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In order to maintain soil organic matter content and/or add N to the system, arable crops are often grown in rotation with pasture leys (which often contain legumes). Earthworm populations have been shown to fluctuate greatly under such rotations, increasing under the pasture phase, but decreasing rapidly under the arable phase.

For example, a pasture soil in Canterbury was measured to contain around 800 earthworms/m² before it was cultivated and put into arable production. Two years later the earthworm population had declined to less than 200 m². Conversely, when an arable field with a population of less than 100 m² was converted to a grazed grass/clover pasture the population increased to between 400 and 600 earthworms/m² after only two years, which shows that the earthworms respond rapidly to the changes in management practices.

In general, over the whole rotation, average earthworm populations are intermediate between those under long-term pasture and long-term arable.

For more information contact:
Dr Trish Fraser

Agricultural practices and earthworm populations

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