Extracellular hydrolytic enzyme activities of the heterotrophic microbial communities of the Rouge River: an approach to evaluate ecosystem response to urbanization.

The potential effects of urbanization on the bioavailability of dissolved organic carbon (DOC) were tested by determining the extracellular enzyme activities of the heterotrophic microbial communities of the Rouge River. The activities of 19 enzymes were monitored across two water samples (river water and groundwater) at different spatial and temporal scales. High phosphatase, esterase, and aminopeptidase activities was observed in site 9 (site most exposed to anthropogenic sources) showed higher concentrations of DOC compared to sites 1 and 8 (sites exposed to less anthropogenic sources), where moderate activities of diverse range of enzymes were observed. High relative contributions of phosphatase, esterase, and aminopeptidase activities to the overall enzyme activity as observed in site 9 stressed the increased importance of peptides as C source for heterotrophic communities and high in-stream carbon processing, which account for high nonspecific extracellular enzyme activities. In contrast, high contribution of glycosyl hydrolases occurred consistently across all sites, which highlights the significance of microbial detrital and plant biomass as carbon sources. Majority of the enzymes showed evidence of activity at various extents during spring and summer. However, higher activities of leucine aminopeptidase, valine aminopeptidase, ß-glucosidase, and α-mannosidase were observed in the summer; and alkaline phosphatase and α-glucosidase in the spring. The results presented here suggest a shift in organic carbon bioavailability across all sites of contrasting urbanization, despite similarities in DOC concentrations. Hence, API ZYM technique can be used as an effective indicator of river water and groundwater system health across an urban gradient.

Salt-adapted bacteria isolated from the Rouge River and potential for degradation of contaminants and biotechnological applications.

The current work extends the phenotypic and molecular characterization of the bacterial culture collection from the Rouge River to gain an understanding of the physiology of the strains and their potential for biotechnological applications. Phenotypic and molecular analyses were performed on six unique strains. Most of the strains tested for hydrolytic activities were positive for the production of enzymes, in contrast to previously described species that showed very little hydrolase activities. Little antibiotic resistance was seen among the strains, although Halobacillus (strain 9-gw1-su5-2) was found to be the most resistant to antibiotics. Results revealed the physiological diversity of the strains in terms of their ability to metabolize unusual and refractory substrates. Of the 31 toxic organic compounds, 2 to 18 were used by the strains. Clostridium (strain 9-gw1-su5-2) exhibited the broadest utilization capability. The isolates were versatile in their nutrient abilities and represented a potential source of bacteria and/or genetic material for the degradation of contaminants and biotechnological applications.

Reduction of compost phytotoxicity during the process of decomposition.

Hog manure from windrows composted at different operating strategies was used in a bioassay to determine phytotoxicity. Twelve windows that differed in composting strategies (i.e. turning frequency and moisture content adjustment) were built. The effects of hog manure water extracts on seed germination and primary root growth of cress (Lepidum sativum L.) was measured. The germination index (GI, a product of relative seed germination and root elongation) was related to the chemical characteristics (electrical conductivity, nitrogen compounds, C:N ratio, heavy metals and humification parameters) of the hog manure. The water-extractable chemical properties of the hog manure that showed the highest negative correlation with GI were extractable Cu, extractable Zn and NH(4)(+)N, demonstrating that these chemical compounds gradually decrease during composting due to transformation to other compounds and immobilization effects. A GI>80 (an indicator of the disappearance of phytotoxicity) was reached when the concentrations of NH(4)(+)-N, extractable Cu, and extractable Zn were 2gkg(-1), 15mgkg(-1), and 15mgkg(-1), respectively. Multiple regression analysis revealed that NH(4)(+)-N was the most important factors affecting the phytotoxicity of the hog manure. Composting strategies employed affected the speed of composting, time of maturation, and disappearance of phytotoxicity. The disappearance of phytotoxicity corresponded with the time of maturation of the hog manure. If optimum composting conditions (windrows turned every 4d with weekly moisture adjustment to 60%) are met, phytotoxicity disappears within 56d.

Metabolic diversity of the heterotrophic microorganisms and potential link to pollution of the Rouge River.

