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), and inorganic 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 structure and functions is 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 will allow for the development of an 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 acquisition of this basic understanding is key to 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

1. 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 resistant 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. 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 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 4C 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 pick up 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 in fact a shift in the community structure resulting from litter applications. DNA extractions have been completed on all of the soils collected to date. Polymerase chain reactions (PCR) amplifying the 16S RNA gene fragment (338F to 907R) are currently being performed and we are able to amplify DNA from the soils. Denaturing gradient gel electrophoresis (DGGE) analysis of the PCR products for determination of changes in the microbial diversity has been initiated. Bacteria were isolated from soil by plating dilutions on 10% tryptic soy agar and incubating for 7 days at 25C. Following incubation, isolates have been transferred to 10% TSA plates treated with bacitracin and monensin at varying concentrations. Isolates that were able to grow on the highest antibiotic concentration are considered to be antibiotic resistant. At this time, isolate DNA is being amplified using PCR and the structure of the isolate community is being analyzed using DGGE. Furthermore, data analysis of the 2003 data continues and the sampling schedule for 2004 has been established.

Impacts and Contributions/Outcomes

Preliminary enzyme data was presented at the S297 Soil Microbiology Meeting in Blacksburg VA, May 25, 2003. Additionally, the biomass and enzyme data from the summer of 2003 was presented in a poster at the 2003 American Society of Agronomy (ASA)/ Soil Science Society of America (SSSA) annual meeting in Denver, CO, November 2-6, 2003.

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.