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Showing papers in "Soil Biology & Biochemistry in 1992"


Journal ArticleDOI
TL;DR: In this article, the decomposition and nutrient release patterns of three woody agroforestry plant species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays) stover and rice (Oryza sativa) straw, were investigated under field conditions in the humid tropics, using litterbags of three mesh sizes (0.5, 2 and 7 mm) which allowed differential access of soil fauna.
Abstract: Decomposition and nutrient release patterns of prunings of three woody agroforestry plant species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays) stover and rice (Oryza sativa) straw, were investigated under field conditions in the humid tropics, using litterbags of three mesh sizes (0.5, 2 and 7 mm) which allowed differential access of soil fauna. The decomposition rate constants ranged from 0.01 to 0.26 week−1, decreasing in the following order; Gliricidia prunings >Leucaena prunings > rice straw > maize stover >Acioa prunings. Negative correlations were observed between decomposition rate constants and C:N ratio (P < 0.004), percent lignin (P < 0.014) and polyphenol content (P < 0.053) of plant residues. A positive correlation was observed between decomposition rate constant and mesh-size of litterbag (P < 0.057). These results indicate that both the chemical composition of plant residues and nature of the decomposer played an important role in plant residue decomposition. Nutrient release differed with quality of plant residues and litterbag mesh-size. Total N, P, Ca and Mg contents of plant residues decreased with time for Gliricidia and Leucaena prunings, maize stover, and rice straw, and increased with time for Acioa prunings. There was some indication of N immobilization in maize stover and rice straw; P immobilization in Leucaena prunings and rice straw; and Ca immobilization in maize stover, rice straw and Gliricidia and Leucaena prunings. Acioa prunings immobilized N, P, Ca and Mg. All plant residues released K rapidly. Nutrient release increased with increasing mesh-size of litterbags, suggesting that soil faunal activities enhanced nutrient mobilization.

577 citations


Journal ArticleDOI
TL;DR: In this article, two strains (a Penicillium sp. and a Pseudomonas sp.) having high abilities to solubilize inorganic phosphates (hydroxylapatite and calcium hydrogenphosphate dihydrate) were screened from 600 colonies isolated from forest soils.
Abstract: Two strains (a Penicillium sp. and a Pseudomonas sp.) having high abilities to solubilize inorganic phosphates (hydroxylapatite and calcium hydrogenphosphate dihydrate) were screened from 600 colonies isolated from forest soils. Some of their physiological properties (nutrition, O 2 -demand, temperature) were investigated. It was possible to distinguish between solubilization through release of organic acids and still unknown mechanisms. Artificial acidification of the culture medium with HCl did not cause considerable P solubilization compared with our two isolates. In nonsterile soil both organisms caused a marked increase in the P fraction extracted with Licl solution.

534 citations


Journal ArticleDOI
TL;DR: Soil samples taken from eight long-term agricultural monoculture and rotation experimental plots were examined for their profiles of fatty acids in either phospholipid or lipopolysaccharide fractions and it was shown that this method has the potential to differentiate between the soils, even on a management level.
Abstract: Soil samples were taken from eight long-term agricultural monoculture and rotation experimental plots and examined for their profiles of fatty acids in either phospholipid or lipopolysaccharide fractions The more specific constituents related to microorganisms were tested for their ability to estimate the biomass and to differentiate community structureMore than100 fatty acids, including unsubstituted, straight- and branched-chain,unsaturated and hydroxy fatty acids were detected in the soils sampledGood correlations between the total amounts of fatty acids derived from phospholipids and the microbial biomasses and activities obtained by different classical procedures were observed (correlation coefficients were above 097) This indicates that the fatty acids were closely linked to soil microorganisms and that this method can be used in the study of soil microbial ecologyIn addition,each of the eight soils was characterized by its own pattern of fatty acids, either as phospholipids,or as lipopolysaccharidesThis shows that this method has the potential to differentiate between the soils,even on a management levelThe most apparent difference was registered in terms of the relation of the monoenoic to the normal fatty acids among the eight soilsThe black fallow and the fields cultivated with potatoes showed approximately equal amounts of both, the green fallow and the fields cultivated with wheat displayed a ratio of 17:10 and the grassland 13:10 The soil with crop rotation showed considerably more fatty acids in terms of the number in the normal fraction,while the grassland contained more hydroxy fatty acids than the soils from arable land

469 citations


Journal ArticleDOI
TL;DR: In this paper, three methods to estimate soil microbial biomass, namely, CHC13 fumigation-incubation (CFI), CFE and SIR, were compared with each other and with arginine ammonification and basal respiration using soils over a wide range of textural classes and organic matter content.
Abstract: Three methods to estimate soil microbial biomass, CHC13 fumigation-incubation (CFI), CHC13 fumigation-extraction (CFE), and substrate-induced respiration (SIR), were compared with each other and with arginine ammonification and basal respiration using soils over a wide range of textural classes and organic matter content. Biomass and activity of the soil microflora were significantly related to clay, soil organic C and especially to total N content. Values for microbial biomass C as estimated by CFI, CFE and SIR were highly correlated and not affected by soil texture. Only the estimation of biomass C by CFE was slightly influenced by soil organic matter including the two peat soils into the regression analysis. While the absolute values for biomass C deviated considerably when estimated by CFI, CFE and SIR, the ranking of the soils was the same for all these methods. These differences were usually not caused by the abiotic soil conditions we examined. The factors to convert the additional amount of organic C extracted after CHC13 fumigation or the substrate-induced respiration to microbial biomass C are discussed.

