration. The experiment was conducted at Ohio Agricultural Research and Development Center. Only minor variations of soil organic carbon (SOC) and nitrogen (N) fractions with depth under plow tillage (PT). The SOC, total nitrogen (TN), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) concentrations were higher under grassland and forestland in the top 0–15 cm depth than arable soils. No-tillage (NT) also increased SOC and N fractions concentrations in the surface soils than PT. Compared to arable, grass and forest could significantly improve proportions of MBC and MBN, and reduce proportions of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). NT and forest also increased the ratio of SOC/TN, MBC/MBN, and DOC/DON. Overall, grass and forest provided more labile C and improved C sequestration than arable. So did NT under arable land-use.  相似文献   

4.
Reduction of Phosphate sorption in soils by some organic compounds as dependent on pH 3 soils of pH 4.1, 5.9, and 7.1 were treated with aqueous solutions (at 3 concentrations) of 37 organic compounds (organic acids, phenolics, uronic acids, sugars); following an equilibration with 32P-diammonium phosphate the recovery of 32P was measured in the soil extract. All tested compounds did not show any effects at a concentration of 0.1 mg/g soil. Sugars, uronic acids, 2-keto-D-gluconic acid and most amino acids (with the exception of Glu, Asp, Cys, Phe which raised the recovery of 32P by 2 to 3%) were ineffective even at the highest rate (10 mg/g soil). Aromatic acids and phenolics increased the recovery to a greater extent (highest increases with gallic acid: 8 to 11% depending on the soil). Effects were greatest with aliphatic acids like citric acid (45 to 48%), isocitric acid (8 to 64%), malic acid (12 to 57%), and malonic acid (8 to 38%). Only these four acids as well as ascorbic and isoascorbic acid markedly increased the recovery of 32P even at a concentration of 1 mg/g soil. The effects of these acids (with the exception of malonic acid) decreased with increasing soil pH. By adding HCl to the soil in controls, it could be shown that the increased recovery rates of 32P were not caused by the decrease in pH.  相似文献   

5.
As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiated in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent cultivated or forage sites. Generally, the cultivated and forage sites had denser soil profiles than the forest sites. Based on an equivalent soil mass, to accommodate differences in soil bulk density, the paired forest and cultivated sites showed that cultivation decreased the mass of organic C (35%) and total N (10%) in the soil profile of the Podzolic soils, but increased organic C (25%) and total N (37%) in the Brunisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use of forages increased soil stored organic C and N by 55% and 35%, respectively. Organic C fractions were mainly of significance in the A horizon. Soil microbial biomass C was greater in the forested, compared to the cultivated soil, but the proportion of soil organic C as microbial biomass C (1.3% to 1.6%) was similar. The proportion, however, was greater (2.1%) for the forage soil, compared to the corresponding cultivated (1.3%) soil, suggesting that organic C was continuing to increase under the former. The relatively large proportion (19%) of organic C found in the light fraction of forest soils in the A horizon was decreased (up to 70%) by cultivation. In contrast, the proportion of macro-organic C present in the soil sand fraction was not greatly influenced by cultivation. Overall, soils in eastern Canada have a relatively large potential to store organic matter. The study illustrates the importance of soil type and cultivation interactions for maintenance of soil organic matter storage, and the positive influence of forages in this regard in agroecosystems.  相似文献   

6.
To test the impact of a range of long-term land use types on the partitioning of microbial residues among soil particles, samples from a Mollisol with plots under 100 years of continuous arable cropping, 30 years of simulated overgrazing to severely degraded bare soil, or 30 years of grassland restoration were investigated. The microbial residues, which were assessed among three particle-size fractions (<2, 2–20, and 20–250 μm) by amino sugar extraction, exhibited change with particle size and land use. Converting arable cropping to bare soil induced substantial depletion of amino sugars associated with the clay-size fraction, as a proportion of total carbon (C) and total soil mass, but not the silt- and sand-size fractions. Alternatively, switching arable soil to grassland increased amino sugar stocks in both the clay- and sand-size fractions. Analysis of the relative input of fungal and bacterial derived amino sugars indicated that fungal sources are the most dynamic with respect to land use change. These results highlight the selective vulnerability of microbial C pools in finer fractions under low plant C input and the selective recovery in specific fractions upon restoration, emphasizing the importance of the conversion of plant organic matter into mineral-associated microbial residues to promote stable soil organic C.  相似文献   

