Effect of sewage sludge additions on Nocardia in soil

The population of Nocardia in soil under pasture increased 100 × over 14 months following the application of dried sewage sludge. Nocardia were isolated using selective media and on each of five samplings numbers of Nocardia in the control plots were very similar (

5.0 × 10³g^?1 dry weight), indicating both the reliability of the isolation technique, and that the steady increase in numbers of Nocardia was a real effect of dried sludge application. Amendment with wet sludge, which contains less organic matter did not have the same effect of stimulating growth of the soil population of Nocardia. On the basis of diagnostic tests and lipid analysis the organisms isolated all belong to the N. asteroides taxon. The potential benefits and hazards of inducing Nocardia population growth are discussed     

Runoff and losses by erosion in soils amended with sewage sludge

In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha⁻¹ of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha⁻¹ of composted sludge, 50 t ha⁻¹ of fresh sludge and 11ċ3 t ha⁻¹ of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 John Wiley & Sons, Ltd.     

Turnover of organic matter in a Miscanthus field: effect of time in Miscanthus cultivation and inorganic nitrogen supply

To accurately predict the potential environmental benefits of energy crops, the sequestration of carbon in soil needs to be quantified. The aim of this study was to investigate the mineralisation rate of the perennial C₄ grass Miscanthus giganteus and Miscanthus-derived soil organic matter under contrasting nitrogen supply. Soils were collected from sites where Miscanthus had been grown for 11 and 18 years, respectively, and where a C₃-grass (Lolium spp.) had been grown for 7 years. The soils were incubated for 4 months at two levels of soil inorganic nitrogen with or without dead root material of Miscanthus.Addition of root material (residues) increased carbon mineralisation of indigenous organic matter when no nitrogen was added. Added inorganic nitrogen decreased carbon mineralisation in all soils. Nitrogen addition did not affect carbon mineralisation of the residues. Using the ¹³C fraction to calculate the proportion of respiratory CO₂ derived from Miscanthus showed that nitrogen addition decreased carbon mineralisation in soils, but it did not affect carbon mineralisation of the residues. Nitrogen mineralisation was highest in the C₃ grass soil without added residues. Nitrification decreased pH, especially in the treatments where nitrogen was added. The Miscanthus-derived organic matter is at least as stable as C₃ grassland-derived organic matter. Furthermore, the turnover time of the organic matter increases with time under Miscanthus cultivation.The CENTURY soil organic matter sub-model was used to simulate the organic matter decomposition in the experiment. Carbon mineralisation was accurately simulated but there were unexplained discrepancies in the simulation of the δ¹³C in the respiration from the treatment with residues. The δ¹³C in respiration did not decrease with time as predicted, indicating that lignin accumulation did not influence the measurements.     

Earthworm populations of experimental birch plots on a Calluna podzol

Experimental plots set up by G. W. Dimbleby to test the effect of birch on the soil of a podzolized heather moor were sampled for earthworms after 8, 10 and 27 yr. Of 213 worms collected, one was Dendrobaena octaedra (Savigny, 1826) and the remainder were Bimastos eiseni (Levinsen, 1884). No worms were found on the heather control plots and a single specimen only was taken on plots screefed and sown with Molinia. The population density on plots treated with birch litter, taking 1 yr with another, averaged approximately 1.7 worms m^?2 with a biomass < 1 g m^?2.On the Callunetum surrounding the experimental plots worms were sampled by a trapping method. Only B. eiseni was found. On the Callunetum and on the experimental plots worm numbers were correlated with the calcium content of the 0–3 cm soil horizon. Parts of the experimental site and surrounding Callunetum are subject to intermittent waterlogging. The development of the earthworm population in these areas appears to be restricted by occasional reducing conditions in the upper organic horizon.     

