ABSTRACT
Dynamic soil chemical interactions with conservation agricultural practices and soil biota are largely unknown. Therefore, this study aims to quantify long-term (12-yr) impacts of cover crops, poultry litter, crop rotations, no-tillage, and their interactions on dynamic soil properties and to determine their relationships with nutrient cycling, crop yield, and soil biodiversity (soil microbial and earthworm communities). Main effects were 13 different cropping sequences of soybean [ (L.) Merr.], corn ( L.), and cotton ( L.) at the Research and Education Center at Milan, TN, and eight sequences of corn and soybean at the Middle Tennessee Research and Education Center, Spring Hill, TN. Sequences were repeated in 4-yr phases from 2002 to 2014. Split-block cover crop treatments consisted of winter wheat ( L.), hairy vetch ( Roth), poultry litter, and a fallow control. Soil C and nutrient fluxes were calculated at surface (0-5 cm) and subsurface (5-15 cm) layers during Years 0, 2, 4, 8, and 12. After 12 yr, weighted means (0-15 cm) of soil pH, P, K, Ca, Mg, total N, and C were greater under poultry litter-amended soils compared with cover crops ( < 0.05). In addition, continuous corn sequences resulted in greater soil K, N, and C concentrations than soybean-soybean-corn-corn rotations ( < 0.05). Poultry litter treatments were positively correlated with greater soil fertility levels, as well as higher crop yield and soil biodiversity. These results underscore linkages between manure additions and cropping sequences, within the nutrient cycling, soil health, and crop production continuum.
Subject(s)
Agriculture/methods , Fertilizers , Soil/chemistry , Animals , PoultryABSTRACT
[This corrects the article DOI: 10.1371/journal.pone.0146651.].
ABSTRACT
The Lone Star tick, Amblyomma americanum, transmits several bacterial pathogens including species of Anaplasma and Ehrlichia. Amblyomma americanum also hosts a number of non-pathogenic bacterial endosymbionts. Recent studies of other arthropod and insect vectors have documented that commensal microflora can influence transmission of vector-borne pathogens; however, little is known about tick microbiomes and their possible influence on tick-borne diseases. Our objective was to compare bacterial communities associated with A. americanum, comparing Anaplasma/Ehrlichia -infected and uninfected ticks. Field-collected questing specimens (n = 50) were used in the analyses, of which 17 were identified as Anaplasma/Ehrlichia infected based on PCR amplification and sequencing of groEL genes. Bacterial communities from each specimen were characterized using Illumina sequencing of 16S rRNA gene amplicon libraries. There was a broad range in diversity between samples, with inverse Simpson's Diversity indices ranging from 1.28-89.5. There were no statistical differences in the overall microbial community structure between PCR diagnosed Anaplasma/Ehrlichia-positive and negative ticks, but there were differences based on collection method (P < 0.05), collection site (P < 0.05), and sex (P < 0.1) suggesting that environmental factors may structure A. americanum microbiomes. Interestingly, there was not always agreement between Illumina sequencing and PCR diagnostics: Ehrlichia was identified in 16S rRNA gene libraries from three PCR-negative specimens; conversely, Ehrlichia was not found in libraries of six PCR-positive ticks. Illumina sequencing also helped identify co-infections, for example, one specimen had both Ehrlichia and Anaplasma. Other taxa of interest in these specimens included Coxiella, Borrelia, and Rickettsia. Identification of bacterial community differences between specimens of a single tick species from a single geographical site indicates that intra-species differences in microbiomes were not due solely to pathogen presence/absence, but may be also driven by vector life history factors, including environment, life stage, population structure, and host choice.