7.
The effect of endogeic earthworms (Octolasion tyrtaeum) and the availability of clay (Montmorillonite) on the mobilization and stabilization of uniformly 14C-labelled catechol mixed into arable and forest soil was investigated in a short- and a long-term microcosm experiment. By using arable and forest soil the effect of earthworms and clay in soils differing in the saturation of the mineral matrix with organic matter was investigated. In the short-term experiment microcosms were destructively sampled when the soil had been transformed into casts. In the long-term experiment earthworm casts produced during 7 days and non-processed soil were incubated for three further months. Production of CO2 and 14CO2 were measured at regular intervals. Accumulation of 14C in humic fractions (DOM, fulvic acids, humic acids and humin) of the casts and the non-processed soil and incorporation of 14C into earthworm tissue were determined.Incorporation of 14C into earthworm tissue was low, with 0.1 and 0.44% recovered in the short- and long-term experiment, respectively, suggesting that endogeic earthworms preferentially assimilate non-phenolic soil carbon. Cumulative production of CO2-C was significantly increased in casts produced from the arable soil, but lower in casts produced from the forest soil; generally, the production of CO2-C was higher in forest than in arable soil. Both soils differed in the pattern of 14CO2-C production; initially it was higher in the forest soil than in the arable soil, whereas later the opposite was true. Octolasion tyrtaeum did not affect 14CO2-C production in the forest soil, but increased it in the arable soil early in the experiment; clay counteracted this effect. Clay and O. tyrtaeum did not affect integration of 14C into humic fractions of the forest soil. In contrast, in the arable soil O. tyrtaeum increased the amount of 14C in the labile fractions, whereas clay increased it in the humin fraction.The results indicate that endogeic earthworms increase microbial activity and thus mineralization of phenolic compounds, whereas clay decreases it presumably by binding phenolic compounds to clay particles when passing through the earthworm gut. Endogeic earthworms and clay are only of minor importance for the fate of catechol in soils with high organic matter, clay and microbial biomass concentrations, but in contrast affect the fate of phenolic compounds in low clay soils.  相似文献   

8.
Prolonged intensive arable cropping of semiarid grassland soils in the South African Highveld resulted in a significant loss of C, N and associated living and dead microbial biomass. To regenerate their soils, farmers converted degraded arable sites back into secondary pastures. The objective of this study was to clarify the contribution of microorganisms to the sequestration of C and N in soil during this regeneration phase. Composite samples were taken from the topsoils of former arable land, namely Plinthustalfs, which had been converted to pastures 1-31 years ago. Amino sugars were determined as markers for microbial residues in the bulk soil and in selected particle-size fractions. The results showed that when C and N contents increased during the secondary pasture usage, the amino sugar concentration in the bulk soil (0-5 cm) recovered at similar magnitude and reached a new steady-state level after approximately 90 years, which corresponded only to 90% of the amino sugar level in the primary grassland. The amino sugar concentration in the clay-sized fraction recovered to a higher end level than in the bulk soil, and also at a faster annual rate. This confirms that especially the finer particles contained a high amount of amino sugars and were responsible, thus, for the restoration of microbially derived C and N. The incomplete recovery of amino sugars in bulk soil can only in parts be attributed to a slightly coarser texture of secondary grassland that had lost silt through wind erosion. The soils particularly had also lost the ability to restore microbial residues below 5 cm soil depth. Overall, the ratios of glucosamine to muramic acid also increased with increasing duration of pasture usage, suggesting that fungi dominated the microbial sequestration of C and N whereas the re-accumulation of bacterial cell wall residues was less pronounced. However, the glucosamine-to-muramic acid ratios finally even exceeded those of the primary grassland, indicating that there remained some irreversible changes of the soil microbial community by former intensive crop management.  相似文献   

