Dennis W. Hoffman

Pathogen prevalence and influence of composted dairy manure application on antimicrobial resistance profiles of commensal soil bacteria.

Composting manure, if done properly, should kill pathogenic bacteria such as Salmonella and Escherichia coli O157:H7, providing for an environmentally safe product. Over a 3-year period, samples of composted dairy manure, representing 11 composting operations (two to six samples per producer; 100 total samples), were screened for Salmonella and E. coli O157:H7 and were all culture negative. Nonpathogenic bacteria were cultured from these compost samples that could theoretically facilitate the spread of antimicrobial resistance from the dairy to compost application sites. Therefore, we collected soil samples (three samples per plot; 10 plots/treatment; 90 total samples) from rangeland that received either composted dairy manure (CP), commercial fertilizer (F), or no treatment (control, CON). Two collections were made appoximately 2 and 7 months following treatment application. Soil samples were cultured for Pseudomonas and Enterobacter and confirmed isolates subjected to antimicrobial susceptibility testing. Three species of Enterobacter (cloacae, 27 isolates; aeroginosa, two isolates; sakazakii, one isolate) and two species of Pseudomonas (aeruginosa, 11 isolates; putida, seven isolates) were identified. Five Enterobacter isolates were resistant to ampicillin and one isolate was resistant to spectinomycin. All Pseudomonas isolates were resistant to ampicillin, ceftiofur, florfenicol, sulphachloropyridazine, sulphadimethoxine, and trimethoprim/sulfamethoxazole and most isolates were resistant to chlortetracycline and spectinomycin. Pseudomonas isolates were resistant to an average of 8.6, 7.9, and 8 antibiotics for CON, CP, and F treatments, respectively. No treatment differences were observed in antimicrobial resistance patterns in any of the soil isolates examined. Results reported herein support the use of composted dairy manure as an environmentally friendly soil amendment.

MODELING THE EFFECTIVENESS OF CONSERVATION PRACTICES AT SHOAL CREEK WATERSHED, TEXAS, USING APEX

This study was conducted to evaluate the performance of the Agricultural Policy/Environmental eXtender (APEX) model using daily storm event runoff and sediment yields (1997-2005) collected at the outlet of the 22.5 km2 Shoal Creek watershed. This watershed only has intermittent streams. The watershed is within the U.S. Armys Fort Hood military reservation in central Texas. It received a combination of erosion control practices including implementation of gully plugs and contour soil ripping. APEX was calibrated and validated with a 183-subarea configuration delineated from a 5 m digital elevation model. Results from model calibration and validation confirmed that APEX was able to realistically estimate daily runoff and sediment yield for both the pre- and post-BMP conditions, as evidenced by R2 values ranging from 0.60 to 0.80 and Nash-Sutcliffe efficiency (EF) values ranging from 0.58 to 0.77 with an exception of 0.33. During the post-BMP period, the total sediment yield was significantly less than that from the pre-BMP period, even though the corresponding total precipitation amount from the post-BMP events (1025 mm) was more than that from the pre-BMP events (668 mm). The simulated sediment yield was summed up to 24.3 Mg ha-1 for the pre-BMP events and 7.6 Mg ha-1 for the post-BMP events, which were very close to the measured values of 24.9 and 8.1 Mg ha-1, respectively. The benefits of the existing BMPs were quantified as a reduction of 52% in runoff and 86% in sediment yield based on comparisons between predictions from the run using the pre-BMP model setup and measured values under BMP conditions. The results suggest that APEX is capable of simulating conservation practices on military landscapes, and that it a useful tool for scenario analysis to evaluate the effectiveness of conservation practices.

