Understanding the impacts of anaerobic digestate on the ecosystem services provided by grassland soils

Producing biogas through on-farm anaerobic digestion of organic feedstocks, sourced from the agricultural sector, is of growing interest as a sustainable energy source. These feedstocks may include energy crops such as maize or sugar beet. However, environmentally sustainable biogas production requires the use of livestock manure/slurry as a feedstock, often co-digested with other inexpensive feedstocks including waste potatoes, whey and food waste. To maximize the economic and environmental benefits from anaerobic digestion, anaerobic digestate (AD) should be returned to land as a soil conditioner and, more desirably, as an alternative to inorganic fertilisers. In many livestock production systems, this will involve AD application to intensive grassland soils. However, despite initial research, for example under the DC-Agri project, the benefits and risks of applying AD to grassland soils are yet to be fully evaluated. Critical research questions that remain outstanding include how AD application affects: farm dependency on inorganic fertilisers; soil microbial communities and other soil biota; water resources; gas efflux to the atmosphere; and grass yield and quality.

Therefore, the overall aim of this project is to quantify the impact of AD application on grassland soil ecosystems. Working with our CASE partner Cockerham Green Energy Ltd, the following objectives will be addressed:

Quantify temporal changes in the physical and geochemical forms of phosphorus (P), nitrogen (N) and carbon (C) in AD compared to feedstocks.
Assess the impact of AD application to intensive grasslands on the functional activity and composition of the soil microbial community and additional soil biota.
Determine changes in the forms and bioavailability of P, N and C within intensive grassland soils following AD application, alongside impacts on grass yield and quality.
Measure the impacts of AD application on N and P export to water and on greenhouse gas plus ammonia (GHG+A) emissions from intensive grassland soils.