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1.
The decrease of NMR visibility of the C signal in soil samples due to the association between organic carbon (OC) and the topsoil mineral surface was investigated. CPMAS 13C‐NMR spectra were obtained for soil particle‐size fractions (< 2 μm, 2–20 μm, > 20 μm) and bulk soils from an agricultural topsoil (Chernozem) that had received three different amendments (no fertilization, mineral fertilization (NPK), mineral (NPK) and organic (cattle manure) fertilizations) at Bad Lauchstädt, Germany. The soil organic carbon content of the three soils depended on the degree of soil fertilization. There was no constant relationship between the total NMR signal intensity and the total amount of organic carbon (TOC) for all size fractions. Indeed, a key role played in the C signal intensity by the paramagnetic ferric ion from the clay content in soil fractions and bulk soils was confirmed. Thus, we describe the variations of C signal intensity by taking into account the distribution of clay‐associated OC and non‐associated OC pools. Depending on the amendment, the C signal visibility was weakened by a factor of 2–4 for the clay‐associated OC. This estimation was rendered possible by combining mineral specific surface area (SSA) measurements with the N2 gas adsorption method (BET method) and determination of TOC and iron concentrations. This approach contributes to the quantitative evaluation of the CPMAS 13C‐NMR detection.  相似文献   

2.
Methods to quantify organic carbon (OC) in soil fractions of different stabilities often involve time-consuming physical and chemical treatments. The aim of the present study was to test a more rapid alternative, which is based on the spectroscopic analysis of bulk soils in the mid-infrared region (4000-400 cm−1), combined with partial least-squares regression (PLS). One hundred eleven soil samples from arable and grassland sites across Switzerland were separated into fractions of dissolved OC, particulate organic matter (POM), sand and stable aggregates, silt and clay particles, and oxidation resistant OC. Measured contents of OC in each fraction were then correlated by PLS with infrared spectra to obtain prediction models. For every prediction model, 100 soil spectra were used in the PLS calibration and the residual 11 spectra for validation of the models. Correlation coefficients (r) between measured and PLS-predicted values ranged between 0.89 and 0.97 for OC in different fractions. By combining different fractions to one labile, one stabilized and one resistant fraction, predictions could even be improved (r=0.98, standard error of prediction=16%). Based on these statistical parameters, we conclude that mid-infrared spectroscopy in combination with PLS is an appropriate and very fast tool to quantify OC contents in different soil fractions.  相似文献   

3.
Surface mining is known to drastically reduce soil organic carbon (OC) pools through various mechanisms associated with topsoil salvage, stockpiling and respreading. Stockpiling is an important management practice; however, the effects of this practice on reductions and recovery of soil aggregation and aggregate OC are poorly understood. Objectives of this research were to monitor soil aggregation and aggregate OC in the surface of a short‐term stockpile (<3 yr) followed by a second movement of stockpiled soils to a temporary location. Samples were analysed for aggregate size distribution, aggregate fractions, OC, and organic matter turnover using 13C natural abundance. Macroaggregate proportions increased and microaggregate proportions decreased after 3 yr of storage, possibly indicating recovery of soil structure. Following the removal of the stockpile and placement in a temporary pile, macroaggregation decreased and free silt and clay fractions increased relative to initially stockpiled soils. The second disturbance resulted in greater destruction of aggregate structure than the initial disturbance during topsoil salvage. Aggregate organic matter (as indicated by OC) increased significantly between the early sampling of the stockpiled soils (<1 yr in storage) and the placement of the topsoil in a temporary pile in macroaggregates and remained the same for microaggregates. Organic matter not protected within aggregates decreased with storage time as this material was available for utilization by microbes while aggregate protected organic matter (OM) remained unchanged or slightly increased for macro‐ and microaggregates with stockpile storage time. Aggregate δ13C values did not indicate inclusion of new OM within soil aggregates after 3 yr of topsoil stockpiling. Short‐term stockpiling was beneficial for aggregation in the surface layers where plant roots and microbial communities were active; however, subsequent movement of the topsoil resulted in a greater loss of soil aggregation relative to the initial topsoil salvage without impacting soil OC.  相似文献   

