Legacy phosphorus in Alabama Hartsells soil after long-term amendment with broiler litter.

Numerous studies have investigated effects of long-term manure application on total phosphorus (P) and inorganic P (Pi ), but few have evaluated soil organic P (Po ). Little is known about crop management effects on Po in soils with varying minerology. In this study, sequential fractionation was used to characterize specific P forms after 25 years of broiler litter (BL) or ammonium nitrate (Con) applications to an Alabama Hartsells soil. Crops (corn [Zea mays L.], soybean [Glycine Willd.], and corn or soybean with a wheat [Triticum aestivum L.] cover crop) were under conventional tillage (CT) or no-tillage (NT). Regardless of crop, tillage, or fertilizer type, the proportion of extractable Pi was relatively stable at 21%-49% at 0-5 cm and 25%-45% at 5-10 cm. Extractable Pi ranged from 0.69 to 2.4 mg g-1 . BL increased total extractable Pi (p ≤ 0.001) at 0-5 cm and 5-10 cm. Total extractable P was influenced at 0-5 cm (p ≤ 0.006) by both tillage and fertilization type, but not at 5-10 cm or at either depth in soybean plots. Long-term BL application increased total extractable soil P at 0-5 cm. In corn systems, CT did not reduce P loading to topsoil or result in P leaching to lower soil depths, compared to NT. Soybean and soybean-wheat reduced P loading in BL plots, compared to corn and corn-wheat. Soil Po was classed in the order of monoesters > phytate and polyphosphates, where most was extractable with NaOH. BL increased extractable Po in all fractions. Care should be taken when applying BL to highly weathered soils to avoid legacy Po accumulation. Soybean rotations and cover crops could help remediate P-laden soils after repeated BL application.

Dietary mitigation of enteric methane emissions from ruminants: A review of plant tannin mitigation options.

Methane gas from livestock production activities is a significant source of greenhouse gas (GHG) emissions which have been shown to influence climate change. New technologies offer a potential to manipulate the rumen biome through genetic selection reducing CH4 production. Methane production may also be mitigated to varying degrees by various dietary intervention strategies. Strategies to reduce GHG emissions need to be developed which increase ruminant production efficiency whereas reducing production of CH4 from cattle, sheep, and goats. Methane emissions may be efficiently mitigated by manipulation of natural ruminal microbiota with various dietary interventions and animal production efficiency improved. Although some CH4 abatement strategies have shown efficacy in vivo, more research is required to make any of these approaches pertinent to modern animal production systems. The objective of this review is to explain how anti-methanogenic compounds (e.g., plant tannins) affect ruminal microbiota, reduce CH4 emission, and the effects on host responses. Thus, this review provides information relevant to understanding the impact of tannins on methanogenesis, which may provide a cost-effective means to reduce enteric CH4 production and the influence of ruminant animals on global GHG emissions.

Antibiotic resistance gene profile changes in cropland soil after manure application and rainfall.

Land application of manure introduces gastrointestinal microbes into the environment, including bacteria carrying antibiotic resistance genes (ARGs). Measuring soil ARGs is important for active stewardship efforts to minimize gene flow from agricultural production systems; however, the variety of sampling protocols and target genes makes it difficult to compare ARG results between studies. We used polymerase chain reaction (PCR) methods to characterize and/or quantify 27 ARG targets in soils from 20 replicate, long-term no-till plots, before and after swine manure application and simulated rainfall and runoff. All samples were negative for the 10 b-lactamase genes assayed. For tetracycline resistance, only source manure and post-application soil samples were positive. The mean number of macrolide, sulfonamide, and integrase genes increased in post-application soils when compared with source manure, but at plot level only, 1/20, 5/20, and 11/20 plots post-application showed an increase in erm(B), sulI, and intI1, respectively. Results confirmed the potential for temporary blooms of ARGs after manure application, likely linked to soil moisture levels. Results highlight uneven distribution of ARG targets, even within the same soil type and at the farm plot level. This heterogeneity presents a challenge for separating effects of manure application from background ARG noise under field conditions and needs to be considered when designing studies to evaluate the impact of best management practices to reduce ARG or for surveillance. We propose expressing normalized quantitative PCR (qPCR) ARG values as the number of ARG targets per 100,000 16S ribosomal RNA genes for ease of interpretation and to align with incidence rate data.

Tetracycline and Sulfonamide Antibiotic Resistance Genes in Soils From Nebraska Organic Farming Operations.

