Determining the presence of earthworms in soil has become easier. Hill Labs is delighted to announce the release of our new earthworm eDNA (environmental DNA) test which detects the DNA of earthworms in soil. A first for New Zealand, this soil test provides an indication of one of the biological components of soil health.
While there is a growing interest in soil health, it is difficult to define. It is generally accepted that there are three interrelated aspects of soil health - physical, chemical and biological. These components together impact how healthy and productive a soil is. Physical and chemical components have been well researched but biological components are more challenging. There are a large number of ‘critters’ who live in the soil and measuring earthworms provides a high-level view of the biological aspects of soil health.
The presence of earthworms in soil is commonly seen as a positive indicator of soil health. Fondly referred to as the ecological engineers of soil, earthworms contribute to the aeration and cycling of nutrients in soil, as well as helping create good soil structure and breaking down organic matter.
There are three main ecological groups of earthworms that each perform a different function in the soil:
Hill Labs uses molecular technology in other parts of the business and realised that this technology could be applied to measuring earthworm abundance in soil. The test detects the eDNA, or tiny traces of genetic material left behind as earthworms pass through the soil. For now, the test measures the eDNA of New Zealand’s most prominent earthworm species, Aporrectodea caliginosa. There are plans to expand this testing and we are working closely with industry to understand what will be most impactful and valuable for farmers and growers.
Results are expressed as pg/g of the eDNA of A. caliginosa and not as the number of earthworms per square metre as reported in field visual assessments. While there is good correlation between the two methods (Figure 1) and they both assess an earthworm population, they are different. A field visual assessment measures the number of earthworms present in a particular spade square at a particular time compared to this new test which measures the DNA of A. caliginosa present in soil at a particular time.
This test was developed using mostly pastoral soils and it is important to note that it is possible arable and horticultural soils may naturally contain lower levels of earthworm eDNA. This is due to crop soil samples generally being taken at a greater depth where A. caliginosa is less likely to be found. Additionally, lower levels of plant and animal residues that encourage earthworm activity are present and cultivation activities often reduce earthworm abundance.
Through the project, we learnt that DNA can behave differently in different soil types and significant effort was put into developing a method that corrects for these differences. We also learnt that eDNA is stable once soil is dried and ground. It is recommended that soil samples are delivered to the lab promptly after sampling, and samples that are taken on a Friday are stored in a fridge and sent on the Monday.
This test is an easy and convenient way to measure earthworm abundance compared to current methods available. It is an alternative that may give a different picture as it measures residual DNA of earthworms, as opposed to individually counting them. It is recommended users follow a similar testing regime to existing soil health tests, where a baseline is built over 3 to 5 years and followed by intermittent testing to monitor changes over time.
We would like to thank Dr. Nicole Schon, Our Land and Water and Bob Longhurst for their contributions in making this test possible. Nicole is based at Lincoln AgResearch and is New Zealand’s leading earthworm specialist and provided invaluable background and guidance for this project. We look forward to continuing to work with her as we further develop the test. Our Land and Water provided funding for the initial stages of development of the test and we are thankful for their contribution. Read more about Our Land and Waters contribution here. Bob is with Pastoral Nutrient Management kindly assisted with sample collection.
We are committed to supporting farmers and growers in their sustainability journeys and in making confident decisions. Measures of the biological aspect of soil health are generally difficult and this test is a welcome addition to our suite of soil tests.
More information can be found in the earthworm eDNA technical note or by contacting us directly at ag.csm@hill-labs.co.nz or 0508 HILL LABS.
