Maximising the benefits of cover crops through optimising the use of rotations, nitrogen fertiliser and organic manures

  • Paul Cottney

Student thesis: Doctoral ThesisDoctor of Philosophy


The use of cover crops is highlighted as a method to enhance the sustainability of crop production. This involves growing species of plants over winter on land that would otherwise be left fallow. Cover crops sequester nutrients, protect soil from the elements through mitigation of excess rainfall, enhance crop diversity and can positively impact soil health. This project investigates if the practice of integrating cover crops in arable rotations can improve spring barley yields whilst facilitating lower nitrogen inputs. Under controlled conditions, they provided both yield and nutrient cycling benefits. However, under field conditions such yield benefits did not materialise. Cover crops were found to sequester considerable amounts of nutrients over winter and improved soil availability of nitrogen, sulphur and potassium.

This project addresses the lack of cover crop field research in Northern Ireland. A limited number of species were found to be suited to the conditions and rotations in this region. It was found that when cover crops are sown early i.e. after the harvest of winter barley, select species respond to organic manures and sequester nutrients by transforming them into biomass. This means that application of slurry to cover crops is a more sustainable land management practice than applying them to fallow land. However, this is dependent on species choice and sowing date. Species respond differently to later sowing. When sown late, phacelia produced the highest amount of biomass and accumulated 70 kg/ha of nitrogen which is half the requirement of a spring barley crop. Cover crops were found to have a limited effect on the short-term enhancement of soil structure and soil biology, based on the measurements used. However, this project demonstrates that cover crops have significant potential in the region of Northern Ireland as a biofertiliser that improves soil fertility whilst contributing to the long-term enhancement of soil health.

Amendments to agricultural policy to subsidise cover cropping would increase their use whilst helping to achieve greater agricultural sustainability at a regional scale.

Thesis embargoed until 31 December 2023.
Date of AwardDec 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsDepartment of Agriculture, Environment and Rural Affairs
SupervisorPaul Williams (Supervisor), Lisa Black (Supervisor) & Ethel White (Supervisor)


  • Cover crops
  • spring barley
  • nitrogen cycling

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