Conservation Effects Assessment Project research in the Leon River and Riesel watersheds

The Leon River basin was selected as a benchmark watershed for the Conservation Effects Assessment Project to complement the historical USDA Agricultural Research Service experimental watersheds near Riesel, Texas. Excessive nutrient and bacteria concentrations contributed by agricultural, urban, and natural sources are the primary water quality concerns. Modeling and field evaluations of the hydrologic impact and soil and water quality response to tillage and nutrient management practices are the primary research themes of this project. Water quality data from 15 Leon River watersheds (0.3 ha [0.75 ac] to 6,070 km2 [2,340 mi2]) and 13 Riesel watersheds (1.2 ha [3.0 ac] to 70.4 ha [174 ac]) has improved modeling of phosphorus transformation and transport routines. Modeling research also coupled field- and farm-scale model output to improve the basin-scale Soil and Water Assessment Tool (SWAT) for the national assessment of conservation practices. Additional key products of Conservation Effects Assessment Project research include innovative erosion control methods on military lands, enhanced carbon sequestration estimates for various agricultural land uses, and improved understanding of environmental and economic impacts of organic fertilizer application.

Evaluation of removal of orthophosphate and ammonia from rainfall runoff using aboveground permeable reactive barrier composed of limestone and zeolite

This paper evaluates the design and performance of an Aboveground Permeable Reactive Barrier (APRB) system made of polyethylene mesh bags (FlowBags) containing crushed limestone and zeolite for adsorption of orthophosphate-P (PO4-P) and ammonia-N (NH4-N) from rainfall runoff. Laboratory batch experiments, simulated runoff experiments and actual APRB implementations were performed to evaluate the performance of the APRB. Batch experiments were performed to determine adsorption efficiency of crushed zeolite and limestone as reactive materials in APRB for removal of dissolved ammonium nitrogen and orthophosphate phosphorus from aqueous solutions under controlled laboratory conditions. Adsorption efficiencies of zeolite and limestone were tested individually and in combination. Results show adsorption efficiency increases when the materials are used in combination. Effects of particle size, contact time, pH, and temperature were studied. Major emphasis was given to short contact times because the contact of rainfall runoff water under field conditions with APRBs would be ∼5 minutes. Maximum removal of ∼70% PO4-P and NH4-N was seen at 45°C in 5 minutes within a pH range of 8–11. Optimum adsorbent concentration was 0.3 ppm with 20 g limestone and 10 g of zeolites. Simulated field experiments and actual APRB field installations showed variable results. Results from field evaluations of APRB showed mixed results from very high to negligible removal of orthophosphate-P and ammonia-N at different monitoring sites and storm events. Such variability may be due to the design of the bags, other biotic and abiotic factors and various physical factors, which are absent in the laboratory conditions. Some APRB design problems were also observed under field conditions and solutions are suggested. Overall results indicate that APRBs composed of combinations of crushed zeolite and limestone will offer an effective low maintenance and green alternative to remove dissolved nutrients from runoff and protect surface water resources from eutrophication.

Contour ripping is more beneficial than composted manure for restoring degraded rangelands in Central Texas

Rangelands in the United States that have been the site of military training exercises have suffered extensive ecological damage, largely because of soil compaction, creation of ruts, and damage to or destruction of vegetation--all of which lead to higher runoff and accelerated erosion. In this paper we report on a study carried out within the Fort Hood Military Reservation in Central Texas, where we evaluated the extent to which application of composted dairy manure and contour ripping affect soil infiltrability, amount of runoff, and nutrient concentrations in runoff. We conducted experiments at two locations, using rainfall simulation at one and monitoring discharge from small (0.3-ha) watersheds at the other. At the rainfall simulation site, we used six levels of compost application: 4, 8, 12, 16, 20, and 24 Mg/ha. We found that compost application had little effect on runoff, soil infiltration, sediment production, or nutrient concentrations in the runoff--except at the micro-watershed scale (12 and 24 Mg/ha); in this case, nutrient concentrations in runoff were initially high (for the rainfall simulations done immediately after compost application). In contrast, contour ripping--carried out 22 months after compost application on two of the micro-watersheds--was highly effective: runoff on the treated micro-watershed was reduced by half compared with the untreated micro-watershed. Our results suggest that (1) one-time applications of composted dairy manure do little to enhance infiltration of degraded rangelands over the short term (at the same time, these experiments demonstrated that compost application poses very little risk to water quality); and (2) for degraded rangelands with limited infiltration capacity, contour ripping is an effective strategy for increasing infiltration rates.

