Biosolids and livestock manure are valuable high-carbon soil amendments, but they commonly contain antibiotic residues that might persist after land application. While composting reduces the concentration of extractable antibiotics in these materials, if the starting concentration is sufficiently high then remaining residues could impact microbial communities in the compost and soil to which these materials are applied. To examine this issue we spiked biosolids compost feedstock with ciprofloxacin at a concentration (19 ppm), approximately 5-fold higher than normally detected by LC-MS/MS (1-3.5 ppm). This feedstock was placed into mesh bags that were buried in aerated compost bays. Once a week a set of bags was removed and analyzed (treated and untreated, three replicates of each; 4 weeks). Addition of ciprofloxacin had no effect on recovery of resistant bacteria at any time point (P = 0.86), and a separate bioassay showed that aqueous extractions from materials with an estimated 59 ppm ciprofloxacin had no effect on the growth of a susceptible strain of E. coli (P = 0.28). Regression analysis showed that growth of the susceptible strain was diminished when compost was spiked with a wide range of ciprofloxacin (0-160 ppm; P<0.007), consistent with adsorption as the primary mechanism of antibiotic sequestration. Because bioassays reflect the bioavailability of residues whereas analytical assays do not, we recommend that similar bioassays be incorporated into studies of other antibiotic residues to better assess the risk that these residues pose for proliferating resistant populations of bacteria.
Author
Youngquist, Caitlin caitlinmp@gmail.com University of Wyoming
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This study measured in situ relative soil N mineralization rates (flux) during three growing seasons of continuous no-till (2013 and 2014) corn in Carrington, ND. We applied fresh (FM) and composted beef feedlot manure (CM) only once in spring 2012 at N rates of 90, 180, and 240lbs/A as FM, and 90 and 180lbs as CM. These rates were applied based on the calculation that 50% of N from FM and 25% of N from CM, would be available the first year. Other treatments were urea at 90, 150, 180, and 240lbs N/A, plus a check at 0lbs/A. In 2013 and 2014 urea was applied to respective plots, based on soil test, to raise the N levels to the respective 2012 N levels. We used the randomized complete block design with four replicates. Three replicates were used to measure soil N (NO3- + NH4+) mineralization rates bi-monthly with Plant Root Simulator probes (PRS™), from the urea fertilized and manured plots at the 0, 90 and 180lb levels at 4-6 leaf growth stage. Four pairs of PRS™ probes were buried in the top 6 inches near corn roots and replaced every two weeks for four sampling dates. We measured yields, protein content, and N uptake.
Yields were generally low in all three years of this study, well below the average for this region. Bi-monthly N mineralization was significantly higher as N increases with urea as N source during the early sampling dates (Figures 2 and 3) and subsequently declined to similar levels as the manure treatments. It is therefore possible that the plants benefited from higher early uptake of N from urea up to the early stages of peak corn N uptake but not enough to produce significantly higher yields than the manure treatments. Analysis of variance showed no significant treatment effects for yields in 2012 (α = 0.05) but grain protein differences were significant. These differences were observed only between the check and 180 lbs N in 2012. The highest mean grain yield was recorded with the 90 lbs N treatment where, the residual soil N at planting was just 33 lbs. The protein level was also significantly higher than the check and CM plot that received 180 lbs N in 2012, and with a soil residual N prior to 2013 planting, at 35 lbs. Each year, grain yields responded positively to N rates (applied as urea) and residual N levels from FM but not with CM. Since corn was grown for three continuous years, unsurprisingly yields declined with years of production since N was not applied to the FM and CM treatments after first application in year one. Similarly, yield decline was observed with urea over the three years but not as steep as the FM and CM treatments. The FM at 240 lbs N, and urea at 180 and 240 lbs treatments produced significantly higher grain protein than the check in 2012 (data not shown). Lower N mineralization and very likely, lower N availability was observed with the CM treatments especially at 180 lbs N, which consistently scored the lowest mean yield and protein in 2013 and 2014. Grain yields were consistently higher at 90 lbs N than 180 lbs N with the CM treatment. 
Summer droughts of 2012 and 2013 at this site and possibly, factors associated with continuous corn production (e.g. disease, temporal N immobilization) compounded the effects of urea treatments even though N uptake was consistently higher with urea. Total N taken up in corn grains from the FM and CM treatments increased with N rates but decreased with time (Table 1). From this study, corn grains took up more N from the plots treated with FM than the CM over the three-year period of the study. Subsequent changes in soil conditions such as moisture, N leaching, temperature, can sometimes limit the efficiency of inorganic fertilizer uses, and favoring low cost alternative uses such as manure especially if the prevailing conditions enhance N mineralization from manure or soil organic matter. Based on N input plus soil N status at the beginning of planting every year, corn N uptake efficiency was in the order: Check>FM>CM>Urea, with efficiency decreasing at higher N rates. The minimum proportion of grain N uptake by any treatment to the single highest N uptake for any urea-N treatment (considered as a reference) in a given year, was 42% for the check in 2013.
Applying livestock manure from lagoon storage through center pivot irrigation has long been considered a low-labor, uniform method of application that can deliver nutrients in-season to a growing crop. Three challenges with this system have been odor, pivot nozzle clogging and loss of nitrogen. A new innovation in lagoon treatment addresses these challenges. Low-power circulators were installed at a Northeast Nebraska commercial hog finishing facility and used to aerate the lagoon by moving oxygen-rich water and beneficial microbes to the bottom of the lagoon, reducing odor and potent greenhouse gases while lowering disease pathogen risk. This process preserved nitrogen and made it 40-60% more available in the first year of application. Circulation also reduced lagoon solids and bottom sludge, resulting in reduced agitation and dredging expense. Having a continuously well-mixed lagoon facilitated accurate manure nutrient sampling and consistent nutrient concentration delivery to the irrigation system. Combined with the ease of calibration of the center pivots, precision uniform nutrient application was achieved. Center pivot application had several additional advantages over tractor-based systems: less soil compaction, optimal nutrient timing during plant growth, higher uniformity, lower labor and energy costs, and eliminating impact on public roads. The circulators combined with flush barns and center pivot irrigation creates a complete turn-key manure management system.
The purpose of the project was to evaluate the effectiveness of low powered circulators to treat livestock waste in lagoons. The objective was to evaluate how the addition of circulators to a livestock pond would change: 1. Odor levels, 2. Pivot nozzle clogging problems, and 3. Nitrogen loss.