9.
The extraction of soils by the electro-ultrafiltration (EUF) method yields organic N which has been used as an index for mineralisable N in soils. This EUF extractable organic fraction contains a mixture of various N compounds not yet completely identified. It has been proposed that the amino N compounds are more indicative for the potentially mineralisable N in soils than the total organic N extracted (Mengel et al., 1999). An amendment of soils with easily mineralisable organic matter may, therefore, alter the amino N concentrations of the organic N extracted. Our determination of the amino N compounds aimed to prove this hypothesis. The principle of our experiment was to mix soil with green manure, bacterial biomass and cellulose, respectively, and to incubate the treated soil aerobically for 80 days at 20°C in the laboratory. Control treatments without organic amendment were also incubated. Soil samples were taken several times during the incubation period and analysed for the inorganic N (NO3−-N and NH4+-N) and for the EUF extractable organic N. Amino acids and amino sugars were determined in the hydrolysed EUF extracts. The concentrations of amino acids and amino sugars in the organic N extracted varied with time and differed between the treatments. Glutamic acid has been found to be the most relevant amino acid in the EUF extracts and was particularly indicative for the existence of mineralisable green manure in the soil. Glucosamine was the most relevant amino sugar in the EUF extracts and this amino sugar appears to be indicative for the easily mineralisable relics of microbial cells in the soil.  相似文献   

10.
Concentrations of soluble soil sugars, soluble phenolic acids, and free amino acids were measured in three forest communities at the FACTS-II Aspen FACE Site near Rhinelander, WI, in order to better understand how elevated atmospheric CO2 and O3 are influencing soil nutrient availability and cycling. Sugars, phenolic acids, and amino acids are mostly derived from plant and microbial processes, and have the potential to be influenced by changes in carbon inputs. We hypothesized that concentrations in the soil would parallel increases seen in biological activity, due to greater net primary productivity under elevated CO2 and seasonal patterns of root growth. Chemical analysis of soils revealed marginally significant increases of total soluble sugars and total soluble phenolic acids in the elevated CO2 treatment (+27 mg kg−1, +0.02 μmol g−1), but there were no significant differences in concentrations due to elevated O3 or CO2+O3. Total free amino acid concentrations were not affected by any of the treatments, but significant shifts in individual amino acids were observed. Elevated CO2 and the interaction treatment (elevated CO2+O3) increased aspartic acid concentrations, while elevated O3 treatment decreased the concentration of valine. Concentrations of sugars increased throughout the growing season, while phenolic acids were constant and amino acids decreased. The birch-aspen community had the highest concentration of phenolic acids and sugars overall, while maple-aspen had the lowest. These findings suggest that concentrations of soluble sugars, soluble phenolic acids, and free amino acids in the soil are strongly influenced by soil properties, plant and microbial activity, plant community composition, and to a lesser degree, changes in atmospheric CO2 and O3.  相似文献   