4.
The effect of temperatures of −2.5 to +20 °C on the biodegradation of concentrations 0.2-50 μg cm−3 of pentachlorophenol (PCP), phenanthrene, pyrene and 2,4,5-trichlorophenol (TCP) was studied in soils sampled from an agricultural field and a relatively pristine forest in Helsinki, Finland. At the temperatures simulating seasonal variation of boreal soil temperatures [Heikinheimo, M., Fougstedt, B., 1992. Statistic of Soil Temperature in Finland. Meteorological Publications 22. Finnish Meteorological Institute, Helsinki, Finland], the response of mineralization of PCP, phenanthrene and 2,4,5-TCP was the most effective in the rhizosphere fraction of the forest humus soil at the substrate concentrations of ?5 μg cm−3. In the control incubation, performed at constant temperature of +20 °C, the mineralization yields of the model pollutants were highest in the agricultural soil with the highest applied substrate concentration (50 μg cm−3). The results suggest that the high level of pollutant mineralization at +20 °C resulted from the apparent adaptation of the soil microbial community to the high substrate concentration. No such adaptation occurred when the soils were incubated at temperatures simulating the actual boreal soil temperatures. The present results stress the role of adjusting the incubation conditions to environmentally relevant values, when assessing biodegradation of anthropogenic organic compound in boreal soils.  相似文献   

5.
Biochemical characterization of urban soil profiles from Stuttgart, Germany   总被引：1，自引：0，他引：1  
The knowledge of biochemical properties of urban soils can help to understand nutrient cycling in urban areas and provide a database for urban soil management. Soil samples were taken from 10 soil profiles in the city of Stuttgart, Germany, differing in land use—from an essentially undisturbed garden area to highly disturbed high-density and railway areas. A variety of soil biotic (microbial biomass, enzyme activities) and abiotic properties (total organic C, elemental C, total N) were measured up to 1.9 m depth. Soil organic matter was frequently enriched in the subsoil. Microbial biomass in the top horizons ranged from 0.17 to 1.64 g C kg−1, and from 0.01 to 0.30 g N kg−1, respectively. The deepest soil horizon at 170-190 cm, however, contained 0.12 g C kg−1 and 0.05 kg N kg−1 in the microbial biomass. In general, arylsulphatase and urease activity decreased with depth but in three profiles potentially mineralizable N in the deepest horizons was higher than in soil layers directly overlying. In deeply modified urban soils, subsoil beside topsoil properties have to be included in the evaluation of soil quality. This knowledge is essential because consumption of natural soils for housing and traffic has to be reduced by promoting inner city densification.  相似文献   

6.
Woody plant invasion of grasslands is prevalent worldwide. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by C3 trees/shrubs have been replacing C4 grasslands over the past 150 yr, resulting in increased soil organic carbon (SOC) storage and concomitant increases in soil total nitrogen (STN). To elucidate mechanisms of change in SOC and STN, we separated soil organic matter into specific size/density fractions and determined the concentration of C and N in these fractions. Soils were collected from remnant grasslands (Time 0) and woody plant stands (ages 10-130 yr). Rates of whole-soil C and N accrual in the upper 15 cm of the soil profile averaged 10-30 g C m−2 yr−1 and 1-3 g N m−2 yr−1, respectively, over the past 130 yr of woodland development. These rates of accumulation have increased soil C and N stocks in older wooded areas by 100-500% relative to remnant grasslands. Probable causes of these increased pool sizes include higher rates of organic matter production in wooded areas, greater inherent biochemical resistance of woody litter to decomposition, and protection of organic matter by stabilization within soil macro- and microaggregates. The mass proportions of the free light fraction (<1.0 g cm−3) and macroaggregate fraction (>250 μm) increased linearly with time following woody plant invasion of grassland. Conversely, the mass proportions of free microaggregate (53-250 μm) and free silt+clay (<53 μm) fractions decreased linearly with time after woody invasion, likely reflecting stabilization of these fractions within macroaggregate structures. Carbon and N concentrations increased in all soil fractions with time following woody invasion. Approximately half of the C and N accumulated in free particulate organic matter (POM) fractions, while the remainder accrued in stable macro- and microaggregate structures. Soil C/N ratios indicated that the organic C associated with POM and macroaggregates was of more recent origin (less decomposed) than C associated with the microaggregate and silt+clay fractions. Because grassland-to-woodland conversion has been geographically extensive in grassland ecosystems worldwide during the past century, changes in soil C and N storage and dynamics documented here could have significance for global cycles of those elements.  相似文献   

