Margins take centre stage

More than 30 people joined arable plant and invertebrate specialist Emily Swan as she led a farm walk around impressive margins on the Holkham Estate.

The group looked at the various outcomes that can be achieved depending upon when, how and where you plant your cultivated margins.

Margins: A definition

For people new to the concept of arable field margins, these are herbaceous strips or blocks around arable fields that are managed to provide benefits for wildlife or to reduce water and soil run-off into water courses. Where they are managed for wildlife they are classed as a priority habitat. Arable field margins are usually sited on the outer 2-12m margin of the arable field. The limit of arable field margin priority habitat is defined by the extent of any management undertaken specifically to benefit wildlife.
Arable field margins include cultivated, low-input margins; margins sown to provide seed for wild birds; margins sown with wild flowers or agricultural legumes and managed to provide pollen and nectar resources for invertebrates; and margins providing permanent grass strips with mixtures of tussocky and fine-leaved grasses.

The importance of cultivated margins in enhancing biodiversity is increasingly being understood. This was highlighted by the findings of the Biodiversity Audit of the North Norfolk Coast by the UEA Environmental Research team, and is outlined in the diagram below.

As the graphic above explains, cultivated margins are one of the most important resources for increasing and enhancing biodiversity in the farmed landscape and Emily was able to show the group firsthand how the margins in North Norfolk were allowing some very rare species to re-establish themselves. This includes Corn Spurrey which is an increasingly rare arable plant that exists on acidic, chalky land.

During the course of the walk, the group was able to see how the team at Holkham had tried a range of different margins with varying levels of success. As Emily was swift to point out, there is no one magic bullet. Different margins will work for different people depending upon the context of their situation. Where one farmer/landowner may get a lot of biodiversity in a strip of margin, another will get a proliferation of one particular plant – the name that continuously cropped up during the talk was Fat Hen!

Emily’s advice was to try something and see what happened. She also advocated giving margins time because different plants will make their appearance at different times and a margin will not look the same from one year to the next.

However, while Emily advocated trial and error as a means to discovering what worked well on your land, she did have three golden rules:

  1. Aim to get plenty of colour into your margins by including a wide range of diverse plants in your seed mix
  2. Ensure you have three levels of growth – bare or barely covered soil (for beetles and other invertebrates, plus ground nesting birds; short plants that give some ground cover; and tall plants.
  3. Make sure your soil is between 50 and 90 per cent covered. Too bare or too lush will both be detrimental to a diversity of plants and invertebrates.

In addition, this advice from Defra will help anyone seeking to introduce arable field margins onto their land:

Ensure that margins are protected from agricultural inputs to adjacent crops.

Where possible, locate margins in a range of locations to provide variety of aspect, soil type and shading.

Maximise the diversity of margins to provide a range of habitats for species. Field margins have
an important role in increasing the permeability of an otherwise hostile environment thereby
aiding the movement of species through the landscape.

Select the most appropriate management options for specific objectives. For example,
uncropped cultivated margins have been demonstrated to be the most suitable option for arable
plants, exhibiting the widest diversity of annuals, perennials, grasses, forbs (non-woody broadleaved
plants other than grass), and spring and autumn germinating species (Still and Byfield,
2007), while tailored sown mixes deliver the greatest benefit for farmland birds.

In planted margins, increase the diversity of flowering species to ensure the continued provision
of pollen and nectar throughout the extended season.