11.
The definition of humusforms from soils under cultivation. II. Quantity and quality of soil organic matter In the new edition of the German textbook “Practical Studies in Soil Science” the authors presented a proposal of mapping humusforms in arable soils in order to characterize soil and site ecology (Schlichting et al., 1995). This proposal was developed from the definitions “Ochric”, “Mollic” and “Umbric” of the Soil Taxonomy and the FAO classification. The characterization of humusforms in 45 arable surface soils was carried out according to this proposal while soil organic matter (SOM) composition was investigated by means of wet chemistry and CPMAS 13C-NMR spectroscopy. “Mollic” in contrast to “Umbric” humusforms could be characterized by a higher carbonyl/carboxyl carbon content probably deriving from proteins, polysaccharides and humic substances. In addition the mollic epipedon contains 10% more litter compounds, whereas in the umbric epipedon humic acids are of major importance. The humin fraction in the mollic epipedon is thought to be raised by the formation of Ca-humates. Our data suggest, that with regard to microbial decomposition a surplus of available organic matter is present in the mollic horizons. The ochric-like epipedon has a much lower humus content compared to “Mollic” and “Umbric” horizons and exhibits the highest amounts of soluble organic matter as well as aromatic and carboxylic C-compounds in the humic fraction. Our data suggest, that SOM quantity and quality of the mollic, umbric and ochric epipedons differ substantially. These findings suggest that the proposal of Schlichting et al. (1995), which was extended by Blume & Beyer (1996), should be regarded as a useful basis to discuss the development of humusforms in soils under cultivation and facilitate soil survey in order to improve site characterization.  相似文献   

12.
Long‐term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse‐textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle‐size fractions. Long‐term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi‐exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt‐ and clay‐sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation.  相似文献   

13.
THE NATURE OF ALKALI-SOLUBLE SOIL ORGANIC PHOSPHATES   总被引：2，自引：0，他引：2  
Fractionation of the phosphates in a sodium hydroxide extract of an arable soil has shown the presence of a number of esters of a type not previously detected in soils. These included several mono-phosphorylated carboxylic acids with C to P ratios of approximately 7 or 8 to I and two esters each containing glycerol, myoinositol, chiroinositol and an unidentified component. Another ester, probably containing two phosphate groups, was also detected but was not completely separated from other compounds containing no P. These esters constituted only approximately 3 per cent of the total soil organic P but considerable losses of organic P occurred during the extraction and isolation procedures. The amounts of the inositol phosphates, nucleoside phosphates, and inorganic pyrophosphate in the extract were also measured.  相似文献   

14.
Nitrogen biomarkers and their fate in soil   总被引：3，自引：0，他引：3  
More than 90 % of the nitrogen (N) in soils can be organically bound, but the mechanisms and rates by which it is cycled have eluded researchers. The objective of this research was to contribute to a better understanding of the origin and transformation of soil organic N (SON) by using amino sugars and the enantiomers of amino acids as markers for microbial residues and/or aging processes. Studied samples presented here comprised (1) soil transects across different climates, (2) arable soils with different duration of cropping, and (3) radiocarbon‐dated soil profiles. The results suggested that increased microbial alteration of SON temporarily results in a sequestration of N in microbial residues, which are mineralized at later stages of SON decomposition. Microorganisms increasingly sequestered N within intact cell wall residues as frost periods shortened. At a mean annual temperature above 12–15 °C, these residues were mineralized, probably due to limitations in additional substrates. Breaking the grassland for cropping caused rapid SON losses. Microbial residues were decomposed in preference to total N, this effect being enhanced at higher temperatures. Hence, climate and cultivation interactively affected SON dynamics. Nevertheless, not all SON was available to soil microorganisms. In soil profiles, L‐aspartic acid and L‐lysine slowly converted into their D‐form, for lysine even at a similar rate in soils of different microbial activity. Formation of D‐aspartate with time was, therefore, induced by microorganisms while that of D‐lysine was not. The racemization of the two amino acids indicates that SON not available to microorganisms ages biotically and abiotically. In native soils, the latter is conserved for centuries, despite N deficiency frequently occurring in living terrestrial environments. Climate was not found to affect the fate of old protein constituents in surface soil. When native grassland was broken for cropping, however, old SON constituents had become available to microorganisms and were degraded.  相似文献   