7.
Paddy soil management is generally thought to promote the accumulation of soil organic matter (SOM) and specifically lignin. Lignin is considered particularly susceptible to accumulation under these circumstances because of the recalcitrance of its aromatic structure to biodegradation under anaerobic conditions (i.e ., during inundation of paddy fields). The present study investigates the effect of paddy soil management on SOM composition in comparison to nearby agricultural soils that are not used for rice production (non‐paddy soils). Soil types typically used for rice cultivation were selected, including Alisol, Andosol and Vertisol sites in Indonesia (humid tropical climate of Java) and an Alisol site in China (humid subtropical climate, Jiangxi province). These soil types represent a range of soil properties to be expected in Asian paddy fields. All upper‐most A horizons were analysed for their SOM composition by solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy and for lignin‐derived phenols by the CuO oxidation method. The SOM composition was similar for all of the above named parent soil types (non‐paddy soils) and was also not affected by paddy soil management. A substantial proportion (up to 23%) of the total aryl‐carbon in some paddy and non‐paddy soils was found to originate from condensed aromatic‐carbon (e.g ., charcoal). This may be attributed to the burning of crop residues. On average, the proportion of lignin was low and made up 20% of the total SOM, and showed no differences between straw, particulate organic matter (POM), and the bulk soil material. The results from CuO oxidation are consistent with the data obtained from solid‐state 13C NMR spectroscopy. The extraction of lignin‐derived phenols revealed low VSC (vanillyl, syringyl, cinnamyl) values for all investigated soils in a range (4 to 12 g kg−1 OC) that was typical for agricultural soils. In comparison to adjacent non‐paddy soils, the data do not provide evidence for a substantial accumulation of phenolic lignin‐derived structures in the paddy soils, even for those characterized by higher organic carbon (OC) contents (e.g ., Andosol‐ and Alisol (China)‐derived paddy soils). We conclude that the properties of the parent soil types are more important for the lignin content of the soils than the effect of paddy management itself.  相似文献   

8.
Enzyme activities and microbial biomass in coastal soils of India   总被引：1，自引：0，他引：1  
Soil salinity is a serious problem for agriculture in coastal regions, wherein salinity is temporal in nature. We studied the effect of salinity, in summer, monsoon and winter seasons, on microbial biomass carbon (MBC) and enzyme activities (EAs) of the salt-affected soils of the coastal region of the Bay of Bengal, Sundarbans, India. The average pH of soils collected from different sites, during different seasons varied from 4.8 to 7.8. The average organic C (OC) and total N (TN) content of the soils ranged between 5.2-14.1 and 0.6-1.4 g kg−1, respectively. The electrical conductivity of the saturation extract (ECe) of soils, averaged over season, varied from 2.2 to 16.3 dSm−1. The ECe of the soils increased five fold during the summer season (13.8 dSm−1) than the monsoon season (2.7 dSm−1). The major cation and anion detected were Na+ and Cl−, respectively. Seasonality exerted considerable effects on MBC and soil EAs, with the lowest values recorded during the summer season. The activities of β-glucosidase, urease, acid phosphatase and alkaline phosphatase were similar during the winter and monsoon season. The dehydrogenase activity of soils was higher in monsoon than in winter. Average MBC, dehydrogenase, β-glucosidase, urease, acid phosphatase and alkaline phosphatase activities of the saline soils ranged from 125 to 346 mg kg−1 oven dry soil, 6-9.9 mg triphenyl formazan (TPF) kg−1 oven dry soil h−1, 18-53 mg p-nitro phenol (PNP) kg−1 oven dry soil h−1, 38-86 mg urea hydrolyzed kg−1 oven dry soil h−1, 213-584 mg PNP kg−1 oven dry soil h−1 and 176-362 mg PNP g−1 oven dry soil h−1, respectively. The same for the non-saline soils were 274-446 mg kg−1 oven dry soil, 8.8-14.4 mg TPF kg−1 oven dry soil h−1, 41-80 mg PNP kg−1 oven dry soil h−1, 89-134 mg urea hydrolyzed kg−1 oven dry soil h−1, 219-287 mg PNP kg−1 oven dry soil h−1 and 407-417 mg PNP kg−1 oven dry soil h−1, respectively. About 48%, 82%, 48%, 63%, 40% and 48% variation in MBC, dehydrogenase activity, β-glucosidase activity, urease activity, acid phosphatase activity and alkaline phosphatase activity, respectively, could be explained by the variation in ECe of saline soils. Suppression of EAs of the coastal soils during summer due to salinity rise is of immense agronomic significance and needs suitable interventions for sustainable crop production.  相似文献   

