Title:

Microorganisms and Sustainable Agriculture

Investigators:

Lloyd F. Elliott, 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 Agronomist
Ann Kennedy, USDA-ARS Soil Scientist
Mark Azevedo, USDA-ARS, Microbiologist
Joyce Loper, USDA-ARS Plant Pathologist
Fred Crowe, Oregon State University

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 and possibly for genetic codes within the organisms. 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 systems. The probes will be used to test for related naturally occurring organisms as influenced by the cropping system. In this manner, we hope to obtain an approach for temporal measurements in changes in soil quality. Alternate methods are being tested. These studies are important to the development of more efficient cropping systems for grass and legume seed production. To date pseudomonads have been isolated that inhibit plant growth. 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. Studies are continuing on the effect of soil type of cropping system on inoculum efficacy.

It is very important that microbial indicators of sustainable 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, and Poa trivialis have been obtained and the isolate efficacy is being tested in the growth chamber. Field tests are planned for the 1996-97 crop year.

Fourteen isolates that stop weed seed germination have been obtained and about 20 others that inhibit weed root growth. The toxin produced by the seed germination inhibitors is excreted from the cells and appears stable for at least two weeks in the culture medium and much longer when frozen. Filtering through filters that remove proteins and lipopolysaccharides does not affect activity of the toxin(s). Preparations are being made to identify the toxin(s) using high resolution mass spectrometry technology. Generally, the inhibitory activity of the root growth inhibitory microorganisms is removed by filtration. Preliminary results indicate the organisms are of the Pseudomonas genus.

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 work is being summarized in final form, as an ARS publication. The composting studies have been completed.

Publications:

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)

Churchill, D. B., Horwath, W. R., Elliott, L. F., and Bilsland, D. M. Perennial ryegrass response to application of composted grass seed straw. J. Applied Seed Production 13:16-21. 1996.

Elliott, L. F., Lynch, J. i\/l., and Papendick, R. I. The microbial component of soil quality. In: Soil Biochemistry, Vol. 9. G. Stotzky and Jean-Marc Bollag (eds.) pp. 1.22. Marcel Dekker, Inc. NY. 1996.

Elliott, L. F. Microbiological interactions in no-till systems. Proceedings: No Tillage National Congress in Argentina. 1996.

Elliott, L. F., and Chevalier, P. Diversification for new management systems in the Pacific Northwest. Amer. J. for Altern. Agric. 11(2):77-82. 1996.

Horwath, W. R., Elliott, L. F., and Churchill, D. B. Processes regulating grass straw composting. Proceedings: European Commission Intrnational Symposium: The Science of Composting, Bologna, IT. Marco de Bertoldi, Paola Sequi, Bert Lemmes, and Tiziano Papi (eds.) Blackie Academic and Professional. London. pp. 627-636. 1996.

Horwath, W. R., Elliott, L. F., and Churchill, D. B. Development of low-input, composting of high C/N ratio crop residues. Proceedings: European Commission international Symposium: The Science of Composting, Bologna, IT. Marco de Bertoldi, Paola Sequi, Bert Lemmes, and Tiziano Papi (eds.) Blackie Academic and Professional. London. pp. 1181-1187. 1996.

Katoianova, N., Kostov, O., and Elliott, L. F. Microbial properties of three Bulgarian paddy soils and relationships to soil resiliency. Mes. Fac. Landbouw. Univers. Gent, 60/1:43-52. 1996.