The heterotrophic microbial communities of the Rouge River were tracked using Biolog Ecoplates to understand the metabolic diversity at different temporal and spatial scales, and potential link to river pollution. Site less impacted by anthrophogenic sources (site 1), showed markedly lower metabolic diversity. The only substrates that were utilized in the water samples were carbohydrates. Sites more impacted by anthrophogenic sources (sites 8 and 9) showed higher metabolic diversity. Higher functional diversity was linked to the physico-chemical and biological properties of the water samples (i.e. higher concentrations of DO, DOC, chlorophyll, and bacterial density). Biolog analysis was found to be useful in differentiating metabolic diversity between microbial communities; in determining factors that most influence the separation of communities; and in identifying which substrates were most utilized by the communities. It can also be used as an effective ecological indicator of changes in river function attributable to urbanization and pollution.

Diversity of sulfate-reducing genes (dsrAB) in sediments from Puget Sound.

The aims of this study were to characterize the population structure and diversity of sulfate-reducing bacteria (SRB) from three distinct sites at Puget Sound, and relate the biogeochemical properties of the sediments to the sulfate-reducer communities. The population composition and diversity of sulfate-reducing bacteria carrying dsrAB genes from surface Puget Sound sediments was investigated using a polymerase chain reaction-based cloning approach. Sediment cores were collected from three different locations: Carr Inlet (C1A), Shallow Bud Inlet (S1A), and Turning Basin (T1A). A total of 498 dsrAB clones were sequenced from the three sites. Ecological indices indicated that T1A had the highest diversity and evenness values and C1A had the lowest. Correlations were also found between diversity indices and geochemical parameters. The diversity of the SRB decreased with decreasing carbon concentrations and sulfate reduction rates, and increasing levels of oxygen. A phylogenetic comparison revealed that the majority of the dsrAB sequences were associated with the delta-proteobacterial phylotypes Desulfonema, Desulfococcus and Desulfosarcina, suggesting that complete oxidizers with high substrate versatility dominate in the sediments. The environmental conditions and energy sources available in the sediments may have dictated microbial community structure and diversity of SRBs. Distinctive community structures of SRBs in Puget Sound sediments were found to vary at different sites with different redox profiles. The dominance of the Desulfobacteraceae-like sequences may be due to the presence of a diverse spectrum of substrates in the sediments. This study represents one of the first efforts to characterize the population of sulfate-reducing microbes in the oxygenated regions of Puget Sound sediments. The phylogenetic identification of dsrAB genes in the sediment samples allows the composition of sulfate-reducing prokaryotic communities to be inferred, and working hypotheses about their likely carbon substrates to be formed.

Microbial community profiling and characterization of some heterotrophic bacterial isolates from river waters and shallow groundwater wells along the Rouge River, southeast Michigan.

This study was conducted to elucidate microbiological characteristics of river water and groundwater communities in order to improve our conceptual and predictive understanding of river and groundwater ecosystem processes, functioning and management. Rouge River bacterial communities from shallow groundwater and river water were screened using Biolog Ecoplates, which test for oxidation of selected carbon sources and by culturing heterotrophic bacteria. The isolates cultured from the samples were also characterized using the 16SrRNA gene-based approach. The patterns of utilization of the groups of carbon substrates by the microbial communities revealed differences between river water and groundwater samples. Carbohydrates, polymers, carboxylic acids and amino acids were highly utilized by the microbial communities in the river samples, while carbohydrates, polymers, amino acids and phenolic compounds were metabolized in the groundwater samples. Sequence comparison results showed that the most prevalent phylum in all sites was the Firmicutes (low G+C, mostly gram-positive bacteria). The dominant isolates from this phylum were similar to Bacillus spp., (98% nucleotide identity), which represented approximately 62% of the total number of unique isolates. Also prevalent were the gamma-Proteobacteria, which were dominated by 16S rRNA sequences 98-99% similar to that of Pseudomonas spp. The observed profile of carbon sources metabolized reflected the catabolic potential of the river water and groundwater community. Many of the isolates recovered have been known to metabolize several organic substrates, and may have potential use in remediation organic contaminants from the Rouge River. Direct incubation water samples in Biolog Ecoplates produced patterns of metabolic response useful in the classification and characterization of river water and groundwater microbial communities. Heterotrophic bacteria isolated from the sites may play important roles in the fate of many organic and inorganic contaminants from the Rouge River, although future studies are needed to understand their response to these contaminants.