Transgenic Bt plants decompose less in soil than non-Bt plants

Bt plants are plants that have been genetically modified to express the insecticidal proteins (e.g. Cry1Ab, Cry1Ac, Cry3A) from subspecies of the bacterium, Bacillus thuringiensis (Bt), to kill lepidopteran pests that feed on corn, rice, tobacco, canola, and cotton and coleopteran pests that feed on potato. The biomass of these transgenic Bt plants (Bt+) was decomposed less in soil than the biomass of their near-isogenic non-Bt plant counterparts (Bt−). Soil was amended with 0.5, 1, or 2% (wt wt⁻¹) ground, dried (50 °C) leaves or stems of Bt corn plants; with 0.5% (wt wt⁻¹) ground, dried biomass of Bt rice, tobacco, canola, cotton, and potato plants; with biomass of the near-isogenic plants without the respective cry genes; or not amended. The gross metabolic activity of the soil was determined by CO₂ evolution. The amounts of C evolved as CO₂ were significantly lower from soil microcosms amended with biomass of Bt plants than of non-Bt plants. This difference occurred with stems and leaves from two hybrids of Bt corn, one of which had a higher C:N ratio than its near-isogenic non-Bt counterpart and the other which had essentially the same C:N ratio, even when glucose, nitrogen (NH₄NO₃), or glucose plus nitrogen were added with the biomass. The C:N ratios of the other Bt plants (including two other hybrids of Bt corn) and their near-isogenic non-Bt counterparts were also not related to their relative biodegradation. Bt corn had a significantly higher lignin content than near-isogenic non-Bt corn. However, the lignin content of the other Bt plants, which was significantly lower than that of both Bt and non-Bt corn, was generally not statistically significantly different, although 10-66% higher, from that of their respective non-Bt near-isolines. The numbers of culturable bacteria and fungi and the activity of representative enzymes involved in the degradation of plant biomass were not significantly different between soil amended with biomass of Bt or non-Bt corn. The degradation of the biomass of all Bt plants in the absence of soil but inoculated with a microbial suspension from the same soil was also significantly less than that of their respective inoculated non-Bt plants. The addition of streptomycin, cycloheximide, or both to the soil suspension did not alter the relative degradation of Bt+ and Bt− biomass, suggesting that differences in the soil microbiota were not responsible for the differential decomposition of Bt+ and Bt− biomass. All samples of soil amended with biomass of Bt plants were immunologically positive for the respective Cry proteins and toxic to the larvae of the tobacco hornworm (Manduca sexta), which was used as a representative lepidopteran in insect bioassays (no insecticidal assay was done for the Cry3A protein from potato). The ecological and environmental relevance of these findings is not clear.     

Survival of sclerotia of Sclerotium cepivorum berk. In muck soil as influenced by drying and the location of sclerotia in soil

The proportion of viable sclerotia of Sclerotium cepivorum placed in field plots in Burnaby, British Columbia, decreased with time (P = 0.05). Sclerotia that had been air-dried for 48–72 hr had a lower percentage survival than those that had not been dried. Sclerotia placed on the soil surface decayed more rapidly than those buried at 15 cm (P = 0.05). Loss of viability was due to decay of sclerotia rather than to a reduction in the ability of the sclerotia to germinate which did not decline with time (P = 0.05). After 16 months in the field 23.6; 2.1; 11.7 and 8.9% of the sclerotia remained viable in the not-dried buried, not-dried surface, dried buried and dried surface treatments respectively.     

不同类型的污泥对土壤微生物性质的影响: 地中海退化土的田间试验研究

The recycling of suitable organic wastes can enhance soil fertility via effects on soil physical, chemical and biological properties. To compare the effects of digested (DS), thermally dried (TDS) and composted dewatered (CDS) sewage sludge on soil microbiological properties, an experiment was conducted at field sites for more than one year (401 d) when applied to two Mediterranean degraded soils (loam and loamy sand soils). All three types of sewage sludge had a significant effect on measured parameters. I...     

