Title:

Microorganisms and Sustainable Agriculture

Investigators:

Lloyd F. Elliott, USDA-ARS Research Microbiologist
William Horwath, USDA-ARS Research Microbiologist
Donald Churchill, USDA-ARS Agricultural Engineer
George Mueller-Warrant, USDA-ARS Agronomist
Stephen Griffith, USDA-ARS Plant Physiologist
Jeffrey Steiner, USDA-ARS Research Agronomist
Steve Alderman, USDA-ARS Research Plant Pathologist
Ann Kennedy, USDA-ARS Soil Scientist
Fred Crowe, Oregon State University

Progress:

Objective 1:

Develop microbial indicators of sustainable cropping systems.

Gene probes are being developed to follow specific rhizosphere colonists. The probes will be developed for natural products produced by the microorganisms. The background will be tested in the rhizosphere of grass grown as a monoculture and grass grown in a rotation with and without fertilizer inputs. The natural organisms for which genetic probes have been developed will be introduced into the rhizosphere and survivability determined as influenced by cropping system. To date pseudomonads have been isolated that inhibit plant growth. However, we have had difficulty preparing transposon mutants so that genetic markers can be determined for the development of gene probes. Alternate approaches are being tested. These studies are important to the development of more efficient cropping systems for grass and legume seed production. The inhibitory bacteria associated with grass roots do appear to present a crop yield constraint.

The successful release and application of wild type and genetically engineered microorganisms into soil systems has been impeded because efficacy in the field in unpredictable. evidence is presented showing that the plant-inoculum interaction can be strongly influenced by cropping system and soil type and that no one factor relating to soil quality or inoculum delivery can explain microbial function. These results suggest that field trials conducted without these considerations will be of dubious value. In addition, studies in one cropping system or soil type are not readily applicable to other systems. Development of inoculum technologies and understanding inoculum response in different cropping and soil systems will be valuable to the development and implementation of systems for the biological control of weeds for example.

It is very important that microbial indicators of sustainable grass and legume seed cropping systems be developed so that the effect of management and rotations on sustainability can be determined. In this way, more efficient cropping systems can be devised. Currently, we have no means of measuring progress.

Objective 2:

Develop biological control of weeds using deleterious rhizobacteria.

Several new isolates of deleterious rhizobacteria against Poa annua downy brome, and perennial ryegrass have been obtained and will be included in field trials for weed and volunteer control.

Further tests of deleterious rhizobacteria against Poa annua were conducted during the 1994-95 growing season at Hyslop. A large area was carbon-band seeded to perennial ryegrass and was oversown in early winter with annual bluegrass seed. A moderately low rate of diuron was used at the seeding to control broadleaf weeds but it did not effect the later sown annual bluegrass. Several isolates were applied but most of the annual bluegrass stand was killed by inclement weather causing the results to be difficult to interpret.

A deleterious rhizobacterium, D-7, that was effective against downy brome in winter wheat was tested against downy brome in Kentucky bluegrass at the Experiment Station in Madras, Oregon, during the fall and winter of 1994-95. Replicated trials were installed and the efficacy of the organism determined. Multiple application of the organism during late winter resulted in excellent downy brome control in some cases, but results were spotty. More work is needed on the delivery of the inoculum and factors affecting efficacy.

Objective 3:

Develop predictions for the decomposition of high C:N ratio residues.

The mechanisms of the low-input, on-farm composting project have been described. The feasibility of utilizing grass seed straw residues in the process has been shown. The work is being summarized in final form, and the composting studies will be discontinued.

Publications:

Horwath, W. R. and L. F. Elliott. 1995. Microbial C and N dynamics during mesophilic and thermophilic incubations of ryegrass. Biol. and Pert. of Soils, 1 1-9.

Horwath, W. R., L. F. Elliott, and D. B. Churchill. Processes regulating grass straw comporting. Proceedings: European Commission International Symposium: The Science of Composting, Bologna, IT. (Accepted May 1995)

Horwath, W. R., L. F. Elliott, and D. B. Churchill. 1995. Mechanisms regulating composting of high carbon to nitrogen ratio grass straw. Proceedings: Symposium on the Biogeochemistry of Compost. R. L. Wershaw and Cal Kuska an International Symposium. Comp. Sci. and Util. 3:22-30.

Elliott, L. F. The role of microorganisms in sustainable agriculture. Proceedings: Microbial Ecology International Symposium, Mexico. City. (Accepted May 1995)

Lynch, J. M. and L. F. Elliott. Bioindicators: Perspectives and potential value for landusers, researchers, and policy makers. In: C. E. Pankhurst, B. M. Doube, and V. S. S. R. Gupta (eds), Bioindicators of Soil Health. CABI, Wallingford, Oxon. (Accepted October 1995)