Bryan L. Woodbury

Electrical conductivity monitoring of soil condition and available N with animal manure and a cover crop

Development of sustainable agricultural management systems will depend, in part, on the ability to better use renewable resources, such as animal manure, and to synchronize the levels of soil available N with crop plant needs during the growing season. This study was conducted at the US Meat Animal Research Center in the central USA to determine whether differences in electromagnetic (EM) soil conductivity and available N levels over a growing season can be linked to feedlot manure/compost application and use of a green winter cover crop. A series of soil conductivity maps of a research cornfield were generated using global positioning system (GPS) and EM induction methods. The study site was treated over a 7-year period with manure and compost at rates matching either the phosphorus or the nitrogen requirements of silage corn (Zea mays L.). The plot was split for sub-treatments of a rye (Secale cereale L.) winter cover crop and no cover crop. Image processing techniques were used to establish electrical conductivity (EC) treatment means for each of the growing season surveys. Sequential measurement of profile weighted soil electrical conductivity (EC a) was effective in identifying the dynamic changes in available soil N, as affected by animal manure and N fertilizer treatments, during the corn-growing season. This method also clearly identified the effectiveness of cover crops in minimizing levels of available soil N before and after the corn-growing season, when soluble N is most subject to loss. The EM method for assessing soil condition provides insights into the dynamics of available N transformations that are supported by soil chemical analyses. This real-time monitoring approach could also be useful to farmers in enhancing N use efficiencies of cropping management systems and in minimizing N losses to the environment.

Fate and transport of antimicrobials and antimicrobial resistance genes in soil and runoff following land application of swine manure slurry.

Due to the use of antimicrobials in livestock production, residual antimicrobials and antimicrobial resistance genes (ARGs) could enter the environment following the land application of animal wastes and could further contaminate surface and groundwater. The objective of this study was to determine the effect of various manure land application methods on the fate and transport of antimicrobials and ARGs in soil and runoff following land application of swine manure slurry. Swine manure slurries were obtained from facilities housing pigs that were fed chlortetracyline, tylosin or bacitracin and were land applied via broadcast, incorporation, and injection methods. Three rainfall simulation tests were then performed on amended and control plots. Results show that land application methods had no statistically significant effect on the aqueous concentrations of antimicrobials in runoff. However, among the three application methods tested broadcast resulted in the highest total mass loading of antimicrobials in runoff from the three rainfall simulation tests. The aqueous concentrations of chlortetracyline and tylosin in runoff decreased in consecutive rainfall events, although the trend was only statistically significant for tylosin. For ARGs, broadcast resulted in significantly higher erm genes in runoff than did incorporation and injection methods. In soil, the effects of land application methods on the fate of antimicrobials in top soil were compound specific. No clear trend was observed in the ARG levels in soil, likely because different host cells may respond differently to the soil environments created by various land application methods.

SEASONAL AND SPATIAL VARIATIONS OF DENITRIFYING ENZYME ACTIVITY IN FEEDLOT SOIL

Animal waste models, used by producers to apply best management practices for waste control, are only crude approximations for nitrogen lost from the feedlot. Ammonia loss has been widely studied and accounts for the majority of gaseous nitrogen lost from a feedlot soil; however, denitrification has not been thoroughly investigated. The objectives of this study were to determine the seasonal denitrification enzyme activity (DEA) of a feedlot soil and evaluate potential controlling mechanisms. Electromagnetic mapping techniques were used to identify three locations within the feedlot pen. Three depths (unconsolidated surface material, 0–0.10 m, 0.10–0.20 m) were isolated at each location and analyzed for DEA, nitrification activity, denitrifier most probable number, soil moisture, pH, volatile solids, total carbon, and total nitrogen. Denitrification enzyme activity varied from 0.0 to 132.2 mmol gsoil –1 hr –1 based on season, depth, and spatial location. However, no single factor was perfectly correlated with DEA across all locations and depths. The seasonal average DEA of the unconsolidated surface material maintained significantly higher levels when compared to other depths. Downgradient surface materials maintained DEA levels greater than 60 mmol gsoil –1 hr –1 even when soil temperatures were near 0 ³ C. Also, the seasonal average DEA below 0.10 m for all locations was near zero during the entire investigation, significantly less than the other depths. We conclude that a range of environmental factors, alone or in conjunction, influence DEA depending upon location within the pen and soil depth.

Fate of antimicrobials and antimicrobial resistance genes in simulated swine manure storage

The behavior of three antibiotics (bacitracin, chlortetracycline, and tylosin) and two classes of antibiotic resistance genes (ARGs), tet and erm, were monitored in swine manure slurry under anaerobic conditions. First-order decay rates were determined for each antibiotic with half-lives ranging from 1 day (chlortetracycline) to 10 days (tylosin). ARGs were monitored in the swine manure slurry, and losses of approximately 1 to 3 orders of magnitude in relative abundance were observed during the 40 day storage period. First-order degradation profiles were observed for chlortetracycline and its corresponding resistance genes, tet(X) and tet(Q). Tylosin was degraded to approximately 10% of the starting concentration by day 40; however, the relative abundance of erm(B) remained at 50-60% of the initial relative abundance while the relative abundance of erm(F) decreased by 80-90%, consistent with tylosin. These results indicate that tet resistance genes respond primarily to chlortetracycline antimicrobials, and may be lost when the parent tetracycline compound is degraded. In contrast, erm(B) resistance gene may respond to a range of antimicrobials in animal manure, and may persist despite losses of tylosin.