Halophilic and halotolerant bacteria from river waters and shallow groundwater along the Rouge River of southeastern Michigan.

The use of sodium chloride to melt highway and road snow is believed to have a significant effect on the groundwater ecosystem of the rivers where the salt from the roads drain. As the river composition changes, the bacterial population also changes to favour those bacteria that are more suited to the higher salt concentrations. In this experiment, we surveyed the cultivable salt-loving organisms (halophiles) on three sites that encompass the Rouge River (Lotz; site 1, Lilly, site; 8, and Ford Field, site 9). A total of 125 isolates were surveyed. Representative isolates of distinct morphologies were subjected to physiological test, using API strips and identified by 16 rDNA sequence analysis. The 16S rDNA sequences were analyzed and compared with sequences from Genbank. Results indicated that the SSU rRNA sequences of the bacterial isolates were similar to six major genera, Bacillus, Staphylococcus, Halobacillus, Paenabacillus, Halomonas, and Clostridium. Half of the isolates sequenced were similar to Bacillus spp. The API assay showed that the majority of the isolates were positive for the enzymes tryptophane deaminase, gelatinase and beta-galactosidase. Indole production, acetoin production and citrate utilization were not observed for any isolates. Fermentation of carbohydrates was observed for very few isolates. The primary enzyme found in all isolates was arginine dihydrolase, which might be an indicator of the presence of such enzyme in halophilic and halotolerant bacteria present in the Rouge River.

Stability in a denitrifying fluidized bed reactor.

This study evaluates changes in the microbial community structure and function of a pilot-scale denitrifying fluidized bed reactor during periods of constant operating conditions and periods of perturbation. The perturbations consisted of a shutdown period without feed, two disturbances in which biofilms were mechanically sheared from carrier particles, and a twofold step increase in feed nitrate concentration. In the absence of perturbations, nitrate removal was stable and consistently greater than 99%. The structure and dynamics of the microbial community were studied using cloning and sequencing techniques and terminal restriction fragment length polymorphism (T-RFLP) of the SSU rRNA gene. Under unperturbed operating conditions, stable function was accompanied by high constancy and low variability of community structure with the majority of terminal restriction fragments (T-RFs) appearing throughout operation at consistent relative abundances. Several of the consistently present T-RFs correlated with clone sequences closely related to Acidovorax (98% similarity), Dechloromonas (99% similarity), and Zoogloea (98% similarity), genera recently identified by molecular analyses of similar systems. Significant changes in community structure and function were not observed after the shutdown period. In contrast, following the increase in loading rate and the mechanical disturbances, new T-RFs appeared. After both mechanical disturbances, function and community structure recovered. However, function was much more resilient than community structure. The similarity of response to the mechanical disturbances despite differences in community structure and operating conditions suggests that flexible community structure and potentially the activity of minor members under nonperturbation conditions promotes system recovery.

Diversity of biogeochemical cycling genes from Puget Sound sediments using DNA microarrays.

Oligonucleotide-based microarray permits the simultaneous analysis of thousands of genes on a single chip, so that a better picture of the interactions among thousands of genes can be investigated at the same time. Our oligo microchips contained 763 50-mer probes that scan the region of different functional genes encoding amoA, pmoA, nirS, nirK, nifH, and dsrAB. These genes code for key enzymes in the ecosystem processes of nitrification, methane oxidation, denitrification, nitrogen fixation and sulfur reduction, respectively. We used these oligochips to characterize the distribution of the above genes from Puget Sound sediments at different depths. The composition and distribution of genes from shallower sediments (depths 00.5 cm, 2.0-2.5 cm, 5.0-5.5 cm, and 25.0-25.5 cm) were highly similar but were different from those collected at deeper depths (depths 50-50.5 cm and 84.0-84.5 cm). The deeper sediments present a different community structure with a markedly lower diversity than the shallower depths. Analysis of positive hybridization signals also revealed presence of genes common to all samples. The majority of these genes were similar to those retrieved from various environments (i.e. soils, groundwater, river water, strotomites, marine sediments, and estuarine sediments). Parallel coordinate display showed that the most dominant functional guilds are those that are involved in nitrogen cycling. Our results also indicated that this technology has potential as a tool in revealing a comprehensive "snapshot" of the functional gene composition in marine sediments, although more work is needed to understand the biological meaning of each detectable hybridization signal.

