Earthworms again under the spotlight

AgResearch scientists are again seeking help to gain a better understanding of the distribution of one of the little known heroes of New Zealand agricultural production.

Earthworms play a vital role in the soil by decomposing organic matter, making nutrients available to plants and creating burrows in the soil to improve the movement of air and water.

There are three main types of earthworms in our pasture systems, with the dung and topsoil earthworms being common but the deeper burrowing earthworms are often absent. Studies have shown the introduction of surface active earthworms improves annual pasture growth significantly as well as boosting environmental performance and extending the growing season. Studies in the 1980s found earthworms to increase grass growth by over 20%.

However, Dr Nicole Schon, a soil biologist and earthworm expert at AgResearch in Lincoln says there’s still not a great deal known about the earthworm distribution and scientists believe there are still significant areas that don’t have any at all. That’s partly because earthworms are all exotic, having arrived accidentally with the first European settlers and as a result their distribution was sporadic.

Therefore, this winter farmers, land managers and other members of the community are encouraged to take a few minutes of their time to survey and then share information about the earthworm population on their property.

“The instructions are simple to follow and available online under the useful links section of www.agpest.co.nz . The results themselves can then be loaded onto the NatureWatch website, where people share what they see in nature and learn about New Zealand animals, plants, and fungi. (www.naturewatch.co.nz)

Dr Schon’s request follows the ‘Great Kiwi Earthworm Survey’ conducted last year with funding from Beef+Lamb NZ that resulted in over 100 responses from across New Zealand.

Results from the survey showed sites typically contained only 2-4 earthworm species, Dr Schon says.

“All regions contained the dung and topsoil earthworms. Deep burrowing earthworms were reported in Southland for the first time. However, they were not observed in the photos from the Bay of Plenty/East Cape, Central Plateau, and Canterbury/North Otago which shows that deep burrowing earthworms were still absent from large areas of land.”

Whether earthworms remain an important component of our pasture systems after fertiliser application was investigated in a study funded by Beef+Lamb New Zealand in order to determine the relevance of earthworms in today’s pasture systems.

“Pasture growth was measured throughout the year and was found to be greater in the areas containing all types of earthworms compared to pastures which did not. Pasture growth benefited the most from earthworms during the time they were most active, autumn to early spring. Even after the application of both urea and superphosphate earthworms still had a positive influence on pasture growth, increasing growth by more than 5%,” says Dr Schon.

“For this study we selected three sites in the lower North Island where the deep burrowing earthworms were known to have been and these were compared to nearby sites where the deep burrowing earthworm had not yet established. While we need to be cautious in interpreting these results, as we cannot exclude other factors that may be affecting pasture growth from the analysis, it would appear that having all types of earthworms present in the soil benefits pasture growth. These results are supported in the literature. ”

Dr Schon says a fully functional soil should contain all three types of earthworms for sustained production. In one spade spit ideally you should have at least one dung earthworm, 14 topsoil earthworms and one deep-burrowing earthworm.

To participate in this year’s worm survey, go to http://agpest.co.nz/useful-links/ for instructions, and www.naturewatch.co.nz to upload results.