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Turning over the soil to prepare it for planting is a fixture of the agricultural calendar, but it’s also devastating for earthworms. Conventional tillage uses a plough to invert the soil and bury weeds and leftover crops, but it also exposes earthworms to predators and harsh weather, compacts the soil, and destroys organic matter rather than leaving it to decompose. Afterwards, earthworm numbers take up to ten years to recover. By contrast, in land planted without tilling—usually by drilling seeds into the soil—earthworm numbers are 137 per cent higher, according to research published in Global Change Biology, which looked at 215 field studies from 40 countries, from as far back as 1950. Organic matter in the soil was also up 196 per cent. No-tillage is becoming more popular around the world, because it conserves soil structure and reduces erosion, although more herbicides are generally used to kill weeds. Anecic worms, which take food from the surface but dive deep between soil layers and set up permanent burrows, were particularly affected by conventional tillage, as were epigeic worms, which live in surface mulch. While earthworms found in cultivated land in New Zealand are non-native, these guests now have a critical ecosystem role, recycling organic matter, making nutrients more available to plants, and improving soil structure.

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