9.
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10.
China's rice paddies, accounting for 19% of the world's total, play an important role in soil carbon (C) sequestration. In order to reduce uncertainties from upscaling spatial processes of the DeNitrification-DeComposition (DNDC) model for improving the understanding of C sequestration under recommended management practices (RMPs), we parameterized the DNDC model with a 1:1,000,000 polygonal soil database to estimate how RMPs influence potential C sequestration of the top 30 cm of Chinese paddy soils and to identify which management practices have the greatest potential to increase soil organic carbon (SOC) in these soils. These practices include reduced/no tillage, increasing crop residue return, and increasing manure applications. A baseline and eleven RMP scenarios were projected from 2009 to 2080, including traditional and conservation tillage, increasing crop residue return, increasing manure incorporation, and the combination of these practices. The results indicated that C sequestration potential under modeled RMPs increased compared to the baseline scenario, and varied greatly from 29.2 to 847.7 Tg C towards the end of the study period with an average rate of 0.7 to 20.2 Tg C yr− 1. In general, increasing crop residue return was associated with higher rates of C sequestration when compared to increasing manure application or practicing conservation tillage. The simulations demonstrated that the most effective soil C sequestration strategy probably involves the implementation of a combination of RMPs, and that they vary by location.  相似文献   

11.
The puddling of paddy soils is the most common method of lowland rice cultivation in Asian countries and results in a complete distortion of the soil structure of the puddled layer and the formation of a distinct plough pan. In addition, the soil structure and the interrelated chemical and biological parameters in these soils are influenced by the alternating of flooding and drying stages. Since physical properties are basic features for the availability of water and nutrients characteristics such as soil structure and soil moisture have been recorded at the different stages of rice growth in detail. For a better understanding these results have been compared with micropedological investigations. For these purposes undisturbed microcosms filled with paddy soils of three different sites from south east China were taken and planted with rice in a climate chamber.Management-induced dynamics have been reflected very prominently as far as bulk density, pore size distribution and soil moisture of the puddled layer are concerned. The properties of the undisturbed plough pan did not change during all stages of the experiment. Most significant effects of soil puddling have been found in the soil with a clay content of more than 40%. Comparing the different sampling stages after puddling the soils with high clay contents have shown the greatest variety in pore size distribution.Micropedological investigations demonstrated the different texture-influenced aspects of pore size distribution and the arrangement of soil structure in the topsoil in detail. Micrographs verified the changes of microhabitats caused by soil structure dynamics. The structural alteration consequences different living-conditions of microorganisms and, therefore, population dynamics related to the management of paddy soils which has been reflected in this study.  相似文献   

