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1.
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2.
To calculate the biomass from the size of the flush that follows fumigation, the fraction (k) of the killed biomass C that is respired as CO2 must be known. This was measured for a range of organisms: two yeasts Succharomyces cerevisiae and Candida utilis), two fungi (Cylindrocarpon sp. and Penicillium chrysogenum), an actinomycete (Streptomyces clavuligerus), seven bacteria (Aerobacter aerogenes, Bacillus subtilis, Clostridium histolyticum, Escherichia coli, Microccus lysodeikticus, Pseudomonas fluorescens and Nitrosomonas europaea) and a soil invertebrate (Lumbricus terrestris). The organisms were mixed with soil and fumigated; the consumption of O2, evolution of CO2 and mineralization of N were then measured under the standard conditions used to measure the flush. Control values obtained with fumigated soil alone were deducted, assuming that the added organisms did not cause a priming action. Taking all the organisms together, 50·0 ± 8·2% of the C originally present was mineralized in the 10 days following fumigation, giving a mean value of 0·5 for k.Experiments with earthworms showed that fumigation with CHCl3 did not appreciably increase the amounts of C and N mineralized from organisms that were already dead and that k was independent of the amount of organism added.From a consideration of the results in this and in the preceding three papers, it is concluded that the flush following fumigation can be used to give a rough measure of the amount of biomass in a soil.  相似文献   

3.
《土壤圈》2022,32(1):1-2
This special issue, for celebrating the 30th Anniversary of Pedosphere (founded in 1991), contains 15 articles reviewing recent advances and the state of the art of important topics, including some emerging topics, in soil science. The first article in this issue, by Du et al., is a meta-analysis systematically reviewing the effect of elevated carbon dioxide (CO2) on nitrogen oxide (N2O) emission from global agricultural soils, depending on other soil and experimental conditions.  相似文献   

4.
Abstract

The widely used hot‐water extraction method for soil boron was compared with acid ammonium acetate (AAAc) and acid ammonium acetate‐EDTA (AAAc‐EDTA) for boron determination. According to the results AAAc and AAAc‐EDTA were similar in their extracting power but these extracted only about one third of the boron amounts of the hot water extraction method. This sets special requirements for the sensitivity of the method of determination if these extractants are used. There was no significant difference in the correlation between timothy boron and soil boron assessed with studied methods and the coefficient of correlation ranged from 0.34 to 0.37. Interpretation for AAAc and AAAc‐EDTA tests was derived of that of the hot water method in use in Finland. The sensitivity of the ICP method was too poor to accurately separate between most deficient classes but there was no problems in separation between soils in need of boron fertilization and those which are satisfactory with respect to boron.  相似文献   

5.
Abstract

Since only one extraction is required to determine a large number of nutrients, many laboratories employ universal extractants to determine the available nutrients in a soil sample. This paper compares the universal ammonium bicarbonate‐DTPA (AB‐DTPA) method developed by Soltanpour and Schwab (1977) with the traditional methods, ammonium acetate (NH4OAc) test for exchangeable cations and the Lindsay and Norwell (1969) test for the micronutrients. Results from the analysis of 28 soils by these methods were compared. Most soils were selected from those used by the Spanish Working Group for the Standardization of Analytical Methods. In most cases, statistical correlations between methods presented good agreement for each element, but depending on the soil pH range, some elements needed two correlations. Also, when results for wet and dry soils were compared, variability was lower when the AB‐DTPA extraction method was used. We concluded that, besides being faster, the AB‐DTPA method is valid for Spanish soils, even for calcium (Ca) extraction in calcareous soils, where the ammonium acetate method fails due to excessive Ca solubilization.  相似文献   

6.
Strains of bacteria with differing degrees of overall (phenetic) similarity have been paired and grown together and separately in both acid and alkaline soils from a pine forest. A decrease in yield of an organism when grown in the presence of a second organism was taken as evidence of competition. It was shown that, contrary to expectations, pairs of organisms with different degrees of similarity might have similar competitive interactions. It is postulated that this is because one key property could result in a marked change in competitive ability while not markedly altering the taxonomic relationships of the organisms. The possibility that spatial separation of organisms can result in two or more organisms with identical functions becoming established in soil is discussed.  相似文献   

7.
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8.
Tillage effect on organic carbon in a purple paddy soil   总被引：18，自引：0，他引：18  
The distribution and storage of soil organic carbon （SOC） based on a long-term experiment with various tillage systems were studied in a paddy soil derived from purple soil in Chongqing, China. Organic carbon storage in the 0-20 and 0-40 cm soil layers under different tillage systems were in an order： ridge tillage with rice-rape rotation （RT-rr） 〉 conventional tillage with rice only （CT-r） 〉 ridge tillage with rice only （RT-r） 〉 conventional tillage with rice-rape rotation （CT-rr）. The RT-rr system had significantly higher levels of soil organic carbon in the 0-40 cm topsoil, while the proportion of the total remaining organic carbon in the total soil organic carbon in the 0-10 cm layer was greatest in the RT-rr system. This was the reason why the RT-rr system enhanced soil organic carbon storage. These showed that tillage system type was crucial for carbon storage. Carbon levels in soil humus and crop-yield results showed that the RT-rr system enhanced soil fertility and crop productivity. Adoption of this tillage system would be beneficial both for environmental protection and economic development.  相似文献   