321 citations


Journal ArticleDOI
TL;DR: The system was used to determine the active and total microbial biomass in soil and earthworm faecal particles and resulted in very different shapes to O 2 uptake curves, indicating damage to microorganisms due to sudden moisture alterations.
Abstract: A system to analyse the respiratory response of soil microcompartments by automated electrolytic microrespirometry is described. The system is computer controlled and allows simultaneous measurements of 16 samples. The minimum detection level is 0.83 μg O 2 and the capacity of the system can be extended up to about 2500 μg O 2 h − . The frequency of measurements is optional and ranges from about 10 s to 1 h. The system was used to determine the active and total microbial biomass in soil and earthworm [Aporrectodea caliginosa (Savigny)] faecal particles (mean age of 4 days) by the O 2 uptake method. Active microbial biomass was increased in earthworm faeces (+17%), but the percentages of active microorganisms were similar in faeces (5.0%) and soil (4.5%). Addition of diluted nutrients instead of dry matter resulted in very different shapes to O 2 uptake curves, indicating damage to microorganisms due to sudden moisture alterations. The usefulness of the microrespirometer system to investigate microbial properties of soil microcompartments is discussed.

284 citations


Journal ArticleDOI
TL;DR: In this article, the properties of 23 soils were found to be correlated with native biomass C, with the extent of decomposition of added [ 14 C]glucose and [ 14 Medicago littoralis plant residues after 44 and 66 weeks incubation respectively and with the concentrations of substrate-derived C found in the microbial biomass and non-biomass residues.
Abstract: Relationships were established between the properties of 23 soils Particularly identified were those soil properties correlated with (i) native biomass C, with (ii) the extent of decomposition of added [ 14 C]glucose and [ 14 Medicago littoralis plant residues after 44 and 66 weeks incubation respectivelyand with (iii) the concentrations of substrate-derived C found in the microbial biomass and non-biomass residues The native biomass C and biomass 14 C from glucose and M littoralis were highly correlated with each other and with soil clay content and other related soil properties, eg CEC and total soil pore space For glucose-amended soils total residual 14 C was also correlated with soil clay content Differences between soils in the concentration of total residual organic 14 C were due entirely to differences in the amounts of 14 C present in the microbial biomass Thus, statistically non-biomass 14 C accounted for a constant proportion of input 14 C In contrast with glucose decomposition, total residual organic 14 C from M littoralis decomposition was not significantly correlated with clay content and related properties except when the statistical analyses were confined to soils of neutral to alkaline pH Soils of mildly acidic pH retained more residual non-biomass 14 C than did neutral to alkaline soils of similar clay contents The close direct correlations between biomass 14 Cand biomass 14 C from glucose and plant material metabolismand soil properties indicated that soil charge or structure or both are important factors influencing microbial biomass accumulation in soils These factors may override such influences as substrate type, concentration and efficiency of utilisation in determining biomass C concentration in soils after long (1 yr) incubation

267 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall poccosins and gum swamps) which occur along a natural soil nutrient availability gradient.
Abstract: Production of soil gases is important in nutrient and carbon cycling, particularly in peatlands due to their large atmospheric emissions of several greenhouse gases. We examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall pocosins and gum swamps) which occur along a natural soil nutrient availability gradient. Short pocosins occur in the ombrotrophic center of the bog complexes and are extremely nutrient-deficient; tall pocosins are slightly less nutrient-deficient; and gum swamps are relatively nutrient-rich. Short pocosin had the lowest soil CO 2 production rates under both aerobic and anaerobic conditions in laboratory experiments, while rates in tall pocosin were similar to or somewhat less than in the gum swamp. Methanogenesis rates were extremely low in laboratory experiments, and indicate that CH 4 production is not a significant pathway of carbon flow in these peatlands. Methane production is also low in relation to other peatlands. Amendment experiments indicate that the poor substrate quality of the highly decomposed, humified peat limits both CO 2 and CH 4 production rates, even though the peat is 95% organic matter. Low soil nutrient concentrations and low pH do not directly limit soil respiration in these peatlands, although there is a positive feedback of nutrients with organic matter inputs and litter quality, causing greater soil respiration in nutrient-rich sites. In situ CO 2 emissions similarly differed between the communities, with highest rates in the gum swamp and lowest rates in the pocosins. Emissions were highly seasonal with soil temperature explaining the majority of the temporal variability. Maximum potential CH 4 emission estimates derived from laboratory temperature relationships and in situ soil temperature data indicate that pocosins make an insignificant contribution to the global atmospheric CH 4 flux. The continued existence of peatlands in warm climates may to a large extent depend on the low substrate quality of their soil organic matter, which maintains low decomposition rates under both aerobic and anaerobic conditions.

