Earthworms rapidly enrich soil and plants, new UCD study finds

Earthworms rapidly enrich soil and plants

Allison Bray

February 24 2022 07:29 PM

The humble earthworm could do the same job as high-cost soil fertilisers, new research from UCD has found.

A study by Prof Olaf Schmidt from the School of Agriculture and Food Science at University College Dublin found that earthworms rapidly enrich soil and plants through nitrogen excreted in their mucus.

It’s well known that earthworm presence in the soil can increase crop yield in the long run by releasing nitrogen that is otherwise locked away in soil organic matter as worms burrow.

But their ability to enrich soil was traditionally seen as “beneficial but indirect, slow and cumulative”, he pointed out in the study that appears in the peer-reviewed journal Soil Biology and Biochemisty.

But Prof Schmidt said the study reveals that this may not be the case after all.

A team of researchers from Ireland, Germany and China was able to track the nutrient transfer from earthworms into soil, wheat seedlings, and greenflies (aphids) using a method called stable isotope tracers, he said.

They found earthworm-derived nitrogen was acquired by greenflies after just two hours under laboratory conditions, and after 24 hours in the field. The researchers were astonished just how fast worm nitrogen moved through soil, to roots, into plants and into the insects feeding on plant sap.

“The real novel insight [we found] is that nitrogen from worms is going into crops really fast. Up to now we assumed this involved slow decomposition processes and microbial cycling. But our experiments show that nitrogen (N) and carbon (C) movement from living soil animals to plants can be extremely rapid,” Prof Schmidt said.

“This is very exciting because it suggests that earthworms probably supply nitrogen directly to crops, and they do it exactly when crops need it most because both earthworm activity and crop growth are sort of synchronised, by environmental factors, mostly temperature and moisture,” he added.

This could be significant for farmers trying to reduce their use of synthetic fertiliser at a time when the cost of synthetic fertiliser has sharply risen as the world’s supply chains continue to recover from the COVID-19 pandemic and energy prices rise, he added.

“This work could inform how farmers manage land, soil life and nitrogen supply,” he said.

“By adopting cropping practices that promote earthworms, these dynamic nitrogen benefits will also be maximised. We knew from previous research that good earthworm populations contribute agronomically significant amounts of nitrogen to the soil, but we did not know that they can supply crops with nitrogen in such a dynamic fashion.”

“All forms of nitrogen supplied naturally, from the soil's own stores, through decomposition and mineralisation, are economically and environmentally highly valuable and desirable, so we should maximise them,” he added.

“I don't think earthworms will replace all mineral and organic fertilizers, but their full use as a natural nutrient supply could offset the use and cost of mineral/synthetic fertilizers.”