Chantal J. Beauchamp

Potential of Rhizobium and Bradyrhizobium species as plant growth promoting rhizobacteria on non-legumes: Effect on radishes (Raphanus sativus L.)

Bradyrhizobia and rhizobia are symbiotic bacterial partners forming nitrogen fixing nodules on legumes. These bacteria share characteristics with plant growth promoting rhizobacteria (PGPR). Nodule inducing bacteria, like other PGPR, are capable of colonizing the roots of non-legumes and produce phytohormones, siderophores and HCN. They also exhibit antagonistic effects towards many plant pathogenic fungi. The potential of nodule inducing bacteria to function as PGPR, was examined by using radish as a model plant. Three percent of the 266 strains tested were found to be cyanogens, while a majority (83%) produced siderophores. Fifty eight percent of the strains produced indole 3-acetic acid (IAA) and 54% solubilized phosphorus. Some of the bacterial species examined were found to have a deleterious effect while others were neutral or displayed a stimulatory effect on radishes. Bradyrizobium japonicum strain Soy 213 was found to have the highest stimulatory effect (60%), and an arctic strain (N44) was the most deleterious, causing a 44% reduction in radish dry matter yield. A second plant inoculation test, performed in growth cabinets, revealed that only strain Tal 629 of B. japonicum significantly increased (15%) the dry matter yield of radish. This indicates that specific bradyrhizobia have the potential to be used as PGPR on non-legumes.

Composting of de-inking paper sludge with poultry manure at three nitrogen levels using mechanical turning : behavior of physico-chemical parameters

De-inking paper sludge (DPS) is rich in carbon (C) but poor in nitrogen (N). Thus, it has a high C:N ratio which limits the composting process. Accordingly, the goal of this study was to investigate the effect of three N treatments on DPS composting. Compost piles of 100 m3 were formed by mixing raw DPS with poultry manure and chicken broiler floor litter, giving on average 0.6%, 0.7% and 0.9% total N. The changes in physico-chemical parameters, total weight and fiber losses, and maturity of composting piles of DPS were monitored during 24 weeks. The compost piles had a neutral to alkaline pH throughout the study. Inorganic N decreased whereas organic N increased over time for all treatments. These changes in magnitude were different among N treatments resulting in a final total N content of 0.9% for the 0.6% N treatment whereas final total N contents of 0.7% and 0.9% N were measured for the 0.7% and 0.9% N treatments. The total weight, cellulose and hemicellulose losses were higher in 0.6% N treatment giving the lowest C:N ratio after 24 weeks of composting. However, none of the 24 week-old composts of DPS were mature based on their final C:N ratio and colorimetric test of maturity. Except for copper, their final total trace element contents meet most known standards or guidelines for organic soil conditioners. Overall, 0.6% N treatment was the best to enhance DPS composting using mechanical turning, but a period of more than 24 weeks was required to reach compost maturity.

Dynamics of water-soluble carbon substances and microbial populations during the composting of de-inking paper sludge.

Composting is an alternative method to dispose of de-inking paper sludge (DPS). Today, few studies have investigated the water-soluble carbon (WSC) substances as indicators of the decomposition process and the microbial changes taking place during the composting of DPS. Accordingly, the goal is to study their dynamics during the composting of DPS at three nitrogen levels, 0.6%, 0.7% or 0.9% total N, using mechanical turning. The changes in WSC substances, microbial biomass carbon (MBC) and, total and DPS microbial populations were monitored during 24 weeks. Also, microorganisms were identified and tested for the production of selected enzymes. Regardless of N treatments, the dynamic of WSC substances indicated that cellulose and hemicellulose fractions of DPS fibers were mainly biodegraded during the first 8 weeks while the more resistant carbon (C) fractions were biodegraded thereafter. MBC also evolved regardless of N treatments but was correlated to WSC substances. Its high values decline mostly after 12 weeks indicating the exhaustion of this source of C energy for microbial growth and the stabilisation of DPS organic matter. The dynamic and identified microorganisms were comparable to those observed in other composting processes. However, the results pointed out that those mostly implicated in the hydrolysis of DPS fibers were the thermophilic actinomycetes and fungi and, by comparison to the 0.6% or 0.7% N treatment, they decreased in presence of the 0.9% N treatment. Most microorganisms were hemicellulolytic bacteria, while actinomycetes and fungi were capable of degrading a wide variety of substrates. Overall, dynamics of WSC substances and microbial populations indicated that during composting, DPS decomposition obey a two phase decay while, contrary to the lowest N treatment, the 0.9% N treatment has slowed down this process by harming the important microbial populations implicated in the degradation of DPS fibers.

Decomposition of de-inking paper sludge in agricultural soils as characterized by carbohydrate analysis.

