• Energy Research

Extreme weather events are increasing in frequency and magnitude with profound effects on ecosystem functioning. Further, there is now a greater likelihood that multiple extreme events are occurring within a single year. Here we investigated the effect of a single drought, flood or compound (flood + drought) extreme event on temperate grassland ecosystem processes in a field experiment. To assess system resistance and resilience, we studied changes in a wide range of above- and below-ground indicators (plant diversity and productivity, greenhouse gas emissions, soil chemical, physical and biological metrics) during the 8 week stress events and then for 2 years post-stress. We hypothesized that agricultural grasslands would have different degrees of resistance and resilience to flood and drought stress. We also investigated two alternative hypotheses that the combined flood + drought treatment would either, (A) promote ecosystem resilience through more rapid recovery of soil moisture conditions or (B) exacerbate the impact of the single flood or drought event. Our results showed that flooding had a much greater effect than drought on ecosystem processes and that the grassland was more resistant and resilient to drought than to flood. The immediate impact of flooding on all indicators was negative, especially for those related to production, and climate and water regulation. Flooding stress caused pronounced and persistent shifts in soil microbial and plant communities with large implications for nutrient cycling and long-term ecosystem function. The compound flood + drought treatment failed to show a more severe impact than the single extreme events. Rather, there was an indication of quicker recovery of soil and microbial parameters suggesting greater resilience in line with hypothesis (A). This study clearly reveals that contrasting extreme weather events differentially affect grassland ecosystem function but that concurrent events of a contrasting nature may promote ecosystem resilience to future stress.

At each site measurements were taken from sixteen plots, organised within a randomised complete block design. Four plots did not receive fertilizers (controls), four plots received urea only, four plots received urea and urea-inhibitors, and 4 plots received Ammonium-nitrate (Nitram). Cumulative NH3 emissions were measured using a wind tunnel technique, at a daily resolution for 21 days following each N fertiliser application. Nitrous oxide emissions were measured using a combination of static manual and static automatic (combined with an Isotopic N2O Analyser, Los Gatos Research Inc. San Jose, CA, USA) chambers. Using the manual static chambers, the resolution of N2O measurements following N fertiliser application was 3 x weekly for weeks 1 and 2, 2 x weekly for weeks 3 and 4, and 1 x weekly thereafter. Using the automatic static chambers, the resolution of N2O measurements following N fertiliser application was approximately every six hours. Samples for soil NH4 and NO3 analyses were collected at the same temporal resolution as the N2O sampling using manual static chambers. Herbage yield measurements were carried out on the day of cutting, and samples of the fresh-cut herbage were couriered within 24 h to external contractors (Trouw Nutrition GB, Blenheim House, Ashbourne, UK and Sciantec Analytical Laboratories, Stockbridge Technology Centre, York, UK) for quality analyses of (CP, ME, NDF, ADF and DM). Digestibility was calculated. All results were entered into Excel spreadsheets providing individual datasets for each set of N parameters. Data were exported from Excel as .csv files for ingestion into the EIDC. The data consists of nitrogen (N) offtake, N emissions and soil N parameters, and herbage quality parameters from a three-cut silage plot trial located at two grassland sites within the UK collected between April and October 2016. The sites were Rothamsted Research at North Wyke in Devon and Bangor University at Henfaes Research Station in North Wales. At each site measurements were taken from 16 plots, organised within a randomised complete block design. Fertiliser was applied three times and three cuts were performed, all parameters measured were following a fertiliser application. Nitrogen parameters measured were crude protein (CP) of herbage, ammonia (NH3) emissions, nitrous oxide (N2O) emissions, and soil ammonium (NH4) and nitrate (NO3). Herbage quality parameters measured were dry matter, acid-digestible fibre (ADF), ash, CP, metabolizable energy (ME), and non-digestible fibre (NDF) and digestibility (D) was calculated. Nitrogen offtake, losses and fluxes were measured to determine the N use efficiency and the economic viability of different N fertilisers. Measurements were undertaken by members of staff from Bangor University, School of Environment, Natural Resources & Geography and Rothamsted Research, Sustainable Agricultural Sciences – North Wyke. Data was collected for the Newton Fund project "UK-China Virtual Joint Centre for Improved Nitrogen Agronomy". Funded by Biotechnology and Biological Sciences Research Council (BBSRC) and NERC - Ref BB/N013468/1

Fertiliser nitrogen (N) is essential for maintaining agronomic outputs for our growing population. However, the societal, economic and environmental impacts of excess reactive N from fertiliser is rarely assessed. Here the agronomic, economic and environmental efficacy of three N-fertiliser sources, ammonium-nitrate (AN), urea (U), and inhibited-urea (IU; with NPBT) were evaluated at two grassland sites. Dry matter yield and herbage quality were measured at each silage-cut. Additionally, NH3-N and N2O-N losses were measured and used to calculate the effective N source cost and externality costs, which account for associated environmental and societal impacts. We found no effect of different N sources on yield or herbage quality. However, NH3-N emissions were significantly reduced under the IU treatment, by 48–65%. No significant differences in cumulative N2O emissions were observed. Incorporating externality costs increased fertiliser prices by 1.23–2.36, 6.51–16.4, and 3.17–4.17 times the original cost, for AN, U and IU, respectively, transforming U from the cheapest, to the most expensive of the N sources examined. However, with no apparent yield differences between N-fertiliser sources there is no economic incentive for the land-manager to use the more environmentally and socially acceptable option, unless externality costs are incorporated into fertiliser prices at the point of sale.