The abundance and distribution of soil microbial populations, i.e., microbial diversity is widely promoted as a key tenant of sustainable agricultural practices and/or soil health. A common approach ...to describing microbial diversity is phylogenetic analysis with high-throughput sequencing of microbial DNA. However, owing to the tremendous amounts of data generated, a continuing effort is required to better assess the effects of agricultural management systems on soil microbial diversity. Here, we report on the combined effects of management systems on bacterial and fungal diversity in a loessal agricultural soil located in north-central Mississippi, USA. Amplicon sequencing was performed using 16S rRNA-gene and ITS2 from soil samples collected from a three-year study with combinations of maize-soybean crop rotation, tillage practices, and winter vegetative covers. Differences were found in microbial fungal β-diversity among the management systems, with distinct clustering patterns for no-tillage combined with either winter weeds or bare-fallow. Management systems showed a significant influence on soil pH and bulk density, which were positively correlated with fungal community composition. Developments in the description and interpretation of soil microbial diversity will contribute to a more accurate understanding of its role in the various functions and processes important to agricultural soil management.
Soil biological properties are important for the stabilization and preservation of a good soil structure. Management practices can affect the diversity and population of microorganisms, which could ...beneficially change soil properties and promote a more sustainable dryland crop production. This study was established near Pontotoc, MS, USA (34°07′ N, 88°59′ W) on an Atwood silt loam (fine-silty, mixed, semiactive, thermic Typic Paleudalf) to evaluate the impacts of cover crops, planting dates and fertilizer sources (poultry litter, inorganic fertilizer and no fertilizer) on selected biologically related soil properties in a no-tillage, dryland soybean production. Soil analyses included total carbon and nitrogen, permanganate oxidizable carbon (POXC), easily extractable glomalin-related soil protein (EE-GRSP), water stable aggregate (WSA) and soil pH. Cover crop production and soybean yield were also determined. The results indicated that the fertilizer source had an impact on total nitrogen, EE-GRSP and soybean yield. Total N was 6% higher with poultry litter at the early planting date compared to no fertilizer (control) (p < 0.0018) and at the late planting date, when total N and EE-GRSP were increased by 11% and 13%, respectively, with poultry litter compared to no fertilizer. Additionally, soil pH was reduced by 0.25 units in the poultry litter-amended treatment. Soybean yield was increased by 68% and 51% in early-planted soybean and 42% and 40% in late-planted soybean with poultry litter and inorganic fertilizer, respectively, compared to no fertilizer. This study revealed that biological soil properties and soybean yield were influenced by poultry litter application. The results showed no significant effects of cover crops over the short time period of the study.
Conservation alternatives that include no-tillage (NT) and cover crops (CCs) reduce soil erosion in row-crop agroecosystems. However, little information is available about how these alternatives ...affect soil textural properties responsible for soil fertility. This study evaluated the soil particle size distribution and volumetric water content after three years of consistent management in a raised bed system. There were four treatment systems in a dryland maize/soybean rotation on a silt loam soil (Oxyaquic Fraglossudalfs) that included: NT + CCs, conventional tillage (CT) + CCs, CT + winter weeds, and CT + bare soil in winter in northwest Mississippi. The NT + CC system retained 62% more coarse sand in the furrow than the other systems (2.1% compared to 1.3%; p = 0.02). Regardless of the location, the NT + CC system (2.5%) retained 39% more fine sand than the CT + CC system (1.8%; p = 0.01), suggesting that coarse and fine sands were being trapped in furrows combining NT + CC systems, minimizing their off-site transport. In furrows, CCs increased soil volumetric water content by 47% compared to other winter covers. In beds, NT + CCs increased bed water contents by 20% compared to CT + CCs (17.1 to 14.3%; p < 0.01). Implementing conservation alternatives may promote the retention of sand fractions in silty loam soils that are important in supporting soil fertility and crop sustainability.
