14 September 2001

Cultivation is the key to diversity

A three-year ADAS field experiment showed that cultivation

timing and depth in uncropped field margins had a big

influence on the type of wildlife-friendly annual plants that

thrive. Nigel Critchley, who led the research, explains

IN this DEFRA-funded research, a 6m-wide field boundary strip was cultivated each year, but left uncropped and with no other cover sown, to allow the weed flora to regenerate naturally.

It is a technique that is suitable for well-drained sands or sandy loams, and shallow, chalky soils. These uncropped wildlife strips have been used for some years by farmers in the Breckland ESA and under the Arable Stewardship Pilot Scheme in East Anglia and the West Midlands.

In the experiment, we assessed a range of cultivation regimes, with the aim of maximising species diversity and reducing the risk of pernicious weeds becoming dominant. We also aimed to keep the management simple by keeping inputs to a minimum and using existing farm machinery.

Plots were set up at three sites, in the Suffolk Breckland, on the Hampshire chalk, and on acidic sandy loam in North Yorkshire. Cultivations were either by ploughing to a depth of 15-20cm, or by power harrowing to 5cm. These operations were carried out once a year, either in September or March, and the type of cultivation was varied over three years in some plots.

A diverse range of plant species established itself at each site, including rare species such as pheasants-eye, dense-flowered fumitory, and rough poppy. Some scarce species also appeared unexpectedly, such as prickly poppy at the North Yorkshire site.

Not surprisingly, the cultivation timing and depth determined which species became established each year. This means that it is relatively easy to maximise diversity by varying the cultivation timing and depth between margins in any one year. Also, by using a different timing and depth over a number of years at each site, a wider range of species will be able to establish and set seed.

On the lighter soils, shallow autumn cultivations produced highest diversity, although varying this from time to time will help to prevent build-up of grasses or perennials. If the crop rotation includes spring and winter cropping, then the strips can simply be cultivated at the same time as the rest of the field, but left uncropped.

If the vegetation is tall, then topping immediately before cultivation might be necessary. After three years, there was some indication that grasses and perennials were building up, so these might need to be controlled in the longer term using graminicides or spot treatment. To be safe, sites with a history of pernicious weed infestation should be avoided.