Regulation of parasitism by host density: The Bdellovibrio-Rhizobium interrelationship

Rhizobium strains of the cowpea group did not lose viability readily when added to soil, but Bdellovibrio acting on these rhizobia were found in 32 of 90 soils examined. Bdellovibrio did not initiate replication in liquid media at low host densities, but it did multiply once the Rhizohium numbers increased through growth to about 10⁸ ml^?1. From about 10⁴ to 6 × 10⁵ ml^?1Rhizohium cells survived attack by the parasites in liquid media. In nutrient-free buffer, no significant increase in vibrio abundance was evident if the rhizobial frequency was low. whereas Rhizobium populations containing 6 × 10⁸ cells ml^?1 were lysed rapidly. Bdellovibrio did not multiply when introduced into sterile soil with small numbers of the host, but it replicated when the rhizobia were abundant because of the latter's use of soil organic matter for growth or because of the deliberate addition of 10⁸Rhizohium g^?1. Nevertheless, the host persisted in such vibrio-rich soil samples. The abundance of indigenous bdellovibrios increased appreciably in nonsterile soil if the rhizobia were introduced in large but not small numbers. It is suggested that a major reason for the lack of elimination of the host population in soil by its parasites is the need for a critical host cell frequency, large Rhizobium numbers being required for Btiellovibrio to initiate replication and low numbers of surviving hosts no longer being able to support the parasite.     

Physicochemical requirements in the environment of the earthworm Eisenia foetida

Survival and/or growth were used to assess optimum and potentially deleterious physico-chemical conditions in the environment of the earthworm Eisenia foetida. Maximum weight was gained between 20 and 29°C with horse manure or activated sludge as food. Maximum weight gain as a function of moisture in activated sludge occurred between 70 and 85%. All worms died within a week at pH values <5 or >9; optimum pH for gain in weight centered around 7.0 Soluble salts in excess of 0.5% were lethal, though ammonium acetate caused 100% mortality at a concentration of 0.1%; concentrations in manures contaminated by urine or cattle slurry may be lethal, while those present in noncontaminated manure, with an electrolytic conductivity of 1.5–3mmhos, support weight gain. Inorganic chemicals that are commonly used to coagulate sludges, often as a preliminary to land application, were innocuous at concentrations higher than those normally used at wastewater treatment plants. Anaerobically digested sludges are toxic to earthworms, and are characterized by low oxidation-reduction potentials; when placed upon a soil substrate the redox potential increases slowly, and though the sludge tested in this study was nontoxic at Eh values in excess of 250 mV, it provided insufficient nutriment to E. foetida to allow weight gain. With activated sludge as food, growth of E. foetida occurred more rapidly when soil was present, independently of whether it was placed as a substrate beneath the sludge or mixed into the sludge. Growth occurred more rapidly when activated sludge was placed on substrates which allowed drainage, though loam or ashed loam appeared superior to others, such as glass beads or sand; the growth promoting factor is related to the inorganic fraction of the soil.     

Survival of Coniothyrium minitans associated with sclerotia of Sclerotinia sclerotiorum in soil

The development and survival of the mycoparasite Coniothyrium minitans associated with sclerotia of the plant pathogen Sclerotinia sclerotiorum was studied in pasteurised and non-sterile (untreated) soil. Using scanning electron microscopy, developing pycnidia were first seen within the sclerotial medulla at 7 days post-inoculation with the mycoparasite in pasteurised soil. However, by 14 days post-inoculation, pycnidia had developed fully in both pasteurised and non-pasteurised treatments, and conidial droplets were exuded onto the outer surface of the infected sclerotia. Thirty days post-inoculation, irrespective of soil treatment, the majority of the sclerotial medulla had been converted to pycnidia, with the sclerotial rind remaining largely intact. The pycnidia and dried intact droplets were still observed 6 months post-inoculation with C. minitans, although the conidia on the outer surface of the dried droplets had largely collapsed by this stage. Germinability studies at 10 months post-inoculation showed that approximately 13% of the conidia in dried droplets were still viable. This work shows the potential for infected sclerotia of S. sclerotiorum to provide a unique reservoir for the survival of C. minitans.     

