Rethinking Manure Application: Increase in Multidrug-Resistant Enterococcus spp. in Agricultural Soil Following Chicken Litter Application

The current study investigated the impact of chicken litter application on the abundance of multidrug-resistant Enterococcus spp. in agricultural soil. Soil samples were collected from five different strategic places on a sugarcane farm before and after manure application for four months. Chicken litter samples were also collected. Enterococci were enumerated using the Enterolert®/Quanti-Tray 2000® system and confirm and differentiated into species using real-time PCR. The antibiotic susceptibility profile of the isolates was determined using the disk diffusion method following the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. The overall mean bacterial count was significantly higher (p < 0.05) in manure-amended soil (3.87 × 107 MPN/g) than unamended soil (2.89 × 107 MPN/g). Eight hundred and thirty-five enterococci (680 from soil and 155 from litter) were isolated, with E. casseliflavus being the most prevalent species (469; 56.2%) and E. gallinarum being the least (16; 1.2%). Approximately 56% of all the isolates were resistant to at least one antibiotic tested, with the highest resistance observed against tetracycline (33%) and the lowest against chloramphenicol (0.1%); 17% of E. faecium were resistant to quinupristin-dalfopristin. Additionally, 27.9% (130/466) of the isolates were multidrug-resistant, with litter-amended soil harbouring more multidrug-resistant (MDR) isolates (67.7%; 88/130) than unamended soil (10.0%; 13/130). All isolates were susceptible to tigecycline, linezolid and gentamicin. About 7% of the isolates had a multiple antimicrobial resistance index > 0.2, indicative of high antibiotic exposure. Although organic fertilizers are regarded as eco-friendly compared to chemical fertilizers for improving soil fertility, the application of untreated animal manure could promote the accumulation of antibiotics and their residues and antibiotic-resistant bacteria in the soil, creating an environmental reservoir of antimicrobial resistance, with potential human and environmental health risks.

Effet des amendements organiques sur la croissance et le rendement de la pomme de terre (Solanum tuberosum) cultivée sur un sol dégradé dans la région de Kabinda, République Démocratique du Congo

Le bas niveau de la fertilité des sols à Kabinda et la rareté des engrais chimiques sur le marché orientent les agriculteurs à recourir à une fertilisation palliative et durable. Cette étude a été réalisée dans le but d’évaluer l’effet des amendements organiques sur la croissance et le rendement de la pomme de terre. L’essai était installé suivant un dispositif en blocs complets randomisés. Les traitements en cinq répétitions ont été constitués d’un témoin (T0), de la bouse de vache (T1), de cendres (T2) et de la biomasse fraiche de Entada abyssinica (T3). Les observations ont porté sur les paramètres de croissance et de rendement et l’analyse de la variance (ANOVA) a été appliquée pour la comparaison. Les résultats obtenus renseignent que la pomme de terre se comporte positivement sous effet d’amendements (P<0.05) comparativement au sol non amendé. Le plus grand nombre de feuilles est démarqué nettement au traitement à base des cendres avec 4 feuilles contre 2 feuilles pour le témoin. L’apport de la cendre à la dose de 10 kg/ha sur la culture de la pomme de terre a augmenté le rendement de 1 t/ha par rapport au sol non amendé. L’utilisation de ces amendements dans une région comme Kabinda contribuerait au développement de l’agriculture en luttant contre l’insécurité alimentaire et la pauvreté. Ainsi donc, L’utilisation de la cendre est recommandable pour la production de la pomme de terre vu ses effets sur la culture et sa disponibilité dans la ville de Kabinda.Mots clés : Fertilité, engrais chimiques, production, Solanum tuberosum , Kabinda. English Title: Effect of organic amendments on growth and yield of potato (Solanum tuberosum L.) on soil degraded in Kabinda area, Democratic Republic of CongoThe low level of soil fertility in Kabinda and the scarcity of chemical fetilizers on the market guide farmers to seel palliative and sustainable fertilization. This study was carried out in order to assess the effect of organic amendments on the growth and potato yield. The trial was installed using a ramdomized complete block system. Five Treatments in five repetitions, consisted of a witness (T0), cow dung (T1), ash (T2) and Entada abyssinica fresh biomass (T3). Observations focused on growth and yield parameters and analysis of variance (ANOVA) at the 5% threshold was applied for comparison betwen treatments. The results obtained indicate that the potato behaves positively under the effect of amendments (P<0.05) compared to unamended soil. The greatest leaves number is clearly demarcated in the ash based treatment with 4 leaves versus 2 leaves for the witness treatment. The addition of ash to the potato crop increased the yield by 1 t/ha compared to the unamended soil. The use of ash is recommendable for the production of potato in the city of Kabinda.Keywords : Fertility, chemical fertilizers, production, Solanum tuberosum, Kabinda