The response of soil microbial communities to management practices is composite, as it depends on the various environmental factors which contribute to a shift in the microbial communities. In this ...study we explored the impact of combinations of soil management practices on microbial diversity and community composition in a dryland soybean production system. Soil samples were collected from the experimental field maintained under no till, cover crops, and fertility treatments, at Pontotoc Ridge-Flatwoods Branch Experiment Station, MS, USA. Targeted amplicon sequencing of 16S rRNA and ITS2 genes was used to study the bacterial and fungal community composition. Poultry litter amendment and cover crops significantly influenced soil bacterial diversity. Fertilizer sources had significantly different bacterial communities, as specific microbial taxa were strongly influenced by the changes in the nutrient availability, while cover crops influenced the soil fungal community differences. Differential enrichment of advantageous bacterial (Proteobacteria, Actinobacteria and Acidobacteria) and fungal (Mortierellomycota) phyla was observed across the treatments. Soil pH and easily extractable glomalin-related soil proteins (EE-GRSP) were correlated with bacterial communities and aggregate stability (WSA) was influenced by the poultry litter amendment, thus driving the differences in bacterial and fungal communities. These findings suggest that a long-term study would provide more inferences on soil microbial community response to management changes in these dryland soybean production systems.
Microbial diversity patterns have been surveyed in many different soils and ecosystems, but we are unaware of studies comparing similar soils developing from similar parent materials in contrasting ...climates. In 2008, developmental chronosequences with ages ranging from 105 to 500,000 years across Georgia (GA) and Michigan (MI) were studied to investigate how bacterial community composition and diversity change as a result of local environmental gradients that develop during pedogenesis. Geographic factors were studied between and within locations spanning two scales: (1) regionally between 0.1 and 50 and (2) ~1700 km apart. The diversity was surveyed using high-throughput pyrosequencing, and variance partitioning was used to describe the effects of spatial, environmental, and spatio-environmental factors on bacterial community composition. At the local scale, variation in bacterial communities was most closely related to environmental factors (rM = 0.59, p = 0.0001). There were differences in bacterial communities between the two locations, indicating spatial biogeography. Estimates of bacterial diversity were much greater in MI (numbers of OTU, ACE, and Chao1) and remained 2–3× greater in MI than GA after removing the effect of soil properties. The large differences in diversity between geographically separated bacterial communities in different climates need further investigation. It is not known if the rare members of the community, which contributed to greater bacterial diversity in GA relative to MI, play an important role in ecosystem function but has been hypothesized to play a role in ecosystem resiliency, resistance, and stability. Further research on the link between bacterial diversity and spatial variability related to climate needs further investigation.
Soil bacterial and fungal community compositions have a significant influence on plant community structure and diversity because of their key role in nutrient cycles in the soil. Studies conducted on ...microbial diversity in relation to soil development could provide insight on how changes in microbial community structure influence ecosystem functions. Soil chronosequences are excellent systems for evaluating soil genesis, nutrient availability and biologically significant elements and their implications for ecosystem functioning. This study was conducted to assess the changes in soil bacterial and fungal communities associated with the dynamics of soil physico-chemical and vegetative characteristics along a sand chronosequence by using phospholipid fatty acid (PLFA) profiling. Soil samples were collected and analyzed from different successional stages in a soil chronosequence with ages ranging from 105 years to 4010 years. The results showed that soil microbial PLFAs changed significantly with increasing soil age. Bacterial PLFAs were higher in younger soils while the old soils had higher fungal PLFAs. Correlation analysis showed that plant community composition had the strongest correlation with soil microbial community structure, followed by soil pH. This could be attributed to a shift in nutrient concentration and quality of the litter inputs along the chronosequence. The results showed that there was a close relationship between plant succession and pH in shaping the soil microbial communities along the soil development gradient.
•We studied changes in soil bacterial and fungal community structure along a soil chronosequence.•We used PLFA profiling to characterize the soil microbial communities.•We observed higher bacterial abundance in younger soils and fungal abundance in older soils.•Plant community distribution and soil pH had the strongest effect on the PLFA profile of soil microbial communities.