15.
Various methods exist for the isolation of particulate organic matter (POM), one of the soil‐organic‐matter (SOM) fractions reacting most sensitive on land‐use or soil‐management changes. A combination of density separation and ultrasonic treatment allows to isolate two types of POM: (1) free POM and (2) POM occluded in soil aggregates. POM fractions are closely linked to their biochemical function for the formation and stabilization of aggregates, therefore methods using different aggregate sizes may result in different POM fractions isolated. We evaluated two physical fractionation procedures to reveal whether they yield different POM fractions with respect to amount and composition, using grassland and arable soils with sandy‐loam to sandy–clay‐loam texture and thus low macroaggregate stability. Method I used air‐dried aggregates of <2.0 mm size and a low‐energy sonication for aggregate disruption, method II used field‐moist aggregates <6.3 mm and a high‐energy–sonication procedure for aggregate disruption. POM fractions were analyzed by elemental analysis (C, N) and CPMAS 13C‐NMR spectroscopy. With both methods, about similar proportions of the SOM are isolated as free or occluded POM, respectively. The free‐ and occluded‐POM fractions obtained with method I are also rather similar in C and N concentration and composition as shown by 13C‐NMR spectroscopy. Method II isolates a free‐ and occluded‐POM fraction with significantly different C and N concentrations. NMR spectra revealed significant differences in the chemical composition of both fractions from method II, with the occluded POM having lower amounts of O‐alkyl C and higher amounts of aryl C and alkyl C than the free POM. Due to the use of larger, field‐moist aggregates with minimized sample pretreatment, two distinctly different POM fractions are isolated with method II, likely to be more closely linked to their biochemical function for the formation and stabilization of aggregates. High‐energy sonication as in method II also disrupts small microaggregates <63 µm and releases fine intraaggregate POM. This fraction seems to be a significant component of occluded POM, that allows a differentiation between free and occluded POM in sandy soils with significant microaggregation. It can be concluded, that microaggregation in arable soils with sandy texture is responsible for the storage of a more degraded occluded POM, that conversely supports the stabilization of fine microaggregates.  相似文献   

16.
《CATENA》2001,43(3):177-189
Soil utilization has, for many years, strongly influenced the properties of soils in the undulating terrain of the Lublin Upland. Population increase and suitability of the soils (particularly Luvisols, Cambisols and Chernozems derived from loess and loess-like formations) for arable agriculture were the main reasons for deforestation. This led to erosion, which caused changes in soil morphology and the development of a mosaic soil cover. Accelerated erosion was strongest on slopes exceeding 18%. It resulted in selective loss of clay. The main changes in silty soils developed from loess and loess-like deposits occurred in the first few decades after cultivation started. They included a decrease in organic matter content from an average of 2.3% organic C in the forest soils to about 1% in the arable soils. No further changes in humus content were observed, but the proportion of fulvic acids increased at the expense of humic acids. The pHKCl rate decreased at the slope foot from about 5.8 to 5.0. Morphological changes in rendzinas were much lower than in the soils derived from loess. We do not expect big changes in these soils in the next 100 years if their use remains the same.  相似文献   

17.
The preservation of plant residues is important for sustainable arable cropping. Lignin is a marker for plant residues in soils. We have investigated influences of the length of cultivation on the dynamics of lignin. Composite samples were taken from the top 20 cm of soils that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province of South Africa. Lignin‐derived phenols were determined in the <2 µm (clay), 2–20 µm (silt), 20–250 µm (fine sand) and 250– 2000 µm (coarse sand) size separates. With increasing length of cultivation, the concentration of such phenols decreased to 36% of that in the grassland. The lignin contents as proportions of the total carbon did not change during cultivation, suggesting that there was no selective enrichment of lignin moieties as C was lost as a result of cultivation. The loss rate constants of lignin concentrations in particle‐size fractions increased in the order clay (0.17 year?1) ≤ silt (0.18 year?1) < fine sand (0.20 year?1) < coarse sand (0.22 year?1). Increasing ratios of phenolic acids to aldehydes in bulk soil, silt and fine sand fractions with increasing length of cultivation indicated that side chains were being oxidized. The ratios in the silt fraction, however, decreased after 10–20 years. We attribute this to a loss of lignin together with silt by wind erosion, resulting in a rejuvenation of lignin compounds in the remaining silt‐sized pools of C.  相似文献   