Restoration of Military Training Lands: Development of Decision Support Tools

Sustainable management of military training lands is critical to the ongoing mission of preparing U.S. military forces to fight and win wars. Development of next generation biophysical and economic models for planning and assessment of military land restoration programs can provide a vital decision support tool for military land managers worldwide. Providing accurate decision support for determining appropriate best management practice (BMP) selection based on available knowledge is critical and can provide accountability for restoration funding. Utilizing a multitude of data including hydrologic, vegetation, soils and erosion data from the U.S. Armys Fort Hood military installation, a team of scientists is working to parameterize the Agricultural Policy extender (APEX) simulation models capabilities for application on highly disturbed military training lands. Development on lands under such harsh disturbance regimes will provide a robust technology that can be easily adapted to rangeland and other ecosystems under less stressful disturbance conditions. Results of preliminary model parameterizations indicate potential benefits in the development and application of hydrologic models to address erosion reduction practices utilized on Fort Hood.

Stream Rehabilitation on a Rural/Urban Watershed

Friar’s Creek, located in Temple, Texas was selected to evaluate responses to stream restoration. Friar’s Creek is located within a moderately urbanized watershed (approximate area: 10 sq mi) where parts of the stream have been widened and deepened to handle increased runoff from urban development. The proposed Friar’s Creek project area is experiencing dramatic changes in channel morphology due to upstream channel modifications. This project represents an opportunity to implement and demonstrate stream restoration techniques using primarily natural materials; simultaneously, we assessed the biological integrity of the stream reach before and after the project. To handle the increased flow from urbanizing areas, channel dimensions were modified along 800 m of selected reaches to help maintain the channel bank. Site specific native wetland vegetation and grasses was selected and planted to help stabilize the channel bank. In addition, stream integrity was determined before implementation via fish and macrophyte surveys. This paper presents a summary of the activities associated with the project.

Monitored Estimates of Fort Hood Sediment Loadings in Cowhouse Creek

Blackland Research and Extension Center (BREC) scientists, and Integrated Training Area Management (ITAM) personnel, have utilized water quality measurements to document BMP efficiency in the Fort Hood Cowhouse Creek watershed. The volume of sediment loadings from the Cowhouse Creek into Lake Belton are a growing concern. The water quality evaluation program began in 1995 and continues today. Gauging stations equipped with flow loggers, storm water samplers and rain gauges are located at each watershed inflow and outflow sites. Storm runoff water samples are analyzed gravimetrically for sediment concentration. Sediment concentrations are combined with flow measurements to determine sediment load associated with individual storm events. BREC is using the monitored sediment and flow data from Cowhouse Creek to estimate sediment loadings from this Fort Hood watershed.

Assessments and Restoration Implementations on a Central Texas Rural-Urban Stream

Friar’s Creek, located in Temple, Texas has been selected to evaluate responses to stream restoration. Friar’s Creek is located within a moderately urbanized watershed (approximate area: 10 sq mi) where parts of the stream have been widened and deepened to handle increased runoff from urban development. The proposed Friar’s Creek project area is experiencing dramatic changes in channel morphology due to upstream channel modifications. This project represents an opportunity to implement and demonstrate stream restoration techniques using primarily natural materials; simultaneously, we will assess the biological integrity of the stream reach before and after the project. To handle the increased flow from urbanizing areas, channel dimensions were modified along 250 m of a selected reach to help maintain the channel bank. Site specific native wetland vegetation and grasses have been selected and planted to help stabilize the channel bank. In addition, stream integrity was determined before implementation via fish and macrophyte surveys. This paper presents a summary of the activities associated with the project.

Rural/Urban Stream Rehabilitation in Central Texas

Friar’s Creek, located in Temple, Texas has been selected to evaluate response to stream restoration. Friar’s Creek is located within a moderately urbanized watershed (approximate area: 10 sq mi) where parts of the stream have been channelized to handle increased runoff from urban development. The proposed Friar’s Creek project area is experiencing dramatic changes in channel morphology due to upstream channel modifications. This project represents an opportunity to implement and demonstrate stream restoration techniques using primarily natural materials; simultaneously, we will assess the biological integrity of the stream reach before and after the project.