261 citations


Journal ArticleDOI
TL;DR: The effects of endogeic earthworms on the soil organic matter (SOM) dynamics of moist tropical soils are: (i) a sharp increase of mineralization during digestion; (ii) the presence in fresh casts of large amounts of mineral nutrients which are reorganized in microbial biomass at the scale of days to weeks depending on soil properties; and (iii) a subsequent blocking of mineralisation at a scale of months to years in the compact structure of ageing casts (i.e. older than 1-2 weeks) as discussed by the authors.
Abstract: The effects of endogeic earthworms on the soil organic matter (SOM) dynamics of moist tropical soils are: (i) a sharp increase of mineralization during digestion; (ii) the presence in fresh casts of large amounts of mineral nutrients which are reorganized in microbial biomass at the scale of days to weeks depending on soil properties; (iii) a subsequent blocking of mineralization at the scale of months to years in the compact structure of ageing casts (i.e. older than 1–2 weeks). It is hypothesized that, at the larger scale of soil profile and years, activities of earthworms will result in an acceleration of SOM turnover and the accumulation of labile rather than passive organic matter.

255 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the current Rothamsted model for the turnover of organic C in soil to calculate how the organic C content of the topsoils from the four sites would change with time for a range of annual inputs.
Abstract: Soil samples collected from four of the Rothamsted long-term field experiments over the last 100 yr were used to follow the effects of management on soil organic matter content. The experimental sites were:Broadbalk and Geescroft Wildernesses, both on old arable land that had been fenced off in the early 1880s and allowed to revert naturally to deciduous woodland; the unmanured plot in the Rothamsted Park Grass Continuous Hay Experiment, started in 1856; the unmanured and one of the NPK plots in the Broadbalk Continuous Wheat Experiment started in 1843. Total C, radiocarbon and (in some cases) soil microbial biomass C were measured in stored and contemporary soil samples. The current Rothamsted model for the turnover of organic C in soil was then used to calculate how the organic C content of the topsoils from the four sites would change with time for a range of annual inputs. The inputs that generated the best fit to the measured values were: Broadbalk Wilderness 3.5 t C ha−1 yr−1; Geescroft Wilderness 2.5 t C ha−1 yr−1;unmanured plot on Park Grass 3.01 t C ha−1 yr−1; unmanured plot on Broadbalk Wheat 1.3 t C ha−1 yr−1; NPK plot on Broadbalk Wheat 1.71 t C ha−1 yr−1. The model also generated the radiocarbon content of soil organic C for these inputs of C, knowing the 14C content of the atmosphere over the period 1840–1985. The marked increase in the 14C content of soil organic C brought about by thermonuclear testing during the 1960's was accurately represented by the model. The quantities of soil microbial biomass (measured by fumigation-incubation) in the top 23 cm of soil from the four sites were: Broadbalk Wilderness,1.571 t C ha−1; Geescroft Wilderness, 0.58 t C ha−1; unmanured plot on Park Grass,1.621C ha−1; unmanured plot on Broadbalk Wheat, 0.47 t C ha−1; NPK plot on Broadbalk Wheat, 0.76 t C−1.The values for soil microbial biomass C generated by the model for the above annual inputs agreed closely (with one exception) with the measured values. For a site under steady-state conditions, the annual input of organic matter to the soil plus the annual removal of organic matter from the site (if any) gives the Net Primary Production (NPP). NPP thus calculated was 4.0 t C ha−1 yr−1 for the unmanured plot on Park Grass, 2.2 for the unmanured plot on Broadbalk and 5.2 for the NPK plot on Broadbalk. The two Wilderness sites are still accumulating C in both soil and vegetation and here NPP is given by annual input to the soil, plus the annual increment of C in the trees. NPP calculated in this way was 4.8 t C ha−1 yr−1 for Broadbalk Wilderness and 3.3 for Geescroft Wilderness. This new way of estimating NPP, from measurements made on soil organic matter, needs to be tested on a wider range of soils, climates and vegetation types before it can be generally recommended. However, it has many potential advantages, not least that it can give a value for NPP that is integrated over many years from a single sampling. For sites under steady-state conditions it is not essential to have stored soil samples—the necessary measurements can be made on contemporary samples alone.

247 citations


Journal ArticleDOI
TL;DR: In this paper, the results showed that the most effective humic fraction on both plant nitrate uptake and hormone-like activity had the highest acidic functionality and the smallest molecular size, whereas both the aliphatic and aromatic content of extracts did not appear to play a role.
Abstract: Humic extracts with distinct chemical and physical-chemical characteristics, obtained by various soil extractants and from different sources, were used to study their biological activity. The humic structural features were related to the rate of nitrate uptake by barley seedlings and growth regulation in watercress and lettuce. Chemical analysis of functional groups, molecular weight distribution, and NMR quantitative spectra were used to characterize the humic extracts. Results showed that the most effective humic fraction on both plant nitrate uptake and hormone-like activity had the highest acidic functionality and the smallest molecular size, whereas both the aliphatic and aromatic content of extracts did not appear to play a role. Low molecular size fractions obtained from the original material by disaggregating the humic macromolecule through the formation of a sort of inverse micelle by acetic acid addition, showed results that confirmed the effectiveness of the combination of high acidity and low molecular size in influencing the biological activity of the plant system tested.

