Poultry litter (PL) is a by-product of broiler production. Most PL is land applied. Land-applied PL is a valuable nutrient source for crop production but can also be a route of environmental contamination with manure-borne bacteria. The objective of this study was to characterize the fate of pathogens, fecal indicator bacteria (FIB), and bacteria containing antibiotic resistance genes (ARGs) after application of PL to soils under conventional till or no-till management. This 2-yr study was conducted in accordance with normal agricultural practices, and microbial populations were quantified using a combination of culture and quantitative, real-time polymerase chain reaction analysis. Initial concentrations of in PL were 5.4 ± 3.2 × 10 cells g PL; sp. was not detected in the PL but was enriched periodically from PL-amended soils. was detected in PL (1.5 ± 1.3 × 10 culturable or 1.5 ± 0.3 × 10 genes g) but was rarely detected in field soils, whereas enterococci (1.5 ± 0.5 × 10 cells g PL) were detected throughout the study. These results suggest that enterococci may be better FIB for field-applied PL. Concentrations of ARGs for sulfonamide, streptomycin, and tetracycline resistance increased up to 3.0 orders of magnitude after PL application and remained above background for up to 148 d. These data provide new knowledge about important microbial FIB, pathogens, and ARGs associated with PL application under realistic field-based conditions.

Confined animal feeding operations can facilitate the spread of genes associated with antibiotic resistance. It is not known how cattle removal from beef cattle backgrounding operation affects the persistence of antibiotic resistance genes (ARGs) in the environment. We investigated the effect of cessation of beef cattle backgrounding operation on the persistence and distribution of ARGs in the beef cattle backgrounding environment. The study was conducted at a pasture-feedlot type beef cattle backgrounding operation which consisted of feeding and grazing areas that were separated by a fence with an access gate. Backgrounding occurred for seven years before cattle were removed from the facility. Soil samples (n = 78) from 26 georeferenced locations were collected at the baseline before cattle were removed, and then one year and two years after cattle were removed. Metagenomic DNA was extracted from the soil samples and total bacterial population (16S rRNA), total Enterococcus species and class 1 integrons ( int I1), and erythromycin ( erm B and erm F), sulfonamide ( sul 1 and sul 2) and tetracycline ( tet O, tet W and tet Q) resistance genes were quantified. Concentrations of total bacteria, Enterococcus spp., class 1 integrons, and ARGs were higher in the feeding area and its immediate vicinity (around the fence and the gate) followed by a gradient decline along the grazing area. Although the concentrations of total bacteria, Enterococcus spp., class 1 integrons and ARGs in the feeding area significantly decreased two years after cattle removal, their concentrations were still higher than that observed in the grazing area. Higher concentrations over two years in the feeding area when compared to the grazing area suggest a lasting effect of confined beef cattle production system on the persistence of bacteria and ARGs in the soil.

Soil salinity encroachment is an increasing concern in many irrigated lands, because of the undesirable effects of soluble salts on agricultural production and on water quality. From this point of 10 view, the design and management of irrigation districts can be evaluated by monitoring the soil salinity.There are few cases in the world where comparisons can be undertaken from 'historic' data sets for extents other than individual plots. We demonstrate a monitoring procedure using electromagnetic induction (EMI) survey in an irrigated district in Spain. This district is the only one having an established soil salinity baseline. The EMI data acquired at the same plots were converted to soil 15 electrical conductivity by calibrating with augered soil samples. The presented calibrations improve the baseline for future comparisons and for the treatment and understanding of new acquisitions of field data in next surveys. A shortcoming inherent to destructive soil sampling is its potential for biasing effects on long-term monitoring of soil salinity by means of GPS or other means of accurate localization and relocalization of soil sampling, the herein called "localization paradox", rarely treated 20 in scientific papers. The localization paradox is relevant for any variable soil property requiring repeated sampling. This issue is discussed, and a way for its overcoming by using EMI readings displaced from the augering is presented. EMI needs calibration with a reduced number of soil samples analyzed in the lab. The adoption of our data treatment procedures will facilitate soil salinity monitoring. 25

Beef cattle backgrounding operations that grow out weaned calves for feedlot finishing contain several environmentally significant constituents. A better understanding of these constituents and their environmental distribution will aid in the development of effective management guidelines for sustainable beef production. This research investigated soil nutrients, bacterial, and veterinary pharmaceutical concentrations across a small backgrounding beef feedlot on a karst landscape. Results indicated that all contaminants were highly concentrated in the feeder area (FD) and were lower in the other feedlot areas. The FD soils had a pH of 8.2, 59 mg kg soil organic matter (SOM), 2002 mg kg soil test phosphorus (STP), 99.7 mg kg NH-N, and 18.3 mg kg NO-N. The other locations were acidic (5.9-6.9 pH) and contained 39 mg kg SOM, 273 mg kg STP, 21.5 mg kg NH-N, and 2.0 NO-N mg kg. Bacteria populations in the FD averaged 2.7 × 10 total cells, 3.9 × 10 spp., 2.9 × 10 spp, and 4.5 × 10 cells per gram of soil. spp. and spp. concentrations were 1 to 4 orders of magnitude lower at the other locations. showed lower dynamic range and was generally uniformly distributed across the landscape. Antibiotic and parasiticide concentrations in the FD were 86.9 ng g monensin, 25.0 ng g lasalocid, and 10.3 ng g doramectin. Their concentrations were 6- to 27-fold lower in the other feedlot locations. Contaminant management plans for this small feedlot will therefore focus on the feeder and nearby grazing areas where soil nutrients, bacteria populations, and veterinary pharmaceuticals were most concentrated.

Cow-calf production plays a significant role in the beef production chain. However, it is not typically monitored for antimicrobial resistance (AMR). We determined the baseline level of bacterial AMR in pre-weaned calves prior to feedlot entry and evaluated wheat grazing and age effects on their occurrence. Two grazing experiments, with 16 cow-calf pairs each, were conducted on tall fescue or wheat. Fecal samples were cultured for the detection of tetracycline (TETr )-, 3rd generation cephalosporin (3GCr )-resistant, and extended spectrum β-lactamase (ESBL) producing E. coli. Isolates were characterized for resistance to other antibiotics and resistance mechanisms. Concentration (P <0.001) and prevalence (P =0.007) of TETr E. coli were significantly higher in the claves (5.1 log10 CFU/g and 93%, respectively) than in the cows (4.4 log10 CFU/g and 80%, respectively). Wheat grazing did not affect TETr E. coli phenotypically however, it significantly (P =0.005) expanded the resistant population carrying tet(A) over tet(B). Fecal prevalence of 3GCr- and ESBL producing-E.coli was 31.3% and 3.4%, respectively with no significant effects of age (P =0.340) or wheat grazing (P =0.597). All 3GCr – and ESBLs producing- E. coli isolates were multidrug resistant. 3GCr were positive for blaCMY-2 (73%) or blaCTX-M (27%) and blaCTX-M-15 was the most prevalent (94%, n=17) among the CTX-M positive isolates. Wheat grazing significantly (P <0.001) expanded 3GCr population carrying blaCTX-M while reducing the blaCMY-2 carrying population. Five of the seven ESBL producing E. coli isolates were positive for blaCTX-M. Our study found age-dependent occurrence of TETr E. coli, and that wheat grazing expanded the resistant population carrying certain resistance mechanisms over others. Cow-calf production is a significant reservoir for antibiotic resistant bacteria of significant public health importance such as 3GCr- and CTX-M type ESBLs producing-E. coli.