18.
14C-labelled cellulose was added to seven different soils containing silt + clay (particles < 0.02 mm) in amounts which varied from 8 to 75 per cent. The cellulose was allowed to decompose, and the amounts of labelled C transformed into metabolites hydrolyzable into amino acids were determined. The amounts of labelled amino acid C in the soils were proportional to their content of silt + clay. After 30 days of incubation labelled amino acid C remaining in the soil with the lowest content of silt + clay constituted 6 per cent of the carbon added in cellulose, as compared with 18 per cent in the soil with the highest content of silt + clay. These values had decreased to 5 and 13 per cent respectively after 2 years of incubation. The order between the soils in the content of labelled amino acid C established during the first month of incubation, was thus roughly maintained throughout the period of incubation. The biological half-life of the labelled C in amino acids varied in the seven soils during the last year of incubation from 3 to 8 years. The variation was, however, not related to the amount of silt + clay.n the soils had been incubated with the labelled material for 2 years, samples of the soils were exposed to “stress” treatments: air drying-rewetting; increased biological activity caused by addition of glucose, and exposure to chloroform vapour. The treatments resulted in an evolution of labelled C in CO, which was 5–10 times larger than the evolution from untreated samples. The increase in the CO2 evolution caused by the treatments in the different soils was, however, not related to the amount of silt + clay, and a high content of this material did not protect organic material against the effect of the treatments.is concluded that the silt + clay fraction ensures stabilization of amino acid metabolites produced during the period of intense biological activity that follows the addition of decomposable, energy rich material to the soil. The amount of amino acid metabolites stabilized increased with increasing concentration of silt + clay, but the rate of decay of the amino acid material during later stages was largely independent of the concentration of silt + clay.  相似文献   

19.
Classical chemical fractionation of soil sulphur (S) into HI‐reducible S and carbon‐bonded S does not separate S in soil into fractions that have differing mineralization potentials. Other techniques are needed to separate organic S into more labile and less labile fractions of biological significance, irrespective of their bonding relations. We have sequentially fractionated soil S and carbon (C) into their ionic forms released onto ion‐exchange resins and organic S and C extracted in alkali of increasing concentration. We evaluated the technique on pasture and arable soils that had received various fertilizer and cultivation treatments. Total S and C were greater in the soil of the fertilized pasture than in that of the unfertilized pastures. Continuous arable cropping decreased total soil S and C, whereas restoration to pasture caused an accumulation. Resin, 0.1 m NaOH, 1 m NaOH and residual fractions accounted for between 1–13%, 49–69%, 4–16% and 19–38% of total soil S and between 5–6%, 38–48%, 5–7% and 46–53% of total soil C, respectively. Among different S and C fractions, the size of the 0.1 m NaOH and residual fractions changed more with the change in land use and management. The 0.1 m NaOH fraction had a narrower C:S ratio (50–75:1) than did the residual fraction (96–141:1). The significant degree of change in these two fractions, caused by differences in land management, indicates that they may be useful indicators of change in ‘soil quality’.  相似文献   

20.
Summary Humic acids from two Brazilian topsoils under savanna grassland and five soil fungal melanins were characterized by elemental, functional group and infrared analysis. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for several other fungal melanins and soil humic acids. Compared with the soil humic acids, the infrared spectra of the fungal melanins showed greater detail, indicative of higher aliphaticity. They were similar to the type III infrared spectra of humic acids, which are characteristically high in proteinaceous material and polysaccharides. The infrared spectra of the humic acids from the two Brazilian soils studied were classified as type I, which includes most soil humic acids. Notwithstanding the greater detail, in some areas the fungal melanin spectra were similar to those reported for other fungal melanins and humic acids of different origins. The probable contribution of the melanic fungi to the formation of soil humic polymers is discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号