232 citations


Journal ArticleDOI
TL;DR: Soil respiration responded to management like microbial biomass-C but varied significantly over the season with the smallest respiration found in the driest month (October) and the largest respiration at end of the rains in May.
Abstract: The effects of clearfelling a tropical rainforest and establishing pasture on soil microbial biomass and nitrogen transformations were assayed monthly over 1 yr in three adjacent systems in the central Amazon region: (1) virgin rainforest; (2) slashed-and-burnt forest; and (3) recently established pasture. The amounts of soil organic matter (SOM) and soil microbial biomass-carbon (biomass-C) were substantial in all systems. Total soil-C ranged between 1.9 and 5.2% depending on management and soil layer, whereas biomass-C ranged between 3.5 and 5.3% of total soil-C. The soil biomass-C decreased upon slashing-and-burning to 64% of its original value (1287 μg g −1 ) in the forest (0–5 cm soil layer) and increased after establishment of pasture to 1290 μg g −1 , but remained unchanged in the deeper 5–20 cm soil layer. No significant seasonal variation was measured in any system or soil layer. Soil respiration responded to management like microbial biomass-C but varied significantly over the season with the smallest respiration found in the driest month (October) and the largest respiration at end of the rains in May. Pools of mineral N varied considerably in all systems and soil layers and displayed identical seasonal variations. The forest topsoil contained the highest amounts (on average 47 μg N g −1 ) and the pasture soil the smallest amounts (on average 24 μg N g −1 ). The transition of the forest ecosystem to a pasture resulted in increased NO 3 − concentrations. Net N-mineralization and net NO 3 − production monitored during short-term laboratory incubations were used as indices of N mineralization and nitrification. No significant differences in N-mineralization indices were measured between systems, but substantial within season variations were recorded in all systems and soil layers. The variations were synchronized in time with extreme net N-mineralization in September and net N-mineralization in October. Significant nitrification indices were measured in all systems. They were identical in the systems, except for small indices found in topsoil of the slashed and burnt area, where, on the other hand, certain localized areas with extreme nitrification rates were detected.

Journal ArticleDOI
TL;DR: The general principles of how earthworm populations can be manipulated and managed for environmental improvement are illustrated, including earthworms can be used as key indicators to predict the effects of chemicals on other soil invertebrates and methods of testing chemicals against earthworms in field and laboratory are reviewed.
Abstract: During the past 25 yr, research by the authors at Rothamsted Experimental Station investigated many aspects of the utilization of earthworms in land improvement and environmental management. Results of some of these investigations are summarized in this paper with the aim of illustrating the general principles of how earthworm populations can be manipulated and managed for environmental improvement. The use of earthworms in land improvement and reclamation: we investigated the effects of inoculating earthworms of the species Lumbricus terrestris L., Aporrectodea longa (Ude), Aporrectodea caliginosa (Sav.) and Allolobophora chlorotica (Sav.) into intact soil profiles in the laboratory, plots on direct-drilled, arable land in the field and newly-capped waste disposal sites that had few or no earthworms. In all these studies the earthworms increased significantly in number and rate of growth and yield of plants growing on the inoculated sites. Earthworms for inoculation were obtained by field collection after watering soil with dilute formaldehyde solution. The use of earthworms in organic waste management: the life cycles and productivity of Eisenia fetida (Sav.), Eudrilus eugeniae (Kinberg), Perionyx excavatus (Michaelsen) and Dendrobaena veneta (Rosa), and their potential in processing animal and plant wastes, from sewage, agricultural, domestic, urban and industrial sources are summarized. The preprocessing of wastes, their population ecology, optimum stocking rates, the mechanization of processing and utilization of the product are discussed. Results of experiments on the effects of temperatures of 10, 15, 20 and 25°C and a range of soil moisture contents of 70, 75, 80, 85 and 90% on the growth, cocoon production and cocoon hatching of the four species are summarized. The use of earthworms in assessment of the environmental effects of chemicals: earthworms can be used as key indicators to predict the effects of chemicals on other soil invertebrates. Methods of testing chemicals against earthworms in field and laboratory are reviewed. Two standardized laboratory test methods, one exposing earthworms to chemicals on filter paper and one to chemicals in artificial soils are described, and the median lethal concentration (LC 50 ) for chloracetamide, pentachlorophenol, chlordane, carbaryl, potassium bromide, copper sulfate and trichloracetic acid calculated, based on assays done in 34 laboratories. The relevancy of the two tests in environmental toxicity testing is reviewed.