There is widespread agreement that agricultural antibiotic resistance should be reduced, however, it is unclear from the available literature what an appropriate target for reduction would be. Organic farms provide a unique opportunity to disentangle questions of agricultural antibiotic drug use from questions of antibiotic resistance in the soil. In this study, soil was collected from 12 certified organic farms in Nebraska, evaluated for the presence of tetracycline and sulfonamide resistance genes (n = 15 targets), and correlated to soil physical, chemical, and biological parameters. Tetracycline and sulfonamide antibiotic resistance genes (ARGs) were found in soils from all 12 farms, and 182 of the 196 soil samples (93%). The most frequently detected gene was tetG (55% of samples), followed by tet(Q) (49%), tet(S) (46%), tet(X) (30%), and tetA(P) (29%). Soil was collected from two depths. No differences in ARGs were observed based on soil depth. Positive correlations were noted between ARG presence and soil electrical conductivity, and concentrations of Ca, Na, and Mehlich-3 phosphorus. Data from this study point to possible relationships between selected soil properties and individual tetracycline resistance genes, including tet(O) which is a common target for environmental samples. We compared organic farm results to previously published data from prairie soils and found significant differences in detection frequency for 12 genes, eight of which were more commonly detected in prairie soils. Of interest, when tetracycline ARG results were sorted by gene mechanism, the efflux genes were generally present in higher frequency in the prairie soils, while the ribosomal protection and enzymatic genes were more frequently detected in organic farm soils, suggesting a possible ecological role for specific tetracycline resistance mechanisms. By comparing soil from organic farms with prairie soils, we can start to determine baseline effects of low-chemical input agricultural production practices on multiple measures of resistance.

Temporal Nitrous Oxide Emissions from Beef Cattle Feedlot Manure after a Simulated Rainfall Event.

Nitrous oxide (NO) is a greenhouse gas (GHG) emitted from agricultural operations. The objective of this research was to quantify NO-N emissions from simulated open-lot beef cattle feedlot pens after rainfall. A recirculating-flow-through, non-steady state chamber system consisting of five 1-m steel pans was designed for quantifying emissions. A lid was placed sequentially on each pan, and headspace air was recirculated between the pan and a real-time NO analyzer, measuring concentrations every 1 s. Air-dried manure (89.2% dry matter) from a commercial feedlot in the Texas Panhandle was placed in the pans and then 0, 6.3, 12.7, 25.4, or 50.8 mm of water was applied to simulate a one-time rainfall event. Emissions of NO-N were monitored for 45 d, where two distinct episodes of NO-N production were observed over time. The first NO-N episode had a duration of 10 h and peaked 2 h after rainfall at a flux of 1.0 to 200 mg m h. The second episode had a duration of 40 d and peaked 15 d after rainfall at a flux of 0.06 to 35 mg m h. The second episode accounted for 69 to 91% of the cumulative NO-N emitted over the 45-d period. Each millimeter of rainfall increased cumulative NO-N emitted by 167.9 mg m ( = 0.99, < 0.001). This rainfall vs. cumulative emissions relationship will be useful for modeling annual NO-N emissions from open-lot beef cattle feedlots, and for assessing the effectiveness of best management practices for reducing feedlot GHG emissions.

Nitrous Oxide Emissions from Open-Lot Cattle Feedyards: A Review.

Nitrous oxide (NO) emissions from concentrated animal feeding operations, including cattle feedyards, have become an important research topic. However, there are limitations to current measurement techniques, uncertainty in the magnitude of feedyard NO fluxes, and a lack of effective mitigation methods. The objective of this review was to assess NO emission from cattle feedyards, including comparison of measured and modeled emission rates, discussion of measurement methods, and evaluation of mitigation options. Published annual per capita flux rates for beef cattle feedyards and open-lot dairies were highly variable and ranged from 0.002 to 4.3 kg NO animal yr. On an area basis, published emission rates ranged from 0 to 41 mg NO m h. From these studies and Intergovernmental Panel on Climate Change emission factors, calculated daily per capita NO fluxes averaged 18 ± 10 g NO animal d (range, 0.04-67 g NO animal d). This variation was due to inconsistency in measurement techniques as well as irregularity in NO production and emission attributable to management, animal diet, and environmental conditions. Based on this review, it is clear that the magnitude and dynamics of NO emissions from open-lot cattle systems are not well understood. Further research is required to quantify feedyard NO fluxes and develop cost-effective mitigation methods.

Characterization of organic matter in beef feedyard manure by ultraviolet-visible and fourier transform infrared spectroscopies.

Manure from beef cattle feedyards is a valuable source of nutrients and assists with maintaining soil quality. However, humification and decomposition processes occurring during feedyard manure's on-farm life cycle influence the forms, concentrations, and availability of carbon (C) and nutrients such as nitrogen (N) and phosphorus (P). Improved understanding of manure organic matter (OM) chemistry will provide better estimates of potential fertilizer value of manure from different feedyard sources (e.g., manure accumulated in pens, stockpiled manure after pen scraping) and in settling basin and retention pond sediments. This will also assist with identifying factors related to nutrient loss and environmental degradation via volatilization of ammonia and nitrous oxide and nitrate leaching. We used Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies to characterize structural and functional properties of OM and water-extractable OM (WEOM) from different sources (surface manure, manure pack, settling basin, retention pond) on a typical commercial beef feedyard in the Texas Panhandle. Results showed that as beef manure completes its on-farm life cycle, concentrations of dissolved organic C and N decrease up to 98 and 95%, respectively. The UV-vis analysis of WEOM indicated large differences in molecular weight, lignin content, and proportion of humified OM between manures from different sources. The FTIR spectra of OM and WEOM indicate preferential decomposition of fats, lipids, and proteins over aromatic polysaccharides such as lignin. Further work is warranted to evaluate how application of feedyard manure from different sources influences soil metabolic functioning and fertility.

