Understanding soil health is vital to understanding how to sustainably grow crops and maintain livestock grazing and a key indicator of soil health is the earthworm population. Traditionally scientists extract earthworms from soil pits and manually count the population and identify adults - this is a labour-intensive process and the abundance differs greatly seasonally and due to the weather. Most earthworms are juveniles that cannot be identified to species, and different species burrow to different depths, making it difficult to characterise the populations using soil pit counting.
"Earthworms have been known to play a vital role in soil health since Charles Darwin studied them in the 19th century. But monitoring earthworm populations has remained difficult. eDNA is now an increasingly efficient tool for monitoring biodiversity. The standard methods were poor at detecting earthworm diversity but we have now optimised the technique and confirmed its effectiveness. We are optimistic that eDNA will become a routine tool for helping to make agriculture and food production more sustainable." Dr Penelope Watt, Senior Lecturer in Zoology
eDNA sampling involves collecting, extracting, amplifying and sequencing genetic material that has been left behind by organisms in their environment - in this instance soil samples. This offers many advantages over manual extraction of the earthworms as eDNA is less labour intensive and does not rely on seasonality or depth to detect earthworm species.
The results in this trial have been compared to manual extraction - identifying the same 8 species, and often finding more species per sample. The results also detected juvenile earthworms, which are difficult to identify with hand sorting.
The team are excited about this promising study - the aim next is to standardise the sampling tool and develop more accurate methods for estimating earthworm abundance. The researchers hope that eDNA will allow for a quicker, more accurate and cost effective tool for farmers and policy makers to make decisions about sustainable farming methods.