Journal ArticleDOI
TL;DR: The results showed that Eisenia fetida has a wider tolerance for temperatures than E. eudrilus eugeniae and P. excavatus which allows this species to be cultivated in areas with higher temperatures as well as areas with lower soil temperatures.
Abstract: Since the epigeic species Eudrilus eugeniae, Perionyx excavatus and Eisenia fetida have a potential as waste decomposers or as possible sources of protein, knowledge of their temperature requirements are required in order to cultivate them in large numbers under different environmental conditions. A study was undertaken outdoors as well as indoors of earthworm populations in artificial containers in order to access the influence of high, as well as low, temperatures on the different species. The results were compared with that obtained for control populations kept at a presumably favourable temperature of 25°C. The results showed that Eisenia fetida has a wider tolerance for temperatures than E. eudrilus eugeniae and P. excavatus which allows this species to be cultivated in areas with higher temperatures (often as high as 43°C) as well as areas with lower soil temperatures (often below 5°C). The other two species will have limited outdoor application in vermiculture systems. The winter temperatures in the southern subregion of Africa and not the summer temperatures seem to be the limiting factor in applying Eudrilus eugeniae and P. excavatus in outdoor vermiculture. The incubation period, development and cocoon production of the species at various temperature simulations were also investigated. Regions in southern Africa were identified, based on prevailing temperature conditions, where E. eugeniae and P. excavatus could be utilized in vermiculture systems.


Journal ArticleDOI
TL;DR: In this article, the authors evaluate the hypothesis that soil DOC constitutes a readily available microbial resource, and that DOC concentrations are related to rates of biological decomposition and associated nutrient release from soil organic matter.
Abstract: Dissolved organic carbon (DOC) and C and N mineralization were measured during a 210 day regulated in vitro incubation of soils from an old field successional sequence at Cedar Creek Natural History Area. The objective of the study was to evaluate the hypothesis that soil DOC constitutes a readily-available microbial resource, and that DOC concentrations are related to rates of biological decomposition and associated nutrient release from soil organic matter. Soils from five previously cultivated old fields undergoing secondary succession and an oak savanna were selected because they had demonstrated different patterns of C and N cycling. Although amounts of total C differed dramatically (496–1371 μmol g−1), DOC concentrations of all soils at the time of collection were between 0.70 and 1.30 μmol g−1. During the incubation, total and relative DOC concentrations generally remained constant or increased while mineralization rates decreased. When all soils and incubation intervals were considered, there was no obvious relationship between DOC and instantaneous rates of mineralization. Asymptotic exponential response curves did describe positive associations between DOC and CO2-C mineralization rates at early incubation times (R2 = 0.98 for 14 and 35 days), but not later. Similar models did not show a strong relationship between DOC and net-N mineralization rates. By the end of the incubation, the DOC pool could potentially supply 1.5–3.4 days of total C mineralization, but the instantaneous C mineralization rate at any given DOC concentration was 3–10 times lower than at 14 days. These results reflect decreased DOC utilization relative to supply, and could be caused by the accumulation of recalcitrant DOC.

Journal ArticleDOI
TL;DR: In this paper, a comparative study of tropical rain forest earthworm communities was carried out to identify general patterns of organization, and it was concluded that environmental variables, more than phylogenetic constraints, are the most important factors in determining the structure of these communities.
Abstract: Summary-A comparative study of tropical rain forest earthworm communities was carried out to try to identify general patterns of organization. The study included 5 sites in Mexico and Central America, 3 in South America, 2 in Central and Western Africa and 2 in Southeast Asia. Data base comprised 15 biological variables and 1 I climatic and edaphic variables. Average earthworm values of abundance and biomass were 68 ind m-2 and 12.9 g m-' respectively, which were not very different to those values occurring in temperate woods; however, they were considerably lower when compared to temperate and tropical grasslands. Density and biomass showed a bell shape response in function of annual rainfall, with maximal values between 2000 and 4000 111111. Earthworms were mainly concentrated in the first 0-10 cm of soil depth. Two kinds of communities were differentiated one dominated by litter-feeding epigeics and anecics and the other one by geophagous endogeics. The former group was associated to oligotrophic soils from South America and Africa, whereas the second one was characteristic of the rich, neutral soils of Mexico and Africa (one site). It is concluded that environmental variables, more than phylogenetic constraints, are the most important factors in determining the structure of these communities. Comparisons with other soil macrofauna groups revealed that earthworms are the most important group regarding biomass and rank third in terms of abundance. The importance of these organisms in the dynamics of tropical rain forest soils is discussed in terms of the kind of community found elsewhere.

Journal ArticleDOI
TL;DR: It could be deduced that the vermicompost application has enhanced the activity of these selected microbes in the soil system as high level of Total N in the experimental plot which comparatively received less quantity of fertilisers.
Abstract: The possibility of reducing the use of chemical fertiliser by using vermicompost as organic fertiliser was tested on the summer crop of paddy variety “HAMSA”. The control plot received the recommended dosage of farm yard manure and the chemical fertilisers. The experimental plot received half the recommended dosage of chemical fertilisers and the vermicompost. At the time of seed setting and 2 months after the harvest of the crop, the soil samples were analysed for total microbes, N-fixers, Actinomycetes and spore formers. The percent Mycorrhizal colonisation in the plant system was also assessed. Significant increase in the colonisation of these microbes in the experimental plot over the control plot was observed. The symbiotic association of Mycorrhizae in the roots showed a remarkable difference in infection which was just 2.85% in control plots compared to 10% in the experimental plot. Except for Actinomycetes, the colonies of the other microbes assessed 2 months after the harvest of the crop in the drained plots, showed significantly higher counts in the experimental plots. The stubbles in experimental plots retained higher counts of Mycorrhizae than those in the control plots. It could be deduced that the vermicompost application has enhanced the activity of these selected microbes in the soil system. There was high level of Total N in the experimental plot which comparatively received less quantity of fertilisers. This may be due to the higher count of N-fixers (3.48 x 103) observed in the experimental plot than that of the control plot (2.16 x 103).