Increasing amounts of de-inking paper sludge (DPS) are available from paper mills, and could be used to improve soil fertility because of their high organic matter content. Our aim was to use chemical fractionation and carbohydrate characterization to determine the transformation and decay rates of DPS in diAerent soils when large loading rates are applied. DPS was added to a well-drained silty clay loam (Typic Dystrochrept) and a poorly-drained clay loam (Typic Humaquept) at rates of 0 (control), 50 or 100 Mg dry matter ha ˇ1 . Soil samples were obtained periodically during 726 days after sludge incorporation. Soil organic matter was fractionated into hot-water extractable (HWC), mild-acid extractable (MAC) and strong-acid extractable carbohydrates (SAC), and acid-resistant carbon (ARC). The MAC fraction mostly contained hemicellulosic sugars, whereas SAC fraction included most cellulosic glucose. The contribution of microbial saccharides to the diAerent carbohydrate fractions increased during DPS decomposition. The carbohydrate composition indicated that the chemical fractions reflected the net balance between disappearance of sludge carbohydrates and appearance of newly synthesized microbial carbohydrates. The MAC, SAC and ARC fractions in DPS-amended soils, had relative degradabilities of SAC > MAC > ARC. The sludge used, appeared to decompose according to a two-phase pattern, with an initial rapid-decay phase mostly determined by SAC and ARC disappearance (mean residence time 0.1 and 0.3 year, respectively), and a second slow-decay phase: largely characterized by ARC disappearance (mean residence time 8.5 years). DPS decomposed more slowly at the highest application rate, presumably because the capacity of soil microbes to decompose C was temporarily limited by nutrient deficiency. Chemical fractionation and carbohydrate analysis proved useful to study quantitatively and qualitatively the decomposition and transformation of wood-derived residues in agricultural soils. Crown Copyright 7 2000 Published by Elsevier Science Ltd. All rights reserved.

Active carbon pools and enzyme activities in soils amended with de-inking paper sludge

Application of paper mill wastes generally improves soil organic matter content, biological activity and physical properties. However, the impact of large application rates (>50 Mg ha−1) on soil microflora and their activity has not been assessed. A field study was undertaken on a well-drained clay loam and a poorly drained silty clay loam amended with de-inking paper sludge (DPS) at rates of 0 (control), 50 or 100 Mg ha−1. K2SO4-extractable C (Cext), soil water content (SWC), microbial biomass C (MBC) and different enzyme activity rates were periodically measured in soil during 1075 d following DPS incorporation. Compared with control soils, Cext content increased by 100 to 200%, and soil water content increased by 35% following incorporation of DPS at 100 Mg ha−1. Those differences decreased in time as DPS decomposed. Soil MBC increased proportionally with the rate of DPS amendment and was about twice the amount in soils amended with 100 Mg ha−1 compared with the control. Microbial quotient (ratio of MB...

Vacuum-extraction of peatlands disturbs bacterial population and microbial biomass carbon

Knowledge concerning the microbial characteristics of natural and post-vacuum extracted ombrotrophic peatlands, as well as peatlands under restoration is limited. In one experiment, microbial comparisons of paired neighboring natural and post-vacuum peatlands in eastern Quebec (Canada) were studied to assess the effects of peat mining on microbial indicators and nitrogen (N) cycling. Microbial counts, microbial biomass carbon (MB-C) and N mineralization were examined over two growing seasons. Also, in a second experiment, bio-indicators of the microbial status (microbial counts, MB-C and the quotient of MB-C to total carbon) of one peatland harboring natural, restored and post-vacuum extracted treatments were assessed sporadically over 6 years. The first experiment revealed that peat mining decreased populations of total bacteria, hemicellulolytic and cellulolytic microorganisms and MB-C, but increased peat ammonium content and N mineralization. The bacterial population was found to be lower in the post-vacuum extracted treatment than in natural treatment (control) and under restoration treatment, whereas the actinomycete population was higher in the post-vacuum extracted and restoration treatments than the natural one. Over the 6-year-time course experiment, the MB-C, total C and their quotient revealed a gradual increase in the peatland under restoration, but they remained similar in the post-vacuum extracted peatland treatment. This supports the concept that the total bacterial population and MB-C may be used as an ecological indicator to monitor major site disturbance using paired natural restored peatland.

