Evaluation of Microbial Ecology in Pasture Ecosystems with Long-term Poultry Litter Additions

Evaluation of Microbial Ecology in Pasture Ecosystems with Long-term Poultry Litter Additions

Summary

Microorganisms, as the primary decomposers in the environment, play a key role in facilitating nutrient cycling processes, including the production of enzymes and mineralization of nutrients such as carbon, phosphorus and nitrogen. Despite this fact, understanding of how soil management practices, such as the application of poultry litter to pasture land, influence microbial dynamics and how these changes may affect long-term system sustainability is limited. Soil microbial community dynamics are being assessed in simulated pasture systems receiving one of two rates of untreated poultry litter, alum-treated poultry litter (to reduce ammonia volatilization in broiler houses and phosphorus leaching in soil), or inorganic N fertilizer. The amendment rates are 2.24 Mg/ha and 8.98 Mg/ha for the litters, and 65 kg N/ha and 260 kg N/ha of ammonium nitrate (equal to the nitrogen level in the alum-treated poultry litter at year one of the study). A multi-faceted research approach combining traditional extraction and molecular techniques is being utilized. Microbial community structure and functions are being assessed by measuring microbial biomass, dehydrogenase and phosphatase enzyme activities, and polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis of environmental and antibiotic resistant bacterial communities. The utilization of several microbial assessment tools should improve understanding of soil microbial communities in poultry litter-amended pasture in terms of size, function, diversity and potential for the indigenous populations to develop antibiotic resistance. The goal of this research is to acquire knowledge to use toward the development of sustainable management practices that utilize the microbial community to reduce nutrient leaching and nutrient runoff, and enhance nutrient availability for plant uptake in pasture systems.

Objectives/Performance Targets

Assess the impact of the long-term poultry litter additions on soil microbial biomass and enzyme activity.

Assess the impact of organic amendments on microbial diversity.

Evaluate the contribution of poultry litter to development of antibiotic resistance in microorganisms in the environment.

Accomplishments/Milestones

Soil sampling during 2003 occurred on May 9, prior to amendment application on May 30, and then on June 9, July 6, and Nov 22. Soil sampling during 2004 occurred on April 5, prior to amendment application on April 19 and then on April 29, May 19 and Nov 9. The plots (1.52 x 3.01-m) were subdivided into 8 sub-plots (0.76 x 1.00-m) and one sample was taken at random from each sub-plot to a depth of 5-cm. The samples were then bulked in sterile plastic bags to form one composite per replication and stored on ice until transported back to the lab. The samples were then refrigerated at 4oC and processed within 1 week of sampling. Preliminary results have been determined for all objectives. The enzyme data is showing that the treatments are affecting biological activity. Acid and alkaline phosphatase activities are increased by the high application rates of alum-treated litter and poultry litter as compared to the low application rates, control and ammonium nitrate. Furthermore plots receiving application of high rates of ammonium nitrate resulted in the significant suppression of dehydrogenase activity as compared to the other treatments. The microbial biomass C and P data is inconclusive at this point. However, the microbial biomass N in the high rate of ammonium nitrate fertilizer showed lower concentrations than all other treatments, although this decrease was not always significant. This decrease may represent either a decrease in the size of the microbial community that the measure of microbial biomass C was not sensitive enough to detect or a shift in the microbial community. Molecular diversity analysis is on going and is expected to show a difference among treatments if there is a shift in the dominant bacterial phylotypes resulting from litter applications. DNA extractions have been completed on all of the 2003 soils. Polymerase chain reactions (PCR) amplifying the 16S RNA gene fragment (338F to 518R) are currently being performed since (338F to 907R) was not successful in denaturing gradient gel electrophoresis (DGGE) analyses. DGGE of the PCR products for determination of changes in the microbial diversity is underway. Methods are being optimized for primers 338F and 518R. Bacteria were isolated from soil by plating dilutions on 10% tryptic soy agar and incubating for 7 days at 25C. Following incubation, isolates were transferred to 10% TSA plates treated with bacitracin or monensin at varying concentrations. Isolates that were able to grow on the plates containing antibiotics were considered antibiotic resistant at that concentration. At this time, isolate DNA is being amplified using PCR and the structure of the isolate community is being analyzed using DGGE. Furthermore, all data are being analyzed statistically and preparation of the thesis and publications are underway.

Impacts and Contributions/Outcomes

Year one enzyme and biomass data was presented at the S297 Soil Microbiology Meeting in Pendleton OR, June 6 - 7, 2004. Additionally, the antibiotic data from the summer and fall of 2003 was presented in an oral talk at the Southern Branch American Society of Agronomy (ASA) and as a poster at the 2004 American Society of Agronomy (ASA)/ Soil Science Society of America (SSSA) annual meeting in Seattle WA, October 31 – November 4, 2004.

Tomlinson, P. J. and M. C. Savin. 2004. Antibiotic resistance in run-off and soil receiving poultry litter. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI.
Tomlinson, P. J. and M. C. Savin. 2004. Poultry litter, an influence on antibiotic resistance in soil? In Invited Papers & Abstracts of Contributed Papers [CD-ROM]. Southern Branch ASA, Madison, WI.
Tomlinson, P. J., K. R. Payne, K. R. Brye, and M. C. Savin. 2003. Microbial dynamics in long-term research plots receiving alum-treated and untreated poultry litter. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI.