953 resultados para microbial inoculation


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The use of machinery in agricultural and forest management activities frequently increases soil compaction, resulting in greater soil density and microporosity, which in turn reduces hydraulic conductivity and O2 and CO2 diffusion rates, among other negative effects. Thus, soil compaction has the potential to affect soil microbial activity and the processes involved in organic matter decomposition and nutrient cycling. This study was carried out under controlled conditions to evaluate the effect of soil compaction on microbial activity and carbon (C) and nitrogen (N) mineralization. Two Oxisols with different mineralogy were utilized: a clayey oxidic-gibbsitic Typic Acrustox and a clayey kaolinitic Xantic Haplustox (Latossolo Vermelho-Amarelo ácrico - LVA, and Latossolo Amarelo distrófico - LA, respectively, in the Brazil Soil Classification System). Eight treatments (compaction levels) were assessed for each soil type in a complete block design, with six repetitions. The experimental unit consisted of PVC rings (height 6 cm, internal diameter 4.55 cm, volume 97.6 cm³). The PVC rings were filled with enough soil mass to reach a final density of 1.05 and 1.10 kg dm-3, respectively, in the LVA and LA. Then the soil samples were wetted (0.20 kg kg-1 = 80 % of field capacity) and compacted by a hydraulic press at pressures of 0, 60, 120, 240, 360, 540, 720 and 900 kPa. After soil compression the new bulk density was calculated according to the new volume occupied by the soil. Subsequently each PVC ring was placed within a 1 L plastic pot which was then tightly closed. The soils were incubated under aerobic conditions for 35 days and the basal respiration rate (CO2-C production) was estimated in the last two weeks. After the incubation period, the following soil chemical and microbiological properties were detremined: soil microbial biomass C (C MIC), total soil organic C (TOC), total N, and mineral N (NH4+-N and NO3--N). After that, mineral N, organic N and the rate of net N mineralization was calculated. Soil compaction increased NH4+-N and net N mineralization in both, LVA and LA, and NO3--N in the LVA; diminished the rate of TOC loss in both soils and the concentration of NO3--N in the LA and CO2-C in the LVA. It also decreased the C MIC at higher compaction levels in the LA. Thus, soil compaction decreases the TOC turnover probably due to increased physical protection of soil organic matter and lower aerobic microbial activity. Therefore, it is possible to conclude that under controlled conditions, the oxidic-gibbsitic Oxisol (LVA) was more susceptible to the effects of high compaction than the kaolinitic (LA) as far as organic matter cycling is concerned; and compaction pressures above 540 kPa reduced the total and organic nitrogen in the kaolinitic soil (LA), which was attributed to gaseous N losses.

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The decomposition of plant residues is a biological process mediated by soil fauna, but few studies have been done evaluating its dynamics in time during the process of disappearance of straw. This study was carried out in Chapecó, in southern Brazil, with the objective of monitoring modifications in soil fauna populations and the C content in the soil microbial biomass (C SMB) during the decomposition of winter cover crop residues in a no-till system. The following treatments were tested: 1) Black oat straw (Avena strigosa Schreb.); 2) Rye straw (Secale cereale L.); 3) Common vetch straw (Vicia sativa L.). The cover crops were grown until full flowering and then cut mechanically with a rolling stalk chopper. The soil fauna and C content in soil microbial biomass (C SMB) were assessed during the period of straw decomposition, from October 2006 to February 2007. To evaluate C SMB by the irradiation-extraction method, soil samples from the 0-10 cm layer were used, collected on eight dates, from before until 100 days after residue chopping. The soil fauna was collected with pitfall traps on seven dates up to 85 days after residue chopping. The phytomass decomposition of common vetch was faster than of black oat and rye residues. The C SMB decreased during the process of straw decomposition, fastest in the treatment with common vetch. In the common vetch treatment, the diversity of the soil fauna was reduced at the end of the decomposition process.