Links among Nitrification, Nitrifier Communities, and Edaphic Properties in Contrasting Soils Receiving Dairy Slurry

Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.

AN INEXPENSIVE LABORATORY AND FIELD CHAMBER FOR MANURE VOLATILE GAS FLUX ANALYSIS

Understanding the interactions between the environment and emissions from livestock manure is essential in developing management practices intended to minimize negative environmental consequences. However, protocols and equipment necessary to investigate these interactions at the laboratory or field-scale are cumbersome and can be expensive. An inexpensive dynamic flux chamber (cost <

Protocols for Nationally Coordinated Laboratory and Field Research on Manure Nitrogen Mineralization

400 per unit) was designed to measure gaseous emissions from cattle manure in laboratory and field experiments. The hemispherical stainless steel chamber (emission surface = 0.08 m2) was constructed with an internal gas mixing fan. A port was attached to the chamber top, which facilitated the collection of headspace gas samples for greenhouse gases and volatile organic compounds (VOC) by solid-phase microextraction (SPME). The chamber was tested to evaluate flow characteristics and was found to perform very similarly to a continuous-flow stirred reactor. As such, concentrations measured at the sampling port were indicative of concentrations anywhere in the headspace. In laboratory and field applications, the inexpensive dynamic flux chamber was easy to use and required little operator input to quickly obtain multiple samples to measure the relative emissions of greenhouse gases, ammonia (NH3), and VOC from multiple sites in cattle feedlot pens.

Soil versus pond ash surfacing of feedlot pens: occurrence of Escherichia coli O157:H7 in cattle and persistence in manure.

Abstract The National Program structure of USDA‐ARS provides an opportunity to coordinate research on problems of national and global significance. A team of USDA‐ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency. Experimental design and research protocols were developed and used in common across all participating locations. Laboratory incubations are conducted at each location with a minimum of three soils, three temperatures, two wetting/drying regimes, and two manure treatments. A soil from the central United States (Catlin silt loam, fine‐silty, mixed, superactive, mesic Oxyaquic Argiudoll) is used as an internal reference across all locations. Incubation data are compiled across locations to develop generalized predictions of manure nitrogen mineralization (Nmin). Field validation data are then obtained by monitoring nitrogen (N) transformations in manure‐amended soil cores equipped with anion exchange resin to capture leached nitrate. This field data will be used to compare laboratory‐based predictions with field observations of Nmin in each soil, climatic zone, and manure type represented. A Decision Support System will then be developed for predicting manure N mineralization across ranges in soil, climate, and manure composition. Protocols used by this research team are provided to 1) document the procedures used and 2) offer others detailed information for conducting research on nutrient transformation processes involving collaboration across locations or complementary research between laboratory and field environments.

Status of soil electrical conductivity studies by central state researchers

Reducing Escherichia coli O157:H7 in cattle and their manure is critical for reducing the risk for human foodborne and waterborne illness. The objective of this study was to evaluate the effects of soil and pond ash surfaces for feedlot pens on the prevalence, levels, and/or persistence of naturally occurring E. coli O157:H7 and total E. coli in cattle (feces and hides) and manure. Cattle (128 beef heifers) were sorted among 16 pens: 8 surfaced with soil and 8 surfaced with pond ash. The prevalence of E. coli O157:H7 in feces decreased (P < 0.0001) during the study from 57.0% on day 0 to 3.9% on day 84 but did not differ (P > or = 0.05) between cattle on soil and on pond ash pens at any sampling period. The prevalence of the pathogen on hides and in feedlot surface material (FSM) also decreased (P < 0.0001), with no effect of soil or pond ash surface (P > or = 0.05). Similarly, levels of E. coli in FSM did not differ (P > or = 0.05) at any sampling period, and there were no clear trends for survival differences of E. coli O157:H7 or E. coli in FSM between pond ash and soil surfaces, although E. coli populations survived at 5.0 log CFU/g of FSM on the pen surfaces 6 weeks after the cattle were removed. These results indicate that housing cattle on pens surfaced with pond ash versus pens surfaced with soil does not affect E. coli O157:H7 in cattle or their manure.

TOTAL REDUCED SULFUR CONCENTRATIONS IN THE VICINITY OF BEEF CATTLE FEEDLOTS

Practical tools are needed to identify and advance sustainable management practices to optimize economic return, conserve soil, and minimize negative off-site environmental effects. The objective of this article is to review current research in non-saline soils of the central U.S. to consider bulk soil electrical conductivity (ECa) as an assessment tool for: (1) tracking N dynamics, (2) identifying management zones, (3) monitoring soil quality trends, and (4) designing and evaluating field-scale experiments. The interpretation and utility of ECa are highly location and soil specific; soil properties contributing to measured ECa must be clearly understood. In soils where ECa is driven by NO3-N, ECa has been used to track spatial and temporal variations in crop-available N (manure, compost, commercial fertilizer, and cover crop treatments) and rapidly assess N mineralization early in the growing season to calculate fertilizer rates for site-specific management (SSM). Selection of appropriate ECa sensors (direct contact, electromagnetic induction, or time domain reflectometry) may improve sensitivity to N fluctuations at specific soil depths. In a dryland cropping system where clay content dominates measured ECa, ECa-based management zones delineated soil productivity characteristics and crop yields. These results provided a framework effective for SSM, monitoring management-induced trends in soil quality, and appraising and statistically evaluating field-scale experiments. Use of ECa may foster a large-scale systems approach to research that encourages farmer involvement. Additional research is needed to investigate the interactive effects of soil, weather, and management on ECa as an assessment tool, and the geographic extent to which specific applications of this technology can be applied.