Microbial community dynamics in manure composts based on 16S and 18S rDNA T-RFLP profiles.

Compost processing is assumed to be related to the microbial communities present. However, methods that will evaluate these relationships are not well understood. In this study, terminal restriction fragment length polymorphism (T-RFLP) analysis was used to evaluate the diversity of PCR-amplified bacterial 16S and fungal 18S rDNA communities from manure composts at different stages of composting (initial [day 0], thermophilic [day 24], and mature [day 104]). Results showed that the bacterial and fungal community profiles changed over the composting process, with bacterial communities showing a higher diversity compared with the fungal communities. During the thermophilic stage (day 24), the diversity of the bacterial communities increased, while the fungal communities decreased. As the compost reached maturity (day 104), a reverse pattern was observed between the diversity of bacterial and fungal communities. That is, the 18S rDNA T-RFLP-based diversity indices increased, while the 16S rDNA T-RFLP-based diversity decreased. Differences in temperature profiles at different stages of composting impacted the chemical properties and the diversity of the microbial communities. The day 104 compost (mature) had lower water, organic matter and C contents and higher C and OM loss compared with the day 0 (initial) and day 24 (thermophilic) composts, which affected the diversity of the microbial communities. The results presented here demonstrated that distinctive community patterns from manure composts could be rapidly generated using T-RFLP analysis. The succession of peaks in combination of increasing and decreasing peak heights at different stage of composting indicates the high potential of T-RFLP technique to monitor the dynamics of microbial communities, and their variation qualitatively and quantitatively.

Microbiological parameters as indicators of compost maturity.

AIMS: The objectives of this study were to determine the changes of microbial properties of pig manure collected from pens with different management strategies and composted using different turning and moisture regimes; relate their association with humification parameters and compost temperature; and identify the most suitable microbial indicators of compost maturity. METHODS AND RESULTS: Six different microbial parameters, including total bacterial count, oxygen consumption rate, ATP content, dehydrogenase activity, and microbial biomass C and N, along with humification parameters [humic acid (HA), fulvic acid (FA) and HA : FA ratio] and compost temperature were monitored during composting. Significant positive correlations were found between temperature and microbial properties, including O2 consumption rate, ATP content, dehydrogenase activity, and microbial biomass N. The humification parameters also showed significant correlations with microbial properties of the manure compost. For instance, HA contents of pig manures was positively correlated with total aerobic heterotrophs, and microbial biomass N and C; and negatively correlated with O2 consumption rate, ATP content, and dehydrogenase activity. Among the six microbial parameters examined, dehydrogenase activity was the most important factor affecting compost temperature and humification parameters. Composting strategies employed in this study affected the speed of composting and time of maturation. If the moisture content is maintained weekly at 60% with a 4-day turning frequency, the pig manure will reach maturity in 56 days. CONCLUSIONS: The composting process went through predictable changes in temperature, microbial properties and chemical components despite differences in the initial pig manure and composting strategies used. Among the six microbial parameters used, dehydrogenase activity is the most suitable indicator of compost maturity. Compared with respiration rate, ATP content and microbial biomass procedures, dehydrogenase activity is the simplest, quickest, and cheapest method that can be used to monitor the stability and maturity of composts. SIGNIFICANCE AND IMPACT OF THE STUDY: The results presented here show that microbial parameters can be used in revealing differences between composts and compost maturity. The statistical relationship established between humification parameters and microbial parameters, particularly dehydrogenase activity, demonstrates that it is possible to monitor the composting process more easily and rapidly by avoiding longer and more expensive analytical procedures.

Bacterial community profiles on feathers during composting as determined by terminal restriction fragment length polymorphism analysis of 16S rDNA genes.