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To mitigate soil erosion and enhance soil fertility in orange plantations, the permanent protection of the inter-rows by cover species has been suggested. The objective of this study was to evaluate alterations in the microbial biomass, due to different soil tillage systems and intercropped cover species between rows of orange trees. The soil of the experimental area previously used as pasture (Brachiaria humidicola) was an Ultisol (Typic Paleudult) originating from Caiuá sandstone in the northwestern part of the State of Paraná, Brazil. Two soil tillage systems were evaluated: conventional tillage (CT) in the entire area and strip tillage (ST) (strip width 2 m), in combination with different ground cover management systems. The citrus cultivar 'Pera' orange (Citrus sinensis) grafted onto 'Rangpur' lime rootstock was used. Soil samples were collected after five years of treatment from a depth of 0-15 cm, under the tree canopy and in the inter-row, in the following treatments: (1) CT and an annual cover crop with the leguminous species Calopogonium mucunoides; (2) CT and a perennial cover crop with the leguminous peanut Arachis pintoi; (3) CT and an evergreen cover crop with Bahiagrass Paspalum notatum; (4) CT and a cover crop with spontaneous Brachiaria humidicola grass vegetation; and (5) ST and maintenance of the remaining grass (pasture) of Brachiaria humidicola. Soil tillage and the different cover species influenced the microbial biomass, both under the tree canopy and in the inter-row. The cultivation of brachiaria increased C and N in the microbial biomass, while bahiagrass increased P in the microbial biomass. The soil microbial biomass was enriched in N and P by the presence of ground cover species and according to the soil P content. The grass species increased C, N and P in the soil microbial biomass from the inter-row more than leguminous species.

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To mitigate the impacts of eucalypt monoculture, forestry companies in the Upper Jequitinhonha Valley (MG) have adopted the insertion of strips of native vegetation in-between the commercial plantations. The method used for the creation of these corridors is to allow spontaneous regrowth of native vegetation in areas previously under eucalypt. The objective of this study was to evaluate the effect of cover crops on microbial and soil properties for a detailed description of the restoration process of native vegetation in forest soils of the Jequitinhonha Valley. The treatments were represented by an initial restoration stage (< 4 years) with or without remaining eucalypt and the advanced restoration stage (> 4 years) with or without remaining eucalypt, plus the three controls: commercial eucalypt plantation, Cerrado vegetation and native forest. Soil samples were collected for three consecutive years in the dry and rainy season (August and February, respectively). The microbial activity, regardless of the presence of remaining eucalypt , did not differ among the restoration areas, except for the metabolic quotient (qCO2) in the rainy season of February 2007. At this time, this microbial activity was higher in the advanced restoration stage without eucalypt than initial restoration without eucalypt and advanced restoration with eucalypt. The restoration areas, in general, did not differ from the control: eucalypt plantation and Cerrado either. Compared to the forest, the levels of organic C, microbial C, basal respiration (Rbasal) and hydrolysis of fluorescein diacetate (FDA) in the restoration areas were, in general, lower and did not differ in qCO2 and microbial quotient (qMIC). In general, the soil quality was similar in the initial and advanced restoration stages. Most of the soil and microbial properties in the three years indicated that the restoration areas were most similar to the Cerrado. In the advanced restoration areas without eucalypt compared to Cerrado, the lower Rbasal in the 3rd year and the lower FDA and qMIC and higher qCO2 in the 2nd year indicated that the removal of the remaining eucalypt trees was unfavorable for restoration.

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The rate of carbon dioxide production is commonly used as a measure of microbial activity in the soil. The traditional method of CO2 determination involves trapping CO2 in an alkali solution and then determining CO2 concentration indirectly by titration of the remaining alkali in the solution. This method is still commonly employed in laboratories throughout the world due to its relative simplicity and the fact that it does not require expensive, specific equipment. However, there are several drawbacks: the method is time-consuming, requires large amounts of chemicals and the consistency of results depends on the operator's skills. With this in mind, an improved method was developed to analyze CO2 captured in alkali traps, which is cheap and relatively simple, with a substantially shorter sample handling time and reproducibility equivalent to the traditional titration method. A comparison of the concentration values determined by gas phase flow injection analysis (GPFIA) and titration showed no significant difference (p > 0.05), but GPFIA has the advantage that only a tenth of the sample volume of the titration method is required. The GPFIA system does not require the purchase of new, costly equipment but the device was constructed from items commonly found in laboratories, with suggestions for alternative configurations for other detection units. Furthermore, GPFIA for CO2 analysis can be equally applied to samples obtained from either the headspace of microcosms or from a sampling chamber that allows CO2 to be released from alkali trapping solutions. The optimised GPFIA method was applied to analyse CO2 released from degrading hydrocarbons from a site contaminated by diesel spillage.

