Target-N2O  Targeting N2O emission hotspots in dairy pastures for mitigation action: microbes, stable isotope methods and modelling.

Photographer: Background

Recent studies have established farm-scale features where livestock congregate as ‘hot-spots’ of emissions of the powerful greenhouse gas, nitrous oxide (N2O). Cattle urination density correlates with time spent at a location resulting in the non-homogenous distribution of nutrients deposited within excreta. Increased livestock traffic can also result in elevated levels of soil compaction leading to potentially favourable edaphic conditions for losses of nitrogen from the agricultural system. Farm-scale N2O emission hot-spots may represent economically attractive areas for targeted nitrification inhibitor application, as the inhibitor could be applied over a relatively small area, minimising costs associated with quantity of product required and labour associated with application to soil. There are limited studies, however, investigating the efficacy of nitrification inhibitors within such areas.

Project outline

The project described here, is funded under the Horizon 2020 Marie-Skłodowska-Curie Actions Individual Global Fellowship programme. This training-through-research fellowship supports international mobility and knowledge exchange for the awarded researcher, Dr Karina Anne Marsden. The project is comprised of a two year outgoing phase (2018-2020), hosted by Prof. Richard Eckard at The Primary Industries Climate Challenges Centre, University of Melbourne, followed by a return year with the project PI, Prof. Dave Chadwick at Bangor University (2020-2021).

In the outgoing phase, Karina will learn new techniques in molecular ecology, stable isotope methods and modelling and will bring those skills back to Bangor University in her return year. The overarching aims of project are to determine the agronomic and environmental cost-benefits of a targeted nitrification inhibitor (DMPP) application strategy in N2O emission hot-spots of intensive dairy pastures.This study aims to meet four objectives each aligned with a work package: 

Factors influencing nitrification inhibitor performance

The first objective of the Target-N2O project is to explore the factors influencing N2O emissions and DMPP performance in hot-spot feature soils. This is being investigated through a series of laboratory incubations, exploring the importance of the interaction of urine, dung and compaction on N2O emissions and DMPP efficacy. This includes testing whether standard rates of DMPP application are sufficient to reduce nitrification within areas highly frequented by cattle. A radio-isotope tracer technique is also being used to investigate mineralisation rates, sorption and desorption of the nitrification inhibitor within different spatial locations of dairy pastures. This will help to determine the appropriate application rates of DMPP required to reduce nitrification rates and N2O emissions from emission hot-spots in dairy pastures.

Microbial community composition and function

The second objective of the project is to investigate the molecular ecology of hot-spot feature soils to determine whether N cycling differs in pasture areas with a history of high livestock impact. Here, Karina is learning methods in molecular ecology, including quantification of key nitrogen cycling genes in pasture soil. This will provide an evidence-base to determine whether soils around farm-scale features with high livestock occupancy (e.g. drinking troughs and gateways) differ in N cycling microbial function and whether they should be addressed as spatially distinct zones in N cycle models and national greenhouse gas inventories.

N losses and turnover rates

The objectives of this work package are to quantify N losses and turnover rates in areas of dairy pastures highly frequented by livestock. This is being investigated across dairy pastures in both sub-tropical and temperate regions and includes determination of urine N2O emission factors and quantification of N2 losses via the application of stable isotopes. Here, Karina is working with Queensland University of Technology in Brisbane. The information is being used to improve rate constants within the modelling component which comprises the following objective.

Cost-benefit analysis, farm systems and N cycle modelling

The final work package is to investigate the whole farm value of a targeted nitrification inhibitor application strategy. Essentially the aim is to model paddock and farm scale implications and conduct a cost-benefit analysis of a targeted DMPP mitigation strategy. This is being achieved through a combination of a spreadsheet modelling approach to develop a conceptual farm scale N balance and through use of the biophysical pasture model, DairyMod. This will allow assessment of whether targeting emission hotspots in dairy pastures for mitigation action is a financially viable option for dairy farmers and whether it reduces overall N losses. 

Further information

Further information including project updates and Project blog and contact details can be found on the Target-N2O Project page at Bangor University.