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Urban sewage sludge (USS) is increasingly applied to agricultural soils, but mixed results have been reported because of variations in reuse conditions. Most field trials have been conducted in cropping systems, which conceal intrinsic soil responses to sludge amendments due to the rhizosphere effect and farming practices. Therefore, the current field study highlights long‐term changes in bare soil properties in strict relationship with soil texture and USS dose. Two agricultural soils (loamy sand [LS] and sandy [S]) were amended annually with increasing sludge rates up to 120 t ha−1 yr−1 for 5 yr under unvegetated conditions. Outcomes showed a USS dose‐dependent variation of all studied parameters in topsoil samples. Soil salinization was the most significant risk related to excessive USS doses. Total dissolved salts (TDS) in saturated paste extracts reached the highest concentrations of 37.2 and 43.1 g L−1 in S soil and LS soil, respectively, treated with 120 t USS ha−1 yr−1. This was also reflected by electrical conductivity of the saturated paste extract (ECe) exceeding 4,000 µS cm−1 in both treatments. As observed for TDS, fertility indicators and bioavailable metals varied with soil texture due to the greater retention capacity of LS soil owing to higher fine fraction content. Soil phytotoxicity was estimated by the seed germination index (GI) calculated for lettuce, alfalfa, oat, and durum wheat. The GI was species dependent, indicating different degrees of sensitivity or tolerance to increasing USS rates. Lettuce germination was significantly affected by changes in soil conditions showing negative correlations with ECe and soluble metals. In contrast, treatment with USS enhanced the GI of wheat, reflecting higher salinity tolerance and a positive effect of sludge on abiotic conditions that control germination in soil. Therefore, the choice of adapted plant species is the key factor for successful cropping trials in sludge‐amended soils. [ABSTRACT FROM AUTHOR]

The agricultural reuse of urban sewage sludge (USS) modifies soil properties depending on sludge quality, management, and pedo‐environmental conditions. The aim of this microcosm study was to assess C mineralization and subsequent changes in soil properties after USS addition to two typical Mediterranean soils: sandy (Soil S) and sandy loam (Soil A) at equivalent field rates of 40 t ha−1 (USS‐40) and 120 t ha−1 (USS‐120). Outcomes proved the biodegradability of USS through immediate CO2 release inside incubation bottles in a dose‐dependent manner. Accordingly, the highest rates of daily C emission were recorded with USS‐120 (3.7 and 3.9 mg kg−1 d−1 for Soils S and A, respectively) after 84 d of incubation at 25 °C. The addition of USS also improved soil fertility by enhancing soil macronutrients, microbial proliferation, and protease activity. Protease showed significant correlation with N, total organic C, and heterotrophic bacteria, reflecting the biostimulation and bioaugmentation effects of sludge. Soil indices like C/N/P stoichiometry and metabolic quotient (qCO2) varied mostly with mineralization rates of C and P in both soils. Despite a significant increase of soil salinity and total heavy metal content (lead, nickel, zinc, and copper) with USS dose, wheat germination was not affected by these changes. Both experimental soils showed intrinsic (Soil A) and incubation‐induced (Soil S) phytotoxicities that were alleviated by USS addition. This was likely due to the enhancement of biodegradation and/or retention of phytotoxicants originating from previous land uses. Urban sewage sludge amendments could have applications in soil remediation by reducing the negative effects of allelopathic and/or anthropogenic phytoinhibitors. [ABSTRACT FROM AUTHOR]