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Inoculation with arbuscular mycorrhizal fungi (AMF) of tree seedlings in the nursery is a biotechnological strategy to improve growth, survival after transplanting, biomass production and to reduce the use of fertilizers. Archontophoenix alexandrae and Euterpe edulis are palm species used in southern Brazil to produce the palm heart, the latter being included in the list of threatened species due to the overexploitation of its native population. The purpose of this paper was to evaluate the effect of mycorrhizal inoculation on growth and physiological parameters of A. alexandrae and E. edulis. After germination, the seedlings were inoculated (AMF) or not (CTL) with AMF in the treatments. Values of chlorophyll content, biomass and shoot phosphorus were not statistically different between the AMF and CTL treatments, after five months in the greenhouse. Inoculation with AMF significantly increased the levels of starch and soluble carbohydrates in shoots and roots of both species. Under field conditions, AMF had no effect on stem diameter and height after 12 and 24 months, but total plant biomass and leaf, stem and root biomass were greater in AMF than in CTL plants. The data indicated that AMF inoculation in the nursery has a strong effect on biomass accumulation after growing for 24 months under field conditions. Therefore, AMF inoculation should be considered an important strategy to increase growth and production of these economically important tropical palm species.

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Microbial processes have been used as indicators of soil quality, due to the high sensitivity to small changes in management to evaluate, e.g., the impact of applying organic residues to the soil. In an experiment in a completely randomized factorial design 6 x 13 + 4, (pot without soil and residue or absolute control) the effect of following organic wastes was evaluated: pulp mill sludge, petrochemical complex sludge, municipal sewage sludge, dairy factory sewage sludge, waste from pulp industry and control (soil without organic waste) after 2, 4, 6, 12, 14, 20, 28, 36, 44, 60, 74, 86, and 98 days of incubation on some soil microbial properties, with four replications. The soil microbial activity was highly sensitive to the carbon/nitrogen ratio of the organic wastes. The amount of mineralized carbon was proportional to the quantity of soil-applied carbon. The average carbon dioxide emanating from the soil with pulp mill sludge, corresponding to soil basal respiration, was 0.141 mg C-CO2 100 g-1 soil h-1. This value is 6.4 times higher than in the control, resulting in a significant increase in the metabolic quotient from 0.005 in the control to 0.025 mg C-CO2 g-1 Cmic h-1 in the soil with pulp mill sludge. The metabolic quotient in the other treatments did not differ from the control (p < 0.01), demonstrating that these organic wastes cause no disturbance in the microbial community.

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Studies on microbial activity and biomass in forestry plantations often overlook the role of litter, typically focusing instead on soil nutrient contents to explain plant and microorganism development. However, since the litter is a significant source of recycled nutrients that affect nutrient dynamics in the soil, litter composition may be more strongly correlated with forest growth and development than soil nutrient contents. This study aimed to test this hypothesis by examining correlations between soil C, N, and P; litter C, N, P, lignin content, and polyphenol content; and microbial biomass and activity in pure and mixed second-rotation plantations of Eucalyptus grandis and Acacia mangium before and after senescent leaf drop. The numbers of cultivable fungi and bacteria were also estimated. All properties were correlated with litter C, N, P, lignin and polyphenols, and with soil C and N. We found higher microbial activity (CO2 evolution) in litter than in soil. In the E. grandis monoculture before senescent leaf drop, microbial biomass C was 46 % higher in litter than in soil. After leaf drop, this difference decreased to 16 %. In A. mangium plantations, however, microbial biomass C was lower in litter than in soil both before and after leaf drop. Microbial biomass N of litter was approximately 94 % greater than that of the soil in summer and winter in all plantations. The number of cultivable fungi and bacteria increased after leaf drop, especially so in the litter. Fungi were also more abundant in the E. grandis litter. In general, the A. mangium monoculture was associated with higher levels of litter lignin and N, especially after leaf drop. In contrast, the polyphenol and C levels in E. grandis monoculture litter were higher after leaf drop. These properties were negatively correlated with total soil C and N. Litter in the mixed stands had lower C:N and C:P ratios and higher N, P, and C levels in the microbial biomass. This suggests more effective nutrient cycling in mixed plantations in the long term, greater stimulation of microbial activity in litter and soil, and a more sustainable system in general.