Our understanding on the effects of tillage intensity on the soil microbial community structure and composition in crop production systems are limited. This study evaluated the soil microbial ...community composition and diversity under different tillage management systems in an effort to identify management practices that effectively support sustainable agriculture. We report results from a three-year study to determine the effects on changes in soil microbial diversity and composition from four tillage intensity treatments and two residue management treatments in a corn-soybean production system using Illumina high-throughput sequencing of 16S rRNA genes. Soil samples were collected from tillage treatments at locations in the Southern Coastal Plain (Verona, MS, USA) and Southern Mississippi River Alluvium (Stoneville, MS, USA) for soil analysis and bacterial community characterization. Our results indicated that different tillage intensity treatments differentially changed the relative abundances of bacterial phyla. The Mantel test of correlations indicated that differences among bacterial community composition were significantly influenced by tillage regime (rM = 0.39, p ≤ 0.0001). Simpson’s reciprocal diversity index indicated greater bacterial diversity with reduction in tillage intensity for each year and study location. For both study sites, differences in tillage intensity had significant influence on the abundance of Proteobacteria. The shift in the soil bacterial community composition under different tillage systems was strongly correlated to changes in labile carbon pool in the system and how it affected the microbial metabolism. This study indicates that soil management through tillage intensity regime had a profound influence on diversity and composition of soil bacterial communities in a corn-soybean production system.
The metabolic diversity of soil microbiota embodies diverse functional capabilities that support ecosystem resilience, driving essential biogeochemical processes and facilitating the optimization of ...sustainable agricultural systems. Integrating cover crops into agricultural systems cultivates a diverse array of metabolic activities among soil microbes, synergistically enhancing ecosystem services and bolstering soil health for sustainable and productive farming practices. In an effort to gain deeper insights and expand our knowledge, we conducted a study examining the effects of cover crops and fertilizer sources, thereby shedding light on their combined impacts on the metabolic activity dynamics of soil microbial communities. In this investigation, we employed a split-plot design with two factors: (a) cover crop with three solo cover crop species—Cereal rye (Secale cereale), wheat (Triticum aestivum), hairy vetch (Vicia villosa), and one mixture of mustard (Brassica rapa) and cereal rye (Secale cereale) (CC-mix), (b) Fertilizer source includes poultry litter, chemical fertilizer, and no-fertilizer treatments. We assessed the metabolic potential of soil microbiota by using carbon substrates utilizing Biolog EcoPlates. The findings revealed that the plots with CC-mix treatment exhibited greater metabolic diversity compared to the other treatments, while among the fertilizer sources, poultry litter demonstrated higher metabolic activity. Furthermore, both treatment factors predominantly metabolized carbohydrates and polymers compared to other carbon substrate categories. The principal component analysis accounted for 46.4% of the variance, collectively represented by PC1 and PC2, emphasizing the substantial contributions of carbohydrates, amino acids, and carboxylic acids to the observed metabolic diversity. Canonical correspondence analysis revealed that pH had positively correlated with microbial functional diversity, whereas total carbon (TC), total nitrogen (TN), and water-stable aggregates (WSA) showed a negative correlation. In conclusion, cover cropping and type of fertilizer source had a notable impact on soil microbial functional diversity, with the cover crop mixture exhibiting a more pronounced influence than the individual cover crop treatments.
Highly delaminated poly(dicyclopentadiene)/clay nanocomposites were synthesized by in situ polymerization of dicyclopentadiene/organically modified montmorillonite clay dispersions. ...Dicyclopentadiene/clay suspensions were sonicated for various times to enhance the degree of delamination prior to curing. The d spacings of the clay in nanocomposites were monitored using X-ray diffraction (XRD), and the extent of delamination was examined by transmission electron microscopy (TEM) and preliminary neutron scattering studies. A new approach, use of confocal laser microscopy, was employed to follow the dispersion of clay layers, tagged by a fluorescent dye, within the liquid monomer. It is evident that XRD cannot be used alone as a criterion for exfoliation. TEM showed that increasing the clay concentration at constant sonication gave an increase in average tactoid size. The largest improvement in composite mechanical properties occurred at clay loading levels (0.5−1 wt %). Significant increases in T g, elastic bending moduli, flexural moduli, and flexural strengths were found at 0.5−1 wt % clay loadings, where the highest degree of delamination/exfoliation also occurred.
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