Composting is one of the more economical and environmentally safe methods of recycling feather waste generated by the poultry industry, since 90% of the feather weight consists of crude keratin protein, and feathers contain 15% N. However, the keratin in waste feathers is resistant to biodegradation and may require the addition of bacterial inocula to enhance the degradation process during composting. Two keratin-degrading bacteria isolated from plumage of wild songbirds and identified as Bacillus licheneformis (OWU 1411T) and Streptomyces sp. (OWU 1441) were inoculated into poultry feather composts (1.13 x 10(8) cfu g(-1) feathers) and co-composted with poultry litter and straw in 200-l compost vessels. Composting temperatures, as well as CO(2) and NH(3) evolution, were measured in these vessels to determine the effects of inoculation on the rate and extent of poultry feather decomposition during composting. Terminal restriction fragment length polymorphisms of 16S rRNA genes were used to follow changes in microbial community structure during composting. The results indicated that extensive carbon conversion occurred in both treatments (55.5 and 56.1%). The addition of the bacterial inocula did not enhance the rate of waste feather composting. The microbial community structure over time was very similar in inoculated and uninoculated waste feather composts.

Evaluation of organic matter and nutrient composition of partially decomposed and composted spent pig litter.

Characterization of soil-applied organic material is necessary in order to clarify the nature of the organic matterand nutrients in it. In this study, the organic matter and nutrient contents of the spent pig litter (a mixture of partially decomposed pig manure and sawdust) was characterized before and after windrow composting to: (1) determine their changes during composting, and (2) assess the suitability of the composted spent litter as a soil amendment. Results demonstrated that the time required to reach maturity, and the composition of composted spent litter, depended on the chemical properties of the initial compost feedstock as well as the compost strategies used during composting. Total N, P, and K concentrations of the composted litter depended on chemical properties of the initial material. On the other hand, C:N ratio, humic and fulvic acid and cation-exchange capacity were influenced by differences in composition of the initial spent litter and composting strategy. If moisture content was maintained weekly at 60% with a four-day turning frequency, the litter reached maturity in 56 days. Maturation of spent litter was accompanied by a decline in total C, water-extractable metals, NH(4)(+)-N, increase in ash, (NO(3)(-)+NO(2)(-)-N, humic acid, humic acid:fulvic acid ratio, and cation exchange capacity, and elimination of phytotoxicity. The stability of nutrient and organic matter, acceptable pH and electrical conductivity values, and low levels of undesirable components such as heavy metals and phytotoxic compounds of the spent litter provided substantial evidence that agronomically suitable compost can be obtained after composting in windrows.

Isolation and characterization of rhizobacteria from composts that suppress the severity of bacterial leaf spot of radish.

ABSTRACT Composts can induce systemic resistance in plants to disease. Unfortunately, the degree of resistance induced seems highly variable and the basis for this effect is not understood. In this work, only 1 of 79 potting mixes prepared with different batches of mature, stabilized composts produced from several different types of solid wastes suppressed the severity of bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae compared with disease on plants produced in a nonamended sphagnum peat mix. An additional batch of compost-amended mix that had been inoculated with Trichoderma hamatum 382 (T(382)), which is known to induce systemic resistance in plants, also suppressed the disease. A total of 11 out of 538 rhizobacterial strains isolated from roots of radish seedlings grown in these two compostamended mixes that suppressed bacterial leaf spot were able to significantly suppress the severity of this disease when used as inoculum in the compost-amended mixes. The most effective strains were identified as Bacillus sp. based on partial sequencing of 16S rDNA. These strains were significantly less effective in reducing the severity of this disease than T(382). A combined inoculum consisting of T(382) and the most effective rhizobacterial Bacillus strain was less effective than T(382) alone. A drench applied to the potting mix with the systemic acquired resistance-inducing chemical acibenzolar-S-methyl was significantly more effective than T(382) in several, but not all tests. We conclude that systemic suppression of foliar diseases induced by compost amendments is a rare phenomenon. Furthermore, inoculation of compost-amended potting mixes with biocontrol agents such as T(382) that induce systemic resistance in plants can significantly increase the frequency of systemic disease control obtained with natural compost amendments.