Examination of environmental quality of raw and composting de-inking paper sludge

Paper sludges were traditionally landfilled or burned. Over the years, the use of paper sludges on soils has increased, as well as the concerns about their environmental effects. Therefore, the chemical characterization of paper sludges and their young (immature) compost needed to be investigated, and over 150 inorganic and organic chemicals were analyzed in de-inking paper sludge (DPS). In general, nitrogen, phosphorus and potassium contents were low but variable in raw DPS and its young compost. The contents of arsenic, boron, cadmium, cobalt, chromium, manganese, mercury, molybdenum, nickel, lead, selenium, and zinc were also low and showed low variability. However, the copper contents were above the Canadian compost regulation for unrestricted use and required a follow-up. The fatty- and resin acids, and polycyclic aromatic hydrocarbons were the organic chemicals measured at the highest concentrations. For resinic acids, care should be taken to avoid that leachates reach aquatic life. For polycyclic aromatic hydrocarbons, naphthalene should be followed until soil content reaches 0.1 microg g(-1), the maximum allowed for soil use for agricultural purposes according to Canadian Environmental Quality Guidelines. In young compost, the concentration of these chemical families decreased over time and most compounds were below the detection limits after 24 weeks of composting. In raw DPS, among the phenol, halogenated and monoaromatic hydrocarbons, dioxin and furan, and polychlorinated biphenyl families, most compounds were below the detection limits. The raw DPS and its young compost do not represent a major threat for the environment but can require an environmental follow-up.

Decomposition of paper de-inking sludge in a sandpit minesoil during its revegetation.

Paper de-inking sludge was used as an organic amendment for revegetating an abandoned sandpit in Quebec, Canada. In situ patterns of sludge decomposition and of total nitrogen and phosphorus dynamics were characterized in a litter bag study. In a one-time operation, sludge was applied at a rate of 0 or 105 Mg dry matter ha−1, along with N at 3, 6 or 9 kg Mg−1 sludge and P at 0.5 or 1.0 kg Mg−1 sludge. Sludge and fertilizers were incorporated into the top 0.21 m of the minesoil and tall wheatgrass (Agropyron elongatum (Host) Beauv.) was seeded. Mass loss was well described by a double exponential model when cumulative degree-days (sum of daily temperature above 0°C) were used as the independent variable. Fifty-one percent of the initial material decomposed with a half life of 0.4 yr, whereas the remaining material had a much slower rate of decay with a half life of 13 yr. The large size and slow decomposition rate of the recalcitrant pool of this material were attributed to the high lignin content and the presence of clay in the sludge. Both N and P in decomposing sludge presented a short accumulation phase followed by a long release phase which likely contributed to the successful revegetation of this disturbed sandpit site.

DEINKING SLUDGE INFLUENCES BIOMASS, NITROGEN AND PHOSPHORUS STATUS OF SEVERAL GRASS AND LEGUME SPECIES

In a greenhouse study, deinking sludge was evaluated as a soil amendment supplemented with four nitrogen (N) fertilization levels for the growth of the grasses Agropyron elongatum (Host.) Beauv. (tall wheatgrass), Alopecurus pratensis L. (meadow foxtail), Festuca ovina var. duriuscula (L). Koch (hard fescue), and four levels of phosphorus (P) for the growth of the legumes Galega orientalis Lam. (galega), Medicago lupulina L. (black medic), Melilotus officinalis (L.) Lam (yellow sweet clover). Fertilizers were applied on the basis of sludge level to maintain uniform carbon (C)/N or C/P ratios across sludge treatments. In one experiment, sand was mixed with 0, 10, 20 or 30% sludge while, in a second experiment, mineral soil was mixed with 0, 27, 53 or 80% sludge (vol/vol). In sand mixtures of 30 and 20% sludge, grasses had similar or greater growth than in unamended mineral soil when N was added at about 6.5 and 8.4 g kg−1 deinking sludge, respectively. For all legumes but Medicago lupulina, P at about 0.8 ...

Physiological characterization of opine-utilizing rhizobacteria for traits related to plant growth-promoting activity

Thirty-two strains of opine-utilizing rhizobacteria were evaluated for physiological traits which have been related to plant growth-promoting activity. Tests included antibiosis against two bacterial and eight fungal pathogens of potato (Solanum tuberosum L.), production of hydrogen cyanide and fluorescent pigment production. On average, 71 and 12% of the bacteria inhibited the growth of Erwinia carotovora subsp. carotovora and Agrobacterium tumefaciens, respectively. The growth of Botrytis sp. was inhibited by 62% of the bacteria, and half of these produced an inhibition zone of more than 7 mm in diameter. Fusarium solani, Colletotrichum coccodes, Phoma exigua, Verticillium dahliae, F. oxysporum, V. albo-atrum and F. sambucinum were antagonized by 43, 34, 31, 25, 19, 18, and 12% of the bacteria, respectively. Only four strains produce hydrogen cyanide. The inhibition of a plant pathogen was not correlated to the production of fluorescent pigment. No strain produced a hypersensitive reaction whereas only three strains induced soft-rot and two produced polygalacturonase. Some opine-utilizing rhizobacteria were strong inhibitors of all plant pathogens, while most were active against specific plant pathogens.