Long-Term Phosphorus Fertilisation: Effects on Nitrogen and Carbon Cycle Dynamics and Greenhouse Gas Fluxes in European Agricultural Soils 

Phosphorus (P) is a crucial nutrient for plant growth, its limitation reduces plant and microbial biomass, affecting soil organic carbon (SOC) sequestration. Changes in soil P content may influence microbial composition, shaping pathways in the carbon (C) and nitrogen (N) cycles and impacting greenhouse gas emissions. In this lab incubation experiment we investigate the impact of different P fertilisation levels in three European long-term experiments (LTE) on N and C transformation processes and greenhouse gas fluxes in agricultural soils using stable isotope techniques (15N and 13C). The study is part of the EJP SOIL project “ICONICA” (Impact of long-term P additions on C sequestration and N cycling in agricultural soils). The soil samples derived from Johnstown Castle, JC (grassland soil, Ireland), Lanna Skara, LS (arable soil, Sweden) and Jyndevad, JY (arable soil, Denmark). Two P levels were examined from each LTE: low P (0 kg P/ha and year) and high P additions (different P application rates among LTEs). The soils were mixed with 13C- and 13C15N- labelled maize biomass, respectively, and received ammonium nitrate (NH4NO3) in the 13C treatment as 15NH4NO3 and NH415NO3, respectively, and unlabelled NH4NO3 in the 13C15N treatment. Soil and gas samples were taken 0, 1, 3, 7 and 10 days after addition of NH4NO3 and were analysed for (15)NH4+-N, (15)NO3--N, organic (15)N, organic (13)C contents as well as for nitrous oxide ((15)N2O), carbon dioxide ((13)CO2), and methane (CH4) fluxes. Preliminary findings display clear differences among the three LTEs as well as the two P levels. Regarding the impact of P fertilisation history: JC soil exhibited elevated CO2 emissions at high P compared to low P level. Significantly, high P levels showed higher CH4 uptake rates in JC and JY soils compared to the respective low P levels. JY had the highest N2O emissions, while JC had the lowest. JC had higher NH4-N values than LS. The highest NO3-N values were measured in JC, and the lowest in JY. In JC, higher NO3-N values were measured in high P compared to low P. The results so far underscore the complex interactions within the carbon-nitrogen-phosphorus cycles under varying P inputs. Further analyses and interpretations are in progress.