Sewage sludge processing determines its impact on soil microbial community structure and function

Composting and thermal drying are amongst the most commonly used post-digestion processes for allowing sanitation and biological stabilization of sewage sludge from municipal treatment plants, and making it suitable as soil conditioner for use in agriculture. To assess the impact of sludge-derived materials on soil microbial properties, fresh (LAF), composted (LAC) and thermally dried (LAT) sludge fractions, each resulting from a different post-treatment process of a same aerobically digested sewage sludge, were added at 1% (w/w) application rate on two contrasting (a loam and a loamy sand) soils and incubated under laboratory conditions for 28 days. Soil respiration, microbial ATP content, hydrolytic activities and arginine ammonification rate were monitored throughout the incubation period. Results showed that soil biochemical variables, including the metabolic quotient (qCO₂), were markedly stimulated after sludge application, and the magnitude of this stimulatory effect was dependent on sludge type (precisely LAT > LAF > LAC), but not on soil type. This effect was related to the content of stable organic matter, which was lower in LAT. Genetic fingerprinting by PCR–DGGE revealed that compositional shifts of soil bacterial and, at greater extent, actinobacterial communities were responsive to the amendment with a differing sludge fraction. The observed time-dependent changes in the DGGE profiles of amended soils reflected the microbial turnover dependent on the sludge nutrient input, whereas no indications of adverse effects of sludge-borne contaminants were noted. Our findings indicate that composting rather thermal drying can represent a more appropriate post-digestion process to make sewage sludge suitable for use as soil conditioner in agriculture.     

Production and carrying capacity for the earthworm Lumbricus terrestris in culture

Approximately 8 h were required at 25°C for food to pass from mouth to anus in the earthworm Lumbricus terrestris. Gut load per unit transit appeared inversely related to nitrogen content; values of about 2 and 44 mg dry castings per 100mg dry worm were obtained with activated sludge and mineral soil, respectively. Production of biomass was greater in a substrate of activated sludge and loam relative to activated sludge and cellulose, despite higher concentrations of nitrogen in the latter. Optimum population density was about 8 earthworms (31 g live wt) in 1000cm³ 2:1 sludge:soil. Growth occurred at a maximum rate between 15 and 25°C. A yield of approximately 4% biomass (dry wt) was obtained on a mixture of activated sludge and loam, based on the content of organic matter present.     

Population dynamics of the mycoparasite, sporidesmium sclerotivorum, and its host, sclerotinia minor, in soil

The infection and survival of sclerotia of Sclerotinia minor and the production ofmacroconidia of the mycoparasite, Sporidesmium sclerotivorum, were studied in vitro when each fungus was added to soil at various initial inoculum densities. The rate at which S. sclerotivorum invaded host sclerotia and caused their decay varied with the amount of the mycoparasite added to soil. The results suggest that approximately 5 macroconidia of the mycoparasite g^?1 of soil are needed to successfully infect sclerotia and bring about their decay, when soils are sampled and mixed every 2 weeks. The rate at which S. sclerotivorum infects sclerotia of S. minor and causes their decay is also dependent on the initial inoculum density of the host. Each infected sclerotium supports the production of about 15,000 new macroconidia in soil regardless of the initial inoculum density of the host. It is concluded that successful biological control by S. sclerotivorum is dependent on the soil population of both the host and the mycoparasite.     

Differential interaction of Aspergillus niger and Peniophora lycii phytases with soil particles affects the hydrolysis of inositol phosphates

