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Autumn leaves encouraging Earthworm activity

Grass Clippings - Autumn leaves attracting Earthworm activityThe return of the wind reminded the trees it was autumn, whether or not they were ready to let their leaves fall. The beech stays stubborn, already beginning to gild, but the willow on the stream is shedding nicely, giving us back the mountain’s peak and the rising of the moon.

Some proper rain, too, woke the earthworms deep in their burrows, alerting them to their annual job of pulling fallen leaves down into the soil. I won’t say I’ve actually kept watch for this, Charles Darwin having done it for everybody to write his study The Formation of Vegetable Mould Through the Actions of Worms, published in 1881.


Thanks to him, we know that earthworms start pulling at the leaf’s pointy end, to draw it down most easily. He proved this deliberate choice by offering the worms a variety of leaf shapes cut from paper, all of which disappeared sharp-end first.

In Octobers past, this was my month for lifting the maincrop potatoes, taking care to rebury every earthworm tossed aloft, before the attendant robin could pounce. And so, in the UN’s International Year of Soils, it is to the worms and their companions in the top spit of soil – mites, ants, beetles, bristletails, bacteria and all – that my thoughts turn first, ahead of global erosion, desertification, salination, and so on of what Americans, unforgivably, call “dirt”.

Ireland’s farmland may still seem mercifully green, but is, nonetheless, vulnerable. Among the threats named in EU concern for soil protection are loss of biodiversity and organic matter, flooding, and compaction. This helped to prompt Teagasc’s new soil map of the whole of the island, undertaken with the UK’s Cranfield University and a first such digital enterprise (gis.teagasc.ie/isis). With it has come sampling, jointly with UCD scientists, of microbial communities in different soils at 240 locations.

Analysing them is no simple task. One gramme of grassland soil can hold more than a billion organisms of more than 10,000 different bacterial and fungal species. Microbes are, however, the ultimate drivers of nutrient and carbon cycling, and knowing how they work in different soils is essential to the “smart green growth” promised for Ireland’s farming future.

Northern Ireland, meanwhile, is the centre of research into a predator of the island’s largest and most important earthworm, Lumbricus terrestris. This deeply burrowing worm provides drainage and oxygen for the soil and is the notable dragger-down of its humus. Its enemy is the New Zealand flatworm, Arthurdendyus triangulatus, a creature that will even chase a worm down its hole in order to pierce and digest it.

Since arrival in 1963, probably in potting compost, the flatworm has spread across all six counties of Northern Ireland, consuming Lumbricus terrestris by choice, leaving burrowless soil to grow steadily more acidic and waterlogged, and robbing birds and mammals of a staple food.

It has also spread into the Republic, where it is probably greatly under-reported – but also little studied, by Teagasc or, it seems, anyone else. The national Biodiversity Data Centre in Waterford has “sparse” records from the north-west, Galway and Kerry and warns that the flatworm’s gradual, long-term spread could put the drainage and fertility of farmland at risk.

L terrestris is only one of the earthworms. An important group for study in Ireland are the tiny potworms, the Enchytraeidae, perhaps 15mm long. While widely found, sometimes at many millions to a grassland acre, many Irish species are adapted to live in waterlogged or even flooded soils.

The Enchytraeidae make up as much as 70 per cent of the animal life in peatland formed from sphagnum mosses. But a strange, new and minute worm, found at three sites in Mayo’s blanket bogs, has mystified a research team led by UCD’s zoology professor Dr Thomas Bolger.

Only three to four millimetres long, it is a hitherto unknown species in a family of freshwater worms called Phreodrilidae. Another, the first found in Europe, was a single specimen collected from a tributary of the River Lagan in Co Down in 2000. But the worms gathered in Mayo number more than 100 – an established population.

And here is the big puzzle. Phreodrilidae are native to the landmasses – Australia, Africa, South America etc – of the ancient southern supercontinent of Gondwana that began to break up 170 million years ago. How did they get to Irish peatlands? A paper for the Irish Naturalists’ Journal by Dr Bolger and his colleagues, Rudiger Schmelz and Rachel Wisdom, is headed “Invasion from down-under or ancient relict?”.

If so ancient, why this late discovery? Could oceanic migratory birds, such as storm petrels, have dropped them thousands of years ago? As for human transportation from down under to beneath Mayo peatland – that, writes the team “remains a challenge for the imagination”.

Michael Viney’s 2015 book Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks

Article from The Irish Times

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