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of seasonal and year-round tillage on microbial biomass C and extractable ninhydrin-reactive N in increasing depth layers of an Alfisol topsoil.
Abstract: Concentrations of microbial biomass C and extractable ninhydrin-reactive N in increasing depth layers of an Alfisol topsoil were determined periodically over 13 months for soils under two contrasting tillage regimes. Concentrations decreased rapidly with depth to 10 cm, halving approximately 2.5 cm with each. Organic C and total N concentrations also decreased with depth of topsoil, those of the surface layer (0–2.5 cm) being 1.5–2.1 times and 1.3–2.4 times those respectively of the 2.5–7.5 cm layer. Tillage management affected the relative concentrations of biomass C, total organic C and total N in surface and lower depths of topsoil, but only through its influence on surface soil concentrations. Respective concentrations at 0–2.5 cm depths for soils under a direct drill tillage regime were on average 24, 28 and 50% higher than for soils subjected annually to district cultivation practices. Highest values for microbial biomass C were recorded for moist Winter-sampled soils, and the lowest in soils sampled at times of severe desiccation after prolonged hot dry periods in Summer. Seasonal trends in biomass contents were not significantly influenced by tillage practice. Averaged for both tillage regimes, the seasonal decrease in biomass C was 28% for the surface soils and 23% for the subsurface (2.5–7.5 cm) soils. Biomass C concentrations of soils sampled dry from the field, moistened, and assayed without prior incubation were about 10% higher than those of the same samples incubated moist for 2 weeks before assay. We suggest that severe soil desiccation was likely the main cause of the biomass C decline, and that the decline may be underestimated, due (1) in the case of soils moistened without incubation before assay, to restricted hydrolysis-deamination of killed cell protein under the field dry conditions, but not under assay conditions, and (2) in the case of soils moistened and incubated before assay, to growth of cells on substrates from killed cells and non-biomass sources during the preincubation period. In contrast to soil cores sampled seasonally from the field, biomass C concentrations at different depths of the Alfisol topsoil were not significantly affected by controlled drying of undisturbed cores under constant or fluctuating temperature regimes. Neither were the inorganic N contents of the total cores, nor the C and N mineralization activities of soils sampled from different core depths, influenced by the imposed drying treatments, which resulted in gradual and graded losses of soil moisture. During soil drying, nitrate-N accumulated in the surface layer of the cores, but became redistributed on remoistening of the cores. Thus gradual drying of intact soil cores at moderate temperatures did not per se significantly influence the availability for decomposition of organic substrates, which has implications for modelling C and N mineralization in natural environments with intermittent soil drying.

Journal ArticleDOI
TL;DR: In this article, the abundance and distribution of earthworms were studied on the Georgia Piedmont of the Southeastern U.S.A., at sites representing various ecosystem types, management practices, landscape positions, soil textures and soil erosion status.
Abstract: Abundance and distribution of earthworms were studied on the Georgia Piedmont of the Southeastern U.S.A., at sites representing various ecosystem types, management practices, landscape positions, soil textures and soil erosion status. Earthworm abundance showed distinct seasonal patterns, with winter/spring maxima and summer minima. Numbers and biomass ranged from zero in plowed. mono-cropped soil at an upland site to over 1000 m-2 ( > 25g ash-free dry wt m-2) in no-tillage, double-cropped soil on bottomlands. Numbers and biomass in plowed, double-cropped soil, in a bottomland forest, and in grass meadows at both upland and bottomland sites were intermediate. Soil texture, as influenced by water erosion, strongly affected earthworm abundance. Moderately and severely eroded sandy clay loam supported significantly higher earthworm numbers and biomass than did slightly eroded soil with higher sand content. This effect may have resulted from low organic content and water holding capacity of the sandy soils. Of the soil texture variables, silt content was most highly correlated with earthworm biomass. Earthworm abundance was also related to quantity and quality of plant residue inputs in the agroecosystems, and to standing stocks of soil organic carbon across all sites studied. At most agroecosystem and forest sites, the predominant earthworm species were European lumbricids; native Diplocardia spp were most prominent in a meadow soil with high organic content.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the role of extracellular enzymes in plant litter decomposition by placing arrays of white birch ice-cream sticks at eight upland, riparian and lotie sites on a forested watershed in northern New York.
Abstract: Because plant litter decomposition is directly mediated by extracellular enzymes, analyses of the dynamics of their activity may clarify the mechanisms that link decomposition rates to substrate quality and to temperature, moisture and nutrient availability patterns. We investigated this possibility by placing arrays of white birch ice-cream sticks at eight upland, riparian and lotie sites on a forested watershed in northern New York. For 3 yr, samples were analyzed for mass loss, protein, nitrogen and phosphorus accumulation and the activity of 11 classes of extracellular enzymes involved in lignocellulose degradation and nutrient cycling. Despite considerable heterogeneity both within and between sites, decomposition rates were closely related to the activity of lignocellulose-degrading enzymes. A statistical model was developed that accounted for 94% of the variance in mass loss rates as a function of the temporally-integrated activity of these enzymes. Models of this type contribute to our understanding of scale integration and may facilitate the estimation of decomposition rates among landscape units.