The effect of the soil environment on the mobility, stability and catalytic activity of phytase from two sources was compared, as these factors have important implications for the efficacy of enzyme function in soil. Phytase from an ascomycete fungus (Aspergillus niger) and a basidiomycete fungus (Peniophora lycii) was added to soil suspensions from three contrasting soils and activities in the solution and solid phase were monitored. The two enzymes were compared because the P. lycii phytase was known to have greater specific activity and a more acidic isoelectric point (pI) than A. niger and therefore predicted to have different adsorption characteristics. When added to soil suspensions buffered at pH 7.5, both phytases remained in solution in all of the soils. In contrast at near natural soil pH (pH 5.5), only the P. lycii phytase remained in solution, while the A. niger phytase was rapidly adsorbed to the soil solid phase. The extent of this adsorption was reduced, however, in a soil-dependent manner by prior addition of bovine serum albumin (BSA) to the soil suspensions. At the natural pH of the soil, the stability of the P. lycii phytase in soil solution was improved under sterile conditions, whereas degradation of the A. niger phytase was unaffected. Subsequently, P. lycii phytase was shown to be more effective at hydrolysing myo-inositol hexakisphosphate added to the soil. Moreover, the P. lycii phytase also hydrolysed more organic phosphate that was endogenous to a range of soils. This research indicates that the physicochemical properties of fungal phytases affect their mobility and temporal stability and their capacity to hydrolyse inositol phosphates in soil environments.     

Effect of organic matter on the survival of Phytophthora cinnamomi rands in soil

Soil organic matter collected from beneath an unburnt stand of Eucalyptus marginata was added in increasing amounts to lateritic soil. Phytophthora cinnamomi incubated in soils containing 50% or more organic matter was extensively lysed, and many of the sporangia produced were abortive.With increasing organic matter there is an increase in nutrient concentrations and in the microbial population and it is suggested that these factors are the basis of the antagonism.     

Microorganisms in sewage sludge added to an extreme alkaline saline soil affect carbon and nitrogen dynamics

There are plans to vegetate soil of the former lake Texcoco and use wastewater sludge to provide nutrients. However, the Texcoco soil is N depleted, so the amount of N available to the vegetation might be limited and the dynamics of C and N affected. We investigated how emissions of CO₂, N₂O and N₂, and dynamics of mineral N were affected when different types of N fertilizer, i.e. NH₄⁺, NO₃⁻, or unsterilized or sterilized wastewater sludge, were added to the Texcoco soil. An agricultural soil served as control. Sewage sludge added to an alkaline saline soil (Texcoco soil) induced a decrease in concentrations of NH₄⁺ and NO₃⁻. Addition of sewage sludge increased the CO₂ emission rate > two times compared to soil amended with sterilized sludge. The NH₄⁺ concentration was lower when sludge was added to an agricultural soil for the first 28 days and in the Texcoco soil for 56 days compared to soil amended with sterilized sludge. Production of N₂O in the agricultural soil was mainly due to nitrification, even when sludge was added, but denitrification was the main source of N₂O in the Texcoco soil. Microorganisms in the sludge reduced N₂O to N₂, but not the soil microorganisms. It was found that microorganisms added with the sludge accelerated organic material decomposition, increased NH₄⁺ immobilization, and induced immobilization of NO₃⁻ (in Texcoco soil). These results suggest that wastewater sludge improves soil fertility at Otumba (an agricultural soil) and would favour the vegetation of the Texcoco soil (alkaline saline).     

Substrate‐Induced Respiration of a Sandy Soil Treated with Different Types of Organic Waste

A sandy soil was amended with different types of sewage sludge (digested, dried, and composted) and pig slurry. The composted sludges displayed higher organic‐matter stability (39–45%) than only digested sludge (26–39%) or digested + dried sludge (23–32%). The microbial biomass of the dried sludge was undetectable. Digested and composted sludges and pig slurry displayed microbial biomasses (12492–13887 µg g^?1, 1221–2050 µg g^?1, and 5511 µg g^?1, respectively) greater than the soil (108 µg g^?1). The wastes were applied at seven doses, ranging from 10 to 900 g kg^?1. Soils were incubated for 28 days. Substrate‐induced respiration (SIR) was measured for 12 consecutive hours on day 1 and on day 28. The results showed that SIR increased with the dose of organic amendment. However, SIR decreased when moderate doses of pig slurry or high doses of digested + dried sludge were tested. The possibility of using this inhibition as an ecotoxicological indicator is discussed.     

