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The meals after oil extraction from many oilseed crops have nutrition and biofumigation potential for land application. Oilseed meal (SM) from the dedicated bioenergy crop Jatropha curcas were implicated to contain compounds that have antibacterial properties on some soil pathogens. However, little is known about its effect on non-targeted soil microbial community, especially on fungi. SM from Camelina sativa contains moderate level of glucosinolates (GLS) and was under studied. To investigate soil fungal community responses to jatropha and camelina SMs, we conducted a lab based microcosm study, amending soil with 1% SMs of jatropha, camelina, flax, and biomass of wheat straw. Fungal community abundance and structure were analyzed based on the ITS region using qPCR and tag-pyrosequencing. Microbial functional changes were examined by community level physiological profile (CLPP) using Biolog assay. Both SMs from jatropha and camelina showed biofumigant properties and inhibited fungal proliferation. Jatropha SM significantly altered soil fungal community structures with lower fungal biodiversity and higher Chaetomium composition. Camelina SM amended soil promoted Fusarium proliferation. CLPP indicated sequential hierarchy for C metabolism in the oilseed-amended microcosms was generally complex C > phosphate-associated C > carboxylic acids > carbohydrates > amines > amino acids. No significant difference in CLPP was detected due to the type of SM treatment. Our data indicate that both SMs of jatropha and camelina have biofumigant properties and can differentially impact soil microbial communities, and the changes were relatively persistent over time. Microbial functional patterns on the other side were not impacted by SM type. Our study revealed biofumigant and nutritional influence of SMs from dedicated biofuel plants on soil microbial community. This information will help properly using jatropha and camelina SMs for pathogen control while minimizing their negative impacts on non-target microorganisms. However, further studies in the field are demanded to investigate their influences in real practice.

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Developing sustainable management practices including appropriate residue removal and nitrogen (N) fertilization for bioenergy sorghum is critical. However, the effects of residue removal and N fertilization associated with bioenergy sorghum production on soil organic carbon (SOC) are less studied compared to other crops. The objective of our research was to assess the impacts of residue removal and N fertilization on biomass yield and SOC under biomass sorghum production. Field measurements were used to calibrate the DNDC model, then verified the model by comparing simulated results with measured results using the field management practices as agronomic inputs. Both residue removal and N fertilization affected bioenergy sorghum yields in some years. The average measured SOC at 0-50 cm across the treatments and the time-frame ranged from 47.5 to 78.7 Mg C ha-1, while the simulated SOC was from 56.3 to 67.3 Mg C ha-1. The high correlation coefficients (0.65 to 0.99) and low root mean square error (3 to 18) between measured and simulated values indicate the DNDC model accurately simulated the effects of residue removal with N fertilization on bioenergy sorghum production and SOC. The model predictions revealed that there is, in the long term, a trend for higher SOC under bioenergy sorghum production regardless of residue management.

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The meals from many oilseed crops have potential for biofumigation due to their release of biocidal compounds such as isothiocyanates (ITCs). Various ITCs are known to inhibit numerous pathogens; however, much less is known about how the soil microbial community responds to the different types of ITCs released from oilseed meals (SMs). To simulate applying ITC-releasing SMs to soil, we amended soil with 1% flax SM (contains no biocidal chemicals) along with four types of ITCs (allyl, butyl, phenyl, and benzyl ITC) in order to determine their effects on soil fungal and bacterial communities in a replicated microcosm study. Microbial communities were analyzed based on the ITS region for fungi and 16S rRNA gene for bacteria using qPCR and tag-pyrosequencing with 454 GS FLX titanium technology. A dramatic decrease in fungal populations (~85% reduction) was observed after allyl ITC addition. Fungal community compositions also shifted following ITC amendments (e.g., Humicola increased in allyl and Mortierella in butyl ITC amendments). Bacterial populations were less impacted by ITCs, although there was a transient increase in the proportion of Firmicutes, related to bacteria know to be antagonistic to plant pathogens, following amendment with allyl ITC. Our results indicate that the type of ITC released from SMs can result in differential impacts on soil microorganisms. This information will aid selection and breeding of plants for biofumigation-based control of soil-borne pathogens while minimizing the impacts on non-target microorganisms.

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Demand for alternative fuels has sparked renewed interest in the production of biodiesel from oil-rich seeds. Oilseed meals are a byproduct of this process, and given their relatively high nutrient content, land application represents a potential value-added use. In this microcosm-based study, soil microbial community responses to amendments of a glucosinolate-containing brassicaceous oilseed meal (Brassica juncea, mustard), a non-glucosinolate-containing, nonbrassicaceous oilseed meal (Linum usitatissimum, flax), and a nonoilseed biomass (Sorghum bicolor) were characterized using a 28-day time series of replicated 16S rRNA gene and fungal ITS gene sequence libraries. We hypothesized that biomass type and glucosinolate content would alter community composition but that effects would diminish over time. Distinct separation occurred by amendment type, with mustard inducing large increases in the abundance of bacterial taxa associated with fungal disease suppression (e.g. Bacillus, Pseudomonas, and Streptomyces spp.). Dramatic shifts were seen among the fungi, too, with phylotype richness decreasing by > 60% following mustard addition. Changes in bacterial and fungal community composition were rapid, and distinct community types persisted throughout the study. Oilseed amendment, and mustard in particular, has the potential to alter soil microbial community structure substantially, and such changes are likely to be important in the context of ecosystem health.

