Researching the use of willow tree leaves to make farming more carbon-neutral is being undertaken by the Institute for Global Food Security (IGFS) at Queen’s University Belfast.

Willow grows easily and it is already used as a bioenergy crop. The Agrifood & Biosciences Institute (AFBI) NI, with whom IGFS will partner on this project, harvests willow for biomass.

This project will take willow leaves and branches (up to 18mm diameter) left over from this process, and feed to ruminant livestock, sheep in the first instance, to see the effect on emissions.  

Early, in-vitro research at IGFS aimed to evaluate the nutritive value of different willow varieties and their potential to reduce emissions due to bioactive compounds (condensed tannins). Willow was compared with alfafa, a forage with no tannins. Results indicated a high reduction in methane emissions – around 50% – when compared with the alfalfa.

The next stage is feeding willow silage directly to animals, with farm trials, using sheep, scheduled to begin in NI in early 2022. Both ammonia and methane emissions will be measured, along with nutrient value, digestibility and rumen microbiome in the indoors trial.

Another aspect of the project will assess the efficacy of willow trees as part of ‘agroforestry’, where trees are grown in pasture areas so animals can graze naturally on the foliage. Agroforestry has become popular in places like New Zealand as part of a move towards ‘regenerative farming’, but there is a dearth of scientific data. As well as reducing the need for conventional silage, supporters point to other benefits – such as improving soil quality, biodiversity and extending the grazing season.

IGFS lead on this project, Dr Katerina Theodoridou said the 4-year, BBRSC-funded research, in which Reading University is also a partner, was the culmination of much laboratory research.

She said:

“Willow definitely has great early potential but we need evidence from the farms – very little data currently exists on willow silage.

“Measuring the effect of the bio-active compounds on emissions will give us urgently needed evidence that can be used in a practical way to make agriculture more sustainable.”