Process-based Modeling of Ammonia Emission from Beef Cattle Feedyards with the Integrated Farm Systems Model.

Ammonia (NH) volatilization from manure in beef cattle feedyards results in loss of agronomically important nitrogen (N) and potentially leads to overfertilization and acidification of aquatic and terrestrial ecosystems. In addition, NH is involved in the formation of atmospheric fine particulate matter (PM), which can affect human health. Process-based models have been developed to estimate NH emissions from various livestock production systems; however, little work has been conducted to assess their accuracy for large, open-lot beef cattle feedyards. This work describes the extension of an existing process-based model, the Integrated Farm Systems Model (IFSM), to include simulation of N dynamics in this type of system. To evaluate the model, IFSM-simulated daily per capita NH emission rates were compared with emissions data collected from two commercial feedyards in the Texas High Plains from 2007 to 2009. Model predictions were in good agreement with observations and were sensitive to variations in air temperature and dietary crude protein concentration. Predicted mean daily NH emission rates for the two feedyards had 71 to 81% agreement with observations. In addition, IFSM estimates of annual feedyard emissions were within 11 to 24% of observations, whereas a constant emission factor currently in use by the USEPA underestimated feedyard emissions by as much as 79%. The results from this study indicate that IFSM can quantify average feedyard NH emissions, assist with emissions reporting, provide accurate information for legislators and policymakers, investigate methods to mitigate NH losses, and evaluate the effects of specific management practices on farm nutrient balances.

Methane Emissions from a Beef Cattle Feedyard during Winter and Summer on the Southern High Plains of Texas.

Methane (CH) emissions from enteric fermentation by livestock account for about 2.1% of U.S. greenhouse gas emissions, with beef and dairy cattle being the most significant sources. A better understanding of CH emissions from beef cattle feedyards can help build more accurate emission inventories, improve predictive models, and meet potential regulatory requirements. Our objective was to quantify CH emissions during winter and summer at a typical beef cattle feedyard on the southern High Plains in Texas. Methane emissions were quantified over 32 d in winter and 44 d in summer using open-path lasers and inverse dispersion analysis. Methane per capita emission rate (PCER) ranged from 71 to 118 g animal d in winter and from 70 to 130 g animal d in summer. Mean CH PCER was similar in January, February, and May (average, 85.0 ± 0.95 g animal d) and increased to 93.4 g animal d during the June-July period. This increase coincided with increased dietary fiber. Methane loss ranged from 9.2 to 11.4 g CH kg dry matter intake, with lower values during winter. Gross energy intake (GEI) ranged from 135.2 to 164.5 MJ animal d, and CH energy loss ranged from 4.5 to 4.9 MJ animal d. Fraction of GEI lost as CH (Y) averaged 2.8% in winter, 3.2% in summer, and 3.0% overall. These values confirm the Y value currently recommended by the Intergovernmental Panel on Climate Change for Tier 2 estimates of enteric CH from feedlot fed cattle.

Arrhenius equation for modeling feedyard ammonia emissions using temperature and diet crude protein.

Temperature controls many processes of NH volatilization. For example, urea hydrolysis is an enzymatically catalyzed reaction described by the Arrhenius equation. Diet crude protein (CP) controls NH emission by affecting N excretion. Our objectives were to use the Arrhenius equation to model NH emissions from beef cattle () feedyards and test predictions against observed emissions. Per capita NH emission rate (PCER), air temperature (), and CP were measured for 2 yr at two Texas Panhandle feedyards. Data were fitted to analogs of the Arrhenius equation: PCER = () and PCER = (,CP). The models were applied at a third feedyard to predict NH emissions and compare predicted to measured emissions. Predicted mean NH emissions were within -9 and 2% of observed emissions for the () and (T,CP) models, respectively. Annual emission factors calculated from models underestimated annual NH emission by 11% [() model] or overestimated emission by 8% [(,CP) model]. When from a regional weather station and three classes of CP drove the models, the () model overpredicted annual NH emission of the low CP class by 14% and underpredicted emissions of the optimum and high CP classes by 1 and 39%, respectively. The (,CP) model underpredicted NH emissions by 15, 4, and 23% for low, optimum, and high CP classes, respectively. Ammonia emission was successfully modeled using only, but including CP improved predictions. The empirical () and (,CP) models can successfully model NH emissions in the Texas Panhandle. Researchers are encouraged to test the models in other regions where high-quality NH emissions data are available.