In praise of worms

`Gley" is not a word I can warm to, suggesting as it does something close to cold porridge. "Podzol" is scarcely better: a name for one of Beckett's in-sanitary tramps. But a podzolised gley is what the soil maps tell me constitutes our Mayo acre: a meagre mud ground down by the glaciers from sandstone and shale, then leached of its good minerals once men had felled the trees - land not fit for much on any official estimate, and best left to grass.

Can this be the soil that has fed us so generously these past decades - not just with spuds and cabbage, but sweet corn and squashes, basil and beans?

For some people, soil and dirt are the same thing. "Come in and wash your hands!" This, with grimaces, to a child digging in the garden. Even quite bright people use the words interchangeably. But soil is not dirt, in that derogatory sense; it deserves a lot more respect, even love.

It helps, of course, to have the whole story of soil spread out around me: bedrock and boulders, gravel in the streams, a whole mountain slowly wearing down in the wind and rain. I go out in spring to rake the soil for sheer pleasure; scooped up, it sifts through my fingers, cool and soft as velvet.

"Loam" has always seemed a friendly word, yet all it means is soil which is less than one-third clay. Mine is a sandy loam, even a silty one, full of fine grains that give it that sensual, silky feeling in the hand. You can tell a soil's provenance by thoroughly kneading a moist palm-full between finger and thumb: the closer it gets to a sticky ball of plasticine, the higher the content of clay. Even a light loam like mine has its drawbacks when fat Atlantic raindrops batter the seed-beds, breaking down the soil crumbs and washing the finest particles into all the pores. Then the fast-drying winds of spring shrink the crust and weld the particles together like cement. Germinating seeds find themselves heaving up flagstones to get a leaf into the sun.

The answer is humus and more humus: seaweed and compost stirred into the hungry soil. Ideally, its structure should be built of crumbs about the size of a match-head, each a mix of fine rock particles and organic matter that stays together in the rain. A single crumb of soil may hold 100 million bacterial cells producing polysaccharide gums and five metres of fungal threads binding the particles together. Soil that has passed through an earthworm's belly is ready-mixed to make such a stable and fertile gingerbread.

In a topsoil of crumbs there are as many spaces as solids, and thus plenty of holes for water and nutrients to run through, and ducts to carry oxygen to plant roots and the great underground zoo of the animal world.

Along with many-legged creatures such as wood-lice and millipedes and fat larval grubs of beetles and flies, there is a teeming micro-fauna, crawling or swimming through the moist, dark labyrinth of soil-pores. Some of its names would have pleased Lewis Carroll: protozoa, rotifers, gastrotrichs and tardigrades.

Next to the single-celled protozoa, the most abundant animal of soil is the nematode, the eel-worm or roundworm, that writhes, not side to side, but up and down. Most nematodes are best inspected under a microscope where, having transparent skin, they become beautiful, like tiny crystal serpents.

There are, of course, myriad species of nematode but one, in particular, is now famous. Caenorhabditis elegans, also a mere millimetre long, is the only animal to have had all its DNA letters read: an unbelievably precise 19,099 genes. Science is now in a love affair with nematodes, even more than with fruit flies or mice, because its see through body lends itself to counting things and watching cells divide.

Some nematodes are among the worst pests of agriculture, grazing on plant roots or burrowing into them: potato eel-worm is one of the awful warnings of gardening books. But other species have a totally different lifestyle, and one which absorbed a momentous symposium last week at NUI Maynooth. Researchers came from all over Europe to the newly-funded Institute of Bioengineering and Agroecology to discuss the future of insect-killing nematodes as a welcome alternative to chemical pesticides.

The creatures in question belong to two genera, or groups of species, Steinernema and Heterorhabditis, which go through their life cycle as parasites inside insect larvae. They release a bacterium into the insect's bloodstream that reduces it to a nourishing soup, then, upon its death, depart into the soil at a larval stage to find another host.

With a lifecycle of a fortnight, the nematodes lend themselves to rapid mass-production, and their larvae to storage and an easy application: just mix with water and drench the plants. At the Maynooth symposium, much of the talk was of developing markets for EPNs (entemopathogenic nematodes). Mushroom growers can use them to kill the grubs of fungus flies and vegetable-growers the root-fly grubs.

All this could be very big business. Professor Martin Downes, director of the new Maynooth institute, has been working on nematodes for six years and collecting them from all over the world. But he is personally as excited by the technique's potential for Third World agriculture, using production of EPNs from local strains of nematode.

In Ireland, there are two species of Steinernema, found in almost any shovel-full of soil, but Heterorhabditis has only one species here, known so far simply as "the Irish type". It frequents sandy coastal areas - much like Thallabawn - and while it seems suitably impartial in choosing hosts in laboratory conditions, nobody knows what it punctures in the wild. The bacteria it releases are also luminous, so I may yet find myself on hands and knees among the cauliflowers, looking for glowing corpses.

"The New Survey of Clare Island" Seventh Annual Seminar will take place in the Community Centre, Clare Island on Friday, April 28th, starting at 10 a.m.. Information from Royal Irish Academy, tel: 01 6762570.