12.
The long-term storage of soil organic matter (SOM) in forest soils is still poorly understood. In this study, particle size fractionation in combination with accelerator mass spectroscopy (AMS) and solid state 13C nuclear magnetic resonance (NMR) spectroscopy was applied to investigate organic carbon (OC) stabilisation in Cambisol and Luvisol profiles under spruce (Picea abies) and beech (Fagus sylvatica L.) forests. In most samples, OC was preferentially associated with <2 μm fractions. Throughout soil profiles the contribution of OC in the clay fraction to the total OC increased from 27%-53% in A horizons to 44-86% in E, B and EB horizons. The 200-2000 μm fractions from all sites and all depths showed a percentage of modern C (pmC)>100. They were enriched in 14C owing to high inputs of recent material from leaves and roots. Clearly less active material was associated with <2 and 2-20 μm fractions. This demonstrated that the particle size fractionation procedure applied to our study was capable to isolate a young OC fraction in all samples. The pmC values were strongly decreasing with depth but the decrease was much more pronounced in the fine fractions. The <2 and 2-20 μm fractions of B, E and EB horizons revealed radiocarbon ages between 512 and 4745 years before present which indicated that the SOM in those horizons was little affected by the recent vegetation. The major components of labile and stable SOM pools in topsoils and subsoils were always O/N-alkyl C (28-53%) and alkyl C (14-48%) compounds. NMR spectra of bulk soils and particle size fractions indicated that high alkyl C and O/N-alkyl C proportions throughout the soil profile are typical of Cambisols and Luvisols which were not subjected to regular burning. A relation between radiocarbon age and chemical composition throughout soil profiles was not observed. This suggests that the long-term stabilisation of SOM is mainly controlled by the existence of various mechanisms of protection offered by the soil matrix and soil minerals but not by the chemical structure of SOM itself.  相似文献   

13.
The location of soil organic matter (SOM) within the soil matrix is considered a major factor determining its turnover, but quantitative information about the effects of land cover and land use on the distribution of SOM at the soil aggregate level is rare. We analyzed the effect of land cover/land use (spruce forest, grassland, wheat and maize) on the distribution of free particulate organic matter (POM) with a density <1.6 g cm−3 (free POM<1.6), occluded particulate organic matter with densities <1.6 g cm−3 (occluded POM<1.6) and 1.6-2.0 g cm−3 (occluded POM1.6-2.0) and mineral-associated SOM (>2.0 g cm−3) in size classes of slaking-resistant aggregates (53-250, 250-1000, 1000-2000, >2000 μm) and in the sieve fraction <53 μm from silty soils by applying a combined aggregate size and density fractionation procedure. We also determined the turnover time of soil organic carbon (SOC) fractions at the aggregate level in the soil of the maize site using the 13C/12C isotope ratio. SOM contents were higher in the grassland soil aggregates than in those of the arable soils mainly because of greater contents of mineral-associated SOM. The contribution of occluded POM to total SOC in the A horizon aggregates was greater in the spruce soil (23-44%) than in the grassland (11%) and arable soils (19%). The mass and carbon content of both the free and occluded POM fractions were greater in the forest soil than in the grassland and arable soils. In all soils, the C/N ratios of soil fractions within each aggregate size class decreased in the following order: free POM<1.6>occluded POM<1.6-2.0>mineral-associated SOM. The mean age of SOC associated with the <53 μm mineral fraction of water-stable aggregates in the Ap horizon of the maize site varied between 63 and 69 yr in aggregates >250 μm, 76 yr in the 53-250 μm aggregate class, and 102 yr in the sieve fraction <53 μm. The mean age of SOC in the occluded POM increased with decreasing aggregate size from 20 to 30 yr in aggregates >1000 μm to 66 yr in aggregates <53 μm. Free POM had the most rapid rates of C-turnover, with residence times ranging from 10 yr in the fraction >2000 μm to 42 yr in the fraction 53-250 μm. Results indicated that SOM in slaking-resistant aggregates was not a homogeneous pool, but consisted of size/density fractions exhibiting different composition and stability. The properties of these fractions were influenced by the aggregate size. Land cover/land use were important factors controlling the amount and composition of SOM fractions at the aggregate level.  相似文献   