Journal ArticleDOI
TL;DR: Bacterial production rates based on FDDC were 3–8 times higher than those based on O 2 consumption rates determined by 2-week incubations, which suggests that the FDDC can be used as an index of in situ bacterial growth rate in soil.
Abstract: During an 8-week microplot experiment, effects of moisture regime and farm management on microbial numbers and activity were studied. Under integrated management (reduced input farming), bacterial numbers, O2 consumption and N mineralization, respectively, were 1.6, 2.1 and 1.8 times higher than under conventional management (high input farming). These differences may be attributed to 1.3 and 1.4 times higher contents of organic matter and total N in the integrated microplots. One month of drying from a water potential of −0.03 to −0.12 MPa, and subsequent rewetting to −0.01 MPa, did not affect bacterial numbers significantly. However, the relatively small decrease in water potential caused a significant decrease in O2 consumption and N mineralization. After rewetting, respiration increased from 1.3 to 1.5 fold, and N mineralization from 3 to 5 fold. Concurrently, the frequency of dividing-divided cells (FDDC) increased from 10 to 16% in the conventional and to 23% in the integrated microplots. This suggests that the FDDC, which is determined by direct microscopy and requires no incubation, can be used as an index of in situ bacterial growth rate in soil. For marine bacteria, mathematical relationships have been established between specific growth rate (μ) and FDDC. If it is assumed that these relationships are also valid for soil bacteria, FDDCs of 16 and 23%, respectively, may indicate specific growth rates of about 1 and 2 day−1. Bacterial production rates based on FDDC (8.5–45 μg C g−1 day−1) were 3–8 times higher than those based on O2 consumption rates determined by 2-week incubations. Uncertainties of the methods are discussed.

Journal ArticleDOI
TL;DR: Earthworms (Lumbricus rubeltus) were fed on four different soils with light fraction organic material contents but rates of CO2 production, bacterial plate counts, moisture content and concentrations of soluble organic-C were higher in casts compared with the standardized soils ingested by the earthworms.
Abstract: Earthworms (Lumbricus rubeltus) were fed on four different soils with light fraction organic material contents from 3.7 to 76.1% of the soil dry weightand soil water potentials standardized at — 8 kPa. Microbial biomass-C in the soils, as measured with a modified fumigation-extraction method, ranged from 0.4 to 7.5mg C g−1 soil. After gut passage (6–8 h) microbial biomass-C was not changed significantly but rates of CO2 production, bacterial plate counts, moisture content and concentrations of soluble organic-C were higher in casts compared with the standardized soils ingested by the earthworms.

Journal ArticleDOI
Erland Bååth1
TL;DR: The growth rate of bacteria extracted from two different soil types by homogenization-centrifugation was estimated with the [3H]thymidine incorporation technique and radioactivity was also incorporated into RNA and protein.
Abstract: The growth rate of bacteria extracted from two different soil types by homogenization-centrifugation was estimated with the [3H]thymidine incorporation technique. No change in thymidine incorporation rate was found up to 4 h after the preparation of the bacterial solution using distilled water. Radioactivity was also incorporated into RNA and protein. This nonspecific labelling started immediately and appeared linear over time. Incorporation of radioactivity into DNA was about 40%, into RNA 40% and into protein 20%, of incorporation into total macromolecules. The thymidine incorporation rate decreased after addition of Ringer solution, 0.9% NaCl, Winogradsky's salt solution, 50 mM K2HPO4, 50 mm CaCl2, 0.2% Calgon or 0.2% sodium pyrophosphate compared to distilled water alone. Lower concentrations of these additives had lower or negligible effects. The specific incorporation rate at 22°C for bacteria extracted by homogenization-centrifugation was 6.0 × 10−21 mol thymidine cell−1 h−1 for a sandy loam and 4.4 × 10−21 mol thymidine cell−1 h−1 for an acid organic soil. This corresponds to a turnover time of 3.5 days for bacteria from the sandy loam and 4.8 days for bacteria from the organic soil using a conversion factor of 2 × 1018 cells mol−1 thymidine.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the effect of 13C isotopic enrichment on the decomposition of three substrates derived from maize plants in sand inoculated with a soil extract.
Abstract: Variations in the natural abundance of 13C in the CO2 evolved during the biodegradation of three substrates derived from maize plants provide a way of studying the decomposition of plant material in soil. The δ13C isotopic composition of the CO2 evolved (called δC) was followed during the decomposition of root mucilage, roots and glucose (initial composition δS), all from maize plants, in sand inoculated with a soil extract. Results indicate that a negative isotopic enrichment (ϵ = δC − δS < 0) occurred at the beginning and end of the decomposition process, whatever the substrate. For the intermediate stages of mineralization, the isotopic enrichment was small (δC slightly less than δS), or negligible. It is possible to take this enrichment effect into account in biodegradation studies, by introducing a correction factor in the calculation of the true mineralization rate. During the decomposition of the three substrates in soil, the correction factor varied between 1.04 and 1.08 for root mucilage, 1.13 and 1.17 for roots and 1.13 and 1.27 for glucose.