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Araucaria angustifolia (Bert.) O. Kuntze is the main component of the Mixed Ombrophilous forest and, in the State of São Paulo, it is associated with a high diversity of soil organisms, essential for the maintenance of soil quality, making the conservation of this ecosystem a major and pressing challenge. The objective of this study was to identify the physical and chemical properties that are most closely correlated with dehydrogenase enzyme activity, basal respiration and microbial biomass under native (NF) and replanted (RF) Araucaria angustifolia forests in three regions of the state of São Paulo, in winter and summer. The main differentiating factors between the areas were also determined. Each forest was represented by three true replications; at each site, from around the araucaria trees, 15 soil samples (0-20 cm) were collected to evaluate the soil physical, chemical and microbiological properties. At the same points, forest litter was sampled to assess mass and chemical properties. The following microbiological properties were evaluated: microbial biomass carbon (MBC), basal respiration (CO2-C), metabolic quotient (Q: CO2), dehydrogenase enzyme activity (DHA) as well as the physical properties (moisture, bulk density, macroporosity and total porosity), soil chemical properties [pH, organic carbon (org-C), P, Ca, K, Mg, Al, H+Al], litter dry mass, and C, N and S contents. The data were subjected to analysis of variance (TWO-WAY: ANOVA). A Canonical Discriminant Analysis (CDA) and a Canonical Correlation Analysis (CCA) were also performed. In the soil under NF, the values of K, P, soil macroporosity, and litter dry mass were higher and Q: CO2 and DHA lower, regardless of the sampling period, and DHA was lower in winter. In the RF areas, the levels of moisture, porosity and Q: CO2 were higher in both sampling periods, and DHA was higher in winter. The MBC was only higher under NF in the summer, while the litter contents of C, N and S were greater in winter. In winter, CCA showed a high correlation of DHA with CO2-C, pH and H+Al, while in the summer org-C, moisture, Mg, pH and litter C were more associated with DHA and CO2-C. The CDA indicated H+Al, available P, total porosity, litter S content, and soil moisture as the most discriminating variables between NF and RF, but moisture was the most relevant, in both seasons and CO2-C only in winter. The combined analysis of CCA and CDA showed that the contribution of the microbiological variables to a differentiation of the areas was small at both samplings, which may indicate that the period after reforestation was long enough to allow an almost complete recovery of the microbial activity.

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The sugarcane industry, a strategic crop in Brazil, requires technological improvements in production efficiency to increase the crop energy balance. Among the various currently studied alternatives, inoculation with diazotrophic bacteria proved to be a technology with great potential. In this context, the efficiency of a mixture of bacterial inoculant was evaluated with regard to the agronomic performance and N nutrition of sugarcane. The experiment was carried out on an experimental field of Embrapa Agrobiologia, in Seropédica, Rio de Janeiro, using a randomized block, 2 × 3 factorial design (two varieties and three treatments) with four replications, totaling 24 plots. The varieties RB867515 and RB72454 were tested in treatments consisting of: inoculation with diazotrophic bacteria, N-fertilized control with 120 kg ha-1 N and absolute control (no inoculation and no N fertilizer). The inoculum was composed of five strains of five diazotrophic species. The yield, dry matter accumulation, total N in the shoot dry matter and the contribution of N by biological fixation were evaluated, using the natural 15N abundance in non-inoculated sugarcane as reference. The bacterial inoculant increased the stalk yield of variety RB72454 similarly to fertilization with 120 kg ha-1 N in the harvests of plant-cane and first ratoon crops, however the contribution of biological N fixation was unchanged by inoculation, indicating that the benefits of the inoculant in sugarcane may have resulted from plant growth promotion.