14.
Manganese is normally a trace element in soils, but it is important due to its effects on soil chemistry and morphology. There are rare, Mn-rich soils in the Eastern Piedmont of the USA that have not been previously studied. The morphology, mineralogy, and chemical and physical properties of these manganiferous soils were documented in order to better understand their pedogenesis. The soils were found to contain as much as 169 g kg−1 Fe and 140 g kg−1 Mn as oxides (dithionite-citrate-bicarbonate extractable). These high levels of Mn oxides impart an extremely dark color to the soil material (moist Munsell value and chroma commonly < 2/1). Manganiferous soil materials have unusual physical properties such as high particle density (up to 3.25 × 10−6 Mg m−3 on bulk soil), low bulk density (as low as 0.39 × 10−6 Mg m−3), and extremely high porosity (maximum calculated 88%). X-Ray Diffraction and Fourier Transform Infrared spectra show that the dominant Fe oxide and Mn oxide minerals in the soils are hematite and lithiophorite, respectively. Samples of the parent marble were dissolved in acid for Fe and Mn analysis and collection of non-carbonate residues (NCR). Based on the quantities of Fe and Mn in the bedrock, the mineralogy of the NCR, and micromorphological observations, it appears that the black, porous, Mn-rich material is derived directly from the dissolution of marble bedrock and accumulation of silicate residues plus Mn and Fe from within the rock. These soils, which appear to have a similar origin to Mn wad deposits, offer a unique opportunity for future studies of soil Mn due to the naturally high concentration of this metal.  相似文献   

15.
Forests naturally maintained by stand-replacing wildfires are often managed with clearcut harvesting, yet we know little about how replacing wildfire with clearcutting affects soil processes and properties. We compared the initial recovery of carbon (C) and nitrogen (N) pools and dynamics following disturbance in jack pine (Pinus banksiana) stands in northern Lower Michigan, USA, by sampling soils (Oa+A horizons) from three “treatments”: 3-6-year-old harvest-regenerated stands, 3-6-year-old wildfire-regenerated stands and 40-55-year-old intact, mature stands (n=4 stands per treatment). We measured total C and N; microbial biomass and potentially mineralizable C and N; net nitrification; and gross rates of N mineralization and nitrification. Burned stands exhibited reduced soil N but not C, whereas clearcut and mature stands had similar quantities of soil organic matter. Both disturbance types reduced microbial biomass C compared to mature stands; however, microbial biomass N was reduced in burned stands but not in clearcut stands. The experimental C and N mineralization values were fit to a first-order rate equation to estimate potentially mineralizable pool size (C0 and N0) and rate parameters. Values for C0 in burned and clearcut stands were approximately half that of the mature treatment, with no difference between disturbance types. In contrast, N0 was lowest in the wildfire stands (170.2 μg N g−1), intermediate in the clearcuts (215.4 μg N g−1) and highest in the mature stands (244.6 μg N g−1). The most pronounced difference between disturbance types was for net nitrification. These data were fit to a sigmoidal growth equation to estimate potential NO3− accumulation (Nitmax) and kinetic parameters. Values of Nitmax in clearcut soils exceeded that of wildfire and mature soils (149.2 vs. 83.5 vs. 96.5 μg NO3−-N g−1, respectively). Moreover, the clearcut treatment exhibited no lag period for net NO3− production, whereas the burned and mature treatments exhibited an approximate 8-week lag period before producing appreciable quantities of NO3−. There were no differences between disturbances in gross rates of mineralization or nitrification; rather, lower NO3− immobilization rates in the clearcut soils, 0.20 μg NO3− g−1 d−1 compared to 0.65 in the burned soils, explained the difference in net nitrification. Because the mobility of NO3− and NH4+ differs markedly in soil, our results suggest that differences in nitrification between wildfire and clearcutting could have important consequences for plant nutrition and leaching losses following disturbance.  相似文献   