Soil Microbial Community Changes in a Field Treatment with Chlorotoluron, Flufenacet and Diflufenican and Two Organic Amendments

The soil microbial activity, biomass and structure were evaluated in an unamended (S) and organically amended soil treated with two commercial formulations of the herbicides chlorotoluron (Erturon®) and flufenacet plus diflufenican (Herold®) under field conditions. Soils were amended with spent mushroom substrate (SMS) or green compost (GC). Soil microbial dehydrogenase activity (DHA), biomass and structure determined by the phospholipid fatty acid (PLFA) profiles were recorded at 0, 45, 145, 229 and 339 days after herbicide treatment. The soil DHA values steadily decreased over time in the unamended soil treated with the herbicides, while microbial activity was constant in the amended soils. The amended soils recorded higher values of concentrations of PLFAs. Total soil microbial biomass decreased over time regardless of the organic amendment or the herbicide. Herbicide application sharply decreased the microbial population, with a significant modification of the microbial structure in the unamended soil. In contrast, no significant differences in microbial biomass and structure were detected in S + SMS and S + GC, untreated or treated with herbicides. The application of SMS and GC led to a significant shift in the soil microbial community regardless of the herbicides. The use of SMS and GC as organic amendments had a certain buffer effect on soil DHA and microbial biomass and structure after herbicide application due to the higher adsorption capacity of herbicides by the amended soils.

Amending Sandy Soil with Biochar Promotes Plant Growth and Root Colonization by Mycorrhizal Fungi in Highbush Blueberry

Biochar, a carbon-rich, fine-grained residue obtained from pyrolysis of biomass, is known to improve soil conditions and to suppress infection by soilborne pathogens. However, its use as a soil amendment has received relatively little attention by the horticulture industry. Two 12-week experiments were conducted in a greenhouse to determine the potential of using biochar, produced from mixed conifers during conversion of wood to energy, as a soil amendment for highbush blueberry (Vaccinium hybrid ‘Legacy’). Plants in the first experiment were fertilized once a week with a complete fertilizer solution, whereas those the in the second experiment were fertilized once a month with a solution of ammonium sulfate. In both cases, the plants received the same amount of N in total and were grown in pots filled with unamended soil (sandy loam) or soil amended at rates of 10% or 20%, by volume, with biochar or a 4:1 mix of biochar and bokashi (biochar-bokashi). The bokashi was produced from fermented rice (Oryza sativa L.) bran and was added to increase nutrients in the amendment. Half of the plants in each soil treatment were inoculated with Phytophthora cinnamomi Rands, which causes root rot in blueberry. Although pH of the raw biochar was high (8.5), soil pH averaged 4.5 to 5.5 in each treatment. In the absence of P. cinnamomi, plants grown with 20% biochar or 10% or 20% biochar-bokashi had greater leaf area and 30% to 70% more total dry weight than those grown with 10% biochar or in unamended soil. Biochar also improved soil aggregation and increased root colonization by ericoid mycorrhizal fungi. The percentage of roots colonized by mycorrhizal fungi was 54% to 94% in plants grown with the amendments, but was ≤10% in those grown in unamended soil. Plants inoculated with P. cinnamomi were stunted and showed typical symptoms of root rot. Root infection by the pathogen was unaffected by biochar or biochar-bokashi and negated any growth benefits of the amendments. Overall, amending soil with biochar appears to be a promising means of promoting plant growth and mycorrhizal colonization in blueberry, but it may not suppress phytophthora root rot.

