Influence of soil pH and nitrogen fertiliser strategies on greenhouse gas emissions in agricultural systems

Supervisors: Cecile Gubry-Rangin, Andreas PacholskiRichard HeathcoteJonathan Hillier

Project description:

Nitrogen fertilisers are widely used in agricultural practices, but a large proportion (>50%) is lost through nitrification, the microbial conversion of ammonia to nitrate. This significantly reduces nitrogen fertiliser use efficiency (NFUE) and is the major direct and indirect source of emissions of the greenhouse gas nitrous oxide (N2O). In agricultural soils, nitrification is driven by ammonia oxidation, which is performed by two microbial groups: ammonia oxidising archaea (AOA) and ammonia oxidising bacteria (AOB). Soil pH is a major factor determining their distribution and activity. In acid soils, ammonia oxidation is dominated by AOA, while both AOA and AOB are active in neutral and alkaline soils. AOA and AOB grow preferentially on different N fertiliser sources (organic
and inorganic sources for AOA and AOB, respectively) and AOB produce significantly more N2O per ammonia oxidised than AOA. Agricultural management and fertiliser strategies may therefore have a previously unsuspected impact on both global climate change and NFUE.

This project will tackle the following questions:
• To what extent can N2O emissions be reduced by use of organic N fertilisers rather than inorganic or slow-release fertilisers?
• Do fertiliser-driven N2O emissions associated with ammonia oxidation vary with soil pH?
• To what extent can manipulation of soil pH and N-fertilisation strategy reduce nitrification
without compromising crop yield?
• What are the optimal strategies for N-fertilisation sources and soil liming for minimising
GHGE and maximising NFUE and crop yield?

The complementary expertise of the academic and industrial partners will allow a diversified research program, with the following objectives:

1.  Controlled microcosm experiments will be performed with soils of varying pH following addition of different nitrogen fertilisers in the presence and absence of specific differential nitrification inhibitors. AOA and AOB abundance (quantitative PCR),
activity (stable-isotope probing) and diversity (high-throughput sequencing) will be determined, with chemical analysis of nitrification rates and GHGE. Experiments will
provide comprehensive quantitative data on the impact of fertiliser strategy/ soil pH on

2.  These data will form the basis for field trials with selected crop species under different fertiliser regimes, monitoring AOA, AOB, nitrification rates, GHGE and crop yield to identify optimal strategies for mitigation of N2O production, NFUE and crop growth.

3.  Data will be integrated to investigate multiple scenarios of soil pH/fertiliser use through the Cool Farm Tool, improving nitrification algorithms and testing predictions with users.

The student will acquire the full set of skills needed to be recruitable by actors in the sustainable agriculture industry or in academic career, though industrial training during placement in both Eurochem Agro and Cool Farm Alliance.

Both University of Aberdeen and the two CASE partners will provide high-quality postgraduate training supporting their academic, professional and personal development, though some courses to earn transferable and employability skills. The student will be offered specialised courses (e.g. statistics, genomics, mathematical modelling, crop yield trials) and will develop within an excellent and active research environment with a strong commitment to multidisciplinary environmental research and research impact.