16.
Water dispersible clay (WDC) is a good indicator of the risk of soil erosion by water and the consequent losses of nutrients and contaminants in overland flow. We measured the content and studied the properties of WDC in 26 samples of calcareous Xeralfs, Xerepts and Xererts of southwestern Spain collected from fields under different crop and tillage management; the soils ranged widely in total clay content (60–455 g kg− 1), calcium carbonate equivalent (CCE) (< 1–559 g kg− 1) and active calcium carbonate equivalent (ACCE; 2–135 g kg− 1), and were poor in organic carbon and soluble salts. The WDC content was determined by shaking 10 g of soil in 1 L of simulated rainwater for 4 hours. Non-carbonate WDC contents were found to be strongly correlated with the total clay content of the soils and ranged from 1 to 92 g kg− 1 soil (mean = 29 g kg− 1), the non-carbonate WDC/total clay ratio ranging from 0.01 to 0.29 (mean = 0.12). Based on regression analyses, illite was more dispersible than smectite and iron oxides decreased dispersion of clay. Carbonate WDC contents ranged from 1 to 27 g kg− 1 (mean = 8 g kg− 1) and were averaged one third the non-carbonate WDC contents; also, they were strongly correlated with the soil ACCE. WDC was rich in phosphorus (P) relative to the bulk soil. The enrichment ratio (ER) for total P (i.e. the ratio of total P in WDC to total P in soil) ranged from 0.2 to 29 (mean = 5) and was inversely related to the total clay content. On average, about one tenth of the soil total P was exported in the WDC and about one fifth of the total P in WDC was in the form of bicarbonate-extractable P (i.e. relatively soluble or ‘labile’ P). Part of the P in WDC seemingly occurred as metal phosphate particles formed by reaction of P fertilizers with soil. In summary, significant amounts of P can be exported via WDC, even though the proportion of total clay that is water dispersible is substantially lower in these soils than in cultivated soils of other semiarid regions.  相似文献   

17.
Soil loss tolerance limit is defined as the threshold upper limit of soil erosion that can be allowed without degrading long term productivity of specific soils. In India a default soil loss tolerance limit (SLTL) of 11.2 Mg ha− 1 yr− 1 is followed for planning soil conservation activities. The objective of this investigation is to provide a methodology to estimate quantitative SLTL for the Shivalik–Himalayan region in India for suggesting suitable soil conservation measures. A quantitative model was used to integrate potential soil indicators such as infiltration rate, bulk density, water stable aggregate, organic carbon and fertility status to assess soil quality governing soil resistibility to erosion. Scaling functions were used to convert soil parameters to unit less 0 to 1 scale. Normalized values of soil parameters were then multiplied by assigned weights based on relative importance and sensitivity analysis of each indicator. Soils were grouped into 1, 2 and 3 depending on overall additive score. A general guideline developed by the USDA-Natural Resource Conservation Service (NRCS) was followed with certain modifications in depth category for estimation of SLTLs. Soil loss tolerance limits varied from 2.5 to 12.5 Mg ha− 1 yr − 1 compared to single value of 11.2 Mg ha− 1 yr − 1 being followed earlier. Consideration of the newly estimated SLTLs would facilitate site specific conservation planning and prioritising areas for watershed management activities in India.  相似文献   

18.
Global warming leads to the melting of ice caps and glaciers and, consequently, the exposure of new areas of land to the atmosphere and weathering. These areas usually have a high reactivity to both biotic and abiotic changes. Proglacial areas in the Alps usually have a deglaciation time span of around 150 years (time since the end of the “Little Ice Age” in the 1850's). We investigated a chronosequence of very young soils in the proglacial area Morteratsch (Swiss Alps) to derive time-trends of soil organic matter accumulation and evolution. Total organic C and N contents, C and N contents of the various organic matter (OM) density fractions and of the labile (oxidised by H2O2) and stable (H2O2-resistant) fractions were measured. Further characterisation of OM and the various fractions was performed using Diffuse Reflection Infrared Fourier Transform (DRIFT). Soil organic matter has been accumulated over 150 years at very high rates, values lay between 7 and 36 g C/m2/year. This led to a soil organic matter abundance of about 1–5.5 kg C/m2 after 140 years. Even at the start of soil formation, a very stable fraction of soil organic matter was detectable. Stable organic matter (resistant to the H2O2 treatment) comprised about 6% of the total soil organic carbon and 10% of the total nitrogen. At the start of soil formation, a very high proportion of soil organic matter was present in the density fractions < 1.6 g/cm3. After about 140 years, 15% of soil organic carbon and 35–40% of the nitrogen was already present in the highest density fraction (> 2 g/cm3). With time, the quality of soil organic matter changed: a decrease of hydrophobicity, an increase in aromatic compounds in the bulk soil and a decrease in phenolic functional groups in the heaviest density fraction were detectable with increasing age. In general, stable organic matter as well as the density fraction > 2 g/cm3 had a low C/N ratio and were enriched in proteinaceous materials. The adsorption of proteinaceous materials points to a strong organo-mineral association. This process has existed since the very beginning of soil formation.  相似文献   