Journal ArticleDOI
TL;DR: In this paper, Aspergillus niger and Mucor rouxii were evaluated using Freundlich adsorption isotherms and energy dispersive X-ray electron microscopy.
Abstract: Sorption of the nitrate salts of cadmium(II), copper(II), lanthanum(III) and silver(I) by two fungi, Aspergillus niger and Mucor rouxii, was evaluated using Freundlich adsorption isotherms and energy dispersive X-ray electron microscopy. The linearized Freundlich isotherm described the metal sorption data well for metal concentrations of 5 μm-1 Mm metal. Differences in metal binding were observed among metals, as well as between fungal species. Calculated Freundlich K values indicated that metal binding decreased in the order La3+ ⩾ Ag+ > Cu2+ > Cd2+. However, sorption of Ag+ was greater than that of La3+ from solutions of 0.1 and 1 mM metal and likely due to precipitation at the cell wall surface. At the 1 mM initial concentration, there were no significant differences between the two fungi in metal sorption, except for Ag+ binding. At the 5 μM concentration, there was no difference between the fungi in their sorption capacities for the four metals. Electron microscopy-energy dispersive X-ray analysis indicated that silver precipitated onto cells as colloidal silver. The results indicate that Freundlich isotherms may be useful for describing short-term metal sorption by fungal biomass and for comparison with other soil constituents in standardized systems.

Journal ArticleDOI
TL;DR: In this paper, a new approach, based on the application of soluble, dye-labeling and acid-precipitable polysaccharide derivatives, is introduced for the sensitive assay of poly-charide endo-hydrolases extracted from soil.
Abstract: A new approach, based on the application of soluble, dye-labelled and acid-precipitable polysaccharide derivatives, is introduced for the sensitive assay of polysaccharide endo-hydrolases extracted from soil. An extraction procedure involving sodium acetate-acetic acid buffer (pH 5, 0.5M; 5ml g−1 soil) and an assay system adapted to microtitre plates were developed for routine determinations of endo -acting cellulase, xylanase, chitinase, 1,3-β-glucanase and amylase activities. An Acid Brown Earth under a mature beech forest (Fagus sylvatica L., humusform: typical Moder) was studied with respect to distinct, clearly-developed soil horizons (L, F, H, Ahh, Aeh). Enzymes purified by (NH4)2SO4-precipitation and dialysis were assayed for pH and temperature activity profiles. pH optima were determined in the range of 4.5–5.5, temperature optima were in the range of 40–55°C, revealing stable and fairly similar characteristics of these enzymes in the horizons under study. In routine investigations, highest enzyme activities were determined in the L and F horizons. Significantly decreasing activities with increasing soil depth and decreasing organic matter content were determined in the H, Ahh and Aeh horizons, respectively. Cellulase, xylanase and chitinase activities were highly correlated with total-C content of the soil horizons under study 0.871 ⩽r2⩽ 0.954).

Journal ArticleDOI
TL;DR: In this article, the analysis of continuous fertilizer and manurial experiments in tropical conditions of India have shown that soil microbial biomass C and N increased with balanced fertilization, even when the organic C content of the soil did not increase.
Abstract: The analysis of continuous fertilizer and manurial experiments in tropical conditions of India have shown that soil microbial biomass C and N increased with balanced fertilization. The additions of organic amendments increased microbial biomass even when the organic C content of the soil did not increase. The increase in microbial biomass was attributed to better plant growth resulting in higher rhizodeposition. The crop yields and N uptake were higher with the addition of farm yard manure or Sesbania green manure.


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TL;DR: In this paper, the authors used 13C tracer to estimate the underground maize-derived organic carbon at harvest in October, and found that maize derived C in the soil fractions coarser than 200 μm accounted for 12% of the aboveground plant parts.
Abstract: The natural enrichment of 13C in maize plant material, compared to that of indigenous soil organic carbon, was used in the field to estimate the quantity of underground maize-derived C at harvest in October. Maize-derived C in the soil fractions coarser than 200 μm accounted for 12% of the C of the aboveground plant parts. Half of it was situated in the 20 cm wide × 20 cm deep soil portion situated beneath the plant. The soil fraction size-class 200–2000 μm contained 25% of the total and was the dominant size-class in the deeper layers. Because of the low resolution of the 13C tracer, only a 95% confidence interval could be obtained for the quantity of solid material finer than 200 μm: between 1 and 9% of the aerial parts of maize. Contribution of maize-derived C to soil organic matter in early August was not significantly different from that at the harvest date.

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TL;DR: The ecological effects of grassland afforestation have been investigated in a comparative study between different tree species on a sandy-loam substrate, and the results have practical consequences for the choice of tree species in new forest plantations.
Abstract: The ecological effects of grassland afforestation have been investigated in a comparative study between different tree species on a sandy-loam substrate. After 20 yr of forest, the earthworm communities and litter decomposition rates differed considerably, depending on the quality and quantity of the litter fractions produced. Under Quercus palustris , earthworm biomass diminished, and litter accumulation and soil acidification had begun. The results have practical consequences for the choice of tree species in new forest plantations.