Seven culturable bacterial isolates, obtained from the internal stem tissues of Solanum elaeagnifolium and successfully colonizing the internal stem tissues of tomato cv. Rio Grande, were screened for their in vivo antifungal activity against Fusarium oxysporum f.sp. lycopersici ( FOL) and their growth-promoting potential on tomato plants. SV101 and SV104 isolates, assessed on pathogen-challenged tomato plants led to a significant decrease (77-83%) in Fusarium wilt severity and vascular browning extent (76%), as compared to the inoculated and untreated control. Isolates enhanced growth parameters on pathogen-challenged and unchallenged tomato plants. SV104 and SV101 isolates were most effective in suppressing disease and enhancing plant growth. These two isolates were identified as Bacillus sp. str. SV101 () and B. tequilensis str. SV104 (). They displayed antifungal activity against FOL; pathogen growth was inhibited by 64% and an inhibition zone (11.50 and 19.75 mm) against FOL could be formed using whole cell suspensions. SV101 and SV104 extracellular metabolites also inhibited FOL growth by 20 and 55%, respectively, as compared to control. B. tequilensis str. SV104 was shown to produce protease, chitinase, pectinase, IAA and siderophores. Bacillus sp. str. SV101 displayed pectinase activity and was found to be an IAA-producing and phosphate-solubilizing agent. To our knowledge, this is the first study reporting on S. elaeagnifolium use as a potential source of potent biocontrol and plant growth-promoting agents. [ABSTRACT FROM AUTHOR]

A putative endophyticBacillus cereusstr. S42 (KP993206), recovered from surface-sterilised stems ofNicotiana glaucawas assessedin vitroandin vivofor its antifungal potential towardsFusarium oxysporumf. sp.lycopersici(FOL). Pathogen sporulation was significantly inhibited byB. cereusstr. S42. FOL mycelial growth was reduced using its whole-cell suspensions, cell-free culture supernatant and chloroform extract. Its extracellular metabolites remained effective after heating at 50–100 °C with a decline in their activity was observed beyond 100 °C, when added with proteinase K and/or after pH adjustment to 2 and 12. Chitinase gene was detected using PCR amplification. Gas chromatography–mass spectrometry analysis of its chloroform extract matched phthalic acid, dibutyl ester with high level of similarity.B. cereusstr. S42 cell-free culture supernatant and whole-cell suspensions had significantly suppressed Fusarium wilt severity by 87–96% and enhanced tomato growth by 39–79% compared to FOL-inoculated and untreated control. [ABSTRACT FROM AUTHOR]

Nine non-pathogenic bacterial isolates, recovered fromDatura metelorgans and able to colonise the internal stem tissues of tomato cultivar Rio Grande, were screened for their ability to suppress tomato Fusarium wilt disease caused byFusarium oxysporumf. sp. lycopersici(FOL), and to enhance plant growth. S33 and S85 isolates tested were found to be the most effective in decreasing Fusarium wilt severity by 94–95% compared to FOL-inoculated and untreated control. A significant enhancement of growth parameters was recorded on tomato plants inoculated or not with FOL. Both isolates were characterised and identified using 16S rDNA sequencing genes asStenotrophomonassp. str. S33 (KR818084) andPseudomonassp. str. S85 (KR818087). Screenedin vitrofor their antifungal activity towards FOL, these isolates led to 38.7% and 22.5% decrease in pathogen radial growth and to the formation of an inhibition zone of 12.75 and 8.37 mm respectively.Stenotrophomonassp. str. S33 andPseudomonassp. str. S85 were found to be chitinase-, protease- and pectinase-producing strains but unable to produce hydrogen cyanide. Production of indole-3-acetic acid-like compounds, phosphate solubilising ability and pectinase activity were investigated for elucidating their plant growth-promoting traits and their endophytic colonisation ability. [ABSTRACT FROM PUBLISHER]

Seven bacterial isolates, recovered from native Nicotiana glauca plants of the Tunisian Centre-East, and successfully colonizing the internal stem tissues of tomato cv. Rio Grande were screened for their ability to suppress tomato Fusarium wilt, caused by Fusaium oxysporum f. sp . lycopersici , and to enhance plant growth. S18 and S42 isolates were found to be the most effective in decreasing yellowing and wilt symptoms by 94 and 88% and the vascular browning extent by 95–97.5%, respectively, as compared to FOL-inoculated and untreated control. A significant enhancement in growth parameters of tomato plants inoculated with pathogen and treated with S18 and S42 isolates. These two bioactive isolates were characterized and identified using 16S rDNA sequencing genes as Alcaligenes faecalis S18 and Bacillus cereus S42, respectively. Pathogen mycelial growth was inhibited by 44.1 and 42.1% with S42 and S18 isolates, respectively . Using the disc diffusion method, S42 and S18 formed an inhibition zone against FOL of about 11.87–12.37 mm, respectively. The isolate S42 of B. cereus showed a proteolytic and chitinolytic activity. A. faecalis S18 exhibited only chitinolytic activity in chitin-agar medium. This isolate was also able to produce the volatile metabolite hydrogen cyanide. Indole-3-acetic acid production, phosphate solubilizing, and pectinase activity were assessed for these two bioactive isolates for elucidating their plant growth promoting traits and their endophytic colonization ability. This study clearly demonstrated that N. glauca is a potential source for the isolation of potent endophytic bacteria exhibiting Fusarium wilt-suppressive and plant growth-promoting effects on tomato. [ABSTRACT FROM AUTHOR]