19.
Soil amendment with manures from intensive animal industries is nowadays a common practice that may favorably or adversely affect several soil properties, including soil microbial activity. In this work, the effect of consecutive annual additions of pig slurry (PS) at rates of 30, 60, 90, 120 and 150 m3 ha−1 y−1 over a 4-year period on soil chemical properties and microbial activity was investigated and compared to that of an inorganic fertilization and a control (without amendment). Field plot experiment conducted under a continuous barley monoculture and semiarid conditions were used. Eight months after the fourth yearly PS and mineral fertilizer application (i.e. soon after the fourth barley harvest), surface soil samples (Ap horizon, 0-15 cm depth) from control and amended soils were collected and analysed for pH, electrical conductivity (EC), contents of total organic C, total N, available P and K, microbial biomass C, basal respiration and different enzymatic activities. The control soil had a slightly acidic pH (6.0), a small EC (0.07 dS m−1), adequate levels of total N (1.2 g kg−1) and available K (483 mg kg−1) for barley growth, and small contents of total organic C (13.2 g kg−1) and available P (52 mg kg−1). With respect to the control and mineral fertilized soils, the PS-amended soils had greater pH values (around neutrality or slightly alkaline), electrical conductivities (still low) and contents of available P and K, and slightly larger total N contents. A significant decrease of total organic C was observed in soils amended at high slurry rate (12.3 g kg−1). Compared with the control and mineral treatments, which produced almost similar results, the PS-amended soils were characterized by a higher microbial biomass C content (from 311 to 442 g kg−1), microbial biomass C/total organic C ratio (from 2.3 to 3.6%) and dehydrogenase (from 35 to 173 μg INTF g−1), catalase (from 5 to 24 μmol O2 g−1 min−1), BAA-protease (from 0.7 to 1.9 μmol  g−1 h−1) and β-glucosidase (from 117 to 269 μmol PNP g−1 h−1) activities, similar basal respirations (from 48 to 77 μg C-CO2 g−1 d−1) and urease activities (from 1.5 to 2.2 μmol  g−1 h−1), and smaller metabolic quotients (from 6.4 to 7.7 ng C-CO2 μg−1 biomass C h−1) and phosphatese activities (from 374 to 159 μmol PNP g−1 h−1). For example, statistical analysis of experimental data showed that, with the exception of metabolic quotient and total organic C content, these effects generally increased with increasing cumulative amount of PS. In conclusion, cumulative PS application to soil over time under semiarid conditions may produce not only beneficial effects but also adverse effects on soil properties, such us the partial mineralization of soil organic C through extended microbial oxidation. Thus, PS should not be considered as a mature organic amendment and should be treated appropriately before it is applied to soil, so as to enhance its potential as a soil organic fertilizer.  相似文献   

20.
Our objectives were to determine both spatial and temporal variations in soil respiration of a mixed deciduous forest, with soils exhibiting contrasting levels of hydromorphy. Soil respiration (RS) showed a clear seasonal trend that reflected those of soil temperature (TS) and soil water content (WS), especially during summer drought. Using a bivariate model (RMSE=1.03), both optimal soil water content for soil respiration (WSO) and soil respiration at both 10 °C and optimal soil water content (RS10) varied among plots, ranging, respectively, from 0.25 to 0.40 and from 2.30 to 3.60 μmol m−2 s−1. Spatial variation in WSO was related to bulk density and to topsoil N content, while spatial variation in RS10 was related to basal area and the difference in pH measured in water or KCl suspensions. These results offer promising perspectives for spatializing ecosystem carbon budget at the regional scale.  相似文献   

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