9.
1.3-β-Glucanase (laminarinase) activity in soil was measured using laminarin as the substrate. Activity was optimal in sodium acid-maleate buffer at pH 5.4 and followed Michaelis-Menten kinetics. Three methods of analysing kinetic data gave Km values of 0.23, 0.21 and 0.20 mg.ml?1. Vmax values were 0.41, 0.39 and 0.39 μmole glucose, g?1. h?1. The activation energy of the reaction was 49 kJ. mole?1. A proportion of the activity was highly resistant to storage at various temperatures: at 50 C 1,3-β-glucanase had a half-life of 28 days.  相似文献   

10.
As vital components of desert systems, the roles of ants in arid ecological processes have been well documented, while little attention has been given to their effects on soil water. We conducted a six-year investigation in sand dune systems stabilized via revegetation, to explore the hydrological role of ants through comparing the influence of ant nests on rainfall infiltration in different-aged revegetated dunes. The presence of ant nests markedly enhanced infiltration due to weakening the rainfall interception by biological soil crusts (BSCs) in revegetated dunes. The distribution of ant nest was denser in older revegetated areas, due to better developed BSCs of later successional stages, compared to younger revegetated areas. Ants prefer later to early successional BSCs because the later lichen–moss dominated crusts were thicker and their surface was more stable than the early cyanobacteria dominated crusts. Conversely, the crustal rainfall interception was positively correlated with BSC thickness. These findings suggest that the occurrence of ant nests in older revegetated areas benefited to the planted shrubs with deeper root systems and maintain a relative constant cover of shrubs in artificial sand-binding vegetation following an increase in infiltration to deeper soil layers.  相似文献   

11.
A new method for the determination of biomass in soil is described. Soil is fumigated with CHCl3 vapour, the CHCl3 removed and the soil then incubated. The biomass is calculated from the difference between the amounts of CO2 evolved during incubation by fumigated and unfumigated soil. The method was tested on a set of nine soils from long-term field experiments. The amounts of biomass C ha?1 in the top 23 cm of soil from plots on the Broadbalk continuous wheat experiment were 530 kg (unmanured plot), 590 (plot receiving inorganic fertilizers) and 1160 (plot receiving farmyard manure). Soils that had been fallowed for 1 year contained less biomass than soils carrying a crop. A calcareous woodland soil contained 1960 kg biomass C ha?1, and an unmanured soil under permanent grass 2020. The arable soils contained about 2% of their organic C in the biomass; uncultivated soils a little more—about 3%.  相似文献   

12.
Yu  Kun  Duan  Yang  Zhang  Maosheng  Dong  Ying  Wang  Luchen  Wang  Ye  Guo  Xu  Hu  Fusheng 《Journal of Soils and Sediments》2020,20(4):1943-1959
Journal of Soils and Sediments - Land subsidence has caused serious geological damage in many countries, including China. Soil pore number, size, shape, and pore size distribution affect soil...  相似文献   

13.
Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg g−1 h−1 and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks.  相似文献   

14.
Intensification of land use can become a threat to agricultural sustainability if they lead to increased soil erosion. This study examines land‐use changes, soil and water conservation, soil erosion and soil productivity in the Highlands of Kenya. In addition, it examines farmers' perception of livelihood changes. Land‐use changes were determined from interpretations of aerial photographs taken in 1960 and 1996. Additional information on land use, soil and water conservation and livelihood changes were obtained from discussions and interviews with farmers, as well as from field verifications of the most recent aerial photographs. Soil samples were analysed and soil erosion assessed according to the PLUS classification scheme. The results indicate that substantial changes in land use, such as introduction of coffee and high‐yielding maize, and fragmentation of land holdings have taken place. Less land was conserved in 1996 as compared to 1960. Moreover, SWC practices have changed from fanya chini terraces and shifting cultivation to bench terraces and permanent cultivation. Rates of soil nutrients (organic C, N and K) and maize‐yield levels decreased significantly with increasing erosion. Farmers' perception of livelihood changes was differentiated according to farmers' off‐farm resource 60 per cent of the farmers depended on income from the land and thought livelihoods were better in the 1960s. It is concluded that more efforts to decrease soil erosion and investments in land and labour are necessary to sustain soil productivity and hence secure rural livelihoods. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

15.
The growth of five typical but phenetically distinct cocci and Arthrobacter strains, isolated from a pine forest soil, has been investigated. Soil reaction was found to have a marked effect on growth and unless naturally acidic soils were made more alkaline they did not support growth, even in the presence of added nutrients. However, in the presence of fungi which could use the added nutrients, e.g. chitin, mycelial fragments etc., bacterial growth was possible and could be correlated with a decrease in acidity, especially around particles of organic matter. Where the pH rose above 7.9, bacterial growth again decreased. All the bacterial strains tested reacted in the same way, suggesting that they occupied similar microenvironments in both the acidic and alkaline soil horizons examined. Some explanations for the occurrence of nonsporing bacteria in soils in which apparently they cannot grow are suggested.  相似文献   

