Research Feature: Monitoring Soil Microbial Communities as an Indicator of Soil Quality

Posted: May 4, 2009

A series of recent and forthcoming journal articles describe how studies of soil microbial communities might provide early warning signs of declines in soil quality. The studies are the work of Guilherme Chaer, a 2008 soil science graduate student from Brazil and his thesis advisors, professors Dave Myrold and Peter Bottomley.  In this short Web interview, Dave and Peter discuss the concept of soil quality, its link to soil microbiology and Guilherme Chaer's research at OSU.

Related Publications

Chaer, G. M., D. D. Myrold, and P. J. Bottomley. 2009. A soil quality index based on the equilibrium between soil organic matter and biochemical properties of undisturbed coniferous forest soils of the Pacific Northwest. Soil Biology and Biochemistry 41:822-830.

Chaer, G.M., M.F. Fernandes, D.D. Myrold; P.J. Bottomley. 2009. Comparative resistance and resilience of soil microbial communities and enzyme activities in adjacent native forest and agricultural soils. Microbial Ecology: published online 31 March 2009.

Chaer, G.M., M.F. Fernandes, D.D. Myrold; P.J. Bottomley. In Press. Shifts in microbial community composition and physiological profiles across a gradient of induced soil degradation. Soil Science Society of America Journal.

Chaer, G. M. 2008. Response of soil microbial communities to physical and chemical disturbances: implications for soil quality and land use sustainability. Dissertation. Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon.

Who is Guilherme Chaer and how did he come to OSU?

Peter:  Guilherme is Brazilian and works for their national agricultural agency called Embrapa – an agency that is sort of the Brazilian equivalent of the US Department of Agriculture.  He came to OSU through a scholarship funded by the Brazilian government.  We have had several students come to OSU through this program and we have been impressed with their skills and motivation. 

Dave: Guilherme had a desire to increase his expertise in soil microbiology and that made him a good fit for our program.  Now that he has returned to Brazil, he is continuing his research with Embrapa.

These studies relate to the concept of soil quality – how do you define that?

Dave:  Soil quality is a term that has been around for at least a decade – the idea is that you are measuring some range of properties to get an idea of whether the soil is healthy and functioning the way you want it to in the environment.  It is a term that is hard to quantify, yet if you ask any farmer in Oregon, he can identify the spots on his farm where the soil is good and the spots where it is not as good for what he wants to do.  So everyone has an innate sense of what a good soil is – yet trying to actually quantify that has been a big challenge. 

The amount of organic matter in a soil is often used as an indicator of soil quality – the more organic matter, the greater the fertility and the greater the soil productivity.  For example, one of the things that changed a lot in the Great Plains when it was broken by the plow and cultivated is that soil organic matter was depleted rapidly.  But, often by the time you can measure the decline in organic matter, it’s too late – the soil quality has already deteriorated.

How does soil microbiology relate to soil quality?

Dave:  The methods to identify and monitor microbes living in soils have advanced dramatically in recent years.  They open up the possibility that biological properties could be used to measure and monitor soil quality.

Peter:  For example, perhaps we could identify indicator microbes in a soil that, sort of like a canary in a coal mine, would signal when the soil system is under stress and we need to change our management practices.  Do certain microbes disappear from the community or do others appear as the soil responds to a stress like plowing or cultivation?  How does the composition of the microbial community shift in response to soil deterioration?  Perhaps we could use microbial indicators as a sensitive monitoring system – sort of like measuring blood pressure.  Ideally they would give a warning sign when soil productivity was in the early stages of decline, and then we could correct the decline in soil quality.

Dave: Our student, Guilherme was interested in these ideas, so his studies focused on monitoring soil microbial communities and biochemical properties as he subjected the soils to different stresses.  He worked with both soils from the Pacific Northwest and from Brazil and had both lab and field components in his dissertation.  Our paper that just came out in Soil Biology & Biochemistry focuses on developing an index to measure soil quality using biochemical properties.  Guilherme has another paper coming out this summer that describes experiments he carried out in Brazil to monitor changes in the composition and the diversity of a soil microbial community under different tillage regimes. 

Peter: Guilherme is now involved in studies in Brazil that take a step further – they are looking at whether they can observe changes in a microbial community once they stop the tillage disturbance. These studies get at reversability -- once the disturbance stops how does the microbial community respond?

What is the major contribution of Guilherme’s work?

Dave: At OSU, Guilherme focused on the ecological principles of resistance and resilience. Resistance gets at the idea of withstanding change – how much stress can the soil microbial community withstand before it changes, and resilience focuses on the community’s ability to bounce back after a stress has been applied.  Those sorts of ideas play into the soil quality index he put together in the Soil Biology & Biochemistry paper, and it set the basis for the experimental work he continues to do in Brazil.  That’s the scientific perspective behind his work and you can see the practical application of it – it gets at how we can better manage soil productivity and prevent its decline. 

Peter: Guilherme had a focus on uniting ecological concepts with modeling concepts.  He then applied those concepts into something as practical as the agronomic term “soil quality.” That’s pretty special to be able to think about the question in an ecological sense, but also disciplined enough to see whether he could apply a model to it. 


Part of this research was carried out at the Microbial Observatory in the H. J. Andrews Experimental Forest and was supported by a grant from the National Science Foundation Microbial Observatory Program (MCB-0348689).