Nitrogen,Phosphorus, and Potassium Availability in Manure- and Sewage Sludge–Applied Soil

A field experiment with wheat (Triticum aestivum L.) was established over two growing seasons where farmyard manure and sewage sludge, along with conventional fertilizer, were added to soil. We found that ammonium N was at greater concentrations in the organic amendments treatments, indicating more beneficial dynamics (i.e., it can be taken up by plants for a greater amount of time) and thus a longer lasting effect as a nutrient for the test crop. We found that nitrogen (N), phosphorus (P), and potassium (K) uptake increased with added organic amendments. This means that when organic matter along with nutrients are added to soil, productivity may increase beyond preset targets because soil conditions greatly improve, not only chemically but also physically. Nitrates left over at the end of the growing season (residual N) were greater in the high sewage sludge and manure treatments, but not proportionally.     

Survival of sclerotia of Macrophomina phaseolina and Sclerotium cepivorum after drying and wetting treatments

Exposure of sclerotia of Macrophomina phaseolina to 0 and 33% relative humidity (r.h.) for 12 weeks and of Sclerotium cepivorum to 0, 33 and 55% r.h. for 20 weeks did not reduce their germinability on agar. Exposure to 78% r.h. caused high loss of germinability in M. phaseolina and complete loss in S. cepivorum. After 7-day exposures respective moisture contents of sclerotia of M. phaseolina and S. cepivorum were 1 and 2% at 0% r.h.; and 10 and 14% at 78% r.h. M. phaseolina sclerotia held at 0% and 33% r.h. in desiccators for several times up to 12 days did not decrease in subsequent survivability in moist soil, unlike sclerotia held at 78% r.h. for 4 days.More sclerotia of M. phaseolina were colonized by fungi and Streptomyces spp. on alkaline soil than on acid soil. On alkaline soil twice as many sclerotia were colonized after exposure to 0% r.h. as after exposure to 33, 55 and 78% r.h. Colonization of S. cepivorum sclerotia was as high on acid as on alkaline soil and 3 times as high on sclerotia treated at 0% r.h. as on those treated at higher r.h. Attempts to ascertain the effects of colonization on sclerotial viability were unsuccessful. Incubation of sclerotia of M. phaseolina in moist Rumsford sandy loam (50% m.h.c.) for 20 weeks reduced survivability by 43%. At room temperature, alternate drying and wetting of soil containing sclerotia did not appreciably affect survivability of either pathogen. Survivability of S. cepivorum sclerotia was highest when the sclerotia were incubated in air-dried soil (2–3% m.h.c.) for 20 weeks.Incidence of white rot on onion seedlings transplanted to S. cepivorum-infested soil was higher in soil that had been air-dried for 20 weeks than in soil that had been alternately wetted and dried. Sclerotia that were exposed to 0% r.h. for 7 days before soil incubation produced little white rot.     

The biochemical transformation of oak (Quercus robur) leaf litter consumed by the pill millipede (Glomeris marginata)

Soil macrofauna play an essential role in the initial comminution and degradation of organic matter entering the soil environment and yet the chemical effects of digestion on leaf litter are poorly understood at the molecular level. This study was undertaken to assess the selective chemical transformations that saprophagous soil invertebrates mediate in consumed leaf litter. A number of pill millipedes (Glomeris marginata) were fed oak leaves (Quercus robur) after which the biomolecular compositions (lipids and macromolecular components) of the leaves and millipede faeces were compared using a series of wet chemical techniques and subsequent analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). It was found that the concentrations of short chain (<C₂₀) n-alkanoic acids, sterols and triacylglycerols reduced dramatically in the millipede faeces relative to the leaf litter. Hydrolysable carbohydrates and proteins both decreased in concentration in the faeces, whereas similar yields of phenolic components were observed for the cupric oxidation products of lignin, although the oxygenated functionalities were affected by passage through the millipede gut, yielding a more highly condensed state for lignin. This shows that the chemical composition of fresh organic matter entering the soil is directly controlled by invertebrates feeding upon the leaf litter and as such that they are key contributors to the early stages of diagenesis in terrestrial soils.