Using Insects to Assess Soil Quality

Organic Agriculture Centre of Canada

In the future, organic farmers may be able to use tiny, wingless insects to help them easily assess the health of their soils.

Preliminary research has shown that springtails are good bio-indicators of soil quality. What’s needed next is detailed follow-up research and development to create a simple test for farm managers and extension specialists.

Though that process could take five to 10 years, Karen L. Nelson, lead author of the “Influence of agricultural soils on the growth and reproduction of the bio-indicator Folsomia candida” study, has a clear idea of how the test could work.

Farm managers would “place their springtails in the soil for a set number of days, let them grow for a number of days, extract the insects, take a picture with a digital camera, load this on their computer and the image analysis would do it for them. It is actually a very simple test.”

Getting there will take considerably more time and research, yet the benefits would be significant.

Currently, as noted in the study, the standard assessment tools for soil quality require complex biological, physical and chemical data that are costly and time-consuming. Bio-indicators – organisms sensitive to changes in their surroundings – can simplify the process for assessing soil quality.

“The most significant finding is that we believe there is potential for this insect to be used as a bio-indicator for soil health that could lead to a soil health test for farm specialists,” says Nelson.

The type of springtail considered for the test, Folsomia candida, is usually about 1 millimetre long, or the size of a pinhead. It is found in compost and often has a whitish colour. Other types of springtails are different colours and sizes.

Springtails are closely associated with key ecological processes such as decomposition and nutrient cycling. Their feeding behaviour directly influences activity of microscopic organisms that break down dead material and the biomass of the soil ecoystem.

“This close association between the bio-indicators and the system can be exploited in two ways,” states the study. 

In the first way, the composition of the species and changes in the density of the insects “can be considered as early warning indicators of ecosystem change.” This lets farmers know that soil health may be compromised so they can take steps to improve it.

In potato crops, for example, soil health can be degraded fairly quickly by plants taking nutrients from the soil with little natural replacement.  To correct this problem, a longer rotation may be needed or the land may need to be planted with crops such as clover to return nitrogen.

By using biological indicators feeding directly on the resources available in the soil, you get “an early warning indicator,” says Nelson.

In the second way, that of the test, “changes in key life history parameters of bio-indicator species after laboratory exposure can be used to determine the current relative status of these soils.”

Soil health can be determined by measuring springtail body growth. Results showed that changes in the growth of one-day-old springtails over a period of time “will effectively reflect the relative quality of different soil samples,” says the study.

More research is needed. Nelson noted that two of the study’s co-authors, Derek Lynch and Gilles Boiteau, are continuing with Folsomia candida research.

Though having a test using springtails is still in its infancy, the results of the current study show the topic has considerable potential. “One of the hopes of getting the article out (published in Pedobiologia - International Journal of Soil Biology) was to continue the interest and to keep it going,” says Nelson.

Trying to assess soil health could be compared in complexity to assessing air quality, where lichens are now used as bio-indicators. The effectiveness of lichens –
fungi that grow symbiotically with algae – in detecting changes in air quality has become so well known that the United States Forest Service, an agency of the U.S. Department of Agriculture, has a website on the topic. The National Lichens and Air Quality Database and Clearinghouse site states that lichen bio-monitoring is helping federal land managers assess ecological impacts of air pollutants.

Maybe one day, springtails will help farm managers monitor and assess the ecological health of farmers’ soils in the same way lichens are already helping assess air quality.

This article was written by Steve Harder on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the Organic Federation of Canada and industry partners
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Posted March 2011