Farmer diaries: Digging soil pits to assess earthworm burrowing and rooting

At the broad level there is agreement that increasing soil organic matter is good for soil health, earthworms and crop performance. However, there is little UK based data on the impacts of cultivation and organic matter additions on earthworm numbers and crop rooting.

Can good soil management increase deeper burrowing earthworm populations?

The aim of the deep burrowing field lab therefore is to test these practices on working farms and investigate whether previous research adds up when put into commercial practice. Asking the questions:

  1. Can soil management practices such as adding manure and reducing soil disturbance improve numbers of ‘deep burrowing’ earthworms?
  2. Is there any evidence that the burrows created by deep burrowing earthworms are used by crop roots, thus improving rooting depth and crop performance?

This field lab brings together three farmers with researchers at ADAS who want to test whether it’s possible to increase numbers of deep burrowing earthworms in their fields by altering soil management practices. The farmers have each picked treatments that are relevant to their farming system. Treatments included different soil cultivation methods and different forms of organic matter input.

The field lab follows on from a European Innovation Project (EIP) led by ADAS established in 2018. The farmers were keen to continue investigating the effects after the EIP funding finished to determine the effects of the deeper burrowing earthworms.

The above questions are being addressed over the course of the year by measuring soil properties, and earthworm populations, quantifying differences in crop performance and making visual assessments of rooting and burrowing which will be compared between the trial treatment plots.

Digging soil pits

In August the farmers dug soil pits to a depth of below 1 meter in their trial plot areas, enabling them to visually assess the following:

  • Crop rooting depth
  • Number of deep burrowing earthworm burrows
  • Evidence of crop roots utilising burrows
  • Differences in the soil appearance and structure of soil layers

Trialist: Rory Lay, Shropshire.

Rory’s trial field is a sandy clay loam and he has grown winter oilseed rape in the trial field this year. This is the second year that the treatments have been established. He is comparing the following treatments:

  • Strip till plus farmyard manure (FYM)
  • Strip till
  • Deep cultivation, plus FYM
  • Deep cultivation

Rory’s farm standard management is deep cultivation however he wanted to test whether strip tillage which is less disruptive to soil structure would help to increase earthworm numbers. It is hypothesised that the strip till plus FYM treatment would support the highest number of deep burrowing earthworms as this management would provide a food source (the FYM) whilst also not disturbing the soil and existing burrows (unlike the deep cultivation treatments).

Earthworm measurements

Farmer diary: Soil pit in field with deep cultivation, plus FYM

Farmer diary: Soil pit in field with strip till no FYM

Rory noted that earthworms were abundant in all the treatments but that there were noticeably more in the treatments which had received farmyard manure. This correlated with the prediction that the FYM was providing a food source.

The deep cultivation treatments were cultivated in the autumn of 2018 when the trial was established (for the EIP project) perhaps allowing for some earthworm recovery over this period.

Key conclusions from the soil pits

The earthworms were particularly abundant in plots with FYM addition – this is expected as the amendment provides a food source for the worms. There were many observations of oil seed rape roots growing down old earthworm burrows. This is potentially visual proof of the ecosystem services that earthworms provide to farmers. If the worms are allowing the crops to have deeper roots this will hopefully mean they can pull in more water and nutrients from the soil. The theory is that this will make the farm more resilient to drought and less reliant on fertiliser inputs.

What’s next in the field lab

The next step will be to compare how crops have performed between the trial treatment areas using ADAS’s agronomics methodology which tests for statistical significance in yield between trial areas taking into account the underlying environmental variation within the field. This will be a robust test of whether there are statistically significant differences in yield between the trial plots. The group is particularly interested in investigating whether improvements in crop rooting depth due to roots utilising deep burrowing earthworm burrows, has allowed greater access to water and nutrients thus positively effecting yield.

Get involved in your own farmer-led research

To keep informed of how this field lab and others are progressing sign up and become a member of the Innovative Farmers network. Got your own idea for a field lab? Then contact the team to find out how to get involved.


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