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Integrated crop-livestock systems (ICLs) are a viable strategy for the recovery and maintenance of soil characteristics. In the present study, an ICL experiment was conducted by the Instituto Agronômico do Paraná in the municipality of Xambre, Parana (PR), Brazil, to evaluate the effects of various grazing intensities. The objective of the present study was to quantify the levels of microbial biomass carbon (MBC) and soil enzymatic activity in an ICL of soybean (summer) and Brachiaria ruziziensis (winter), with B. ruziziensis subjected to various grazing intensities. Treatments consisted of varying pasture heights and grazing intensities (GI): 10, 20, 30, and 40 cm (GI-10, GI-20, GI-30, and GI-40, respectively) and a no grazing (NG) control. The microbial characteristics analysed were MBC, microbial respiration (MR), metabolic quotient (qCO2), the activities of acid phosphatase, β-glucosidase, arylsuphatase, and cellulase, and fluorescein diacetate (FDA) hydrolysis. Following the second grazing cycle, the GI-20 treatment (20-cm - moderate) grazing intensity) contained the highest MBC concentrations and lowest qCO2 concentrations. Following the second soybean cycle, the treatment with the highest grazing intensity (GI-10) contained the lowest MBC concentration. Soil MBC concentrations in the pasture were favoured by the introduction of animals to the system. High grazing intensity (10-cm pasture height) during the pasture cycle may cause a decrease in soil MBC and have a negative effect on the microbial biomass during the succeeding crop. Of all the enzymes analyzed, only arylsuphatase and cellulase activities were altered by ICL management, with differences between the moderate grazing intensity (GI-20) and no grazing (NG) treatments.

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Maize is among the most important crops in the world. This plant species can be colonized by diazotrophic bacteria able to convert atmospheric N into ammonium under natural conditions. This study aimed to investigate the effect of inoculation of the diazotrophic bacterium Herbaspirillum seropedicae (ZAE94) and isolate new strains of plant growth-promoting bacteria in maize grown in Vitória da Conquista, Bahia, Brazil. The study was conducted in a greenhouse at the Experimental Area of the Universidade Estadual do Sudoeste da Bahia. Inoculation was performed with peat substrate, with and without inoculation containing strain ZAE94 of H. seropedicae and four rates of N, in the form of ammonium sulfate (0, 60, 100, and 140 kg ha-1 N). After 45 days, plant height, dry matter accumulation in shoots, percentage of N, and total N (NTotal) were evaluated. The bacteria were isolated from root and shoot fragments of the absolute control; the technique of the most probable number and identification of bacteria were used. The new isolates were physiologically characterized for production of indole acetic acid (IAA) and nitrogenase activity. We obtained 30 isolates from maize plants. Inoculation with strain ZAE94 promoted an increase of 14.3 % in shoot dry mass and of 44.3 % in NTotal when associated with the rate 60 kg ha-1 N. The strains N11 and N13 performed best with regard to IAA production and J06, J08, J10, and N15 stood out in acetylene reduction activity, demonstrating potential for inoculation of maize.

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The use of organic fertilizers and the inoculation of mycorrhizal fungi in the cultivation of oil crops is essential to reduce production costs and minimize negative impacts on natural resources. A field experiment was conducted in an Argissolo Amarelo (Ultisol) with the aim of evaluating the effects of fertilizer application and inoculation of arbuscular mycorrhizal fungi on the growth attributes of sunflower (Helianthus annuus L.) and on soil chemical properties. The experiment was conducted at the Federal University of Rio Grande do Norte, Brazil, using a randomized block design with three replicates in a 4 × 2 factorial arrangement consisting of four treatments in regard to application of organic fertilizer (liquid biofertilizer, cow urine, mineral fertilizer, and unfertilized control) and two treatments in regard to arbuscular mycorrhizal fungi (with and without mycorrhizal fungi). The results showed that the physiological attributes of relative growth rate and leaf weight ratio were positively influenced by fertilization, compared to the control treatment, likely brought about by the supply of nutrients from the fertilizers applied. The growth and productivity attributes were positively affected by mycorrhization.