TiO2 nanoparticles affect the bacterial community structure and Eisenia fetida (Savigny, 1826) in an arable soil

The amount of nanoparticles (NP), such as TiO2, has increased substantially in the environment. It is still largely unknown, however, how NP might interact with earthworms and organic material and how this might affect the bacterial community structure and their functionality. Therefore, an arable soil was amended with TiO2 NP at 0, 150 or 300 mg kg−1 and subjected to different treatments. Treatments were soil amended with ten earthworms (Eisenia fetida (Savigny, 1826)) with fully developed clitellum and an average fresh mass of 0.5 to 500 g dry soil, 1.75 g tyndallized Quaker® oat seeds Avena sativa (L.) kg−1, or earthworms plus oat seeds, or left unamended. The bacterial community structure was monitored throughout the incubation period. The bacterial community in the unamended soil changed over time and application of oats, earthworm and a combination of both even further, with the largest change found in the latter. Application of NP to the unamended soil and the earthworm-amended soil altered the bacterial community, but combining it by adding oats negated that effect. It was found that the application of organic material, that is, oats, reduced the effect of the NP applied to soil. However, as the organic material applied was mineralized by the soil microorganisms, the effect of NP increased again over time.

Salmonella enterica in Soils Amended with Heat-Treated Poultry Pellets Survived Longer than Bacteria in Unamended Soils and More Readily Transferred to and Persisted on Spinach

ABSTRACT Untreated biological soil amendments of animal origin (BSAAO) are commonly used as biological fertilizers but can harbor foodborne pathogens like Salmonella enterica, leading to potential transfer from soils to fruits and vegetables intended for human consumption. Heat-treated poultry pellets (HTPP) can provide produce growers with a slow-release fertilizer with a minimized risk of pathogen contamination. Little is known about the impact of HTPP-amended soil on the survival of Salmonella enterica. The contributions of RpoS and formation of viable but nonculturable cells to Salmonella survival in soils are also inadequately understood. We quantified the survival of Salmonella enterica subsp. enterica serovar Newport wild-type (WT) and rpoS-deficient (ΔrpoS mutant) strains in HTPP-amended and unamended soil with or without spinach plants over 91 days using culture and quantitative PCR methods with propidium monoazide (PMA-qPCR). Simulated “splash” transfer of S. Newport from soil to spinach was evaluated at 35 and 63 days postinoculation (dpi). The S. Newport WT and ΔrpoS mutant reached the limit of detection, 1.0 log CFU/g (dry weight), in unamended soil after 35 days, whereas 2 to 4 log CFU/g (dry weight) was observed for both WT and ΔrpoS mutant strains at 91 dpi in HTPP-amended soil. S. Newport levels in soils determined by PMA-qPCR and plate count methods were similar (P > 0.05). HTPP-amended soils supported higher levels of S. Newport transfer to and survival on spinach leaves for longer periods of time than did unamended soils (P < 0.05). Salmonella Newport introduced to HTPP-amended soils survived for longer periods and was more likely to transfer to and persist on spinach plants than was S. Newport introduced to unamended soils. IMPORTANCE Heat-treated poultry pellets (HTPP) often are used by fruit and vegetable growers as a slow-release fertilizer. However, contamination of soil on farms may occur through contaminated irrigation water or scat from wild animals. Here, we show that the presence of HTPP in soil led to increased S. Newport survival in soil and to greater likelihood of its transfer to and survival on spinach plants. There were no significant differences in survival durations of WT and ΔrpoS mutant isolates of S. Newport. The statistically similar populations recovered by plate count and estimated by PMA-qPCR for both strains in the amended and unamended soils in this study indicate that all viable populations of S. Newport in soils were culturable.

Survival and Growth of Wild-Type and rpoS-Deficient Salmonella Newport Strains in Soil Extracts Prepared with Heat-Treated Poultry Pellets