16.
A method is described for the rapid and simple assay of soil β-glucosidase activity. It involves colorimetric estimation of ρ-nitrophenol released by β-glucosidase activity when soil is incubated in McIlvaine buffer (pH 4.8) with ρnitrophenyl βd-glucoside and toluene at 30°C for 1 hr. The method has been applied to three different soils. The range of β-glucosidase activity in cultivated soils was from 10.1 to 15.2 mµ mole per min per gram of dried soil. Km value for ρ-nitrophenyl β-d-glucoside was 3.3 × 10-4 M. Optimum pH was 4.8.  相似文献   

17.
Abstract

Rates of substrate disappearance and product formation were compared as measures of urease enzyme activity in an NH4‐fixing and in a non‐fixing soil under tris‐, borate‐ or non‐buffered assay conditions over 4h at 37°C. Tris‐buffered urease activity of the NH4‐fixing soil was 119 μg urea‐N hydrol./g/h or 116 μg (KCl‐extractable) NH4‐N/g/h indicating prevention of NH4 fixation by the buffer; without tris, NH4 production rates amounted to only 35% of coresponding urea hydrolysis rates. Equal rates of urea disappear‐ ance and NH4 formation occurred in the non‐fixing soil irrespective of buffer amendment.

Tris‐inhibition of NH4 fixation during 4h incubation at 37°C, however, depended on NH4 Cl rate and buffer strength. 0.025–0.10 M tris (pH 9.0) reduced NH4 fixation to negligible amounts at < 0.03 M NH4C1 whereas, at 0.06–0.24 M NH4Cl, substantial NH4 fixation occurred in the presence of 0.05 M tris; NH4 fixation in unbuffered soil, however, always exceeded that in tris‐buffered soil. Borate buffer (0.06M, pH 10) did not influence the extent of NH4 fixation.

Tris significantly enhanced urea hydrolysis in the slightly acid, non‐fixing soil but not in the moderately alkaline NH4 ‐fixing soil indicating an effect of soil type on pH optima of urease enzyme activity. The urease activities of both soils in borate were considerably lower than in tris, possibly because of the combined effects of excess alkalinity and high substrate concentration.  相似文献   

18.
Abstract

Several different organisms cause corn (Zea mays, L.) root rot. The extent of damage to the root system varies with the aggressiveness of different causal organisms or different strains of the same causal organism. The attack of the roots by disease organisms could cause changes in the tissue analysis that would lead to misdiagnosing the cause of the problem. Studies were conducted to ascertain changes in selected mineral concentrations in the corn tissue and in plant growth resulting from various degrees of root rot caused by root infections of several different soil borne pathogenic fungi. Thermally pasteurized soil was placed in pots and infested with various fungi isolated from root lesions on corn from field studies. Corn was grown in the infested soil for four weeks in the greenhouse. Plants were harvested, roots indexed for disease, above ground visual symptoms noted, dry weight taken, and tissue analyzed for Ca, Mg, P, and K. Results showed that aerial plant parts of infected plants may exhibit typical nutrient deficiency symptoms which are not necessarily reflected in the mineral analysis of the tissue. Elemental uptake and tissue concentration appeared not to be related to changes in mineral analysis regardless of the relative soil mobility of the nutrient. Related fungi did not cause similar changes in mineral tissue concentration for the same or different minerals. Dry matter yields were reduced about 20% for each unit increase in root disease index. The use of the root disease index appears to have potential as a diagnostic tool and should be evaluated for this purpose.  相似文献   

19.
Abstract

Pyrite in hydromorphic soils is oxidized when it is exposed to the atmosphere. The sulfide oxidation releases hydrogen (H+) ions and other ions into the aqueous solution, and subsequently hydroxy‐sulfates are formed. A laboratory aging experiment was conducted using coastal sulfate‐rich soils in Malaysia to identify and determine the nature and composition of the hydroxy‐sulfates and to explain the mechanism of their formation. Powder X‐ray diffraction (XRD) analysis showed that incubating the pyrite‐bearing soils in the presence of added electrolyte (KCl and NaCl) resulted in the formation of jarosite, natrojarosite, and/or alunite. Subsequent transmission electron microscopy‐energy dispersive X‐ray (TEM‐EDAX) analysis showed that a hydroxy‐sulfate crystal was composed mainly of hydrogen (H), oxygen (O), sodium (Na), aluminum (Al), sulfur (S), potassium (K), and iron (Fe) which was accounted for as jarosite, natrojarosite, and/or alunite by powder XRD. The small amount of fluorine (F), nickel (Ni), titanium (Ti), and manganese (Mn) occurring within the same hydroxy‐sulfate crystal was presumably originated from pyrite. This result points to the formation of hydroxy‐sulfates in acid sulfate soils via psuedomorphic replacement of pyrite under an oxidizing environment.  相似文献   

20.
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