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Laboratory experiments were conducted to describe the influence of glyphosate and fluometuron on soil microbial activity and to determine the effect of glyphosate on fluometuron degradation in soil and by Rhizoctonia solani. Soil and liquid medium were amended with formulated fluometuron alone or with two rates of formulated glyphosate. The soil carbon mineralization was measured hourly for 33 days. The fluometuron remaining in the soil was quantified following 3, 6, 10, 15, 20, 30, and 40 days of incubation. The fluometuron remaining in medium and fungal biomass was measured after 1, 3, 6, 10, 15, and 20 days of incubation. The addition of glyphosate with fluometuron increased C-mineralization and increased the rate of fluometuron degradation relative to fluometuron applied alone. However, more fluometuron remained in the media and less fungal biomass was produced when glyphosate was included.

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Compost application to turfgrass soils may increase dissolved organic C (DOC) levels which affects nutrient dynamics in soil. The objectives of this study were to investigate the influence of compost source and application rate on soil organic C (SOC), DOC, NO(3), and available P during 29 months after a one-time application to St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Compost sources had variable composition, yet resulted in few differences in SOC, DOC, and NO(3) after applied to soil. Available NO(3) rapidly decreased after compost application and was unaffected by compost source and application rate. Available P increased after compost application and exhibited cyclical seasonal patterns related to DOC. Compost application decreased soil pH relative to unamended soil, but pH increased during the course of the study due to irrigation with sodic water. Increasing the compost application rate increased SOC by 3 months, and levels remained fairly stable to 29 months. In contrast, DOC continued to increase from 3 to 29 months after application, suggesting that compost mineralization and growth of St. Augustinegrass contributed to seasonal dynamics. Dissolved organic C was 75%, 78%, and 101% greater 29 months after application of 0, 80, and 160 Mg compostha(-1), respectively, than before application. Impacts of composts on soil properties indicated that most significant effects occurred within a few months of application. Seasonal variability of SOC, DOC, and available P was likely related to St. Augustinegrass growth stages as well as precipitation, as declines occurred after precipitation events.

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Compost application to turfgrasses can increase plant-available nutrient concentrations in soil and improve growth, but may alter micronutrient dynamics and increase leaching and runoff losses. The objectives of this study were to investigate the influence of compost on the seasonal dynamics of plant-available Mn, Fe, Cu, and Zn in soil after a single application to bermudagrass [Cynodon dactylon (L.) Pers.] turf. Extractable Mn increased from 270 to 670 mg kg(-1) and Cu from 0.36 to 9.89 mg kg(-1) from 0 to 29 months. In contrast, extractable Fe and Zn decreased by 52% and 57% during the same time period. Seasonal trends in extractable Mn and Cu were closely related to dissolved organic C (DOC), and appeared influenced by bermudagrass growth and dormancy patterns and subsequent impacts on DOC. Losses of Mn and Cu from the soil surface occurred after high levels of precipitation during winter dormancy but not during the growing season, while Fe and Zn exhibited an opposite pattern. Thus, seasonal variation of soil micronutrients was likely related to seasonal patterns of bermudagrass growth and dormancy and their effects on DOC, and precipitation events which probably leached DOC and complexed nutrients from surface soil. Composts only influenced the magnitude of changes in micronutrient concentrations, as similar seasonal trends occurred for both compost-amended and unamended soils.

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Adoption of glyphosate-based weed control systems has led to increased use of the herbicide with continued use of additional pesticides. Combinations of pesticides may affect soil microbial activity differently than pesticides applied alone. Research was conducted to evaluate the influence of glyphosate-based cotton pest management systems on soil microbial activity. Soil was treated with commercial formulations of trifluralin, aldicarb, and mefenoxam + pentachloronitrobenzene (PCNB) with or without glyphosate (applied as Roundup WeatherMax). The soil microbial activity was measured by quantifying C and N mineralization. Soil microbial biomass was determined using the chloroform fumigation-incubation method. Soils treated with glyphosate alone exhibited greater cumulative C mineralization 30 days after treatment than all other treatments, which were similar to the untreated control. The addition of Roundup WeatherMax reduced C mineralization in soils treated with fluometuron, aldicarb, or mefenoxam + PCNB formulations. These results indicate that glyphosate-based herbicides alter the soil microbial response to other pesticides.

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