Evolution of extracellular enzyme activities during manure composting.

AIMS: The objectives of this work were to determine the extracellular enzyme profiles during composting, relate the activities of these enzymes to the changes in microbial population and compare the enzyme profiles between two manures. METHODS AND RESULTS: API ZYM assay was used to monitor the activities of 19 extracellular enzymes during poultry and pig manure composting. Results showed an overall increase in diversity and relative abundance of enzymes present. The relative abundance and activities of enzymes were higher in poultry manure than in pig manure. Among the 19 enzymes tested, esterase, valine amino-peptidase and alpha-galactosidase were the most abundant enzymes in poultry manure, whereas it was N-acetyl-beta-glucosaminidase for the pig manure. A number of these enzymes correlated with change in numbers of different microbial groups during composting. CONCLUSIONS: The composting process represented a combined activity of a wide succession of environments, as one enzyme/microbial group overlapped the other and each emerged gradually due to the continual change in temperature and progressive breakdown of complex compounds to simpler ones. SIGNIFICANCE AND IMPACT OF THE STUDY: The results presented here show the applicability of the API ZYM test not only in monitoring the quantitative and qualitative fluctuation of the available substrate during composting, but also in revealing differences in composts and compost maturity.

Fate of nitrogen during composting of chicken litter.

Chicken litter (a mixture of chicken manure, wood shavings, waste feed, and feathers) was composted in forced-aeration piles to understand the changes and losses of nitrogen (N) during composting. During the composting process, the chemical [different N fractions, organic matter (OM), organic carbon (C), and C:N ratio], physical, and microbial properties of the chicken litter were examined. Cumulative losses and mass balances of N and organic matter were also quantified to determine actual losses during composting. The changes in total N concentration of the chicken litter piles were essentially equal to those of the organic N. The inorganic N concentrations were low, and that organic N was the major nitrogenous constituent. The ammonium (NH(4)(+))-N concentration decreased dramatically during first 35 days of composting. However, the rapid decrease in NH(4)(+)-N during composting did not coincide with a rapid increase in (NO(3)(-)+NO(2)(-))-N concentration. The concentration of (NO(3)(-)+NO(2)(-))-N was very low (<0.5 g kg(-1)) at day 0, and this level remained unchanged during the first 35 days of composting suggesting that N was lost during composting. Losses of N in this composting process were governed mainly by volatilization of ammonia (NH(3)) as the pile temperatures were high and the pH values were above 7. The narrow C:N ratio (<20:1) have also contributed to losses of N in the chicken litter. The OM and total organic C mass decreased with composting time. About 42 kg of the organic C was converted to CO(2). On the other hand, 18 kg was lost during composting. This loss was more than half (59%) of the initial N mass of the piles. Such a finding demonstrates that composting reduced the value of the chicken litter as N fertilizer. However, the composted chicken contained a more humified (stabilized) OM compared with the uncomposted chicken litter, which would enhance its value as a soil conditioner.

Composting of spent pig litter in turned and forced-aerated piles.

A study was carried out to compare the compositing efficiency of spent litter (a mixture of partially decomposed pig manure and sawdust) in turned and forced-aerated piles. Duplicate piles were built with manual turning (every 4 days) during composting, and duplicate piles were set up with forced aeration using an air pump. The present study demonstrated that the efficiency of composting in the turned and forced-aerated piles was similar. Spent litter in these piles reached maturity at the same time (60 days). The forced-aerated piles went through similar physical, chemical, and microbial changes with the turned piles during composting. The forced-aerated composting system was also as effective as the turned system in eliminating Salmonella sp. in the spent litter. These results suggest that a forced-aerated composting system could be used as an alternative method in composting spent litter. The similarities in temporal changes in temperature, chemical, and microbiological properties of the forced-aerated piles, compared with the turned piles, indicate that addition of a bulking agent under forced aerated composting of spent litter is not necessary. The partially decomposed sawdust in the spent litter provided enough free air space, allowing the delivery of oxygen for the microorganisms in the spent litter piles.

Composting of spent pig litter at different seasonal temperatures in subtropical climate.