The generation of considerable amounts of sewage sludge during wastewater treatment is inevitable and should be carefully addressed. Among the various options available for urban sewage sludge management, the agricultural re-use as a fertilizer/soil conditioner has seen a wide acceptance because of the high amount of nutrients and organic matter contained in this biowaste. Accordingly, the aim of this field-scale study was to evaluate the changes in agricultural soil parameters following two successive annual amendments with increasing amounts of urban sludge (0, 40, 80 and 120 t ha −1 year −1 ). Sludge addition improved the fertility of the topsoil, showing a significant dose-dependent increase of TOC, N, P, and K contents up to the excessive amount of 120 t ha −1 year −1 (1.6%, 0.09, 233 and 21 mg kg −1 , respectively). Consequently, soil biological parameters such as microbial communities and enzymatic activities (dehydrogenase, phosphatase, protease and cellulase) were all enhanced as well. On the other hand, we noticed also a similar increasing trend of soil salinity (EC and Na + ) and phytotoxic heavy metals namely, Cd and Cr (2.4 and 3.8 mg kg −1 at 120 t ha −1 year −1 ). This variation was nonetheless below thresholds; and metal bioavailability to microorganisms and lettuce seeds was likely to be hindered by the non change in soil pH, which varied within a neutral range for all treatments (7.43–7.87). According to the C/N ratio, which reflects organic matter evolution in soil, plots treated at 80 t ha −1 year −1 resulted in C/N values below 15. Therefore, this excessive sludge dose for agricultural reuse is likely to be the best practice that ensures an adequate organic matter mineralization with less contamination after two successive annual amendments. [ABSTRACT FROM AUTHOR]

Abstract The agricultural reuse of urban sewage sludge in degraded croplands has seen a wide acceptance for biowaste recycling and for the improvement of soil fertility. However, soil degradation and health issues may arise from the fact that sludge addition causes chemical and biological contamination if mismanaged. To closely monitor the long term soil-sludge interactions, a field study was conducted over a three-year period under a semi-arid climate. More precisely, changes in topsoil properties were assessed in 4-m2 uncropped plots amended with sludge rates equivalent to 0, 40, 80 and 120 t ha−1 year−1 for two soil textures: soil A (sandy loam) and soil S (sandy). Results showed that all studied parameters changed significantly in a dose-dependent manner for both soils as compared to untreated controls. As such, sludge addition improved consistently TOC, N, P and K content up to soils treated with 120 t ha−1 year−1. The enhancement of soil nutrient status impacted positively on biological properties, including microbial biomass and soil enzyme activities (dehydrogenase, protease and phosphatase). However, the variation of soil properties was more important in soil A characterized by a higher fine fraction thus stronger retention capacity. Accordingly, XRD analysis of soil A revealed several identifiable peaks representing kaolinite and illite clays in contrast to soil S. Unexpectedly, high to excessive sludge doses of 80 and 120 t ha−1 year−1 did not provoke soil degradation after three repeated annual amendments. In fact, pH values in both soils remained within neutral to alkaline range (7.76–8.63); total heavy metals (Cu, Zn, Ni and Pb), soil salinity and fecal coliforms were all below threshold values for contaminated soils. Highlights • Tunisian croplands have low organic matter content due to overexploitation. • Three successive annual sewage sludge amendments improved soil fertility. • Soil biological activities were positively correlated with the sludge dose. • Soil degradation was not observed even at excessive sludge doses. • A finer texture had more impact on soil parameters after sludge addition. [ABSTRACT FROM AUTHOR]