ABSTRACT Manure runoff can transfer pathogens to farmlands or to water sources, leading to subsequent contamination of produce. Untreated biological soil amendments, like manure, can be contaminated with foodborne pathogens, such as Salmonella Newport, which may lead to transfer of the pathogen to fruits or vegetables. Studies have reported the occurrence and survival of Salmonella in manure or manure slurries. However, data on the survival and growth of Salmonella Newport is lacking in matrices simulating runoff. We quantified the survival and growth of wild-type (WT) Salmonella Newport and rpoS-deficient (ΔrpoS) strains in sterile and nonsterile soil extracts prepared with (amended) or without (unamended) heat-treated poultry pellets at 25°C. Salmonella Newport WT and ΔrpoS populations reached a maximum cell density of 6 to 8 log CFU/mL in 24 to 30 h in amended and unamended soil extracts and remained in stationary phase for up to 4 days. Salmonella Newport in amended soil extracts exhibited a decreased lag phase (λ, 2.87 ± 1.01 h) and greater maximum cell densities (Nmax, 6.84 ± 1.25 CFU/mL) compared with λ (20.10 ± 9.53 h) and Nmax (5.22 ± 0.82 CFU/mL) in unamended soil extracts. In amended soil extract, the ΔrpoS strain had no measurable λ, similar growth rates (μmax) compared with WT, and a lower Nmax compared with the WT strain. Unamended, nonsterile soil extracts did not support the growth of Salmonella Newport WT and led to a decline in populations for the ΔrpoS strain. Salmonella Newport had lower cell densities in nonsterile soil extracts (5.94 ± 0.95 CFU/mL) than it did in sterile soil extracts (6.66 ± 1.50 CFU/mL), potentially indicating competition for nutrients between indigenous microbes and Salmonella Newport. The most favorable growth conditions were provided by amended sterile and nonsterile soil extracts, followed by sterile, unamended soil extracts for both Salmonella Newport strains. Salmonella Newport may grow to greater densities in amended extracts, providing a route for increased Salmonella levels in the growing environments of produce.

Mesotrione dissipation and response of soil microbial communities in a soil amended with organic residues

The application of different organic residues as a soil amendment is an agricultural practice used to improve soil fertility by increasing the soil organic matter (OM). However, the OM from these residues can influence the behavior of pesticides applied jointly to the soil. Modification of the pesticide bioavailability in soils is of special interest since it can affect the activity and/or functioning of soil microbial community. Accordingly, the dissipation kinetics of mesotrione in unamended soil (S) and soils amended with sewage sludge (S+SS), green compost (S+C) and commercial pellets (S+P) and its possible effects on the soil microbial communities were studied. Soil biological parameters were determined as indicators of the soil microbial activity, functioning and structure: microbial biomass, dehydrogenase activity, respiration, and analysis of the phospholipid fatty acid (PLFA) profile extracted from the soil. Dissipation was more rapid in unamended soil than in amended soils and half-life (DT₅₀) values followed the order S+SS &gt; S+C ≥ S+P &gt; S. The biomass values increased in the amended soils with the exception of the P-amended soil. However, mesotrione had different effects on this parameter depending on the soil treatment. In general, dehydrogenase activity was stimulated by the addition of the amendment and herbicide to soil. Initially, respiration was higher in the unamended soil (control and treated soils) than the amended soils and mesotrione did not have any effect on this parameter. PLFAs analysis indicated that the overall structure of active microbial communities as well as the relative abundance of certain groups of microorganisms clearly changed according to the type of amendment and the incubation time, but remained unaffected by the application of mesotrione.

Impact of Fungicide Mancozeb at Different Application Rates on Soil Microbial Populations, Soil Biological Processes, and Enzyme Activities in Soil

The use of fungicides is the continuous exercise particularly in orchard crops where fungal diseases, such as white root rot, have the potential to destroy horticultural crops rendering them unsaleable. In view of above problem, the present study examines the effect of different concentrations of mancozeb (0–2000 ppm) at different incubation periods for their harmful side effects on various microbiological processes, soil microflora, and soil enzymes in alluvial soil (pH 6.8) collected from apple orchards of Shimla in Himachal Pradesh (India). Low concentrations of mancozeb were found to be deleterious towards fungal and actinomycetes population while higher concentrations (1000 and 2000 ppm) were found to be detrimental to soil bacteria. Mancozeb impaired the process of ammonification and nitrification. Similar results were observed for nitrifying and ammonifying bacteria. Phosphorus solubilization was increased by higher concentration of mancozeb, that is, 250 ppm and above. In unamended soil, microbial biomass carbon and carbon mineralization were adversely affected by mancozeb. Soil enzymes, that is, amylase, invertase, and phosphatase showed adverse and disruptive effect when mancozeb used was above 10 ppm in unamended soil. These results conclude that, to lessen the harmful effects in soil biological processes caused by this fungicide, addition of higher amount of nitrogen based fertilizers is required.