To investigate the effects of seasonal temperatures on the composting of spent pig-manure sawdust litter (spent litter), two sets of experiments were carried out: one during winter, the other during summer. Physicochemical and microbial parameters including temperature, pH, inorganic N, humification indicators (HA and FA), heavy metals (Cu and Zn), total aerobic heterotrophs, ATP content and dehydrogenase activity were measured to understand changes in the spent litter during composting. Results demonstrated that the composting was faster during summer than winter. The spent litter during the summer trial reached maturity at day 56 whereas that of the winter trial was still immature at the end of composting (days 91). Microbial activities during the thermophilic stage of composting were much lower in the winter trial. Values began to increase during the latter part of composting, indicating that the spent litter in this winter trial was biologically unstable and must be further composted to reach full maturity. The changes in the microbial activities of the spent litter during summer or winter reflected the changes in their temperatures and chemical properties. The maturation of the spent litter during summer was accompanied by stabilization of the microbial and chemical properties and a drop in temperature to ambient level. Results of correlation analysis showed that temperature correlated not only with the microbial parameters but also with most of the chemical parameters. These parameters also correlated with each other. Among all the parameters measured, the trend of temperature changes is the simplest and most rapid parameter that can be used to evaluate the maturity of spent litter.

Effects of bacterial inoculum and moisture adjustment on composting of pig manure.

Spent litter (a mixture of partially composted pig manure and sawdust) was taken from pig pens employing the pig-on-litter system with and without the addition of a commercial bacterial product (Odor control (OC)-organic fertilizers (OF)). A duplicate series of windrows was set up with spent litter which contained the bacterial product and a further duplicate series was set up with spent litter which did not contain the bacterial product. All four sets had their initial moisture content adjusted to 60% but one of each duplicate pair had its moisture content adjusted to 60% during the entire period of further composting in windrows. The rate of further (windrow) composting was significantly different in the litter which contained no bacterial product and which only had its moisture content adjusted at the beginning of the experiment. Decomposition was incomplete in this set even after day 91. In the three other sets, the rate of decomposition was faster and the spent litter became stabilised by day 56. This result suggests that if the bacterial product has been added during the initial pig-on-litter composting process, moisture adjustment during further (windrow) composting is not important. Conversely, if moisture was adjusted during further composting, the addition of bacterial product during initial pig-on-litter composting would be of no value. Such a finding is of remarkable significance in the further composting of spent litter since this indicates that the process could be run on a much more economical basis.

Effects of composting on phytotoxicity of spent pig-manure sawdust litter.

The phytotoxicity of spent pig-manure sawdust litter (spent litter) was evaluated during further composting. Aqueous extracts of the spent litter were prepared by shaking the sample with water (1:10 w/v), and the toxicity of these extracts was determined on relative seed germination, relative root elongation and germination index (GI, a factor of relative seed germination and relative root elongation). The sensitivity of six plant species, namely Brassica parachinensis (Chinese cabbage), Brassica albogalera (Chinese kale), Allium sativum (onion), Cucumis sativus (cucumber), Amaranthus espinosus (Chinese spinach), and Lycopersicon esculentum (tomato) were compared. The effect of different moisture levels during composting on the phytotoxicity of the spent litter was also examined. Phytotoxicity of the spent litter was only evident during the earlier stage of composting (first 14 days) and, that seed germination and root elongation reached 100% (same as the control) towards the end of the composting. The concentrations of the major inhibitors, water-extractable Cu and Zn, and NH4(+)-N of the spent litter, declined during composting, indicating that these inhibitors were gradually eliminated as composting proceeded. Multiple regression analysis showed that the NH4(+)-N content of the spent litter was the most important chemical factor affecting phytotoxicity of the plant species selected for this study. Relative root elongation and GI were more sensitive indicators of phytotoxicity than seed germination. In the present study, the GI's of all plant species were >80% at day 60, indicating that the spent litter had reached its maturation by day 60. The responses of different plant species to the water-extracts of the spent litter were different. Among the six species, Chinese cabbage and Chinese spinach were the most sensitive species, and tomato and cucumber were the least sensitive species to indicate phytotoxicity of the spent litter. Moisture adjustment during the composting process did not affect the results of the phytotoxicity test.