Busy Soil Microbes Provide Macro Field Benefits

May 3, 2002

WOOSTER, Ohio - Adding organic amendments to agricultural fields stimulates soil microbial activity, which in turn may reduce root diseases and promote overall plant health. Brian McSpadden Gardener, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, observed that microbial populations in the soil and around the plant roots increased dramatically when a carbon-rich manure amendment was added at the beginning of the growing season. However, plant growth was marginal. A compost addition, high in nitrogen, applied at the same time had less impact on microbial populations, but a greater positive effect on plant growth. McSpadden Gardener speculates that some of those differences are likely due to the carbon-to-nitrogen ratio of the amendments, which determines how nutrients are distributed between plants and microbes.

"It's clear that a well-balanced ratio of carbon and nitrogen is very important for good yields, less plant diseases and overall healthier plants," said McSpadden Gardener. The study is part of a larger collaborative project with other Ohio State faculty to look at the impact of organic amendments on all facets of crop production in a transitional crop system, including plant disease, crop quality and yield, weed populations, insects and soil variables. "Using compost as a means to provide fertility, as well as weed and pest management control that would normally be provided by fertilizers and chemicals is going to have an impact on plant performance," said McSpadden Gardener. "Generally organic amendments such as manures and composts stimulate soil microbes, but how that increase in microbial activity affects overall plant health is not fully understood. There are hundreds to thousands of microbial species in agricultural soils, and we are just beginning to understand how they interact to affect plant health." McSpadden Gardener said his results indicate that the application of the organic amendments increased microbial activity in general, meaning that no one particular microbe species benefited from the process. "We brought up the level of microbial activity, but we didn't shift the populations. The organic amendments didn't support one species as opposed to another," he said. "That supports the idea that organic amendments contribute to a 'general suppression' where pathogens are starved out by other microbes competing for nutrients and space or the total number of microbes that stimulate plant defenses are increased." With this in mind, the researchers are determining whether organic amendments can be improved upon to stimulate plant defenses and benefit plant health. One possibility, speculates McSpadden Gardener, is to inoculate compost with beneficial microbes before they are incorporated into the soil. That way specific microbes that attack plant pathogens would be available in higher numbers to have a greater impact on warding off plant diseases and increasing plant health. The research suggests, however, that such benefits would only work short-term. "We looked at soil bacteria and fungi at the end of the growing season, Where significant population shifts were evident at mid-season, less striking differences were observed at the end of the season," he said. "This suggests that the residual effects are not long-term and in order to take advantage of the microbial stimulation provided by organic amendments, they need to be added every year." Though the research is yielding more questions than answers, the data points to the ever-increasing role composting can have on agricultural systems. McSpadden Gardener is one of several Ohio State researchers who will be discussing the advantages of composting at the 2002 Composting and Compost Utilization International Symposium May 6-8 at Adam's Mark Hotel in Columbus, Ohio. The symposium will bring together over 400 researchers from 43 nations around the world to discuss new composting technologies and issues related to not only agriculture, but to health, the environment, waste reduction, odor management, heavy metals and air emissions. "Agriculture is one of the big areas of discussion because of all of the advantages composting has in that system," said Fred Michel, an OARDC professor and one of the co-organizers of the symposium. Research has shown that composting can reduce plant pathogens, leading to reduced use in pesticides. Composting can be used as a source of fertility in organic production, an industry that is growing by 20 percent every year in Ohio. Composting manure reduces odors and environmental contamination. In addition, composting is becoming more economically feasible for farmers to adopt. "The purpose of this meeting is to help people understand the benefits that composting can provide," said Michel. Harry Hoitink, an OARDC composting researcher and another co-organizer of the symposium, said that remaining progressive is just as important as educating individuals on the benefits and cost-savings of composting.

"We as Americans cannot decide not to cooperate with the rest of the world in this field. More and more companies that want to sell abroad must meet ISO (International Organization for Standardization) standards and those that cannot meet those standards cannot export and they will get left behind," said Hoitink. Added Michel, "There are things going on around the world that we are behind on." Japan, for example, has developed a 10-year plan to recycle and compost all of its organic waste that would have normally gone to the landfills.

Hoitink sees the need to compost not only yard waste, but food waste as well. "Food waste in landfills generates methane, which is a 20-30 times worse greenhouse gas than carbon dioxide," he said. "The amount of methane that is generated in landfills is equivalent to two million cars on the road everyday in the U.S. It's an amazing figure we don't think about, but something that we obviously need to work on." Benefits from composting are not only impacted from individual efforts, but the practice can change the face of entire industries, said Hoitink. "The nursery industry, for example, has been made possible entirely on the basis of compost use and the development of technologies that didn't exist 20 years ago," he said. The nursery and landscape industry has grown to be the biggest agricultural industry in the U.S. and the third largest agricultural industry in Ohio.

The Composting and Compost Utilization symposium is co-sponsored by the U.S. Environmental Protection Agency, U.S. Department of Agriculture, U.S. Composting Council, American Society of Agricultural Engineers, United Kingdom Composting Association, Composting Council of Canada, Institute of Biological Engineering, Japanese Organics Recycling Association and ORBIT (Organic Recovery and Biological Treatment) Association.

For more information on the symposium, registration information, and agenda listings and proceedings log on to http://www.composting2002.org, or call (610) 967-4135, ext. 22.

Author(s): 
Candace Pollock
Source(s): 
Brian McSpadden Gardener, Fred Michel, Harry Hoitink