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Abstract: This study investigated the use of bark and combined paper sludge to develop a suitable plant growth substrate and to establish a vegetation cover on bark-covered land. Field experiments [...]

Replenishment of soil C and N is essential for sustainable revegetation of minesoils. Our study investigated paper de-inking sludge as the organic amendment for revegetating an abandoned sandpit in Quebec, Canada. Sludge was incorporated at 0 (check) and 105 Mg dry matter ha(super -1) before seeding tall wheatgrass (Agropyron elongatum (Host) Beauv.). Nitrogen (at 315, 630 and 945 kg N ha(super -1) and P (at 52.5 and 105 kg P ha(super -1)) were also applied to all plots. Distribution of C and N was determined periodically in two sizes (53 mu m) and two densities (1.8 g cm(super -3) of soil fractions during 823 d. After 823 d, C concentrations were 43 and 69% of those of Day 5, for the low and high N rates, respectively. With time, the proportion of C in the heavy (>1.8 g cm(super -3) fraction increased from 20 to 55%, but remained near 20% in the fine (53 mu m) fraction. The amount of N recovered in all fractions decreased after Day 86, in accordance with a previous litter bag study. Although inorganic N was positively correlated with total N in all fractions, the fine fraction was the best indicator of the size of the mineral N pool. Addition of sludge to the sandpit favored the restoration of C and N pools, and high levels of mineral N increased this effect. Residues became denser but remained relatively coarse during their decomposition.

A study of two strains of Rhizobium leguminosarum biovar phaseoli and three other plant growth-promoting rhizobacteria (PGPR) shows that rhizobia have higher potential for maize and lettuce root colonization than rhizobacteria. Rhizobial root populations show a fresh weight of log 4.1 CFU/g on maize roots and log 3.7 CFU/g on lettuce roots four and five weeks after seeding, respectively, whereas the corresponding weights for PGPR are log 3.5 and log 3.0 CFU/g.

De-inking paper sludge (DPS) has been traditionally disposed of by burning or landfilling, but could be used as an organic amendment in agricultural soils. Our objective was to assess the impact of DPS incorporation on organic matter and aggregation of a clay loam (Typic Dystrochrept) and a silty clay loam (Typic Humaquept). Whole soil C, particulate ([is greater than] 53 [micro]m) and light fraction (density [is less than] 1.8 Mg [m.sup.-3]) C, and water-stable aggregation were measured periodically during a 3-yr period after a single application of DPS at rates of 0 (control), 50, and 100 Mg [ha.sup.-1]. Microscopic observations of water-stable aggregates were also performed. Adding DPS increased whole soil C content, which remained greater than in the control for the duration of the study. After 2 yr, about 40% of the initial material remained in the soil. The proportion of residual C attributed to DPS and present in the particulate fraction remained constant at 70 to 90% during the first 2 yr of the study, whereas the proportion of residual C present in the light fraction decreased from [is greater than] 95% for fresh DPS to [is less than] 50% after 2 yr. One year after incorporation of DPS, the proportion of water-stable aggregates [is greater than] 1 mm was 2 to 6 times larger in amended soils than in the control. This effect was still statistically significant after 3 yr. Microscopic observations revealed that DPS formed into clusters of wood fibers which became encrusted with mineral particles. We hypothesized that this encrustation provided physical protection to the decaying DPS which remained particulate ([is greater than] 53 [micro]m) in size and progressively densified to [is greater than] 1.8 Mg [m.sup.-3]. As a result, water-stable macroaggregates were formed with DPS as a central core.

Abstract: Knowledge of the microbiology of dinitrogen (N2)-fixing bacteria in compost rich in de-inking paper sludge (DPS) is limited. Dinitrogen (N2)-fixing bacteria from DPS composts were isolated and studied for their N2-fixing activity in vitro and in vivo. Two Gram-negative N2-fixing isolates were identified as Pseudomonas. At 20°C, both isolates revealed that N2-fixing activity was higher than that of three arctic Pseudomonas strains. Their N2-fixing activity was found to occur between 18 and 25°C, a pattern that was similar to the reference isolate Azotobacter ATCC 7486. Composts successfully showed N2-fixing activity after carbohydrate amendments both with and without inoculation of a N2-fixing isolate. These results suggest that DPS composts support N2-fixing bacteria and that N2-fixing activity is dependent on a usable carbohydrate source. [Copyright &y& Elsevier]